EE27 Flashcards
what is density dependence?
when the per capita rate (ie mortality or growth) changes with density
define intra-specific competition
individuals of the SAME species competing for resources (food,space,mates) and leading to a reduction in growth,survivorship or reproduction of at least SOME of the competing organisms`
big populations grow faster because there are more reproducing individuals - is this density dependent?
no, density dependence is per capita
does the per capita growth rate change if r is constant?
no
if you increase N (effective population size) what happens to per capita growth rate
it decreases
when N is low what density dependence effect is there and is there lots of growth?
little density dependence effect but small pop size so growth is limited
when population size is 50% of K what density dependent effect is there and is there lots of growth?
both growth rate and pop size middling so max new individuals added
when N is high what effect does density dependence have?
strong density dependence therefore growth is limited despite large population.
what is the mechanism for density dependence?
competition
Give specific examples of animal competition leading to density dependence.
1) rabbits-overgrazing
2) trees-light and nutrients
3) Eagles-hunting territory/nest sites
4) caterpillars-resource comp,produce pathogens
what is antibiosis?
an antagonist association between 2 organisms in which one is adversely effected e.g poisoning,spirochetes
explain exploitation vs interference
exploitation-indirect,individual responds to level of resource,resource is limited
Interference-direct interaction.individual prevents another exploiting resources e.g defending territory or harem ownership
define scramble competition
all individuals have equal access to a scarce resource and eventually all individuals adversely affected and none survive
define contest competition
dominated and hierarchy based,some individuals have access to adequate resources (those with territory) whilst others will have no access and may die
what is more stabilising scramble or contest comp?
contest. low pop everyone gets territory and in high pop only some do but this means at least some individuals always reproduce e.g florida scrub jays
examples of scramble comp (4)
1) cows grazing in a grassland
2) forest defoliators. If their larvae can find shelter and food then survival is possible, but when all the foliage is destroyed then the population decreases.
3) success of small beetles over large beetles. While larger beetles, similar to larger animals in general, tend to win more often in contest competition, the opposite can be true in a scramble competition
4) Tribonium beetles in a jar of dried peas
interference comp example
ant Novomessor cockerelli and red harvester ants, where the former interferes with the ability of the latter to forage by plugging the entrances to their colonies with small rocks.
what is apparent competition
occurs indirectly between two species which are both preyed upon by the same predator. For example, species A and species B are both prey of predator C. The increase of species A may cause the decrease of species B, because the increase of As may aid in the survival of predator Cs, which will increase the number of predator Cs, which in turn will hunt more of species Bccurs indirectly between two species which are both preyed upon by the same predator. For example, species A and species B are both prey of predator C. The increase of species A may cause the decrease of species B, because the increase of As may aid in the survival of predator Cs, which will increase the number of predator Cs, which in turn will hunt more of species B
what 3 types of competition are there by mechanism
interference,exploitation and apparent
define competition
an interaction between organisms or species in which the fitness of one is lowered by the presence of another
what is the competitive exclusion principle?
species less suited to compete for resources should either adapt or die out (but this is rarely found in natural ecosystems)
what is the room to roam hypothesis?
competition within and between species for resources plays a very relevant role in natural selection, however, competition may play less of a role than expansion among larger clades
what is compensation?
the degree to which larger population numbers are compensated for by higher mortality and lower fecundity
define overcompensation and what comp type is there a tendency towards?
many more die or less are born in the large population, so much so that the large population becomes smaller than the initial small population after a fixed period. Tendency towards scramble comp
