Chapter 54 - Community Ecology

Food webs

A complex diagram representing the many energy pathways in an ecosystem

Which of the following best illustrates ecological succession?

Grass grows on a sand dune, is replaced by shrubs, and then by trees.

The term used to describe a harmless organism resembling a harmful one is _____

In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model.

Which of the following observations would support the hypothesis that Plethodon salamanders did indeed experience character displacement for body size? Select all that apply.

In sympatric populations, smaller P. cinereus adults survive better and reproduce more. Body size is a heritable trait in salamanders. The resources used by both species of salamanders are available in limited supply. The sympatric salamander populations evolved their present body sizes after they became sympatric.

Food diagram true or false

Phytoplankton are primary consumers. False Squids are secondary consumers. True Squids are tertiary consumers. True Leopard seals are quaternary consumers. True

Dominant species

Species that are the most abundant or have the most biomass.

Which of the following groups can be quaternary consumers in this food web?

Sperm whales, elephant seals, leopard seals, and smaller toothed whales can all be tertiary or quaternary consumers in this food web. For example, sperm whales act as quaternary consumers when they eat squids (tertiary consumers) that have eaten carnivorous plankton (secondary consumers), which have eaten krill (primary consumers), which have eaten phytoplankton (primary producers).

Which of the following statements is supported by the trophic relationships shown in the diagram?

Squids eat fishes.

Trophic structure

The different feeding relationships in an ecosystem, which determine the route of energy flow and the pattern of chemical cycling

Which trophic level(s) does the roadrunner occupy?

The grasshopper is a primary consumer, so when the roadrunner eats a grasshopper, it is a secondary consumer. Both the praying mantis and the collared lizard are secondary consumers. When the roadrunner eats these animals, it is a tertiary consumer.

Five different baleen whale species are endangered and may go extinct. What would be the most likely effect of removing all baleen whales from this food web?

The krill population would increase.

Suppose that humans increase their consumption of Antarctic fishes, causing a significant reduction in the size of fish populations. What would be the most likely effect of a reduction in the size of Antarctic fish populations?

The sperm whale population would decrease. The carnivorous plankton population would increase. The elephant seal population would decrease. Human actions can have profound effects on food webs. In this case, humans are competing with sperm whales and elephant seals for fishes, causing the sperm whale and elephant seal populations to decrease. However, not all populations in the food web decrease in response to human actions. The removal of fishes as predators of carnivorous plankton may cause carnivorous plankton populations to increase.

Caribbean coral reef communities have been strongly influenced by an unknown pathogen that causes white-band disease. How can the effect of white-band disease best be described?

a cascade event that shifts the entire makeup of the community

Zoonotic pathogens

are transferred from other animals to humans and cause the largest class of emerging human diseases. Community ecology provides the framework for identifying key species interactions associated with such pathogens and for helping us track and control their spread.

Keystone species

are usually less abundant species that exert a disproportionate influence on community structure.

secondary succession

begins in an area where soil remains after a disturbance.

The longest food chain in this food web includes nine groups of organisms. Which of the following groups is included in that food chain?

birds; The longest food chain includes phytoplankton, copepods, krill, carnivorous plankton, fishes, squids, birds, leopard seals, and smaller toothed whales. The interactions between multiple plankton groups and medium sized consumers increases the length of this food chain.

Species diversity is affected by

both the number of species in a community—its species richness—and their relative abundance. all of them: b. size of an area c. latitude and climate d. species interactions e. frequency and type of disturbance

allopatric populations

closely related species that are geographically separate

Character displacement

describes a situation where the traits of sympatric populations overlap less (diverge more) than the traits of allopatric populations. Character displacement reduces interspecific competition in sympatric populations and is therefore adaptive for each population.

Interspecific competition

drives character displacement by causing natural selection for phenotypes that compete less.

According to the principle of competitive exclusion, two species cannot continue to occupy the same _____.

ecological niche

What do plants produce that supports the higher trophic levels of the community?

energy-containing food molecules

Ecosystem engineers

influence community structure through their effects on the physical environment.

Directional selection

is responsible for character displacement. Directional selection causes the two competing species to evolve in opposite directions. (Remember that character displacement is not the result of disruptive selection. In character displacement, it is two species that become more different, rather than one population becoming more different by splitting into two different phenotypes.)

Ecological succession

is the sequence of community and ecosystem changes after a disturbance.

An organism's "trophic level" refers to _____.

its food source

Cellulose-digesting microorganisms live in the guts of termites and ruminant mammals. The microorganisms have a home and food, and their hosts gain more nutrition from their meals. This relationship is an example of _____.

mutualism

Primary succession

occurs where no soil exists when succession begins

sympatric populations

populations occupying the same geographic area and capable of encountering one another

Consumption of which prey makes the elf owl a tertiary consumer?

praying mantis

More diverse communities typically

produce more biomass and show less year-to-year variation in growth than less diverse communities and are more resistant to invasion by exotic species.

Food chains link the trophic levels from

producers to top carnivores.

bottom-up model

proposes a unidirectional influence from lower to higher trophic levels, in which nutrients and other abiotic factors primarily determine community structure.

The top-down model

proposes that control of each trophic level comes from the trophic level above, with the result that predators control herbivores, which in turn control primary producers.

Which trophic levels do fishes occupy in this food web?

secondary consumers tertiary consumers quaternary consumers

The species-area curve shows that ______.

smaller areas have fewer species

intermediate disturbance hypothesis

the hypothesis that ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels

According to MacArthur and Wilson's hypothesis of island biogeography, species immigration and extinction rates on a particular island correlate to __________.

the island's size and distance from the mainland; The island's size correlates to how many individuals the island can support, and its distance from the mainland correlates to how many individuals will populate the island.

Keystone species are those species _____.

whose absence would cause major disruption in a community