Bio 213-McKee Community Ecology Review name___Claudia Esteves______________________ Read each scenario below and identify any of the following ecological principles that might apply. Ecological principles: Bottom-up controls Character displacement Coevolution Competition Competitive exclusion Disturbance Fundamental niche 1. Keystone species Primary succession Realized niche Resource partitioning Secondary succession Top-down controls (trophic cascade model) Trophic levels Two species of closely-related swallows live in England. The black swallow lives in coniferous forests, and the yellow swallow lives in deciduous forests. In Ireland, where the black swallow has never been introduced, only the yellow swallow is present and it lives in both coniferous and deciduous forests. In this scenario the ecological principles that might apply are resource partitioning, competitive exclusion, fundamental and realized niche. The closely-related swallows living in England could be the result of resource partitioning, the closely-related species are able to coexists in the same place because of the different resources available. Since both species share an environment, each species concentrates in the forest they are best adapted to survive. In the case of the yellow swallow species living in Ireland, we can observe the species fundamental niche which includes coniferous and deciduous forests, and their realized niche in the deciduous forests of England. 2. In a woodland community, three species of rodents coexist: voles, field mice, and shrews. All three species eat seeds and nuts. Each species has a preference for seeds of the most appropriate sizes for their teeth and mouths; however, all three species compete for the same kinds of nuts. An owl species also lives in this woodland community. The owl preys on all three rodent species. During one particular year, a parasite that causes pneumonia in birds is introduced into the community. This parasite dramatically reduces the owl population, which remains low for several years as a result. Following the initial reduction in the owl population, there is a dramatic increase in the population of field mice and a dramatic decrease in the populations of both voles and shrews In this scenario the ecological principles that might apply are keystone species, top-down controls (trophic cascade model), and competitive exclusion. The owl in this case is considered a keystone species, by preying in all three species of rodents the owl population holds a strong Bio 213-McKee control on the rodent communities. In this scenario the owl population declined after a parasite was introduced in the population, the low populations of owls led to a dramatic increase in field mice population in comparison to the other two rodent species, indicating top-down control; where the owl population influences other species populations. Since the population of field mice had a disproportional increase, we might say that the field mice, in the absence of a predator is able to use resources efficiently showing competitive exclusion. 3. A researcher conduced an experiment on two desert islands. The islands were of similar size, climate, and species composition and richness. Originally, the same species of snake was present on both islands (A and B). In her experiment, the researcher removed the snake species from island A. For comparison, the snake species was not removed from island B. She then recorded the number of species on each island each month, for 2 years. Data are presented in the graph below. 45 N u m b e r s p e c i e o s f 40 35 30 25 20 A 15 B 10 5 0 0 5 10 15 20 25 30 Week Construct a hypothesis that explains the difference between the numbers of species present on island A versus B over the 2-year period. Over the 2 year- period the difference between the number of species present on island A in comparison with Island B, can be the result of the disturbance in the Island A population. We may hypothesize that the disturbance in the Island A resulted in a decline of species numbers, a sharp decline in the population can be observed when species were removed from the Island A. Over time the species population in Island A was able to stabilize at low levels without disappearing. In comparison, the undisturbed Island B remained at a constant number of 33 to 45 number of species present in Island B.