How to DO Ecology

Ecology and the Scientific Method

• Science is not a collection of facts

• Ecologists seek to understand patterns in nature using the Scientific Method– the danger of “just-so stories”

– null hypotheses and null models

– the importance of statistics

How to DO Ecology

• The Scientific Method– Review

– Good scientific experiments are designed to distinguish among alternative hypotheses

– Good science proceeds by the falsification of alternative hypotheses

– We can never prove a hypothesis to be true; we can only show (or fail to show) that it is false

How to DO Ecology

• The null hypothesis– States that the observed effect in an

experiment is simply the result of chance and is not due to some biological or other deterministic factor.

– The null hypothesis is either rejected or

– We “fail to reject” the null hypothesis• This does not mean we accept the null hypothesis

How to DO Ecology

• In a study of bat predation on moths, we notice that bats don’t often catch and consume small moths.

How to DO Ecology

• What is the null hypothesis for this example?

• How would you test this hypothesis?

• Interpret the following graph.

by bats

by bats

10%

15%

30%

45%

How to DO Ecology

• Ecological phenomena occur at a variety of scales

• Ecological evidence comes from a variety of different sources

• Ecology relies on truly scientific evidence and the application of statistics

Diversity of Ecological Evidence

1. Observations = Natural Snapshot Experiments

– Careful monitoring within the natural environment to detect patterns

– Descriptive data– One instant in time

Diversity of Ecological Evidence1. Observations = Natural Snapshot

Experiments– Repeated observations can reveal information

not apparent from one or a few observations

Lake Mendota, WI

Diversity of Ecological Evidence

2. Field experiments– Manipulative experiments in the field to

establish cause of observed patterns

Large-scale manipulative experiments at the Konza Prairie Research Natural Area

Large-scale manipulative experiments at the Konza Prairie Research Natural Area

Diversity of Ecological Evidence

3. Laboratory experiments– Controlled conditions– Simplified system– Address specific questions

Diversity of Ecological Evidence

4. Natural Trajectory– Natural phenomenon– Follow system after a

disturbance.

Diversity of Ecological Evidence

5. Mathematical modeling– Often computer-aided

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Laboratory Experiment

Field Experiment

Natural Trajectory Experiment

Natural Snapshot Experiment

Regulation of independent variables

Highest Medium/Low None None

Site matching Highest Medium Medium/Low Lowest

Ability to follow trajectory

Yes Yes Yes No

Maximum temporal scale

Lowest Lowest Highest Highest

Maximum spatial scale Lowest Low Highest Highest

Scope (range of manipulations)

Lowest Medium/Low Medium/High Highest

Realism None/Low High Highest Highest

Generality None Low High High

Scales of Ecological Organization

Individual

Population

Community

EcosystemBiosphere

Biome

Hierarchy in

Ecology

The Importance of Scale

• Ecologists study patterns and processes across a wide range of scales in space and time.

• Scale is important because of the heterogeneity of habitats

Distributions of Populations in Space• Dispersion patterns

– random• very rare

– clumped/aggregated/

contagious/underdispersed• flocking birds• salamanders under logs

– even/regular• tree farm• corn field• sea bird colonies• damselfish on reef

Implies interac-tions

-

+

Random

Clumped dispersionaround resources

Clumped dispersion due to positive social interactions

Clumped dispersion due to positive effect of schooling

Regular dispersion due to negative social interactions

Spatial Scale: E.g. aphids on maple trees

Forest Maple tree Maple leaf

Scale influences perception of patterns• E.g. aphids on maple tree large reference scale

• aggregated (on maples not oaks, on maples not on grass)

– smaller scale• 25 cm2 quadrats (~ 1 leaf): aphids are randomly

distributed• 1 cm2 quadrats: aphids are evenly distributed (avoid

each other)

Effect of Sampling Pattern (Grid) on Population Size Estimates in a population

having a clumped distribution pattern

Temporal Scale

• Relative to organism’s life history

• Ecological time

• Evolutionary time

Scale influences perception of patterns

• Spatial: Habitat fragmentation and species persistence– Spotted owls

– Giant Pandas

Scale influences perception of patterns

• Temporal: Population ups and downs may be normal periodic cycles or may indicate a major change– periodical cicadas

Liane Cochran-Stafira

Scale influences perception of patterns

• Understanding patterns may require long term observations and/or experiments– LTER sites: Long Term Ecological Research

• Hubbard Brook (text)

• Palmer Station (Antarctic)

• Konza Prairie (Kansas)

• Many more

How to DO Ecology

• At the lower levels of the biological hierarchy, processes tend to be more universal.

• Krebs Cycle works essentially the same way in all cells– yeast and whales– Universal to eukaryotes (and pretty similar in

many prokaryotes)

How to DO Ecology

• Now imagine an ecological question which falls at a higher level of the hierarchy.

• What is the role of predation in controlling prey populations?– Wolf and moose in Maine vs northern Canada

• Is it likely the effects of predation will be the same?

– What about lions and wildebeest?

Isle Royale - Wolves and Moose

Wolf Moose Story

• For a long time, Isle Royale had neither moose nor wolf. Then, the first moose swam to the island in about 1900. By 1930, ecologists estimated that the moose population had reached about 3,000. There was evidence that the moose were eating many of the plants on the island.

• In 1933, the moose began to die of starvation. Ecologists had predicted this decline because they understood the food relationship between the moose and plants.

Wolf Moose Story

• The moose population increased again between 1948 and 1950. However, about this time, wolves made their way to the island. As they killed moose for food, the wolf population grew. Eventually, an apparently stable balance of about 600 moose and 20 wolves became established.

• Ecologists pointed to Isle Royale as an example of the way in which predators can control prey and thus contribute to the development of stability in ecosystems.

Wolf Moose Story

• Around 1965, winters on Isle Royale returned to normal, and the wolves caught fewer moose. By the early 1980's, the moose population had again become extremely large, even though the wolf population had also grown. Then the wolf population began to decline, despite the abundance of moose. By the late 1980's, ecologists feared that wolves might disappear from Isle Royale. All of these population changes forced ecologists to reevaluate their thinking about how predators and prey control one another's populations.

• Ecologists recognized that although wolves and moose certainly can influence the size of each other's populations, these animal groups can completely determine one another's population size only under unusual circumstances.

Wolf Moose Story

• In the 1990's, Isle Royale's moose population declined again. Ecological studies indicated that changes in the availability of food plants and nutrients were important factors in this decline.

• For example, the moose would eat the leaves of aspen trees, but not the unpleasant-tasting needles from spruce and fir trees. And since spruce and fir needles also did not taste good to the island's decomposers, the needles piled up on the forest floor, trapping nitrogen and other nutrients from entering the soil. Thus the quality of the soil declined, and the growth of trees was stunted. This has meant less food for the moose and a decline in moose population.

Wolf Moose Story

• As for the wolves of Isle Royale, it appears that inbreeding and diseases (parvo) - not lack of moose-are behind the die-off of the population. Thus, predator-prey models of population control probably are oversimplifications, and what looks like a stable, balanced situation may in fact derive from the interaction of various changeable forces. Natural systems are filled with compensating mechanisms that help stabilize nature.

• Hence populations often need to be understood from the perspective of the entire ecosystem.

Actual evapotranspiration rates: AET is an approximation of primary productivity, it represents water availability as a function of temperature and rainfall.

Population parameters of the Isle Royale ecosystem from 1958-1994. Shaded areas signify periods of forage suppression that may be connected to interactions between herbivores and carnivores.

Coefficients of direct density dependence (solid circles)

Coefficients of direct climatic influence of the North Atlantic Oscillation (open circles)

Results Limiting influences of winter climate in moose

population dynamics, Mediating influence of winter climate in wolf-

moose interactions, Roles of wolf predation and density dependence

in moose dynamics, Direct influence of winter climate on growth

dynamics of balsam fir on Isle Royale. First documentation of direct and simultaneous

influences of large-scale climate on the dynamics at multiple trophic levels.

Mathematical model for moose, wolves, vegetation and climate

Model for wolves, moose, vegetation and climate. This is used to construct a set of equations that can be used to determine how climate affects plants and animals. Conclusion: climate affected top and bottom trophic levels most severely.

Model

Yt = β0 + (3 + β1)Yt-1 + (2 + β2)Yt-2 + (1 + β3)Yt-3 + ω1UDt + ω2UDt-1 + ω3UDt-2 + + ω4UPt + ω5UPt-1    

Zt = γ0 + (2 + γ1)Zt-1 + (1 + γ2)Zt-2 + ω1UDt + ω2UDt-1 + ω3UPt    

Other Factors

Wolves: Inbreeding

Moose: Winter Ticks

Bone Deformities Linked to Inbreeding in Wolves of Isle Royale

Bone Deformities Linked to Inbreeding in Wolves of Isle Royale

• 58% of the wolves on Isle Royale exhibit a congenital malformation in the lumbosacral region or lower back

• 33% display a specific deformity, lumbosacral transitional vertebrae, which can cause full or partial paralysis of the rear legs and tail, as well as back pain. It is a condition also seen in domestic dogs.

• Other malformations were found in the wolves as well.

• For the last 12 years, every one of the dead wolves the researchers have found has displayed bone deformities. In contrast, these deformities occur in only 1 percent of studied wolf populations that are not inbred.

Climate Change Effects

• In 2007 there were 385 moose on Isle Royale, down from 1100 in 2002.

• Causes of deaths– Warm springs and warm autumns

tend to promote a winter tick population that kills in winter

– In summer, older animals died from heat

• The region’s average air temperatures have risen over the last few decades, and Lake Superior’s surface waters have warmed even faster

Dermacentor albipictus

Effects of Ticks• Blood Loss:

– If each female tick takes a total of 2 mL of blood, and if half of the 40,000 ticks on a diseased moose are females, then the females alone will consume 40,000 mL, or 40 litres, of blood. A 400 kilogram moose has a total blood volume of about 32 litres (8% of body weight). Thus, 40,000 ticks will consume, and the moose will have to replace, all of its blood during the 2-month feeding period. Blood is an energy-rich substance, and there is a high cost to the moose in energy and materials to replace the lost blood.

• Skin Irritation– hair loss– distraction from normal feeding behaviour.

Winter Ticks on Moose

Extensive hair loss, reduced muscle size, prominent ribs and other bones, and no body fat

How to DO Ecology

• Can’t usually infer a general principle from a single study.

• Ecologist rely on multiple comparative studies.

• If common themes are found, then we can be more confident in inferring a general principle.

Summary

• Ecological evidence comes from a variety of different sources

• Ecology relies on truly scientific evidence and the application of statistics

• Ecological phenomena occur at a variety of scales– List these for the moose-wolf story

Current Situation

• "And then there are the times when the wolves are silent and the moon is howling.”

— George Carlin

Current Situation

• Isle Royale wolf population typically has between 18 and 27 wolves, organized into three packs.

• Moose population usually numbers between 700 and 1,200.

• The wolf-moose project of Isle Royale, now in its 57th year, is the longest continuous study of any predator-prey system in the world.

Current Situation

• On Isle Royale, wolves are the only predator of moose, and moose are essentially the only food for wolves.

• Between January 2014 and January 2015, the wolf population decreased from 9 to 3 The wolf population was organized into a single social group. The sex and pack of origin for these wolves is unknown.

Current Situation

• In the same time period, the estimated abundance of moose increased by 19% from 1050 to 1250.

Brown Trout Galaxias

Everything is Connected

Effects of an Introduced Species at Multiple hierarchical levels

Fig 1.7

Fig 1.8

Fig 1.9

Fig 1.10

Natural Experiment

Fig 1.11

Manipulative Experiments

Fig 1.13

Fig 1.14

Applied Ecology

What is killing Asian vultures?

Long Billed Vulture White Backed Vultures

Asian Vultures are being killed in large numbers by carcasses containing the drug diclofenac, and NSAID used to inflammation, pain and fever in livestock . The drug is highly toxic to the birds and causes visceral gout leading to kidney failure and death.