Exam 56: Communities

If someone attempted to introduce a tropical species, such as an orangutan, into a polar region such as northern Alaska, it would probably not survive.What factor would likely be most effective in preventing its survival?

The graphs illustrate elk and aspen numbers over several decades in Yellowstone National Park.They show major human management actions (removal and return of wolves; hunting of elk).Given this information, describe how biotic factors affected the community structure of Yellowstone National Park during this century.List each biotic factor and its effect.

At one time, giant African land snails were sold as pets, for teaching purposes, and for food.However, this snail has become a serious pest in habitats around the world.It carries plant pathogens, competes with native snails, eats 500 different species of plants, and even spreads human disease.The least likely way this invasive snail could have entered ecosystems in the United States is by

In the northern Pacific Ocean, sea otters feed on sea urchins and sea stars.Sea urchins feed on kelp, and sea stars feed on mussels.Beginning in the 1700s, sea otters were hunted for their fur and driven nearly to extinction in some areas, resulting in trophic cascades in their communities.When the fur trade ended, sea otter numbers increased and their communities began to recover.One would expect this recovery to lead to increased numbers of _______ and decreased numbers of _______.

Ecologists are not sure whether diversity in a community causes stability or whether diversity and stability are simply correlated.Explain the difference in these two concepts, and explain why the distinction is important.

Does an established community always maintain the same species composition? Give examples of how changing environmental conditions might impact species composition.

An ecologist studying interaction strength in a pond set up laboratory experiments using aquaria.He set up food webs in two aquaria that included these interactions: After populations in the aquaria stabilized, the ecologist removed the small fish from one aquarium.The population of Daphnia there immediately increased rapidly.This indicates that the interactor species (fish) had what effect on the target species (Daphnia)?

The major process that occurred on the Pumice Plain on Mount St.Helens in the years after its eruption was

Suppose succession occurred in a situation like the one at Glacier Bay, except that no nitrogen fixers such as Dryas or alders were available to begin colonization.How might this lack affect the process or outcome of succession?

In their study of diversity and stability in grassland ecosystems, Tilman and his colleagues found that higher species richness in their plots had what effect on stability and productivity?

During secondary succession following habitat destruction of a forest, settlement of new species is affected by both facilitation and inhibition.During which part of succession is each process most active, and how does the interaction of the two processes affect community structure?

If secondary consumers are the highest trophic level in a specific community, how many trophic levels are in this community (not counting decomposers or omnivores)?

The Shannon index of species diversity is calculated using this equation: A laboratory community contains four species, with 10, 15, 25, and 50 individuals per species.Using the Shannon index, determine the species diversity of this community.

Sea otters in marine habitats along the west coast of North America were hunted to near extinction.This caused sea urchins to grow exponentially.They overgrazed and nearly destroyed kelp beds, which provided habitat and food for many fish and other species.After kelp was destroyed, many fish species also declined.This suggests that sea otters act as a _______ species and their loss set off a(n) _______.

Refer to the figure, showing three aspects of biodiversity.Define each of these three aspects.Explain how they interact and how each is important for understanding community structure.

A field of wildflowers has a diverse community of pollinators.A nearby farmer brings in hives of honey bees to pollinate his fields.The honey bees also feed on wildflower pollen, making them competitors of the wild pollinators.In response, some wild pollinator populations decline, but they build up again when the honey bees are removed.Assuming honey bees are the interactors and wild pollinator species are the targets, what is the most definite conclusion that can be made about interaction strength and direction?

Which is the correct chronological order (from earliest to latest) for the succession of plant species in Glacier Bay?

According to research by Joseph Connell, rock barnacles living at lower levels of the intertidal zone grow faster and, through competition, eliminate stellate barnacles from the area.This indicates that rock barnacles have a greater _______ than stellate barnacles.

Competition is an important interaction in most communities.How would differences in interaction strength among competitors be likely to influence community structure?

Human activities are causing many stresses in nearshore estuarine habitats, which are vital habitats for breeding and development of young marine fish and other animals.These stresses are occurring as a result of climate change, pollution, coastal construction, and a variety of other factors.Of the changes that occur in estuaries, which would not be considered a stress?