Fragmentation, Edges, Reserves and Connectivity

•Landscape perspective on wildlife responses to vegetative change

•Edge Effects–Nest predation

•Reserve Design and Theory

•Connectivity

Fragmentation or Habitat Loss?

• Habitat loss can (or cannot) increase isolation of remaining patches and increase (or not) formation of edges

• Fragmentation creates edges and reduces patch size

Habitat Loss is Key Aspect of Landscape Change

• Habitat loss may or may not fragment

• To study fragmentation we must focus on landscapes not patches

• Few studies compare loss and fragmentation– All find loss most

important

• Emphasizing fragmentation rather than loss is misleading, optimistic, and distracts us from need to conserve and restore habitat

(Fahrig 1999)

Lots of Ways to Measure Landscape Pattern

(Hargis et al. 1997)

Fig 9.1 here

• Amount of each class– Critical probability at point of

percolation• 50-65% of landscape depending on

pattern• Aggregation of classes into patches

– Patch size, shape, P/A, edge, density• Frequency distribution of patch

aggregation metrics– Gives landscape its texture

• Spatial distribution of patches– Distances between patches, exact

placement on landscape, distance to important features.

Thresholds in Response to Habitat Loss are Likely

• Factors affecting how much habitat is enough– Greater demographic

potential– Greater survival while

dispersing• Less hostile matrix

– Patch occupancy • Gap cross ability• Habitat connectivity• Area requirements

– Patch carrying capacity(Fahrig 1999)

More habitat also means more

connected habitat

(With 1999)

(Opdam and Wiens 2001)

Conceptualizing Breakup of Habitat with

Increasing Loss

Extinction probability drops when 50% of patches are occupied

(Vos et al. 2001)

Patch occupancy and extinction related to fragmentation for nuthatches

(Opdam and Wiens 2001)

Patch occupancy not clearly related to neutral landscape metrics

(Ecologically Scaled Landscape Indices Vos et al. 2001)

Fig4OverFig 5

Seeing Landscapes from “Organism’s eye” clarifies importance of amount and distribution of habitat

(Ecologically Scaled Landscape Indices Vos et al. 2001)

Case Study of Fragmentation

• In depth study links reproduction, survival, and dispersal to fragmentation– 7% of former habitat left– Lambda = 1.05 in

connected landscape, but 0.94 in fragmented

• Due to increased mortality during dispersal, not reproduction of survival of adults

(Smith and Hellmann 2002)

Beauty is in the eye of the beholder

• “Habitat” loss and fragmentation actually increases resources (habitat) for other species

(Fahrig 1999)

A Bevy of Fragmentation Effects

(Robinson et al. 1992; 3 replicated treatments of 1 large, 6 med or 15 small grasslands)

SnakesSmall mammal persistence

Small Mammals

Other Plants

Clonal Plants

Deer Mouse

Diversity of Edge Effects

DISTANCE FROM EDGE

NE

ST S

UC

CE

SS

(Murcia 1995)

Edge Effects Are Most Common In Ag/Urban Landscapes

0

5

10

15

20

25

Ag/Urban Forest

MATRIX HABITAT

NU

MB

ER

OF

ST

UD

EIS Significant Effect

Effect not SignificantP = 0.053

(Marzluff and Restani 1999; also see Paton 1994 and Andren 1995)

Predator Identification Influences Detection of Edge Effects

0%

20%

40%

60%

80%

100%

Effect No Effect

TYPE OF RESPONSE

PE

RC

EN

TA

GE

OF

ST

UD

IES

No. I.D. Corvids Mammals Corvids and Mammals

More Complete

Understanding

Predator Identification Influences Detection of Fragmentation Effects

0%

20%

40%

60%

80%

100%

Effect No Effect

TYPE OF RESPONSE

PE

RC

EN

TA

GE

OF

ST

UD

IES

No I.D. Corvids Mammals Corvids and Mammals

Better

Understanding

We Need to Understand The Behavior of the Predator

• Habitat selection– Predator and prey

– Matrix, edge, and/or fragment

• Density and diversity– Predator assemblage

– Alternative prey

• Behavior– Searching behavior

– Defensive behavior

Habitat Selection Of Nest Predators

Matrix Habitat Forest Habitat

MatrixSpecialist

ForestSpecialist

ForestGeneralist

MatrixGeneralist

Edge Specialist

Learning how Steller’s Jays forageVigallon and Marzluff (in press)

Incidental Predation

Correlates of s Can Indicate Why Effects Are Not Greater

• Use of edges is related to proximity to human activity (F(1,24) = 5.4; P=0.04)– Anthropogenic food

available in these settings

– Rate of predation on other birds’ nests is highest closest to such edges in our study area

Rel

ativ

e U

se ( )

of

Ed

ge

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

N = 10 N = 15

<1 Km >5 Km

Proximity to Settled Areas and Campgrounds

Edge Effects into Reserves

• Carnivores with large home ranges were most sensitive to reserve size because they range outside of reserve and are killed (intentionally or accidentally) by people

(Woodroffe and Ginsberg 1998)

McArthur and Wilson’s Model

Number of Species

Rate

Extinction

Colonization small large

near

farThis drives concern forsize and connectivity

Lomolino’s (1999)View

• Insular distribution functions– Delineates combinations of

area and isolation where extinction and immigration rates are equal

• Focal species occur where island characteristics produce ratios with extinction<immigration and do not occur where extinction>immigration

• Area determines extinction (pop size)

• Isolation determines colonization

Intercept measures minimum area requirement on mainlandSlope measures inverse of immigration ability

Richness is not Linearly Related to Area

• Driven by resources requirements of individual species– Related to body size

– Skewed toward most species needing few resources

– As with most relationships involving body size, richness will scale with area to the ~.26 power

Richness is not Linearly Related to Isolation

• Threshold relationship up to point where isolation exceeds immigration ability of least vagile species (Dnear)– Related to individual

species’ immigration abilities

• Distribution of slopes of IDFs

– Most are limited

Resources, landscape, and community effects

What Does This Mean For Reserves?

• Size and Isolation likely matter in non linear way

• Colonization is important, may be affected by “permeability” of landscape

• Thresholds of occurrence of each species will occur

• Resources needs and presence of predators, competitors, etc may affect final community composition

• Reserves may include nested subsets of entire fauna (those with positive ratios of immigration to extinction)

Urbanization intensity

UrbanSuburbanExurban

Increasing size

Reserve study design factors(Donnelly and Marzluff)

MediumSmall Large

Landscape designation based on classified LANDSAT satellite image

• 3 Class landcover– Exurban– Suburban– Urban

• 29 Field sites

%U

%U %U

%U

%U

%U

%U

%U

%U

%U

%U

%U%U

%U

%U%U%U

%U

%U

%U

%U

%U

%U

%U%U

%U

%U

%U%U

0 10 kmN

Richness was related to size and landscape

• Landscape– F = 4.3, P < 0.03

– Unexpected direction consistent with intermediate disturbance?

• Size– F = 19.1, P < 0.01

Reserve size

Small Medium Large

Mea

n r

ich

nes

s +

SE

0

5

10

15

20

25

30ExurbanSuburbanUrban

Controlling for sampling effort relegates size to a qualifier for landscape effect

• Detected more species in larger reserves because – Detected more

individuals– Increased chance

of detecting a “new” species

Small Medium LargeMe

an

ra

refi

ed

ric

hn

es

s +

SE

0

5

10

15

20

25

30ExurbanSuburbanUrban

Reserve size

Interaction F = 4.9, P < 0.01

Size matters most in urban

Native forest species showed thresholds of occurrence with size

• Matrix was ordered– % perfect

prediction = 19.2, P < 0.01

• Mean threshold = 42 ± 15 ha

Synanthropic species showed thresholds of occurrence with urban landcover

• Matrix was ordered– % perfect

prediction = 13.5, P < 0.02

• Mean threshold = 40 ± 10 % urban landcover

Designing Reserve Complexes•Enlarge key patches

•May require less total reserved area than lots of small patches

•Increase connectivity(Opdam and Wiens 2002)

•Recognize patch dynamics•Understand succession and disturbance•Reserves should be larger than disturbance patch size•Include internal recolonization sources•Include different ages of disturbance-generated patches(Pickett and Thompson 1978)

(Soulé 1991)

(Shafer 1997)

Do Corridors Provide Connectivity?• Advantages

– Gene flow, rescue, recreates the normal condition of species living in well-connected environments

• Disadvantages– Spread disease, lure animals into poor habitat

• Beier and Noss (1998) review studies and conclude that majority of well-designed ones show benefits outweigh costs– Need more B.A.C. studies that measure demography– Need more observations of real dispersing animals in real landscapes

• Cougars avoid urban barriers

• Argue that burden of proof should be on those who will destroy the connections

Connectivity and Reserve Design(Schmiegelow and Hannon 1999, Hannon and Schmiegelow

2002)

Long-term experimental study at Calling Lake, Alberta

•1993-continuing, 3 replicates of patches of various size and connectivity (100m-wide buffers)•Species turnover is highest in small isolates, indicating extinctions, but also colonizations.•Richness remained equal among treatments indicating replacements of permanent residents on the small, isolated fragments•Resident birds went extinct most frequently•Species vary in their ability (“willingness”?) to cross gaps, but this sensitivity does not predict whether they will remain abundant in connected fragments versus isolated ones•Corridors may help a few resident species (via rescue effects), but they do not appear to offset the impacts of fragmentation (habitat loss, edge creation) for most boreal birds

•May benefit western tanagers and black-throated green warblers most

•May be better to use forest allocated to corridors to actually increase size of reserves instead of connecting small reserves

Manage the Vegetation in the Fragment

• Maintain native vegetation

• Increase foliage height diversity

• Actively discourage lawns

• Manage limiting factors– Small mammals– Cats– Exotic species

Manage the Matrix

• Regulate, enforce, educate to reduce penetration of predators, competitors, humans, chemicals, etc. from matrix into fragment

• Make the habitat in the matrix more like habitat in fragment

• Reduce food supplementation

• Control cat movements

Design Creative Buffers

• Buffering with space alone is not enough

• Buffers must reduce the penetration of undesirable agents from the matrix into the fragment– Harsh, sterile, unihabitable

habitats may be best!– Good habitat may act as a

“wick” rather than a buffer

Recognize the Importance of Distant Lands

• Populations in fragments may be supported by dispersal from distant “source” populations

• Protect distant sources by keeping them DISTANT– develop growth

management policies Wildland

Suburban

Exurban

Urban

Realize That You Cannot Make Fragments Suitable for All Species

• As the matrix becomes more hostile, conservation of many species will be difficult to impossible

• Concentrate on the native species that reproduce and survive well.

• Identify and stop maintaining “sink” populations

• Some fragments may not be suitable as reserves at all– Use as educational centers

Making Parks Successful• Parks appear effective at stopping

land clearing and stemming some threats to biodiversity (Bruner et al. 2001)

– Degree of effectiveness correlates with enforcement, boundary demarcation, compensation of locals

• But is this enough? (Stern 2001)

– Need constituency-building among locals– Otherwise costs of purchase pale in

comparison to costs of social upheaval and conflict

• Community-based conservation is needed in conjunction with preservation

Reserves in Conservation Planning Perspective

• Reserves are not enough– Cornerstone that separates biodiversity from its threats– Need to represent adequately biodiversity of a region

• Past planning has been opportunistic not systematic

– Science and social, economic, and political imperatives need to meet and be compromised

• Design criteria of reserves has been discussed, now need to see how the science of biogeography, metapopulations, evolutionary significant units, and source-sink dynamics, among others are modified to result in on-the-ground reserves

(Margules and Pressey 2000)

Computational Methods Exist to Guide Reserve Network Design

• Goal is to ID sets of reserves that maximize biodiversity in a region (Cabeza and Moilanen 2001)

– With minimal sites, area, or cost– Mathematical optimization problem– Rarely used in practice

• More common is to take most vulnerable sites first, then those representing species that are irreplaceable (Margules and Pressey 2000)

• Regardless, the success of reserves at representing biodiversity and then maintaining it for the long-term is rarely assessed

References• Margules, CR and RL Pressey. 2000. Systematic conservation planning. Nature 405:243-253.• Beier, P and RF Noss. 1998. Do habitat corridors provide connectivity? Conservation Biology

12:1241-1252.• Lomolino, M. V. 1999. A species-based, hierarchical model of island biogeography. Pp. 272-310 in,

The Search for Assembly Rules in Ecological Communities (E. A. Weiher and P. A. Keddy, eds.).Cambridge University Press, New York.

• Cabeza, M. and A. Moilanen. 2001. Design of reserve networks and the persistence of biodiversity. Trends in Ecology and Evolution 16(5) 242-248.

• Pickett, STA and JN Thompson. 1978. Patch dynamics and the design of nature reserves. Biological Conservation 13:27-37.

• Opdam, P., and J. A. Wiens. 2002. Fragmentation, habitat loss and landscape management Pp 202-223 In In Norris, K., and D. J. Pain (editors). Conserving Bird Diversity General Principles and their Application, vol 7. Cambridge University Press, Oxford, UK.

• Schmiegelow, FKA and SJ Hannon. 1999. Forest-level effectgs of management on boreal songbirds: the calling lake fragmentation studies. Pp: 201-221. In: Forest Fragmentation: Wildlife and Management Implications (J. A. Rochelle, L. A. Lehmann, and J. Wisniewski eds.). Brill Academic Publishing, Leiden, The Neatherlands.

• Hannon, SJ and FKA Schmiegelow. 2002. Corridors may not improve the conservation value of small reserves for most boreal birds. Ecological Applications 12:1457-1468.

• MacArthur, RH and EO Wilson. 1967. The theory of island biogeography. Princeton University Press, Princeton, NJ.• Bruner, AG, RE Gullison, RE Riche, and GAB da Fonseca. 2001. Effectiveness of parks in protecting tropical

biodiversity. Science 291:125-128.• Stern, M. 2001. Parks and factors in their success. Science 293:1045.• Oodam, P. and Wiens, JA. 2002. Fragmentation, habitat loss and landscape management. Pp 202-223. in. K Norris and

DJ Pain, eds. Conserving Bird Biodiversity: General principles and their application. Cambridge.• Shafer, C. L. 1997. Terrestrial nature reserve design at the urban/rural interface. Pages 345-378 in M. W. Schwartz,

editor. Conservation in Highly Fragmented Landscapes. Chapman and Hall, New York, NY.• Soulé, M. E. 1991. Land use planning and wildlife maintenance. Journal of the American Planning Association

57:313-323.

References• Clark, JD. Et al. 1993. A multivariate model of female black bear habitat use for a geographic information system. JWM 57:519-526.• Knick, ST and DL Dyer. 1997. Distribution of black-tailed jackrabbit habitat determined by GIS in southwestern Idaho. JWM 61:75-85.• Cody, ML. (ed.). 1985. Habitat selection in birds. Academic Press, San Diego, CA.• Fretwell, SD and Lucas, HL, Jr. 1969. On territorial behavior and other factors influencing habitat distribution in birds. Acta Biotheoret.

19:16-36.• Hilden, O. 1965. Habitat selection in birds. Annales Zoologici Fennici 2:53-75.• James, FC. 1971. Ordinations of habitat relationships among breeding birds. Wilson Bull. 83:215-236.• Klomp, H. 1954. De terreinkeus van de Kievit, Vanellus vanellus (L.). Ardea 42:1-139.• Klopfer, PH and JP Hailman. 1965. Habitat selection in birds. Advances in the Study of Behavior 1:279-303.• Klopfer, PH and JU Ganzhorn. 1985. Habitat selection: behavioral aspects. Pp. 435-453. In. M.L. Cody, ed. Habitat selection in birds.

Academic Press, San Diego, CA. • Partridge, L. 1978. Habitat selection. Pp. 351-376. In. J.R. Krebs and N. B. Davies, eds. Behavioural Ecology, an evolutionary approach.

Sinauer. Sunderland, MA.• Verner, J. 1975. Avian behavior and habitat management. Pp. 39-54. in Procedings of the Symposium on Management of Forest and Range

Habitats for Nongame Birds, Tuscon, AZ. May 6-9 1975.• Wiens, JA. 1972. Anuran habitat selection: early experience and substrate selection in Rana cascadae tadpoles. Animal Behaviour 20:218-220.• Wiens, JA. 1985. Habitat selection in variable environments: shrub-steppe birds. Pp. 227-251 In. M.L. Cody, ed. Habitat selection in birds.

Academic Press, San Diego, CA. • Wiens, JA. and JT. Rotenberry. 1981. Habitat associations and community structure of birds in shrubsteppe environments. Ecological

Monographs 51:21-41.• Smith, JNM and JJ Hellmann. 2002. Population persistence in fragmented landscapes. TREE 17:397-399.• Vos, CC, Verboom, J, Opdam, PFM, and CJF Ter Braak. 2001. Toward ecologically scaled landscape indices. The American Naturalist.

157:24-41.• Marzluff JM and M Restani. 1999. The effects of forest fragmentation on avian nest predation. Pp: 155-169. In: Forest Fragmentation:

Wildlife and Management Implications (J. A. Rochelle, L. A. Lehmann, and J. Wisniewski eds.). Brill Academic Publishing, Leiden, The Neatherlands.

References• Fahrig, L. 1999. Forest loss and fragmentatino: which has the greater effect on persistence of forest-

dwelling animals? Pp: 87-95. In: Forest Fragmentation: Wildlife and Management Implications (J. A. Rochelle, L. A. Lehmann, and J. Wisniewski eds.). Brill Academic Publishing, Leiden, The Neatherlands.

• With, KA. 1999. Is landscape connectivity necessary and sufficient for wildlife management? Pp: 97-115. In: Forest Fragmentation: Wildlife and Management Implications (J. A. Rochelle, L. A. Lehmann, and J. Wisniewski eds.). Brill Academic Publishing, Leiden, The Neatherlands.

• Schmiegelow, FKA and SJ Hannon. 1999. Forest-level effectgs of management on boreal songbirds: the calling lake fragmentation studies. Pp: 201-221. In: Forest Fragmentation: Wildlife and Management Implications (J. A. Rochelle, L. A. Lehmann, and J. Wisniewski eds.). Brill Academic Publishing, Leiden, The Neatherlands.

• Murcia, C. 1995. Edge effects in fragmented forests: implications for conservation. TREE 10:58-62.• Woodroffe, R. and JR Ginsberg. 1998. Edge effects and the extinction of populations inside

protected areas. Science 280:2126-2128.• Robinson, GR, Hold, RD, Gaines, MS, Hanburg, SP, Johnson, ML, Fitch, HS, and EA Martinko.

1992. Diverse and contrasting effects of habitat fragmentation. Science 257:524-526.• Vigallon, S. M. and J. M. Marzluff. In press. IS NEST PREDATION BY STELLER’S JAYS

INCIDENTAL OR THE RESULT OF A SPECIALIZED SEARCH STRATEGY? Auk.