CHAPTER 8POPULATION ECOLOGY THE WOLF WATCHERS CHAPTER 8 POPULATION ECOLOGY THE WOLF WATCHERS Endangered gray wolves return to the American West.

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CHAPTER 2 SCIENCE LITERACY AND THE PROCESS OF SCIENCE SCIENCE AND THE SKY Solving the mystery of disappearing ozone

CHAPTER 8 POPULATION ECOLOGY

THE WOLF WATCHERS

Endangered gray wolves return to the American WestTHE WOLF WATCHERS Endangered gray wolves return to the American West8At the end of this unit you will know:The ecological significance of a populationHow and why populations changeDifferent approaches to reaching carrying capacityThe role of predators in regulating populationsWays of applying population dynamic to conservation and ecosystem management decisionsLearning Outcomes

2Population size and makeup can fluctuate or remain stable. Population stability is often dependent on predators. When human impact results in reduced predation, we may need to manage the system ourselves.Main concept8THE WOLF WATCHERS Endangered gray wolves return to the American West

Case Study Yellowstone Gray Wolf Restoration Project

38THE WOLF WATCHERS Endangered gray wolves return to the American West

Case Study Yellowstone Gray Wolf Restoration ProjectHistory of decline Humans hunted wolves, destroyed habitat by conversion for agriculture, and hunted wolves food sourceselk, deer, and bison.

Wolf populations in Yellowstone had also declined as a result of predator control programs.Protected under the Endangered Species Act of 1973

In 1987, 41 wolves were reintroduced and outfitted with radio collars allowing researchers to track the size of wolf packs, their food sources, and movement patterns.48THE WOLF WATCHERS Endangered gray wolves return to the American West

Populations, all the individuals of a species living together in the same area, fluctuate naturally over time.

Populations increase with birth and immigration and decrease with death and emigration.

Response is often based on access to food, water, nesting sites, and predation.

Population dynamics can be predictable or more random.

Information from tracking helps aid recovery and plan conservation strategies for wolves and for many other threatened plants and animals.

5Populations fluctuate in size and have varied distributionsTERMS TO KNOW:PopulationPopulation dynamicsMinimum viable population8

Below a minimum number of individuals, a species may not be viable long term.

Courtship rituals,flocking, schooling, foraging, and genetic variability are often dependent on population size.Doug Smith, Population Biologist6Populations fluctuate in size and have varied distributionsTERMS TO KNOW:Environmental impact statementPopulation densityPopulation distributionClumped distributionRandom distributionUniform distribution8

Successful population density varies by species. Too low and individuals may not be able to find mates or only mates that are closely related.7Populations fluctuate in size and have varied distributions8

Successful population density varies by species. Too low and individuals may not be able to find mates or only mates that are closely related.

In a population that is too dense, competition, fighting, and disease can become problems.

Location and spacing of individuals within a population may be influenced by a variety of factors.8Populations fluctuate in size and have varied distributions8

Social species such as wolves, elk, and prairie dogs provide examples of clumped distribution.

Individuals are found in groups within the habitat.

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Populations fluctuate in size and have varied distributions8

Random distribution Species that disperse randomly in an environment like wind-blown seeds that germinate where they landIndividuals are spread out irregularly. 10

Populations fluctuate in size and have varied distributions8

Individuals spaced evenly possibly due to territorial behavior or something that suppresses growth.

Creosote bushes in the desert are an example of uniform distribution.

11Populations display various patterns of growth8

Mathematical models describe population growth over time.

Variables include birth ratenumber of births per 1000 individuals per yearminus death ratedeaths per 1000 individual per year.

Growth rate can also be determined by comparing two distinct points over time.320 to 343 represents an increase of 23 animals, or a 7% growth rate (23/320).

12Populations display various patterns of growth8

Mathematical models describe population growth over time

Variables include birth ratenumber of births per 1000 individuals per yearminus death ratedeaths per 1000 individual per year.

Growth rate can also be determined by comparing two distinct points over time.320 to 343 represents an increase of 23 animals, or a 7% growth rate (23/320).

13Populations display various patterns of growth8

Mathematical models describe population growth over time

Variables include birth ratenumber of births per 1000 individuals per yearminus death ratedeaths per 1000 individual per year.

Growth rate can also be determined by comparing two distinct points over time.320 to 343 represents an increase of 23 animals, or a 7% growth rate (23/320).

14Populations display various patterns of growth8

Without environmental limits, a population will reach its maximum per capita rate of increase (r), or biotic potential.

Increase in population is exponential with species exhibiting high biotic potential.

New populations in a environment will often have high biotic potential.

Loss of predators can also result in exponential growth.

Examples include spotted knotweed and deer mice.

thout15Populations display various patterns of growth8

Without environmental limits, a population will reach its maximum per capita rate of increase (r), or biotic potential.

Increase in population is exponential with species exhibiting high biotic potential.

New populations in a environment will often have high biotic potential.

Loss of predators can also result in exponential growth.

Examples include spotted knotweed and deer mice.

thout16Populations display various patterns of growth8

Exponential growth cant last forever:

Resources become scarce.

Individuals starve or are unable to find habitat for reproduction.

Aggression and competition increase.

There is pressure from predation.

Population size increasing while the growth rate decreases is logistical growththe S-shaped curve.17

Populations display various patterns of growth8Exponential growth cant last forever:

Resources become scarce.

Individuals starve or are unable to find habitat for reproduction.

Aggression and competition increase.

There is pressure from predation.

Population size increasing while the growth rate decreases is logistical growththe S-shaped curve.

18Populations display various patterns of growth8Carrying capacity (K) Population size that be sustained indefinitely without long-term damage to the environment

K Depends on growth factorsresources needed to survive and reproduce.

Carrying capacity can increase or drop as resource availability changes.

19A variety of factors affect population growth8

TERMS TO KNOW:Population growth rateBirth rateDeath rateBiotic potential (r)Exponential growthLogistic growthCarrying capacityLimiting factors are resources needed for survival but that may be in short supply. This scarcity will determine carrying capacity.

Resistance factors, such as predation, competition, and disease, will also contribute to controlling population size and growth.

These factors are density-dependent, but other factors such as natural disaster are density-independent since they would occur regardless of the population size.

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A variety of factors affect population growth8TERMS TO KNOW:Density dependentDensity independentReproductive strategiesr-selected speciesK-selected species

Effects of density-dependent factors increase as populations grow.DiseaseCompetitionPredation

21A variety of factors affect population growth8TERMS TO KNOW:Density dependentDensity independentReproductive strategiesr-selected speciesK-selected speciesEffects of density independent factors affect a population, regardless of its size, but can serve to decrease the population.StormFire/FloodAvalanche

22A variety of factors affect population growth8

High rate of population increase and well adapted to exploit unpredictable environments

Will increase quickly as resources become available

23A variety of factors affect population growth8

Low reproductive rates and very responsive to environmental conditions

Decrease or increase slowly as resource availability changes24A variety of factors affect population growth8

K-selected species tend to be stable in undisturbed areas.Slow increases and decreases in response to the environment.TERMS TO KNOW:Boom-and-bust cyclesExtirpationr-selected species with rapid reproductive potential sometimes have sudden population growth with high peaks which may overshoot carrying capacity followed by sudden crashes. Some populations will level off near carrying capacity while others will continue to overshoot and crash.

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A variety of factors affect population growth8

Some populations overshoot carrying capacity, drop below it, and increase and overshoot it again until they settle down close to carrying capacity.

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A variety of factors affect population growth8

Example Isle Royale, MichiganWolves preyed upon moose and the moose population dropped, followed by a drop in the wolf population. As moose populations recovered, so did the wolves until a Parvo epidemic reduced wolves to their lowest point.27

The loss of the wolf emphasized the importance of an ecosystems top predator8Black line shows winter browse line from herbivores Populations do not exist in isolation. Like the Yellowstone example demonstrates, the addition of a keystone species like the wolf can result in observable changes in the behavior of its prey. Cascading effects on other community level processes may follow.

28The loss of the wolf emphasized the importance of an ecosystems top predator8

29The loss of the wolf emphasized the importance of an ecosystems top predator8

Without wolves, beavers thrive and build dams that create lakes and ponds. Elk stay in the willow thickets and overgraze willow needed by the beavers.30The loss of the wolf emphasized the importance of an ecosystems top predator8

With wolves, willows regrow because elk feed in the meadows, where they can watch for wolves rather than in the willow thickets. With more willows, beavers return and the wildlife populations recover.31

PERSONAL CHOICES THAT HELP8

International Wolf Center www.wolf.orgUS Fish and Wildlife www.fws.gov32

UNDERSTANDING THE ISSUE8

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UNDERSTANDING THE ISSUE8

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ANALYZING THE SCIENCE8

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EVALUATING NEW INFORMATION8

www.actionbioscience.org/biodiversity/johnson.html36MAKING CONNECTIONS8

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