ch 17 community structure

9/2/23

ecotone

ecotone

region where two communities come together with a relatively sharp boundary indicated by a rapid replacement of species

serpentine soils

soils toxic to many plants due to the concentration of heavy metals and lack of nutrients

interdependent communities

species depend on each other to exist

independent communities

species do not depend on each other to exist

species richness

the number of species in a community

absolute abundance

the number of individuals of each species that are counted

relative abundance

the proportion of individuals in a community represented by each species

log-normal distribution

a normal, bell-shaped distribution that uses a logarithmic scale on the x axis

rank-abundance curves

show the relative abundance of each species in a community in rank order from the most abundant to the least abundant

species eveness

comparison of the relative abundance of each species in a community

keystone species

a species that substantially affects the structure of communities despite the fact that individuals of the species might not be particularly numerous

intermediate disturbance hypothesis

more species are present in a community that experiences occasional disturbances than in a community that experiences frequent or rare disturbances

food chain

linear representations of how species in a community consume each other and therefore how they transfer energy and nutrients from one group to another in an ecosystem

food webs

complex and realistic representations of how species feed on each other in a community and include links among many species of producers, consumers, detritivorest, scavengers, and decomposers

trophic levels

levels in a food chain or food web of an ecosystem

primary consumers

species that eat producers

secondary consumers

species that eat primary consumers

tertiary consumers

species that eats secondary consumers

omnivores

species that feeds at several trophic levels

guild

within a given trophic level, a group of species that feeds on similar items

direct effect

an interaction between two species that does not involve other species

indirect effect

when two species interact in a way that involves one or more intermediate species

trophic cascade

when indirect effects 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

indirect effects that are caused by changes in the traits of an intermediate species

bottom-up control

when the abundances of trophic groups in nature are determined by the amount of energy available from the producers in the community

top-down control

when the abundance of trophic groups is determined by the existence of predators at the top of the foodweb