disturbance & non equilibrium communities

ecology

disturbance & its measures

distribution

frequency

area/size

intensity

severity

return interval/turnover time

bottom up

manipulations have large effects on plant biomass but near zero effect on herbivore abundance

N>V>H>P

top down

manipulations show strong negative effects on herbivores when predators are present & at same time moderate positive effect on plant biomass

-supports HSS model, not MS

-trophic cascade

N<V<H<P

trophic cascade model

idea that top down model applies to a community organization so that impacts flow down food chain as a series of + & - impacts on successive trophic levels

supply side ecology

view that pop dynamics are driven by immigration of seeds or juveniles from sources extrinsic to local pop, so there is no local control of recruitment process

role of disturbance- great barrier reef

damage from cyclones was highly variable depending on how much the site was protected by the island

role of disturbance- coral reef comm

• violent storms

• not at equilibrium at spatial scale

• lottery comp

• reef fishes:

• fish pop controlled by density dep process> niche diversification hyp

• non equilibrium comm> variable recruitment hyp

role of disturbance- rocky intertidal

tension zone betw land n sea

waves/storms

limiting resource- space

multiple stable states

• when multiple stable states exist> abiotic env of comm be similar for various sites

• occur when the same ecosystem can exist in two or more different conditions, each maintained by its own reinforcing feedbacks

• Both states can persist under similar environmental conditions. A disturbance or gradual pressure—such as pollution, drought, or overgrazing—may push the ecosystem past a threshold, causing it to shift into another state

island species area curve

• islands viewed as traps that catch species that are able to disperse & colonize successfully

• analyze comm structure

• pecies–area curve describes how the number of species in an area changes as the area sampled increases

• as area increases, species number increases

noneq comm- fluctuating env models

env change seasonally or irregularly & the comp ranking of species also fluctuate such that no 1 species can win out

noneq comm- density indep models

pops are at levels at which comp for resources is rare

noneq comm- directional changing env models

hist characteristics & dispersal abilities strongly affect ability of a species to respond to env change

noneq comm- slow competitive displacement models

comp abilities of species are = the process of comp exclusion be very slow