EE Lecture 27: Intraspec Competition Flashcards
what is density dependence
when a per capita growth rate changes with density dependence
define intraspec comp
the interaction of individuals of the same species brought about by the shared requirement for a resource and leading to the reduction in growth/survivorship/fitness of some of the compeiting individuals
what is eqtn for per capita growth rate
(dN/dt) / N = r
what is the following eqtn for
(dN/dt)/N = r
per capita growth rate
what is density dependence model
(dN/dt)/N = r * (1 - N/K)
in density dependence model, what happens when N is small
(dN/dt)/N = r*(1- v.small N/K)
(dN/dt)/n = r
very little effect of density, but small pop so growth is limited
in density dependence model, what happens when N is K (or v high)
(dN/dt)/N = 0 therefore it decreases as N increases
Very strong effect of density, so growth is limited despite large pop
in density dependence model, what happens when N = 0.5*K
both growth rate and pop size are middling, so max new individuals are added
if you want to get a MSY, where can you start trying to harvest without damaging pop too much
start at half carrying capacity
what is the mechanism for density dependence
competitoin
what type competition likely to lead to pop persistance
contest = because some individuals always remain
which type of competition is assumed in the logistic model of smooth decline in popn growth with N
neither- logistic assumes linear increase in mortality or a linear decrease in per capita growth rate
define compensation
the degree to which larger numbers are compensated for by higher mortality and lower fecundity
let X be a small pop , Y a large one, in identical enviros
what is overcompensation?
many more die (or less are born in Y than in X
so many more it ends up smaller than X after a fixed period
let X be a small pop , Y a large one, in identical enviros
what is undercompensation
more die in Y than in C but not so many, so Y still ends up bigger than X
what type of competition does scramble lead to at high densities
scramble comp leads to extreme over compensation
why at high densities does scramble competition lead to extreme over compensation
the increase in numbers is not matched by a decrease in growth rate until all the resources are used, and the pop crashes
at high densities, what type of compensation does contest lead to
exact compensation - as numbers increase, growth rate decreases because there is an exact number of places available in the popn
why at high densities does contest comp lead to exact compensation
because as numbers increase, growth rate decreases so theres an exact number of places available in the popn
what is an allee effect
occurs when the pop growth rate (r or lamda) decreases as the pop density decreases, perhaps because individuals have difficulties finding mates at low densities
why do allee effects occur
might be because at low pop densities, individuals have harder time finding mates
what is the term for when per capita growth rates decrease as population densities decrease
allee effect
give a species that has allee effects
trilobium beetle - pop growth rates reached their lowest at lowest pop density
what does environmental stochasticity refer to
erratic or unpredictable changes in enviro
how does enviro stochasticity differ from demographic stochasticity
enviro refers to changes in average Br or DR of a pop from year to year (can have good/bad years) but demographic stoch. the average pop level BR DR may be constant across years but the actual fates of individuals differ due to random nature of whether each individual reprocuces or not/survives or not
