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Habitat filtering influences plant-pollinator interactions in prairie ecosystems

Journal: Botany

Manuscript ID cjb-2018-0134.R2

Manuscript Type: Article

Date Submitted by the Author: 12-Dec-2018

Complete List of Authors: Bizecki Robson, Diana; The Manitoba Museum, Hamel, Cary; Nature Conservancy of CanadaNeufeld, Rebekah; Nature Conservancy of CanadaBleho, Barbara; Golder Associates Ltd.

Keyword: Functional groups, Habitat filtering, Moisture gradient, Plant-insect interactions, Pollination

Is the invited manuscript for consideration in a Special

Issue? :Not applicable (regular submission)

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Habitat filtering influences plant-pollinator interactions in prairie ecosystems

Diana Bizecki Robson, Manitoba Museum, 190 Rupert Avenue, Winnipeg, MB, R3B 0N2

Cary Hamel, Nature Conservancy of Canada, 200-611 Corydon Ave., Winnipeg, MB, Canada, R3L 0P3

Rebekah Neufeld, Nature Conservancy of Canada, 207-1570 18th Street, Brandon, MB, Canada R7A 5C5

Barbara I. Bleho, Golder Associates Ltd., 100 – 6925 Century Avenue, Mississauga, Ontario, Canada

L5N 7K2

Corresponding Author:

Diana Bizecki Robson

Manitoba Museum

190 Rupert Avenue

Winnipeg, MB

R3B 0N2

Phone: 204-988-0653

Fax: 204-942-3679

E-mail: [email protected]

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mailto:[email protected]

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Abstract

The xeric hypothesis is that bees are more abundant pollinators in dry, temperate biomes than

anthophilous flies, and the habitat filtering hypothesis is that differences in the proportions will impact

plant community composition because different pollinators favour different floral traits. However, few

studies have examined the predictive value of these hypotheses. In particular, differences in plant-

pollinator compositions within biomes, such as the Prairie Ecozone, have not been compared. We

documented plant-pollinator interactions and plant abundance in three Canadian prairie types. Flower

visits in moist tall grass prairie were mainly by flies in the Syrphidae, while visits in the drier fescue and

mixed grass prairie were mainly by long-tongued bees in the Apidae. Short-tongued bee visits were not

significantly different between the prairie types. Insect visits to tubular, zygomorphic, violet/blue- and

white-flowered plants were higher in drier fescue and mixed grass prairie than in moister tall grass prairie.

Further, proportions of plants with these features were lower in the tall grass prairie. Thus differences in

the proportion of flies and long-tongued bees, likely affected by habitat conditions including moisture

levels, appear to be influencing the types of plants that dominate each prairie type providing some support

for these hypotheses.

Key words: Functional groups, habitat filtering, moisture gradient, plant-insect interactions, pollination,

prairie

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Introduction

The xeric hypothesis (Michener 1979) is that bees are more common pollinators in temperate, xeric

habitats than in cool arctic or humid tropical habitats. This is based on the observation that deserts have

more bees than prairies, which have more bees than tundra (Michener 1979). Both temperature and

humidity are thought to be responsible for these differences (Michener 1979; Arroyo et al. 1982; Devoto

et al. 2009). High levels of moisture can flood subterranean bee nests and humid conditions can result in

fungal infection of stored food and immature bees (Michener 1979). Further, bees have higher energy

demands than flies and butterflies due to nest provisioning, which can make living in marginal habitats

difficult for these organisms (Arroyo et al. 1982; Kearns 1992). As a result, anthophilous flies are more

common pollinators than bees in cooler areas such as arctic (Mosquin and Martin 1967; Kevan 1972;

Elberling and Olesen 1999) and alpine (Kearns 1992; Gray et al. 2018; Lefebvre et al. 2018) habitats, and

in moister habitats (Devoto et al. 2005, 2009; Robson 2008). However, not all bees are restricted to xeric

habitats: short-tongued bees in the Halictidae and Andrenidae of North America are more common in

temperate, mesic conditions than in xeric ones (Michener 1979). Unfortunately, studies documenting

variation in abundance of bee families across geographic space remain uncommon likely due to the large

sampling effort required (McCall and Primack 1992; Pellissier et al. 2012; Villalobos and Vamosi 2018).

Flies are less studied than bees but are being increasingly recognized as important pollinators (Larson et

al. 2001; Ssymank et al. 2008; Woodcock et al. 2014). Although flies as a group are typically more

common in moist habitats than dry ones (Kearns 1992; Devoto et al. 2005, 2009; Pellissier et al. 2010),

they are highly diverse and breed in a wide range of conditions (Marshall 2012). Studies to date have not

been able to make any generalized statements regarding why some anthophilous fly families are more

abundant in certain ecosystems than others (Kearns 1992; Devoto et al. 2005, 2009). This may be

because unlike bees, flies are often omnivorous, relying on other animals, or bacteria for food in their

larval stage and on plant resources when adults. Anthophilous bee flies (Bombyliidae) and parasitic flies

(Tachinidae), for example, have larvae that parasitize other insects while soldier flies (Stratiomyidae) are

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mostly aquatic filter feeders as larvae (Larson et al. 2001; Marshall 2012). Additional data on geographic

variation in fly families is needed to help us understand which environmental variables are affecting their

distribution and abundance.

Sargent and Ackerly (2008) hypothesized that the composition of a pollinator community could act as a

habitat filter if the absence of certain pollinators prevents the establishment of some plant species.

Pellissier et al. (2012) state that “changes in the proportion of pollinator functional groups are likely to

trigger changes in the structure and composition of natural plant communities” because different

pollinators favour different floral traits. One trait that influences whether a plant is predominantly bee or

fly visited, is flower type (e.g. open or tubular) (McCall and Primack 1992; Fontaine et al. 2006). This

may be because insects without specialized mouthparts, like most flies, are actually constrained to visit a

smaller subset of species than longer-tongued insects like bees and butterflies (Fontaine et al. 2006;

Vamosi et al. 2014). Symmetry (i.e. actinomorphic or zygomorphic), and colour are other variables that

have been investigated for their impact on pollinators (McCall and Primack 1992; Hegland and Totland

2005; Fontaine et al. 2006; Stang et al. 2006; Woodcock et al. 2014; Inouye et al. 2015; Gray et al. 2018;

Kemp et al. 2018). Bees tend to excel at accessing nectar in complex flowers such as zygomorphic ones

while flies prefer open, actinomorphic ones (McCall and Primack 1992; Fontaine et al. 2006; Pellissier et

al. 2012). Regarding colour, white and yellow flowers are more common in fly-dominated habitats such

as the arctic (Kevan 1972) likely because anthophilous flies are sensitive to UV and yellow light (Lunau

and Maier 1995; Woodcock et al. 2014). Interestingly, longer-tongued bomblyiid flies are an exception to

this general observation; they sometimes prefer bluish flowers that are often tubular (Woodcock et al.

2014). Insects of course do not respond to any of these floral variables in isolation; they experience them

all at approximately the same time so teasing out which factor is most important is difficult and likely

varies somewhat from species to species.

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Although pollination studies in northern prairies have been conducted recently (Robson 2008; Evans

2013; Semmler 2016; Robson et al. 2017; Olynyk 2018), only a few compare the pollinator community or

floral characteristics of different prairie types to each other (Chamberlain et al. 2014; Vamosi et al. 2014).

The purpose of this paper is to evaluate the predictive value of the xeric (Michener 1979) and the habitat

filtering (Sargent and Ackerly 2008) hypotheses within a biome by: (1) documenting if and how the

composition of the insect-pollinated plant and pollinator communities differs among three prairie types in

Canada—tall grass, mixed grass and fescue—using Canonical Correspondence Analysis (CCA),

Sorenson similarity and Mantel tests, and (2) testing several hypotheses regarding any compositional

differences. The specific hypotheses we tested using Generalized Linear Mixed Models (GLMMs) were

that: (1) the proportion of fly, and long- and short-tongued bee floral visits would differ among the three

prairie types, (2) the proportion of fly visits would be higher and that of long- and short-tongued bees

lower, at sites with higher moisture (measured via humidity and annual precipitation), (3) the proportion

of pollinator visits to plants with tubular, zygomorphic and violet/blue-coloured flowers would be lower

at the prairie type with more flies, and (4) the proportion of plants with tubular, zygomorphic and

violet/blue-coloured flowers would be lower at the prairie type with more flies. To do this, plant-

pollinator network data and insect visitation rates from previous studies in the tall grass (Robson 2008,

2010, 2013) and fescue (Robson et al. 2017) prairie were re-analysed and compared to new data collected

at a fifth prairie site consisting of mixed grass prairie.

Methods

Study Sites

Insect floral visitors were observed and sampled at five study sites in three Ecoregions of the Prairie

Ecozone (Ecological Stratification Working Group 1995) in southern Manitoba (Figure 1). There were

three tall grass prairie sites (i.e. Birds Hill Provincial Park (BHPP), Living Prairie Museum (LPM), and

Tall Grass Prairie Preserve (TGPP) (Table 1), one mixed grass prairie site at Yellow Quill Prairie

Preserve (YQPP), and one fescue prairie site at the Fescue Prairie Preserves (FPP). The tall grass prairie

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sites were dominated by tall and mid-grass species such as Andropogon gerardii Vitman, Schizachyrium

scoparium (Michx.) Nash and Sporobolus heterolepis (A. Gray) A. Gray, and were considered either dry,

mesic or wet depending on drainage patterns and landscape position (i.e. upland or lowland). The YQPP

was on sandy, well-drained land and was dominated by mid- and short grasses including Bouteloua

gracilis (Kunth) Lag. ex Griffiths, Koeleria macrantha (Ledeb.) Schult., Hesperostipa spartea (Trin.)

Barkworth and Elymus spp. The fescue prairie site occurred on well-drained, raised flatland dominated

by Festuca halli (Vasey) Piper, K. macrantha, Elymus trachycaulus (Link) Gould & Shin. and H. spartea.

Three sites had well-drained Dark Brown Chernozemic soils with lots of sand or gravel: FPP, YQPP and

BHPP. The presence of the BHPP site on an esker (Holland et al. 1996) made it the driest of the three tall

grass prairie sites. In contrast, the TGPP had Gleysolic soils due to prolonged water saturation and LPM

had Vertisolic soils due to the high clay content. In addition to different soils, the tall grass prairie sites

also had slightly different elevations and annual precipitation but the same number of frost free days. The

FPP had the shortest growing season and the highest elevation, and the YQPP was the driest.

LPM is the smallest preserve, only 0.12-km2, as it is an urban park, within and owned by, the City of

Winnipeg. A few of the plots at LPM were on land that had been burned the spring of the first survey

year (2004). The FPP included plots in the Cleland and Elk Glen properties owned by the Nature

Conservancy of Canada (NCC), as well as some provincial government land. Due to the close proximity

of these properties to each other (<3 km), they are considered as one site in this analysis although they

have also been analyzed separately to calculate insect generalization scores (Robson et al. 2017).

Together the Cleland and Elk Glen properties are 5.8-km2 in size but they are bordered to the north by

Riding Mountain National Park and adjacent to provincially- and privately-owned intact prairie and

boreal forest to the east. The six plots at the Cleland property had been grazed by cattle the year before

the surveys began and those at the Elk Glen property were grazed about eighteen years before. The

YQPP, also owned by NCC, is 8.4-km2 but adjacent to additional intact prairie at the provincial

Assiniboine Corridor Wildlife Management Area and the federal Canadian Forces Base Shilo. All

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pastures where the plots were located at YQPP had been grazed the same years as the surveys were

conducted. The sections of the TGPP surveyed were owned by NCC and Nature Manitoba and were

about 10 km apart. Prescribed fire is utilized as a management tool at TGPP, with a prescribed rotation of

six years at any given site. No fire occurred during the survey period, however. In total the TGPP is 22-

km2 and adjacent to some privately-owned prairie mainly being used for cattle grazing. The largest site

was BHPP at 35-km2 but it is largely surrounded by residential development, aggregate mines and

agricultural cropland, and much of the area in the park is forested.

Vegetation Surveys

Plant-insect visitor datasets from the tall grass (Robson 2008, 2010, 2013) and fescue prairie (Robson et

al. 2017) were compared to a new dataset from the mixed grass prairie (i.e. YQPP). After an initial

reconnaissance of each site, areas with predominantly native prairie were identified. To maximize the

length of time that could be spent surveying insect visitors each day, areas relatively close to access roads

and trails were selected and the plots placed randomly within them. However, the BHPP plots were

selected to contain at least one stem of Symphyotrichum sericeum (Vent.) G.L. Nesom as the research at

this site was conducted in part to document pollinators to this rare Canadian species. We established 24

plots at YQPP, 18 plots at FPP, 16 plots at BHPP, and 6 plots each at LPM and TGPP. At YQPP and FPP

each plot was 4-m2 in size, at BHPP each plot was 2.5-m2 and at LPM and TGPP the plots were 5-m2.

The plots were at least 5-m apart and typically scattered over several kilometers of the preserves to better

capture the biological diversity. Plots were closest together at LPM due to its small size. In total the

plots covered an area ranging from 72-m2 to 150-m2.

In 2014 vegetation surveys at FPP were conducted for four consecutive days, which was repeated four

times in mid-June, -July, -August and -September (16 days total). These surveys were repeated in 2015

on the previously established plots except there were two survey periods in June (early and late), and one

each in July and August (16 days total). In 2016 surveys at YQPP were conducted for two consecutive

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days twice each month of June, July, August and September (16 days total). These surveys were repeated

in 2017 on the previously established plots in May, June, July and August (16 days total). Sampling in

BHPP was conducted for 37 non-consecutive days: 6 days in June (2011), 12 days in July (2010 and

2011), 11 days in August (2008 and 2010), and 8 days in September (2008). Sampling at LPM and TGPP

occurred from June to September on four non-consecutive days each month in both 2004 and 2005 for a

total of 32 days at each site. Surveying at slightly different times each year enabled us to observe a

greater number of plant species than if the plots were visited on the exact same calendar days over two

years. Insect-pollinated plant richness and number of inflorescences in the plots was recorded each

survey day. Due to natural variability in abundance, some plant species were present in more plots than

others and thus were observed for longer periods of time. Nine species had solitary or axillary flowers

which typically gave them a smaller floral display area than the others, which all had multiple flowers per

inflorescence. The floral attributes of each plant (i.e. shape, symmetry and colour) were determined by

examining the species in the field. Plants with open flowers had sepals and/or petals unfused or fused

into tubes <3mm in length while those considered tubular were fused for >3mm in length. Zygomorphic

as opposed to actinomorphic plants had flowers that were bilaterally symmetrical. Colour was as seen by

human eyes. Vouchers of each insect-pollinated plant species surveyed were collected and deposited in

the Manitoba Museum’s (MM) botanical collection. The vouchers were assigned both collection and

catalogue numbers, and were entered into the Museum’s database.

Floral Visitor Surveys

Floral visitor surveys occurred on the same days as the plant surveys for set periods of time (10

minutes/plot at FPP, YQPP and BHPP, and 30 minutes/plot at LPM and TGPP) each sampling day; total

sampling effort at each site ranged from 96 to 128 hours over 2-3 years. The sites were surveyed over at

least two seasons to partially account for inter-annual variation in insect populations, which can be high

(Williams et al. 2001). Surveys were conducted between 09:30 h and 17:00 h when insect foraging

activity is at a maximum (Kevan and Baker 1983) thus nocturnal insects were not observed. The order in

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which the plots were visited was randomized each day. During the survey periods, weather conditions at

the nearest (less than 37 km away) Environment Canada (2018) weather station were recorded, and the

values averaged for each survey year.

All insect visitations to any inflorescences in the plots where the reproductive organs were touched for

more than two seconds were recorded; these visits have been used as a proxy for pollination (Kantsa et al.

2017). Some of the flower-visiting insects (e.g. crabronid wasps in the genus Ectemnius Dahlborn, 1845)

may have been predators of other flower-visiting insects. Regardless of whether the wasps were foraging

for pollen, nectar or prey, they were considered potential pollinators and their visitations recorded.

However, ambush bugs (Phymata spp. Latreille, 1802) and crab spider (Misumena spp. Latreille, 1804)

visits were not recorded as they remain stationary on one inflorescence for a long time and thus were

unlikely to act as pollinators. Henceforth, all insect visitors are referred to as pollinators although some

may have been inefficient relative to other taxa.

The first time an insect taxon was observed a specimen was obtained and given a unique collection

number. When the same (or what appeared to be the same) taxon was observed later, the collection

number was used to link that insect visit to the plant. Although this technique does not allow for

complete identification “on the wing” (resulting in an underestimate of taxa) it does enable evaluation of

insect visitation frequency, which was then used to determine the visitation rate for each plant species.

As the sites had different plant abundances, the mean number of insect visits inflorescence-1 hour-1 was

determined to enable comparison between species. Only days when the plant was in flower were

included as part of the total hour count. Pollinator visits at each site are expressed as a proportion rather

than an absolute number to enable comparison. All insect voucher specimens were identified by

zoologists to the lowest taxonomic level possible using reference specimens at the MM and Wallis

Roughley Entomology Museum in Winnipeg, Manitoba; the specimens were deposited in MM’s zoology

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collection. The vouchers were assigned both collection and catalogue numbers, and were entered into the

Museum’s database.

Data Analysis

The total number of species-species interactions at each site (I) and the connectance (C =100I/ap, where

“a” and “p” represent the number of animal and plant species, respectively), was determined (Jordano

1987). To assess plant and insect compositional differences between sites and determine which

environmental factors were most influential, we used CCA as a method of ordination of the five sites.

CCA is a direct gradient analysis that examines species and environmental data simultaneously (Ter

Braak 1986). The plant data used was the proportion of all plots at each site that contained each species,

while the insect data used was the proportion of all visits at that site by each insect family. Environmental

variables examined were: average temperature, humidity and wind speed during the survey periods,

elevation, and mean annual precipitation and frost free days. Environmental data were log (n+1)

transformed. The Sørensen similarities (where maximum similarity is 0 and 1 is completely dissimilar) in

plant and insect communities between the five sites were calculated. Mantel tests (Monte Carlo

randomization) for association between the environmental variables and both plant and insect matrices

were performed. Geographic locations of all plots were recorded in the field using GPS satellites; the

geographic midpoints between all plots at each site were used for Mantel tests (Monte Carlo

randomization) to determine spatial autocorrelation (McCune and Grace 2002). These tests were carried

out using PC-ORD (McCune and Mefford 1999).

As the numbers of taxa and visitations were significantly skewed and could not be transformed to

approach normality, nonparametric statistics were used. Pearson Chi-square was used to compare

differences in proportions of insect functional groups and families between the sites (Analyze-it Software

Ltd., 1997-2008). We also used GLMMs using the GLIMMIX procedure in SAS v. 9.3 (SAS Institute

2010) to test for differences among prairie types (tall grass vs. mixed grass vs. fescue) in floral attributes

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(shape, symmetry, colour), pollinator visits (by functional group), and flower visits (by floral attribute).

GLMMs are appropriate for hierarchical study designs such as here because they retain subsample units

as replicates, but calculate degrees of freedom separately for each nested spatial scale, resulting in

increased power of detection. These models also allow evaluation of both continuous and categorical

predictor variables.

We first assigned each plant species to the applicable category for each floral attribute and then grouped

count data for number of inflorescence and number of flower visits by each floral attribute. Similarly, we

assigned each pollinator species or genus to the applicable functional group and grouped count data by

pollinator functional group. We then converted count data for number of inflorescence by floral attribute,

number of flower visits by floral attribute, and pollinator visits by functional group to proportional values

to reconcile differences in plot size and visit duration within and among sites. We selected flies (Diptera)

and bees (long-tongued and short-tongued) as our pollinator functional groups in analyses as they were

responsible for 96% of all flower visits and so were of primary interest in our study. We differentiated

long- from short-tongued bees as these groups tend to exploit different flower types, and have different

nesting habitats (Fenster et al. 2004; Sheffield et al. 2014).

To determine if flowering communities differ among prairie types, we evaluated the following floral

attributes as response variables: shape (proportion open flowers), symmetry (proportion actinomorphic

flowers), and colour (proportion violet/blue, white, pink, yellow/orange flowers), totalling six models.

For shape and symmetry, we evaluated only one of two available attribute categories because the two

categories as proportions were perfectly correlated within plots. To determine if pollinator communities

differ among prairie types, we evaluated proportion of total flower visits by flies, long-tongued bees and

short-tongued bees (three models). To determine if floral attributes are visited by pollinators differently

(by proportion of total visits) among prairie types, we evaluated proportion of total pollinator visits to

each floral attribute: shape (proportion of visits to open flowers), symmetry (proportion of visits to

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actinomorphic flowers), and colour (proportion of visits to violet/blue, white, pink, yellow/orange

flowers), totalling six models. Prairie type was the predictor variable in the models, with plot treated as a

random, nesting variable.

We also used GLMMs to evaluate how climate and floral attributes influence pollinator visits. Climate

variables (temperature, humidity, annual precipitation) and floral attributes (shape, colour, symmetry)

were included as predictor variables in each model. We also included an interaction term between

temperature and humidity. Our response variables were proportionate of total flower visits by flies, long-

tongued bees and short-tongued bees (three models). Plot was treated as a random nesting variable.

Results

The environmental differences during the survey periods tended to reflect the average conditions that

occur at these sites over time (Table 2). The most northerly site, FPP, had the lowest temperature and

second lowest humidity reflecting its short growing season, and moderate annual precipitation.

Meanwhile, the YQPP was hot, windy and dry, as is typical in a mixed grass prairie. The three tall grass

prairie sites were the most humid, with TGPP having the highest humidity, and BHPP was the warmest.

The CCA ordinations (Figure 2) showed that humidity and annual precipitation were the variables most

strongly correlated with the first axes for both plants (Humid r = 0.980 and Annu prec r = 0.890) and

insects (Humid r = 0.954 and Annu prec r = 0.827). Temperature was the factor most strongly correlated

with axis 2 for the plants (r = -0.699) but elevation (r = -0.763) for insects. Wind speed and frost free

days were not strongly correlated with either axis. Mantel tests for both plants (r = 0.474, p = 0.138) and

insects (r = 0.064, p = 0.370) indicate that there is a positive (but not significant) association between the

species and environmental matrices. Further, Mantel tests show a positive (but not significant)

association between plants (r = 0.475, p = 0.138) and insects (r = 0.06, p = 0.370) with respect to spatial

differences. Thus sites closer together geographically were no more similar in terms of their vegetation

and insect composition than could be expected by chance, so variables other than distance are influencing

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composition. The sites that had the most similar insect-pollinated plant and insect composition were the

fescue and mixed grass prairie sites: FPP and YQPP (Table 3). The tall grass prairie sites that were most

similar were LPM and TGPP with respect to plants, and LPM and BHPP with respect to insects.

Regarding insects, TGPP was strongly dissimilar to the other sites because there were quite a few insect

taxa (mostly flies) that were present only at that site, or in unusually high quantities.

YQPP had the highest number of plant species surveyed and visited although the percentage of plants

visited was not the highest; LPM had the highest percentage (Table 4). Not all insects could be identified

to species due to varying expertise and lack of good taxonomic keys for some taxa. The percentage of

taxa identified to species ranged from 76% at FPP to only 46% at TGPP; this was because bees (which

are easier to identify) were more abundant at the former site and flies at the latter. The FPP also had the

highest number of insect visitor taxa; 62 more than observed at the site with the lowest number, TGPP.

The connectance of the plant-insect visitor system was highest at TGPP and lowest at LPM. Of the 347

insect taxa observed, only two were seen at all five sites: Bombus ternarius Say, 1837 and B. rufocinctus

Cresson, 18631. Five taxa were observed at four of the sites, 14 at three sites and 32 at two sites. Eight

taxa (three Bombus spp. Latreille, 1802, two Andrena spp. Fabricius, 1775, one Lasioglossum sp. Curtis,

1833 and two Syrphidae) were seen at only one site but made more than 1% of all visits. The five insect

species with the highest mean percentage of flower visits were: Bombus ternarius (18.8%), Toxomerus

marginatus (Say, 1823) (5.9%), Odontomyia pubescens Day, 1882 (3.4%), Andrena asteris Robertson,

1891 (3.3%) and B. griseocollis (De Geer, 1773) (3.1%).

In total, 84 plant species in 24 different families were observed being visited with the majority being in

the Asteraceae (27 species) followed by Fabaceae (13 species) and Rosaceae (12 species). All insect taxa

that were observed visiting the plants, even once, were recorded2. The five plants with the highest total

1 Table S12 Table S2, S3

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number of insect visitor taxa, in decreasing order were: Solidago nemoralis Ait. (88), Solidago rigida L.

(75), Erigeron glabellus Nutt. (60), Solidago canadensis L. (50) and Symphoricarpos occidentalis Hook.

(44). Long-tongued bees were the dominant visitors (i.e. making > 50% of all visits) to 15 plant species.

Two species (Amorpha nana Nutt. and Prunus pumila L.) were only visited by long-tongued bees, three

species were only visited by long-tongued bees and Lepidoptera (Hedysarum boreale Nutt., Lathyrus

venosus Muhl. ex. Willd. and Pediomelum esculentum (Pursh) Rydb.) and Geum triflorum Pursh was only

visited by bees. Short-tongued bees were the dominant visitors to three plant species (Antennaria

parvifolia Nutt., Heuchera richardsonii R.Br. and Hypoxis hirsuta (L.) Coville), and Lepidoptera to two

species (Liatris punctata Hook. var. punctata and Viola pedatifida G. Don). Diptera were the dominant

visitors to 27 plants with four species being visited only by flies: Anticlea elegans (Pursh) Rydb.,

Dasiphora fruticosa (L.) Rydb., Prunella vulgaris L. and Ranunculus rhomboideus Goldie var. multifidus

Nutt. A wasp (i.e. Other Hymenoptera) was the only visitor observed to Amelanchier alnifolia (Nutt.)

Nutt. ex Roemer. The remaining 35 plant species were visited by a variety of functional groups.

Additionally, 23 surveyed plant species were not observed being visited by any insects3.

Although the percentage of long-tongued bee taxa was low at all of the sites (Figure 3), this functional

group was responsible for the majority of the visits at three sites: FPP, YQPP and LPM. However, at

BHPP and TGPP the majority of the visits were by flies. GLMM confirmed that long-tongued bee visits

were significantly different amongst all prairie types with the highest proportion of visits occurring in the

fescue prairie (i.e. FPP) (Table 5). Further, flower visits by flies were significantly higher in tall grass

prairie (i.e. BHPP, LPM and TGPP sites) than in the other two prairie types which had a similar

proportion of visits. Visits by short-tongued bees were not significantly different among the prairie types.

There were some compositional differences with respect to the bee families that were most common at

each site (Figure 4). Apidae was the dominant bee family at all sites. Andrenidae were responsible for

3 Table S4

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more than 20% of all bee visits at the three tall grass prairie sites but less than 10% at the others.

Halictidae were frequently observed at TGPP but not so much at the other sites. No Megachilidae were

observed at either LPM or TGPP.

Fly family composition was also different (Figure 5). Bombyliidae were most common at the two of the

drier sites (i.e. YQPP and BHPP) but infrequently seen at TGPP. Syrphidae were observed at all sites but

most frequently at LPM and TGPP. Flies in the Stratiomyidae and other fly families (e.g. Anthomyiidae

and Scatopsidae) were responsible for about half of all fly visits at TGPP. Muscidae were the most

frequently observed fly family at YQPP and Tachinidae at FPP.

The proportion of visits by different trophic groups of insects (i.e. aquatic, and terrestrial herbivores,

omnivores and saprovores) varied among the sites (Figure 6). The majority of insect visitations at all but

one site were by terrestrial herbivores (mainly bees and butterflies). At TGPP, however, almost half of all

insect visitations were by insects with an aquatic larval stage. Insects that were terrestrial saprovores in

the larval stage were also most commonly seen at TGPP. Insects that were terrestrial omnivores (i.e.

carnivorous in the larval stage and herbivorous in the adult stage) were most frequently seen at BHPP.

The results of GLMM show that the proportion of inflorescences with open versus tubular flowers,

actinomorphic versus zygomorphic flowers and in different colour groups was significantly different (p <

0.05) between some of the prairie types (Tables 6)4. The proportions of insect visits to plants of these

different types differed significantly among prairie types except with respect to visits to open flowers

which were the same at all sites. Tubular flowers were more common and visited more frequently at the

fescue and mixed grass prairie than at the tall grass prairie. Zygomorphic flowers were most common and

visited most frequently at the mixed grass prairie. Plants with violet/blue and white flowers were more

common at mixed grass prairie than at tall grass prairie; fescue prairie had more white flowers but the

4 Table S5

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same number of violet/blue flowers as tall grass prairie. Insect visits to violet/blue and white flowers

were higher at the fescue and mixed prairie than at tall grass prairie. Instead yellow/orange-flowered

plants were more common at tall grass prairie, receiving more visits than at the mixed grass prairie.

Visits by all three functional groups increased with increasing temperature (Table 7). Further, a weak

positive interaction between temperature and humidity (r = 0.075) had a negative influence on fly and bee

visits, indicating that the importance of temperature decreased as humidity increased. High humidity

positively affected both fly and short-tongued bee visits but high annual precipitation only increased fly

visits. Long-tongued bee visits were unaffected by both humidity and annual precipitation. A higher

proportion of actinomorphic flowers increased fly and short-tongued bee visits and decreased long-

tongued bee visits. Fly visits also increased with a higher proportion of open, and white and

yellow/orange flowers while long-tongued bee visits increased with an increasing proportion of all flower

colours.

Only 13 of the 84 plant species surveyed were found at all five sites and only five species were actually

observed being visited at all sites (i.e. Campanula rotundifolia, Dalea purpurea var. purpurea,

Lithospermum canescens (Michx.) Lehm., Solidago rigida, Symphyotrichum ericoides (L.) Nesom)5. An

additional 11 plant species were found at four of the five sites, 14 species at three sites and 13 species at

two sites. Visitation rates to plant species found at most of the sites were sometimes quite different. For

example, open, actinomorphic-flowered plants like Achillea borealis Bong. var. borealis, Comandra

umbellata (L.) Nutt., Solidago rigida, Symphyotrichum laeve (L.) A. Love & D. Love and Zizia aptera

(Gray) Fern. tended to have high visitation rates at the tall grass prairie sites but low rates at the fescue

and mixed grass prairie sites while the opposite was true of zygomorphic and/or tubular plants like

Astragalus agrestis Dougl. ex G. Don., Geum triflorum and Pediomelum esculentum.

5 Table S6

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Discussion

The province of Manitoba, Canada has three distinctive prairie types—fescue, mixed grass and tall

grass—providing an excellent opportunity to assess how plant-pollinator communities in these

ecosystems differ. Our research shows that sites within the same prairie type were not necessarily the

most similar in terms of their plant and insect community composition: the three tall grass prairie sites

were more dissimilar than the fescue and mixed grass prairie sites were to each other. Of the

environmental variables we used in the CCA, humidity and annual precipitation appeared to have the

greatest influence on overall plant and insect composition. At the sites with the highest humidity and

precipitation (i.e. LPM and TGPP), flies were responsible for most of the flower visits and at sites with

the lowest humidity and precipitation (i.e. YQPP and FPP) bees (mostly long-tongued) were responsible

for most of the visits, supporting the xeric hypothesis. However, although bees were more common at the

mixed and fescue prairie, differences in temperature and moisture do not seem to be the reason why. The

GLMM showed that bees were not influenced by annual precipitation. Further, high humidity did not

affect long-tongued bee visits and short-tongued bees responded positively (not negatively as predicted)

to it, similar to flies. Instead, the factor that seemed to affect long-tongued bees the most was the

abundance and type of forage available; the presence of flowers of any colour, but particularly

zygomorphic ones, resulted in more long-tongued bee visits. Other researchers have found that flower

richness and density strongly influence long-tongued bee visitation (Kevan and Baker 1983; Rathcke

1983; Stang et al. 2006; Ebeling et al. 2008) and, as Villalobos and Vamosi (2018) suggest, this could

outweigh the impact of climate on bee visitation in some regions. Another reason this may be is because

Bombus species are noted to be particularly well adapted to foraging under humid conditions (Villalobos

and Vamosi 2018); this genus was the dominant long-tongued bee in our region. With respect to short-

tongued bees, Michener (1979) noted that some families (i.e. Andrenidae and Halictidae) are tolerant of

mesic conditions so our results are not wholly unexpected. Temperature positively affected all three

functional groups likely because most pollinators are not active at cool temperatures due to

thermoregulation limits, and temperatures do not get hot enough in this region to inhibit foraging

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behaviour (Kevan and Baker 1983; McCall and Primack 1992). Although our results roughly parallel

those of Devoto et al. (2005, 2009) and Kearns (1992) who found that flies dominated the wetter portion

of an environmental gradient and bees the drier portion, a clear negative effect of moisture on bees was

not observed within the Prairie Ecozone, although it may explain differences between ecozones where

climatic difference are greater.

The mechanism(s) by which moisture influences pollinator communities is likely via breeding habitat. In

a direct way, moisture can affect the availability of larval habitat for flies. Insects with aquatic larvae or

that preferred saturated soil and/or rotting vegetation to breed in (e.g. Stratiomyidae) were seen most

frequently at the wettest site (i.e. TGPP) but were scarce at drier sites (e.g. BHPP, YQPP). Moisture may

have also affected some long-tongued bee genera (but not the group as a whole). Previous research on

Megachile rotundata (Fabricius 1787) in Manitoba found that pollen ball cells were increasingly infected

with fungus as humidity increased (Pitts-Singer and James 2008). The absence of Megachilidae during

our surveys at LPM and TGPP may have been due to high humidity in 2004 and 2005 as species in this

family have been collected by other scientists at these sites in later years (Semmler 2016).

One non-climatic factor that could have affected some pollinating flies is prey abundance. Bee flies

(Bombyliidae) and parasitic flies (Tachinidae) typically parasitize bees and Lepidoptera (Marshall 2012),

insects that were not seen frequently at LPM and TGPP. Bee flies were most frequently observed at the

two sites where bees were common: BHPP and YQPP. Parasitic flies (Tachinidae), which tend to

parasitize Lepidoptera more than bees, were frequently seen at FPP possibly because this site had the

most floral visits by Lepidoptera, and was in close proximity to intact boreal forests in nearby Riding

Mountain National Park, where forest caterpillars are often abundant (Kuussaari et al. 2007). Syrphids,

whose larvae are usually sapro- or phyto-phages or carnivorous on aphids, were common at all sites; this

may be because syrphid populations are noted to be more stable than those of other terrestrial arthropods

(Owen and Gilbert 1989). Through these data we show that flies cannot be considered one cohesive

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group that responds in the same way to environmental differences, similar to other studies which also

noted a lack of a consistent pattern (Kearns 1992; Lambkin et al. 2011).

Another non-climatic factor that could have affected the plant and pollinator compositions was land

management (Stoner and Joern 2004; Kimoto et al. 2012; Lazaro et al. 2016). Insects that prefer bare

ground for nesting (e.g. Halictidae and Andrenidae) and those that require a blood meal to reproduce (e.g.

Stomoxys calcitrans (L., 1758), may directly benefit from the presence and grazing activities of livestock

(Potts and Willmer 1997; Kimoto et al. 2012; Marshall 2012). The most recently and consistently grazed

site, YQPP, had high populations of Muscidae which may have been breeding in dung or biting the

livestock or wild elk in the area. Grazing by large herbivores also influences plant composition

(Augustine and McNaughton 1998; Olff and Ritchie 1998; Towne et al. 2005; Lazaro et al. 2016). For

example, Cerastium arvense L., a species that needs light for seed germination (Willms et al. 1985, 1988),

was likely more abundant at YQPP due to grazing which removed leaf litter, resulting in a high number of

visits to white flowers at this site. Further, as grazing did not begin at this site until June, later season

plants, such as Solidago spp., were more likely to be eaten or trampled.

The habitat filtering hypothesis (Sargent and Ackerly 2008) predicts that the dominant pollinators will

influence the types of plants in the community by acting “as a sieve that filters which species can

establish and persist” (Pellissier et al. 2012). Thus we expected that sites where bees were the dominant

pollinators would contain more plants they are known to favour in terms of colour, shape and symmetry

than fly-dominated sites. Regarding colour, bee preference for violet/blue flowers and fly preference for

white and yellow flowers has been observed in some studies (McCall and Primack 1992; Lunau and

Maier 1995). Differences in insect preferences appear to have resulted in differences in the dominant

flower colour as the pollinator population shifts from bee- to fly-dominant along a Rocky Mountain

elevation gradient (Gray et al. 2018). In our study, we also found differences in the dominant flower

colour: violet/blue and white-flowered plants were more abundant at the xeric, mixed grass prairie than at

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the mesic tall grass prairie, while yellow/orange-flowered plants were more common at the tall grass

prairie. Further, the plants were not being visited in proportion to their abundances: visits to violet/blue

flowers were almost double at both the fescue prairie than at the tall grass prairie, despite no significant

difference between flower abundance. Tall grass prairie had the most visits to yellow/orange flowers.

Similarly, zygomorphic flowers were more commonly visited at the drier mixed grass prairie than at the

wetter tall grass prairie. Tubular plants whose nectar can simply not be accessed by smaller, shorter-

tongued insects were also more abundant and visited more frequently at the drier sites. Similar patterns

such as these are noted in other studies (Fenster et al. 2004; Fontaine et al. 2006; Gray et al. 2018) and

appear to reflect differences in the abundance of bees.

Additional support for the habitat filtering hypothesis came from comparison of the visitation rates. Few

plant species were found at all the sites, but when they were widespread, they often differed in terms of

how frequently they were visited by the functional groups of insects. The variation in individual plant

visitation rates between the sites appears to partly reflect the abundance of various insect groups at those

sites. For example, Achillea borealis Bong. var. borealis and Comandra umbellata (L.) Nutt.—both

white, actinomorphic plants—were frequently visited at the tall grass prairie sites where flies were

common pollinators but hardly at all at the FPP and YQPP, which were dominated by long-tongued bees.

In contrast, Astragalus agrestis Dougl. ex G. Don—a purple, zygomorphic plant— and Geum triflorum—

a pink, tubular plant—were frequently visited at the sites with more long-tongued bees, and infrequently

visited at the fly-dominated sites. In habitats lacking bees, seed production is lower for tubular (Fontaine

et al. 2006) and zygomorphic, blue-flowered plants (Bell et al. 2005). The implications of our

observations for reproductive output are therefore intriguing: seed production of tubular, zygomorphic

and/or violet/blue-flowered plants may be lower in tall grass prairie than in fescue or mixed grass prairie,

due to the different pollinator compositions. However, the fact that violet/blue flowers were still present

in fairly similar compositions at all sites suggests that reproduction is still adequate to maintain

population sizes. This may be because many plants can compensate for a lack of pollination services by

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selfing when necessary (Bond 1994; Wilcock and Neiland 2002). Alternatively, since these plants are

perennials, they may be remnants from a previous drier climatic cycle (George and Nielsen 2002;

Markham 2014). Short term changes in soil moisture dynamics have little immediate effect on prairie

plant composition; it may take a decade of consistent wet or dry weather to alter the composition of a

plant community (Fay et al. 2000). Further investigation of variation in seed production among common

species at these sites is needed to help clarify what is happening with respect to reproduction.

There were other floral characters that may have been influencing insect visitation that we could not

assess in this study. Flower colours were described as they are seen by human eyes but UV colours and

patterns are known to attract different insects as well (Kevan and Baker 1983; Woodcock et al. 2014;

Kemp et al. 2018). Scent also varies among plant species and bumblebees are attracted to flowers with a

different scent profile than flies (Junker et al. 2012; Larue et al. 2016). The degree to which these factors

may have affected the insect community is unknown but as pollinators “likely experience floral traits as

multimodal sensory information, rather than solely visual or olfactory clues” (Kantsa et al. 2017), the

variables chosen by us are likely still relevant and interrelated.

It is also important to note that the plant species are being filtered by environmental conditions in a direct

way, not just indirectly via the pollinator community (Vinton and Burke 1997). Plants found in only one

prairie type likely have a more narrow tolerance to moisture or soil conditions. For example, Euthamia

graminifolia (L.) Nutt., found only at LPM and TGPP, is common in moist habitats, such as damp prairies

and riparian areas, and possesses characteristics that help it tolerate saturated soil and crowd out

competitors in such conditions (Werner and Platt 1976). In contrast, species with adaptations for dry

environments (e.g. short stature, tap roots, small leaves, etc.) (Knight 1965) such as Astragalus spp. and

Oxytropis spp. were most common at the mixed and fescue prairies.

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In summary, the plant and pollinator communities were different with respect to the dominant species but

the fescue and mixed grass prairie types were more similar to each other compositionally than the tall

grass prairie sites were to each other. The proportion of visits by flies was higher at tall grass than fescue

or mixed grass prairie and the proportion of long-tongued bee visits was highest at fescue followed by

mixed grass prairie. However, short-tongued bee visits were not different between the sites. Further,

tubular, zygomorphic and violet/blue-coloured flowers, and visits to these flowers were lower at the

prairie type with more flies (tall grass prairie) as hypothesized. Thus the habitat filtering hypothesis

(Sargent and Ackerly 2008) that the dominant pollinators influence the plant community has some

support. However, whether temperature and moisture are the most influential variables on pollinator

composition as suggested by Michener’s (1979) xeric hypothesis varies among functional groups.

Temperature affected all three functional groups positively and although the proportion of fly visits was

positively affected by increased humidity and precipitation, short-tongued bees responded positively (not

negatively as expected) to humidity and long-tongued bees were not affected at all. Rather, the presence

of large quantities of flowers, zygomorphic ones in particular, had the greatest impact on long-tongued

bee visits. These mixed results suggest that at least within biomes, floral composition may be a more

important influence on bees than climate. The xeric hypothesis may only be applicable at larger

geographic scales.

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Acknowledgements

Financial support for this research was received from The Manitoba Museum Foundation Inc., Nature

Conservancy of Canada (NCC), World Wildlife Fund Canada, Government of Manitoba, and the Science

and Technology Internship Program and Virtual Museum of Canada, Government of Canada. Special

thanks to Heather Flynn, Robert Wrigley, Sarah Semmler, Reid Miller and Jason Gibbs for preparation

and/or identification of insect specimens. The Government of Manitoba, NCC, the City of Winnipeg and

Nature Manitoba graciously allowed us to conduct research on their lands. Dr. Anne Worley and Sarah

Semmler provided valuable comments on an early draft of this paper and Dr. Rob Currie provided advice

regarding statistical analysis. Lastly, thanks to Manitoba Museum and Nature Conservancy of Canada

staff and volunteers for their assistance, especially Dana Krueger for her work on the supplementary

materials.

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References

Analyze-it Software, Ltd. 1997-2008. Analyze-it Software, Ltd, version 2.11. Leeds, UK. Available from

http://www.analyse-it.com/ [accessed 7 May 2018].

Arroyo, M.T.K., Primack, R., and Armesto, J. 1982. Community studies in pollination ecology in the high

temperate Andes of central Chile. I. Pollination mechanisms and altitudinal variation. Am. J. Bot.

69(1): 82-97. doi:10.2307/2442833.

Augustine, D.J., and McNaughton, S.J. 1998. Ungulate effects on the functional species composition of

plant communities: herbivore selectivity and plant tolerance. J. Wildl. Manage. 62(4): 1165–1183.

doi:10.2307/3801981.

Bell, J.M., Karron, J.D., and Mitchell, R.J. 2005. Interspecific competition for pollination lowers seed

production and outcrossing in Mimulus ringens. Ecology, 86(3): 762-771. doi:10.1890/04-0694.

Bond, W.J. 1994. Do mutualisms matter? Assessing the impact of pollinator and disperser disruption on

plant extinction. Philos. Trans. R. Soc. Lond. Biol. Sci. No. 344(1307): 83-90.

doi:10.1098/rstb.1994.0055.

Chamberlain, S.A., Cartar, R.V., Worley, A.C., Semmler, S.J., Gielens, G., Elwell, S., Evans, M.E.,

Vamosi, J.C., and Elle, E. 2014. Traits and phylogenetic history contribute to network structure across

Canadian plant–pollinator communities. Oecologia, 176(2): 545-556. doi:10.1007/s00442-014-3035-2.

Devoto, M., Medan, D., and Montaldo, N.H. 2005. Patterns of interaction between plants and pollinators

along an environmental gradient. Oikos, 109(3): 461-472. doi:10.1111/j.0030-1299.2005.13712.x.

Devoto, M., Medan, D., Roig‐Alsina, A.R., and Montaldo, N.H. 2009. Patterns of species turnover in

plant‐pollinator communities along a precipitation gradient in Patagonia (Argentina). Austral Ecol.

34(8): 848-857. doi:10.1111/j.1442-9993.2009.01987.x.

Ebeling, A., Klein, A.-M., Schumacher, J., Weisser, W.W., and Tscharntke, T. 2008. How does plant

richness affect pollinator richness and temporal stability of flower visits. Oikos, 117: 1808-18.15.

doi:10.1111/j.1600-0706.2008.16819.x.

Page 24 of 47


Botany

http://www.analyse-it.com/

https://doi.org/10.1890/04-0694

https://doi.org/10.1111/j.0030-1299.2005.13712.x

Draft

Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture

and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and

Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch, Ottawa-Hull,

Ontario.

Elberling, H., and Olesen, J.M. 1999. The structure of a high latitude plant-flower visitor system: The

dominance of flies. Ecography, 22(3): 314–323. doi:10.1111/j.1600-0587.1999.tb00507.x.

Environment Canada. 2018. Historical climate data [online]. Available from

http://climate.weather.gc.ca/index_e.html [accessed 7 May 2018].

Evans, M. 2013. Influences of grazing and landscape on bee pollinators and their floral resources in rough

fescue prairie. Ph.D. thesis, University of Calgary, Calgary, Alberta.

Fay, P.A., Carlisle, J.D., Knapp, A.K., Blair, J.M. and Collins, S.L. 2000. Altering rainfall timing and

quantity in a mesic grassland ecosystem: design and performance of rainfall manipulation shelters.

Ecosystems, 3(3): 308-319. doi:10.1007/s100210000028.

Fenster, C.B., Armbruster, W.S., Wilson, P., Dudash, M.R., and Thomson, J.D. 2004. Pollination

syndromes and floral specialization. Annu. Rev. Ecol. Evol. Syst. 35: 375-403.

doi:10.1146/annurev.ecolsys.34.011802.132347.

Fontaine, C., Dajoz, I., Meriguet, J., and Loreau, M. 2006. Functional diversity of plant-pollinator

interaction webs enhances the persistence of plant communities. PLoS Biol. 4(1): e1.

doi:10.1371/journal.pbio.0040001.

George, S.S., and Nielsen, E. 2002. Hydroclimatic change in southern Manitoba since AD 1409 inferred

from tree rings. Quat. Res. 58(2): 103-111. doi:10.1006/qres.2002.2343.

Gray, M., Stansberry, M.J., Lynn, J.S., Williams, C.F., White, T.E., and Whitney, K.D. 2018. Consistent

shifts in pollinator‐relevant floral colouration along Rocky Mountain elevation gradients. J. Ecol.

106(5): 1910-1924. doi:10.1111/1365-2745.12948.

Hegland, S.J., and Totland, Ø. 2005. Relationships between species’ floral traits and pollinator visitation

in a temperate grassland. Oecologia, 145(4): 586-594. doi:10.1007/s00442-005-0165-6.

Page 25 of 47


Botany

https://doi.org/10.1111/j.1600-0587.1999.tb00507.x

http://climate.weather.gc.ca/index_e.html

https://doi.org/10.1006/qres.2002.2343

https://doi.org/10.1111/1365-2745.12948

Draft

Holland, G., Ottenbriet, K., Punter, D., Punter, E., Shanks, A, and Staniforth, R. 1996. Wild plants of

Birds Hill Provincial Park, Manitoba, Canada, Eco Series 4. Manitoba Naturalists Society, Winnipeg,

Manitoba.

Inouye, D.W., Larson, B.M., Ssymank, A., and Kevan, P.G. 2015. Flies and flowers III: ecology of

foraging and pollination. J. Poll. Ecol. 16(16): 115-133. Available at

http://www.pollinationecology.org/index.php?journal=jpe&page=article&op=view&path%5B%5D=3

33 [accessed 2 May 2018].

Jordano, P. 1987. Patterns of mutualistic interactions in pollination and seed dispersal: Connectance,

dependence asymmetries, and coevolution. Am. Nat. 129: 657-677. doi:10.1086/284665.

Junker, R.R., Höcherl, N., and Blüthgen, N. 2010. Responses to olfactory signals reflect network structure

of flower‐visitor interactions. J. Anim. Ecol. 79(4): 818-823. doi:10.1111/j.1365-2656.2010.01698.x.

Kantsa, A., Raguso, R.A., Dyer, A.G., Olesen, J.M., Tscheulin, T., and Petanidou, T. 2017. Disentangling

the role of floral sensory stimul in pollination networks. Nature Commun. 9(1): 1041.

doi:10.1038/s41467-018-03448-w.

Kearns, C.A. 1992. Anthophilous fly distribution across an elevation gradient. Am. Midl. Nat. 127(1):

172-182. doi:10.2307/2426332.

Kemp, J.E., Bergh, N.G., Soares, M., and Ellis, A.G. 2018. Dominant pollinators drive non-random

community assembly and shared flower colour patterns in daisy communities. Ann. Bot.

doi:10.1093/aob/mcy126.

Kevan, P.G. 1972. Floral colors in the high arctic with reference to insect–flower relations and

pollination. Can. J. Bot. 50(11): 2289-2316. doi:10.1139/b72-298.

Kevan, P.G., and Baker, H.G. 1983. Insects as flower visitors and pollinators. Annu. Rev. Entomol. 28(1):

407-453. doi:10.1146/annurev.en.28.010183.002203.

Kimoto, C., DeBano, S.J., Thorp, R.W., Taylor, R.V., Schmalz, H., DelCurto, T., Johnson, T., Kennedy,

P.L., and Rao, S. 2012. Short‐term responses of native bees to livestock and implications for

managing ecosystem services in grasslands. Ecosphere, 3(10): 1-19. doi:10.1890/ES12-00118.1.

Page 26 of 47


Botany



https://doi.org/10.1111/j.1365-2656.2010.01698.x

https://doi.org/10.1093/aob/mcy126

https://doi.org/10.1139/b72-298

Draft

Knight, D.H. 1965. A gradient analysis of Wisconsin prairie vegetation on the basis of plant structure and

function. Ecology, 46(5): 744-747. doi.org/10.2307/1935018.

Kuussaari, M., Heliölä, J., Luoto, M.. and Pöyry, J. 2007. Determinants of local species richness of

diurnal Lepidoptera in boreal agricultural landscapes. Agric. Ecosyst. Environ. 122(3): 366-376.

doi:10.1016/j.agee.2007.02.008.

Lambkin, C.L., Boulter, S.L., Starick, N.T., Cantrell, B.K., Bickel, D.J., Wright, S.G., Power, N.,

Schutze, M.K., Turco, F., Nakamura, A., and Burwell, C.J. 2011. Altitudinal and seasonal variation in

the family-level assemblages of flies (Diptera) in an Australian subtropical rainforest: one hundred

thousand and counting! Mem. Queensl. Mus. 55(2): 315-331. http://hdl.handle.net/10072/43186

[accessed 2 May 2018].

Larson, B.M.H., Kevan, P.G., and Inouye, D.W. 2001. Flies and flowers: taxonomic diversity of

anthophiles and pollinators. Can. Entomol. 133(4): 439-465. https://doi.org/10.4039/Ent133439-4

[accessed 2 May 2018].

Larue, A.A.C., Raguso, R.A., and Junker, R.R. 2016. Experimental manipulation of floral scent bouquets

restructures flower–visitor interactions in the field. J. Anim. Ecol. 85(2): 396-408. doi:10.1111/1365-

2656.12441.

Lazaro, A., Tscheulin, T., Devalez, J., Nakas, G., and Petanidou, T. 2016. Effects of grazing intensity on

pollinator abundance and diversity, and on pollination services. Ecol. Entomol. 41(4): 400-412.

doi:10.1111/een.12310.

Lefebvre, V., Villemant, C., Fontaine, C., and Daugeron, C. 2018. Altitudinal, temporal and trophic

partitioning of flower-visitors in Alpine communities. Sci. Rep. 8(1): 4706. doi:10.1038/s41598-018-

23210-y.

Lunau, K., and Maier, E.J. 1995. Innate colour preferences of flower visitors. J. Comp. Physiol. A 177(1):

1-19. doi:10.1007/BF00243394.

Markham, J. 2014. Rare species occupy uncommon niches. Sci. Rep. 4: 6012.

Page 27 of 47


Botany

https://doi.org/10.2307/1935018

http://hdl.handle.net/10072/43186

https://doi.org/10.4039/Ent133439-4

https://doi.org/10.1111/1365-2656.12441

https://doi.org/10.1111/1365-2656.12441

Draft

Marshall, S.A. 2012. Flies: The natural history and diversity of Diptera. Firefly Books, Richmond Hill,

Ontario.

McCall, C., and Primack, R.B. 1992. Influence of flower characteristics, weather, time of day, and season

on insect visitation rates in three plant communities. Am. J. Bot. 79(4): 434-442.

doi:10.2307/2445156.

McCune, B., and Mefford, M.J. 1999. PC-ORD for Windows. Multivariate analysis of ecological data.

Version 4.0. MjM Software, Gleneden Beach, Oregon.

McCune, B., and Grace, J.B. 2002. Analysis of ecological communities. MjM Software, Gleneden Beach,

Oregon.

Michener, C.D. 1979. Biogeography of the bees. Ann. Mo. Bot. Gard. 66(3): 277-347.

doi:10.2307/2398833.

Mosquin, T., and Martin, J.E. 1967. Observations on the pollination biology of plants on Melville Island,

N.W.T., Canada. Can. Field-Nat. 81: 201–205.

Olff, H., and Ritchie, M.E. 1998. Effects of herbivores on grassland plant diversity. Trends Ecol. Evol.

13(7): 261-265. Available from http://dx.doi.org/10.1016/S0169-5347(98)01364-0 [accessed 4 March

2017].

Olynyk, M., 2018. Effects of habitat loss, fragmentation, and alteration on wild bees and pollination

services in fragmented Manitoba grasslands. M.Sc. thesis, Department of Biological Sciences,

University of Manitoba, Winnipeg, Manitoba.

Owen, J., and Gilbert, F.S. 1989. On the abundance of hoverflies (Syrphidae). Oikos, 55(2): 183-193.

doi:10.2307/3565422.

Pellissier, L., Pottier, J., Vittoz, P., Dubuis, A., and Guisan, A. 2010. Spatial pattern of floral morphology:

possible insight into the effects of pollinators on plant distributions. Oikos, 119(11): 1805-1813.

doi:10.1111/j.1600-0706.2010.18560.x.

Page 28 of 47


Botany

http://dx.doi.org/10.1016/S0169-5347(98)01364-0

https://doi.org/10.1111/j.1600-0706.2010.18560.x

Draft

Pellissier, L., Alvarez, N., and Guisan, A. 2012. Pollinators as drivers of plant distribution and

assemblage into communities. In Evolution of Plant-Pollinator Relationships. Edited by S. Patiny.

Cambridge University Press, Cambridge, United Kingdom, pp. 392-413.

Pitts-Singer, T.L., and James, R.R. 2008. Do weather conditions correlate with findings in failed,

provision-filled nest cells of Megachile rotundata (Hymenoptera: Megachilidae) in western North

America? J. Econ. Entomol. 101(3): 674-685. doi:10.1603/0022-

0493(2008)101[674:DWCCWF]2.0.CO;2.

Potts, S.G., and Willmer, P. 1997. Abiotic and biotic factors influencing nest-site selection by Halictus

rubicundus, a ground-nesting halictine bee. Ecol. Entomol. 22(3): 319–328. doi:10.1046/j.1365-

2311.1997.00071.x.

Rathcke, B. 1983. Competition and facilitation among plants for pollination. In Pollination Biology.

Edited by L. Real. Academic Press Inc., Montreal. pp. 305-329.

Robson, D.B. 2008. The structure of the flower-insect visitor system in tall-grass prairie. Botany, 86(11):

1266-1278. doi:10.1139/B08-083.

Robson, D.B. 2010. A comparison of flower visiting insects to rare Symphyotrichum sericeum and

common Solidago nemoralis (Asteraceae). Botany, 88(3): 241-249. doi:10.1139/B10-003.

Robson, D.B. 2013. An assessment of the potential for pollination facilitation of a rare plant by common

plants: Symphyotrichum sericeum (Asteraceae) as a case study. Botany, 91(1): 34-42. doi:10.1139/cjb-

2012-0133.

Robson, D.B., Hamel, C., and Neufeld, R. 2017. Identification of plant species for pollinator restoration

in the northern prairies. J. Poll. Ecol. 21(6): 98-108. Available from



Sargent, R.D., and Ackerly, D.D. 2008. Plant–pollinator interactions and the assembly of plant

communities. Trends Ecol. Evol. 23(3): 123-130. doi:10.1016/j.tree.2007.11.003.

SAS Institute. 2010. SAS v. 9.3. Cary, North Carolina.

Page 29 of 47


Botany

https://doi.org/10.1603/0022-0493(2008)101%5b674:DWCCWF%5d2.0.CO;2

https://doi.org/10.1603/0022-0493(2008)101%5b674:DWCCWF%5d2.0.CO;2

https://doi.org/10.1046/j.1365-2311.1997.00071.x

https://doi.org/10.1046/j.1365-2311.1997.00071.x



https://doi.org/10.1016/j.tree.2007.11.003

Draft

Semmler, S.J. 2016. Community composition and pollination network structure in a fire managed

Canadian tall grass prairie. M.Sc. thesis, Department of Biological Sciences, University of Manitoba,

Winnipeg, Manitoba.

Sheffield, C.S., Frier, S.D., and Dumesh, S. 2014. The bees (Hymenoptera: Apoidea, Apiformes) of the

Prairie Ecozone, with comparisons to other grasslands of Canada. In Arthropods of Canadian

grasslands volume 4: biodiversity and systematics, part 2. Edited by J. Giberson and H.A. Carcamo.

Biological Survey of Canada, pp. 427-467.

Ssymank, A., Kearns, C.A., Pape, T., and Thompson, F.C. 2008. Pollinating flies (Diptera): a major

contribution to plant diversity and agricultural production. Biodiversity, 9(1-2): 86-89.

doi:10.1080/14888386.2008.9712892.

Stang, M., Klinkhamer, P.G., and Van Der Meijden, E. 2006. Size constraints and flower abundance

determine the number of interactions in a plant–flower visitor web. Oikos, 112(1): 111-121.

doi:10.1111/j.0030-1299.2006.14199.x.

Stoner, K.J., and Joern, A. 2004. Landscape vs. local habitat scale influences to insect communities from

tallgrass prairie remnants. Ecol. Appl. 14(5): 1306-1320. doi:10.1890/03-5112.

Ter Braak, C.J.F. 1986. Canonical correspondence analysis: a new eigenvector technique for multivariate

direct gradient analysis. Ecology, 67(5):1167-1168. Available from

http://www.jstor.org/stable/1938672 [accessed 13 June 2018].

Towne, E.G., Hartnett, D.C., and Cochran, R.C. 2005. Vegetation trends in tallgrass prairie from bison

and cattle grazing. Ecol. Appl. 15(5): 1550–1559. doi:10.1890/04-1958.

Vamosi, J.C., Moray, C.M., Garcha, N.K., Chamberlain, S.A., and Mooers, A.Ø. 2014. Pollinators visit

related plant species across 29 plant–pollinator networks. Ecol. Evol. 4(12): 2303-2315.

doi:10.1002/ece3.1051.

Villalobos, S., and Vamosi, J.C. 2018. Climate and habitat influences on bee pollinator community

structure in Western Canada. Can. J. Zool. 96(9): 1002-1009. doi:10.1139/cjz-2017-0226.

Page 30 of 47


Botany

https://doi.org/10.1080/14888386.2008.9712892

https://doi.org/10.1111/j.0030-1299.2006.14199.x

https://doi.org/10.1890/03-5112

http://www.jstor.org/stable/1938672

https://doi.org/10.1002/ece3.1051

https://doi.org/10.1139/cjz-2017-0226

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Vinton, M.A., and Burke, I.C. 1997. Contingent effects of plant species on soils along a regional moisture

gradient in the Great Plains. Oecologia, 110(3): 393-402. doi:10.1007/s004420050174.

Werner, P.A., and Platt, W.J. 1976. Ecological relationships of co-occurring goldenrods (Solidago:

Compositae). Am. Nat. 110(976): 959-971. doi:10.1086/283120.

Wilcock, C., and Neiland, R. 2002. Pollination failure in plants: why it happens and when it matters.

Trends Plant Sci. 7(6): 270-277. doi:10.1016/S1360-1385(02)02258-6.

Williams, N., Minckley, R., and Silveira, F. 2001. Variation in native bee faunas and its implications for

detecting community changes. Conserv. Ecol. 5(1): 7. Available from

http://www.consecol.org/vol5/iss1/art7/ [accessed 2 May 2018].

Willms, W.D., Smoliak, S., and Dormaar, J.F. 1985. Effects of stocking rate on a rough fescue grassland.

J. Range Manage. 38(3): 220-225. doi:10.2307/3898970.

Willms, W.D., Dormaar, J.F., and Schaalje, G.B. 1988. Stability of grazed patches on rough fescue

grasslands. J. Range Manage. 41(6): 503-508. doi:10.2307/3899527.

Woodcock, T.S., Larson, B.M., Kevan, P.G., Inouye, D.W., and Lunau, K. 2014. Flies and flowers II:

Floral attractants and rewards. J. Poll. Ecol. 12(8): 63-94. Available at



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Table 1. Location, environmental* and land management information on the five prairie study sites.

Site Prairie

type

Ecoregion Surficial geology Soil order Elevation

(m)

Annual

precip.

(mean mm)

Frost free

days

(mean #)

Land management

during survey years

Fescue Prairie

Preserves

Fescue Boreal

Transition

Glacial till,

sand/silt

Chernozemic 610 510 96-105 Ungrazed † and

unburned

Yellow Quill

Prairie Preserve

Mixed

grass

Aspen

Parkland

Glaciolacustrine,

sand/silt

Chernozemic 409 474 106-115 Grazed and

unburned

Birds Hill

Provincial Park

Dry tall

grass

Lake Manitoba

Plain

Glaciofluvial,

gravel/silt/sand

Chernozemic 265 550 116-125 Ungrazed and

unburned

Living Prairie

Museum

Mesic

tall

grass

Lake Manitoba

Plain

Glaciofluvial,

clay/silt/sand

Vertisolic 239 521 116-125 Ungrazed; two

2004 plots on

burned prairie

Tall Grass Prairie

Preserve

Wet tall

grass

Lake Manitoba

Plain

Glacial till,

gravel/clay/silt/

sand

Gleysolic 301 581 116-125 Ungrazed and

unburned

* Ecological Stratification Working Group 1995, Environment Canada 2018

† Six of the plots had been grazed the year before the study began (2013).

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Table 2. Survey information and mean weather conditions during the survey periods at each study site.

Site Survey

year

Survey

months

Total area

surveyed (m2)

Sampling

effort (hrs)

Weather station

(km & direction

from study site)*

Temperature

(mean ºC±SE)

Humidity

(mean ±SE)

Wind speed (mean

km hr-1 ±SE)

Fescue Prairie

Preserves

2014 Jun-Sep 72 48 Rossburn 4 North

(~21 km S)

16.4±1.6 56.5±3.1 10.8±0.9

2015 Jun-Sep 72 48 18.9±0.6 49.6±1.8 9.2±0.8

Yellow Quill

Prairie Preserve

2016 Jun-Sep 96 64 Brandon (~27 km

NW)

20.7±0.8 58.9±1.7 16.7±1.6

2017 May-Aug 96 64 23.6±1.0 47.3±4.4 19.9±2.3

Birds Hill

Provincial Park

2008 Aug-Sep 100 35 Winnipeg The

Forks (~22 km S)

19.9±0.6 54.1±1.8 22.8±1.5

2010 Jul-Aug 100 32 24.8±0.6 64.6±1.6 15.8±0.8

2011 Jun-Jul 100 32 23.1±0.4 51.2±1.7 20.7±1.1

Living Prairie

Museum

2004 Jun-Sep 150 48 Winnipeg

Richardson Int’l

Airport (~4 km E)

20.9±0.9 58.5±3.8 17.9±2.1

2005 Jun-Sep 150 48 19.6±1.1 57.9±2.8 16.9±1.9

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Tall Grass Prairie

Preserve

2004 Jun-Sep 150 48 Emerson (~36 km

NE)

17.3±1.2 61.1±3.4 13.6±1.5

2005 Jun-Sep 150 48 20.1±1.2 68.3±4.9 15.3±1.6

* Environment Canada

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Table 3. Sørenson similarity of the plant and insect communities between five study sites.

Sørensen Similarity

Plant Community Insect Community

Prairie Type Site FPP YQPP BHPP LPM TGPP FPP YQPP BHPP LPM TGPP

Fescue prairie Fescue Prairie

Preserves (FPP) 0 0.307 0.349 0.355 0.450 0 0.201 0.442 0.340 0.777

Mixed grass

prairie

Yellow Quill Prairie

Preserves (YQPP) 0.307 0 0.411 0.456 0.526 0.201 0 0.436 0.332 0.760

Tall grass prairie Birds Hill Provincial

Park (BHPP) 0.349 0.411 0 0.380 0.416 0.442 0.436 0 0.322 0.603

Living Prairie Museum

(LPM) 0.355 0.456 0.380 0 0.316 0.340 0.332 0.322 0 0.625

Tall Grass Prairie

Preserve (TGPP) 0.450 0.526 0.416 0.316 0 0.777 0.760 0.603 0.625 0

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Table 4. Number of plant and insect taxa surveyed at each site and connectance data.

Plant taxa Insect taxa

Site Surveyed

(#)

Visited

(# = p)

Visited

(%)

Identified to

species

[# (%)]

Identified

to genus

[# (%)]

Identified to

family/order

[# (%)]

Total

(# = a)

Interactions

(I)

Connectance*

Fescue Prairie Preserves 58 47 81 83 (76) 20 (18) 7 (6) 110 469 9.07

Yellow Quill Prairie Preserve 63 49 78 65 (66) 17 (17) 16 (17) 98 377 7.85

Birds Hill Provincial Park 35 26 74 62 (68) 16 (18) 13 (14) 91 204 8.62

Living Prairie Museum 39 32 82 37 (55) 20 (30) 10 (15) 67 159 7.42

Tall Grass Prairie Preserve 46 33 72 27 (46) 23 (40) 8 (14) 58 204 10.66

* Connectance (C = 100I / ap)

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Table 5. Differences among prairie type in proportional representation of insect visits by three functional

groups.

Functional Group Comparison Estimate SE P

Lower

CL

Upper

CL

Long-tongued Bees Fescue vs. Tall grass 20.037 2.096 0.0002 14.650 25.424

Mixed grass vs. Tall grass 13.593 1.845 0.0007 8.851 18.335

Fescue vs. Mixed grass 6.424 2.153 0.0306 0.890 11.957

Short-tongued Bees Fescue vs. Tall grass -2.172 1.376 0.1753 -5.711 1.366

Mixed grass vs. Tall grass 0.303 1.216 0.8131 -2.823 3.429

Fescue vs. Mixed grass -2.472 1.435 0.1455 -6.161 1.217

Diptera Fescue vs. Tall grass -13.991 2.055 0.0010 -19.273 -8.708

Mixed grass vs. Tall grass -13.876 1.805 0.0006 -18.517 -9.234

Fescue vs. Mixed grass -0.115 2.135 0.9590 -5.603 5.372

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Table 6. Mean proportion of inflorescences and insect visits to plants according to flower shape, symmetry and colour at three prairie types.

Prairie type Flower shape (%)* Flower symmetry (%) Flower colour (%)

Open Tubular Actinomorphic Zygomorphic Violet/blue White Pink Yellow/orange

Fescue prairie Inflorescences 54.6 a 45.4 a 80.5 a 19.5 a 34.1 ab 29.4 a 11.1 a 25.5 a

Mixed grass prairie 68.0 b 31.7 b 72.9 b 26.8 b 36.7 a 38.6 b 6.2 b 18.1 b

Tall grass prairie† 70.4 b 25.2 c 77.4 ab 18.2 a 30.6 b 19.2 c 12.4 a 33.4 c

Fescue prairie Insect visits 41.6 31.1 a 56.4 a 16.2 a 30.9 a 15.9 a 3.9 n/a 21.9 ab

Mixed grass prairie 45.5 19.7 b 43.8 b 21.5 b 26.5 a 16.0 a 4.3 n/a 18.5 b

Tall grass prairie† 48.7 12.6 c 53.0 ab 8.2 c 15.9 b 10.1 b 7.5 n/a 27.7 a

* Lowercase letters indicate statistically significant (p < 0.05) differences in proportions among sites using Generalized Linear Mixed Models.

† Includes data from Birds Hill Provincial Park, Living Prairie Museum and Tall Grass Prairie Preserve sites.

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Table 7. Results of the impact of environmental conditions and proportion of flower types on insect visits by three functional groups.

Pollinator Visits Predictor Variable Estimate SE P Lower CL Upper CL

Diptera Temperature 1.6626 0.28 <.0001 1.1135 2.2118

Humidity 0.6267 0.1347 <.0001 0.3626 0.8908

Temperature*Humidity -0.03063 0.006563 <.0001 -0.0435 -0.01776

Annual precipitation 0.2022 0.03343 <.0001 0.1367 0.2678

Proportion open 0.1108 0.02259 <.0001 0.06649 0.1551

Proportion actinomorphic 0.09434 0.03487 0.0069 0.02597 0.1627

Proportion blue 0.09435 0.05918 0.111 -0.0217 0.2104

Proportion white 0.1424 0.0669 0.0334 0.0112 0.2736

Proportion pink -0.03823 0.07064 0.5884 -0.1768 0.1003

Proportion yellow 0.1711 0.06867 0.0128 0.03645 0.3058

Long-tongued Bees Temperature 0.6812 0.2853 0.017 0.1218 1.2406

Humidity 0.02665 0.1369 0.8457 -0.2418 0.2951

Temperature*Humidity -0.01564 0.006687 0.0194 -0.02875 -0.00253

Annual precipitation -0.02629 0.03446 0.4456 -0.09385 0.04128

Proportion open -0.03895 0.02307 0.0915 -0.08419 0.006289

Proportion actinomorphic -0.1464 0.03565 <.0001 -0.2163 -0.0765

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Proportion blue 0.3244 0.06081 <.0001 0.2051 0.4437

Proportion white 0.233 0.06849 0.0007 0.0987 0.3673

Proportion pink 0.3129 0.07258 <.0001 0.1706 0.4553

Proportion yellow 0.3003 0.07067 <.0001 0.1617 0.4389

Short-tongued Bees Temperature 0.5638 0.1935 0.0036 0.1844 0.9432

Humidity 0.2039 0.09287 0.0283 0.02172 0.386

Temperature*Humidity -0.01087 0.004535 0.0166 -0.01976 -0.00198

Annual precipitation 0.007411 0.02314 0.7488 -0.03797 0.05279

Proportion open -0.00685 0.01563 0.6615 -0.03749 0.0238

Proportion actinomorphic 0.05784 0.02414 0.0166 0.01051 0.1052

Proportion blue 0.05862 0.04098 0.1527 -0.02174 0.139

Proportion white 0.04196 0.04631 0.3649 -0.04885 0.1328

Proportion pink 0.07119 0.04891 0.1457 -0.02473 0.1671

Proportion yellow 0.06395 0.04761 0.1794 -0.02943 0.1573

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Figure 1. Location of the five study sites in southern Manitoba. Copyright © 2001-2018, the Government

of Manitoba. All rights reserved. The Government of Manitoba is the owner of copyright in all

information contained in this Manitoba Land Initiative, unless otherwise noted.

Figure 2. Canonical Correspondence Analysis (CCA) joint plots of (a) plant, and (b) insect family

proportions sampled at five sites (triangles): Birds Hill Provincial Park (BHPP), Fescue Prairie Preserves

(FPP), Living Prairie Museum (LPM), Tall Grass Prairie Preserve (TGPP), and Yellow Quill Prairie

Preserve (YQPP). Lines represent environmental variables: average annual precipitation (Ann prec),

elevation (Elevatio), average humidity during survey days (Humid) and average temperature during

survey days (Temp).

Figure 3. Percentage of (a) all taxa, and (b) all visitations in six functional groups of insects at the five

study sites. Pearsons χ2 (20, N = 500) = (a) 31.83 (p = 0.04), and (b) 144.75 (p<0.0001) indicated these

proportions were significantly different.

Figure 4. Percentage of all bee visitations by long- (Apidae, Megachilidae) and short-tongued bees

(Andrenidae, Colletidae and Halictidae) at the five study sites. Pearsons χ2 (20, N = 500) = 116.35,

p<0.0001 indicated these proportions were significantly different.

Figure 5. Percentage of all visitations by the five dominant families of flies (Diptera) and all other

families, at the five study sites. Pearsons χ2 (20, N = 500) = 324.24, p<0.0001 indicated these proportions

were significantly different.

Figure 6. Percentage of all visitations by different trophic groups at the five study sites. Aquatic species

may have been herbivores, omnivores or carnivores on microorganisms. Pearsons χ2 (12, N = 500) =

186.58, p<0.0001 indicated these proportions were significantly different.

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a)

b)

Tall grass prairie

Fescue prairie

Mixed grass prairie

Tall grass prairie

Mixed grass prairie

Fescue prairie

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Draft0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Long-tongued bees Short-tongued beesOther Hymenoptera DipteraLepidoptera Coleoptera/Hemiptera

Inse

ct ta

xa (%

)a)

Fescue Prairie Preserves

Yellow Quill Prairie Preserve

Birds Hill Provincial Park


Tall Grass Prairie Preserve

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Inse

ct v

isita

tions

(%)

Sites

b)

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DraftFescue Prairie

PreservesYellow Quill

Prairie Preserve

Birds Hill Provincial

Park


Tall Grass Prairie

Preserve

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Halictidae

Colletidae

Andrenidae

Megachilidae

ApidaeMea

n in

sect

vis

itatio

ns (%

)

Sites

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DraftFescue Prairie

Preserves


Preserve


Park


Tall Grass Prairie

Preserve

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Other

Tachinidae

Syrphidae

Stratiomyiidae

Muscidae

Bombyliidae

Mea

n in

sect

vis

itatio

ns (%

)

Sites

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DraftFescue Prairie

Preserves


Preserve


Park

Living Prairie

Museum

Tall Grass Prairie

Preserve

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Terrestrial saprovore

Terrestrial omnivore

Terrestrial herbivore

AquaticMea

n in

sect

vis

itatio

ns (%

)

Sites

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draft - university of toronto t-space · draft abstract the xeric hypothesis is that bees are more...

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