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

THE WOLF WATCHERS Endangered gray wolves return to the American West 8 At the end of this unit you will know: The ecological significance of a population How and why populations change Different approaches to reaching carrying capacity The role of predators in regulating populations Ways of applying population dynamic to conservation and ecosystem management decisions Learning Outcomes

Population 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 concept 8 THE WOLF WATCHERS Endangered gray wolves return to the American West Case Study Yellowstone Gray Wolf Restoration Project

8 THE WOLF WATCHERS Endangered gray wolves return to the American West Case Study – Yellowstone Gray Wolf Restoration Project History of decline – Humans hunted wolves, destroyed habitat by conversion for agriculture, and hunted wolves’ food sources—elk, 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.

8 THE 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.

Populations fluctuate in size and have varied distributions TERMS TO KNOW: Population Population dynamics Minimum viable population 8 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 Biologist

Populations fluctuate in size and have varied distributions TERMS TO KNOW: Environmental impact statement Population density Population distribution Clumped distribution Random distribution Uniform 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.

Populations fluctuate in size and have varied distributions 8 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.

Populations fluctuate in size and have varied distributions 8 Social species such as wolves, elk, and prairie dogs provide examples of clumped distribution. Individuals are found in groups within the habitat.

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 land Individuals are spread out irregularly.

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.

Populations display various patterns of growth8 Mathematical models describe population growth over time. Variables include birth rate— number of births per 1000 individuals per year—minus death rate—deaths 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).

Populations display various patterns of growth 8 Mathematical models describe population growth over time Variables include birth rate— number of births per 1000 individuals per year—minus death rate—deaths 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).

Populations display various patterns of growth8 Mathematical models describe population growth over time Variables include birth rate— number of births per 1000 individuals per year—minus death rate—deaths 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).

Populations display various patterns of growth 8 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.

Populations 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.

Populations display various patterns of growth8 Exponential growth can’t 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 growth—the S-shaped curve.

Populations display various patterns of growth8 Exponential growth can’t 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 growth—the S-shaped curve.

Populations display various patterns of growth8 Carrying capacity (K) – Population size that be sustained indefinitely without long-term damage to the environment K Depends on growth factors—resources needed to survive and reproduce. Carrying capacity can increase or drop as resource availability changes.

A variety of factors affect population growth8 TERMS TO KNOW: Population growth rate Birth rate Death rate Biotic potential (r) Exponential growth Logistic growth Carrying capacity Limiting 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.

A variety of factors affect population growth8 TERMS TO KNOW: Density dependent Density independent Reproductive strategies r-selected species K-selected species Effects of density-dependent factors increase as populations grow. Disease Competition Predation

A variety of factors affect population growth8 TERMS TO KNOW: Density dependent Density independent Reproductive strategies r-selected species K-selected species Effects of density independent factors affect a population, regardless of its size, but can serve to decrease the population. Storm Fire/Flood Avalanche

A 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

A variety of factors affect population growth8 Low reproductive rates and very responsive to environmental conditions Decrease or increase slowly as resource availability changes

A 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 cycles Extirpation r-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.

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.

A variety of factors affect population growth8 Example – Isle Royale, Michigan Wolves 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.

The loss of the wolf emphasized the importance of an ecosystem’s top predator8 Black 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.

The loss of the wolf emphasized the importance of an ecosystem’s top predator8

8 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.

The loss of the wolf emphasized the importance of an ecosystem’s 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.

PERSONAL CHOICES THAT HELP8 International Wolf Center US Fish and Wildlife

UNDERSTANDING THE ISSUE8

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ANALYZING THE SCIENCE8

EVALUATING NEW INFORMATION8 ity/johnson.html

MAKING CONNECTIONS8