EE.21 Flashcards
(22 cards)
what is charles eltons definition of a niche?
When an ecologist sees a badger, they “should include in [their] thoughts some definite idea of the animal’s place in the community to which it belongs, just as if [they] had said ‘there goes the vicar’ “
The competitive exclusion priciple
“As a result of competition two similar species scarcely ever occupy similar niches, but displace each other in such a manner that each takes possession of certain particular kinds of food and modes of life in which it has an advantage over its competitors”
G.F. Gause (1934) The Struggle for Existence
what is the current definition of competitive exclusion?
if you have a spatilly uniform environment with just a single resource then given long enough one species will outcompete the others, resulting in the equilibrium species richness to be 1. in other words you cant have more coexisting species than niches
give your own definition of a niche
?
Hutchinsons niche
it is a mathematical way of thinking about a niche, imagining an axis for every quantitative trait important to a species ecology, now put them all at right angles to one another.
n-dimensional hypervolume
Fundamental niche
the area where a species could theoretically live
or
the set of environmental conditions where, in the absence of competitors or natural enemies, our species would be able to increase in numbers
invasion criterion
dN/dt = rN
for increase dN/st must be positive, so the invasion criterion is r>0
the ability to be able to increase when rare
Realised niche
where the species actually lives
this area is smaller than the fundamental niche
outline the current niche view
- a set of constraints on population growth
- interaction between abiotic and biotic factors
- for species to coexist they must exhibit one or more niche differences to stay in equilibrium
- in theoretical models relatively long term coexistence of species occupying the same niche is possible
Ellenberg’s rule
most species grow best on their own at the same level of an environmental factor,, like soil pH or water availability, however when in competition they peak in abundance at different levels.
what are the three forms of niche separation?
- range
- habitat
- resources
Allopatry
species occupying different non overlapping geographic ranges
Symaptry
when species have similar geographic ranges within a given ecosystem however the species live within different habitats, such as on the edge of a forest, and high up in the forest canopy
resource separation
when a species lives in the same geographic range AND same habitat, they are unlikely to show any overlap in resource use
(insects above and below the leaf)
Interspecific competition
competition between species
however this is very hard to define, and may just be manifestations of former interactions - the ghost of competition past
character displacement
morphological difference such as bill or body size
competitive release
Competitive release occurs when one of two species competing for the same
resource disappears, thereby allowing the remaining competitor to utilize the resource
more fully than it could in the presence of the first species
what forms of separation do darwins finches show?
range
habitat
resource
give an example of niche shifts in sympatry
darwins finches - G.fortis and G.fuliginosa differ in percentage of individuals on different islands
give an example of a genus separated by feeding depth
Tringa - Warblers - they are very dissimilar in body and bill size
give an example of a group of birds separated by habitat and foraging behavior
guilds of warblers - they have very similar body size and bill morphology however have different habitats and foraging behavoir
Vacant niche
a controversial concept based on tautology, the test for a vacant niche is to introduce a new species and if it establishes then there was a vacant niche, however if it does not establish then there wasn’t
