Chapter 18 Flashcards
Memorize all.
Communities are often categorized by…
their dominant organisms or by physical conditions that affect the distribution of species.
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.
Ecotones support a large number of species, including those from adjoining habitats, and species specifically adapted to the ecotone.
Aquatic systems are often categorized by
physical characteristics (e.g., stream or lake communities) or by dominant organisms (e.g., coral reef communities).
Communities are often categorized by
their dominant organisms or by physical conditions that affect the distribution of species.
Line-transect surveys
can demonstrate the existence of an ecotone.
Sharp changes in the distribution of species should occur across the ecotone.
Interdependent communities
communities in which species depend on each other to exist.
Independent communities
communities in which species do not depend on each other to exist.
Plant biologist Frederic Clements proposed
most communities are interdependent and act as superorganisms.
Plant biologist Henry Gleason proposed
that most communities consist of species with independent distributions.
If species distributions are independent, they should depend only on __________ _________ _______; there should be gradual changes in species along a line transect.
individual habitat requirements
If species are interdependent, removing a species should cause other species to ___________
decline
if species are independent, removing a species should cause _________ or _________ changes in other species’ fitness.
neutral or positive
Species living under harsh environmental conditions (e.g., high elevation) frequently exhibit ______________.
interdependence
Species richness
the number of species in a community.
Relative abundance
the proportion of individuals in a community represented by each species.
Log-normal distribution
a normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis.
Rank-abundance curves
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 species.
To plot a rank-abundance curve, rank each species in terms of its abundance; the most abundant species receives a rank of 1, the next most abundant species receives a rank of 2, etc.
Species evenness
a comparison of the relative abundance of each species in a community.
most commonly observed relationship between diversity and productivity
Across studies of vertebrates and invertebrates in aquatic and terrestrial systems, a hump-shaped curve.
his indicates that a site with medium productivity has a higher species richness than sites with either low or high productivity.
This suggests that light limitation by dominant plant species _________ ________ _________ in fertilized plant communities.
reduces species richness
Keystone species
a species that substantially affects the structure of communities, although species might not be particularly numerous.
Removal of a keystone species can cause a community to collapse.
Ecosystem engineers
are keystones species that affect communities by influencing the structure of a habitat.
Intermediate disturbance hypothesis
the hypothesis that more species are present in a community that experiences occasional disturbances than in a community with either frequent or rare disturbances.
Food chain
a linear representation of how different species in a community feed on each other.
Food web
a complex and realistic representation of how species feed on each other in a community.
Arrows in a food web indicate
consumption and the movement of energy and nutrients.
Trophic level
a level in a food chain or food web of an ecosystem.
Primary consumer
a species that eats producers.
Secondary consumer
a species that eats primary consumers.
Tertiary consumer
a species that eats secondary consumers.
Omnivore
a species that feeds at several trophic levels.
Guild
within a given trophic level, a group of species that feeds on similar items (e.g., guilds of leaf eaters); members of the group are not necessarily related.
Direct effect
an interaction between two species that does not involve other species.
The direct effect of one species often sets off a chain of events that affect other species in the community.
Indirect effect
an interaction between two species that involves one or more intermediate species.
Trophic cascade
indirect effects in a community that are initiated by a predator.
Density-mediated indirect effect
an indirect effect caused by changes in the density of an intermediate species.
Trait-mediated indirect effect
an indirect effect caused by changes in the traits of an intermediate species.
Trait-mediated indirect effects commonly occur when a predator causes its prey to change its feeding behavior, which alters the amount of food consumed by the prey.
Bottom-up control
when the abundances of trophic groups are determined by the amount of energy available from producers.
Top-down control
when the abundances of trophic groups are determined by the existence of predators at the top of the food web.
Community stability
the ability of a community to maintain a par=cular structure.
Community resistance
the amount a community changes when acted upon by a disturbance (e.g., addition or removal of a species).
Community resilience
the time it takes after a disturbance for a community to return to its original state.
Alternative stable state
when a community is disturbed so much that species composition and relative abundance change, and the new community structure is resistant to further change.
