Lecture 6: Competition and density dependence Flashcards
describe the differences in intraspecific competition when it comes to specialists and generalists
Specialists:
> relatively less overlap, less competition
> possibly reduce competition, but have to find that resource
> specialised foraging or feeding techniques
Generalists:
> intense intraspecific competition
what is the definition of intraspecific competiton?
> interactions between individuals of the same species, as a results of a shared requirement for a resource, leading to a reduction in the survivorship, growth, and/or reproduction of at least some of the competing individuals
what is exploitation?
> competitors frequently don’t interact directly but they deplete common resources
indirect interactions between competitors for shared resources
what is interference?
> competitors might fight or colonise a space making it unavailable to competitors
direct interactions between competitors for shared resources
describe the experiment on cave beetles and cricket eggs
> example of exploitation and interference
at higher density, there are less holes because fighting with other beetles
1 beetle lead to deeper holes
effect on the efficiency at which the beetles can find their prey
refer to graphs
describe one sided nature of competition
> not all competitors do as well as each other
over winter survival of red deer calves in resource limited population on island of Rhum
survival declines as population becomes crowded; smallest individuals at birth most likely to die
effect of intraspecific competition increases as number of competitors increases; i.e., the effects of intraspecific comp. are density dependent.
what is density dependent mortality?
refer to diagram
> region 1) mortality is density independent - no intraspecific competition
> region 2) mortality is density dependent - under-compensating density dependence (rate at which mortality occurs isn’t compensating for the amount surviving)
> region 3) mortality is density dependent - overcompensating density dependence ( rate at which mortality occurs is overcompensating for the amount left)
what is density dependent fecundity?
Plants producing seeds
> low densities: birth rate density independent
> high densities: fecundity declines but in under-compensating manner so total seeds continues to increase
Species infected by fungus
> low densities: number of spores per host in next generation exactly compensating
> high densities: number of spores per host in next generation overcompensating density dependence
what are the formulas used to determine crowding versus density?
1) assume:
1000 insects in a field, on 100 plants
> resource- weighted density = 10 insects/plant
> only accurate measure of competition if all plants same size and all support same number of insects
2) assume:
of 100 plants, 10 support 91 insects and 90 support 1 insect
> RWD = 10 insects/plant
> average density experienced by each insect = 82.9
> [(91x910)+(90x1)/1000] = organism-weighted density
what are the population effects of intraspecific competition?
1) density dependent effects on net recruitment
2) population increase under influence of density dependent effects
change:
> small at low densities
> large at intermediate densities
> small at high densities
results in ‘s’ shaped sigmoidal pattern of pop increase
when is peak recruitment?
> at intermediate densities - dome-shaped curves
what is the logistic equation for population?
dN/dt = rN(K-N)/K >limitations = cannot incorporate range of competitive intensities, always doomed to perfectly compensating density dependence
what is the impact of intraspecific competition on individuals?
> reindeer smaller at higher densities
limpets smaller at higher densities
total biomass (limpets) regulated by intraspecific competition.
