Chapter 18 - Community Structure Flashcards
How might ecologists categorize communities?
By dominant organisms or physical conditions that affect species distribution
Is it common for ecologists to study every species in a community?
No, they typically choose subsets to study.
What is an ecotone?
A boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species.
How can we document the existence of an ecotone?
Line-transect surveys
What is species richness?
The number of species in a community.
What is species richness?
The number of species in a community.
What is relative abundance?
The proportion of individuals in a community represented by each species.
What is a log-normal distribution?
A normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis.
What is a rank-abundance curve?
A curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant.
What is species evenness?
A comparison of the relative abundance of each species in a community.
How have researches examined the effects of resources on species diveristy?
By determining correlations between productivity and species richness in nature.
What is the most common relationship between species richness and productivity? What does this mean?
Hump-shaped curve. Medium productivity has higher richness than high or low productivity.
What does increased fertility due to producer communities? Why?
Decline in species richness; species with competitive advantages outcompete other species, causing the more competitive to increase in number while the others decline/become nonexistant.
How does habitat diversity affect species richness?
Increases it
What is a keystone species?
A species that substantially affects the structure of communities despite the fact that individuals of that species might not be particularly numerous.
What is the intermediate disturbance hypothesis?
More species are present in a community that occasionally experiences disturbances than in a community that experiences frequent or rare disturbances.
What is a food chain?
A linear representation of how different species in a community feed on each other.
WHat is a food web?
A complex and realistic representation of how species feed on each other in a community.
What is a trophic level?
A level in a food chain or food web?
What is a primary consumer?
A species that eats producers.
What is a secondary consumer?
A species that eats primary consumers.
What is a tertiary consumer?
A species that eats secondary consumers.
What is an omnivore?
A species that feeds at many trophic levels.
What is a guild?
Within a given trophic level, a group of species that feeds on similar items.
What is a direct effecT?
An interaction between species that does not involve other species.
What is an indirect effect?
An interaction between two species that involves one or more different intermediate species.
What is a trophic cascade?
Indirect effects in a community initiated by a predator.
Is exploitative competition an example of a direct or indirect effecT?
Indirect
What are density-mediated indirect effects?
An indirect effect caused by changes in the density of intermediate species.
What is a trait-mediated indirect effect?
An indirect effect caused by the changes in the traits of an intermediate species.
What is bottom-up control?
When the abundances of trophic groups in nature are determined by the amount of energy available from the producers in a community?
What is top-down control?
When the abundances of trophic groups in nature are determined by the existence of predators.
