Lecture 8: population dynamics of predation Flashcards
what are predator-prey population dynamics?
> fundamental to ecology to understand predator-prey abundance
predator-prey populations don’t exist in isolated pairs but as part of multi-species systems all affected by the environment
many other examples where predator and prey populations fluctuate in abundance apparently independently of each other
begin with an understanding of the essential components: the predators and prey. simple models
what is the Lotka-Volterra model
> based on differential equations and hence applies to continuous predator-prey interactions
in absence of predators (P), the number of prey (N) will increase exponentially
dN/dt = rN
in absence of prey (N), the number of predators will decline exponentially
dP/dt = -qP
prey will be removed by predators at a rate dependent on prey encounter
encounters will increase with increasing numbers of prey (N) and predators (P)
exact number encounted and consumed will depend on search and attach efficiency of the predator: ‘attack rate’ a
thus, consumption of prey aPN
dN/dt = rN - aPN
what are some givens from the Lotka-volterra model?
> predator birth will increase predator numbers. this is assumed to depend on only two things:
- consumption of prey (aPN)
- and the efficiency with which predators turn this food into offspring (f)
dP/dt = faPN-qP
model can be investigated by finding zero isoclines, or points of zero growth, for prey and predators
REFER TO GRAPHS
describe predator and prey abundance
> with high predator pops, decrease in prey pop
> with low predator pops, increase in prey pop
what happens if you combine the predator and prey phase plane diagrams?
> you get a cycle
> they are linked, and neither can be equal to 0
describe how population regulation works
> both predator and prey population growth/ decline linked by prey consumption (aPN)
for prey population: prey consumption regulates population growth through prey mortality
for predator population: prey consumption regulates population growth through predator reproduction
predator population growth thus determined by:
1) rate at which prey are captured: relationship between consumption rate and number of prey is the functional response
2) increased reproduction due to increased prey consumption, the numerical response
what are the different types of functional responses?
> Type 1: the number of prey taken per predator increases linearly as prey population size increases. Expressed as a proportion of the prey population size, the rate of predation is constant
- independent of prey population size to the point where no further prey can be consumed
- occurs in simple systems
- typical of filter feeders feeding on zooplankton
> Type 2: the predation rate rises at a decreasing rate to a maximum level. Expressed as a proportion of prey populatin size, the rate of predation declines as the prey population grows
- most common
- dragonfly larvae
> Type 3: rate of predation is low at first and then increases sigmodially, approaching an asymptote. The rate of predation is low at low prey population size, rising to a maximum before declining as the rate of predation reaches its maximum
- only response in which initial rate of prey mortality increases with prey density
- clams consumed by crabs per day
REFER TO GRAPHS
what are some reasons behind type 3 functional response?
> refuges in habitat: if these are few most prey will be protected at low densities but not at high densities
search images: predators acquire search images as they forage and find prey. increased foraging efficiencies at low densities
prey switching: predators feed preferentially on alternative prey when preferred prey is a low densities.
what are the different types of numerical responses?
> predator density can increase with increasing prey density by:
- increased reproduction
- movement to areas of high prey density (immigration-aggregative response)
refer to graph
what is the marginal value thorem?
> refer to graph
predicts how long a predator should stay in a patch before leaving and searching for another
in patches of equal quality, time spent there will increase with increased time taken to find the patch
time spent in high quality patches will be greater than time spent in poor quality patches
in nature all patches are reduced to same level of profitability.
what is the crowding effec?
> intraspecific competition in both prey and predators
it has been assumed that predator consumption rate depends only on prey abundance, but it also depends on predator abundance (prey per predator)
mutual interference (hummingbirds, stealing by gulls, prey may ‘hide’ in presence of predators)
- reduced predator consumption rate with increasing predator density.
what is prey crowding?
> prevents prey abundance reaching potential high levels and in turn means that predator levels reduced
what is predator crowding?
> prevents predator abundance reaching potential high levels and in turn means prey levels are not reduced as much
where do predator and prey population exists?
> in heterogenous environment: metapopulation (overall population divided into sub populations
each subpopulation has is own dynamics and here are different rates of dispersal between them
differences lead to damping of population oscillations
EXPERIMENTAL RESULTS
the populations of prey and predator persisted
- patches occupied by both: prey extinction, predator dispersal
- patches occupied by prey alone: rapid growth and dispersal
- patches occupied by predators alone: rapid extinction
- population persisted overall through mosaic of patches
