food webs and patterns in species richness Flashcards
what is a food web
it depicts feeding connection in community ecology
who first described food chains and cycles
elton in 1927
what are some indirect affects to food webs
predator removal
competitor removal
how may the removal of a predator decrease the abundance of a prey species
competitive release= allows the increased abundance of a superior competitor to the prey so prey numbers decrease
what happens in a 3-level chain to plant density
the presence of top predators increases plant desnity as predator decreases herbivores so plants no longer predated on
what happens in a 4-chain to plant desnity
top predators may reduce the abundance of an intermediate predator therefore increasing herbivore density decreasing plant
how can the top-down explanation explain why green plants dominate
because predators (top) keep herbivores (down) in check
how can the bottom up explanation explain why green plants dominate
because plants (bottom) have evolved defences to keep herbivores (top) in check
define species richness
the number of species in a defined spatial unit
what four factors affect species richness
- geographic factors
- factors correlated with latitude e.g. climatic variability
- factors independant of latitude e.g. disturbance
- biotic factors
why do larger islands tend to have increases species richness
- different types of habita
- bigger targets
- hold larger populations of more spcies
outline MacArthur and Wilsons equilibirum theory of island biogeography
- the numbe of species on an island is determined by a balance between immigration and exitinction
