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Chapter 21 On the Tracks of Wolves and Moose Young Gray Wolf-Romeo • Every summer and a few weeks in winter, scientist investigate the Isle Royale’s pack of wolves and herd of moose • Studies for almost 50 years, it is the longestrunning predator prey study in the world. – Scientists would like to understand the dynamic fluctuations of the wolves and moose. – They are trying to learn about ecology Ecology • Ecology is the study of the interactions between organisms, and between organisms and their nonliving environment (land, water, etc.) – The Isle Royale is a great place to study ecology – Uninhabited by humans, protected national park, undistributed by hunting, logging, settlement – No other predators or prey on the island – Island just the right size to study ecology Ecology • Ecologists can study organisms at a number of levels: the individual, the population, the community, and the ecosystem. Ecology • At the individual level, ecologists can study how an individual organisms fares in its surroundings. Ecology • At the population level, ecologists study a group of individuals of the same species living and interacting in the same region. Ecology • At the community level, ecologists study interacting populations of different species. Ecology • At the ecosystem level, ecologists study all the living organisms in an area and the nonliving components of the environment with which they interact. Ecology • Ecology is a multidisciplinary science. It draws not only on many areas of biology but also on many other branches of science, including geography and meteorology as well as mathematics. – Living organism in an area and the nonliving components of the environment with which they interact The study • Vucetich is a population ecologist • Interested in the number of wolves and moose • Much of the counting is done by air. – Wolves are easy to find – Moose are solitary animals and dark colored • Count a few moose and extrapolate for the entire island Distribution patterns • Moose are relatively solitary creatures – Different types of distribution patterns Random Distribution for moose – Random dispersion of individual roaming moose on the island. – The moose are hard to count for research studies. – One type of distribution pattern Moose • The distribution pattern, or the way that organisms are distributed in geographic space, depends on resources and interactions with other members of the population. – For moose, being solitary may help protect them from predation – harder to see in forest – A truly random distribution is rare in nature – Resources may be unevenly distributed, etc., – Distribution pattern are different for wolves and moose- wolves clump Distribution patterns • Distribution patterns generally reflect behavioral or ecological adaptations. Three different types: Distribution patterns • A random distribution may allow individuals to maximize their access to resources. Distribution patterns • A clumped distribution may result when resources are unevenly distributed across the landscape, or when social behavior dictates grouping. Distribution patterns • Uniform distribution usually results from territorial behavior. Moose • Few Moose swam to Isle Royale in 1900 • Moose population exploded on the Isle Royale due to abundant food supply and no natural predators • By 1920, more than a 1000 • Rapid increase in growth rate Population growth • The growth rate of a population is the difference between the birth rate and the death rate of a given population. Population growth • Ecologists describe two general types of population growth: exponential growth and logistic growth. Population growth • Exponential growth is the unrestricted growth of a population increasing at a constant growth rate. • When a population is growing exponentially, it increases by a certain fixed percentage every generation. Increase 20% each year, for example Population growth • Unrestricted growth is rarely, if ever, found unchecked in nature. • As populations increase in numbers, various environmental factors such as food availability and access to habitat limit an organism’s ability to reproduce. Population growth • When populationlimiting factors slow the growth rate, the result is logistic growth―a pattern of growth that starts rapidly and then slows. • Disease, food limitation Population growth • Eventually, after a period of rapid growth, the size of the population may level off and stop growing. • At this point, the population has reached the environment’s carrying capacity ―the maximum number of individuals that an environment can support given its space and resources. Moose • Moose arrived in 1900 • By 1929 they had eaten most of the vegetation • Moose exceeded the island’s carrying capacity in 1935. • The population dropped due to starvation – What happened next to help the moose? – When did the wolves arrive? Population growth • Carrying capacity places an upper limit on the size of any population; • No natural population can grow exponentially forever without eventually reaching a point at which resource scarcity and other factors limit population growth. Population growth • Ecologists use a variety of data to monitor the health of populations. – Moose dropping – Moose bones – Wolf scat – Urine –soaked snow Population growth • Population density is the number of organisms per given area. Wolves kill moose – As the population density of a species increases, individuals of that species may face food shortages. • This is an example of a density-dependent factor―a factor whose influence on population size and growth depends on the number and crowding of individuals in the population. – Wolf predation and plant abundance have greater effect when moose population is large Population growth Biotic refers to the living components of an environment. Not all density-dependent factors are biotic. – Food, predators, diseases • Nonliving, or abiotic, factors like weather and habitat can also influence population size in a density-dependent manner. Population growth • Density-independent factors take a toll on the population no matter how large or small the population is. • Most, but not all, density-independent factors are abiotic.