Chapter 13 Flashcards
Overshoot
when a population grows beyond its carrying capacity;
often occurs when the carrying capacity of a habitat decreases from one year to next (e.g., because less resources are produced).
Die-off
a substantial decline in density that typically goes well below the carrying capacity.
Die-offs often occur when a population overshoots its carrying capacity.
Population cycles
regular oscillation of a population over a longer period of time.
dN/dt=
rate of change in population size
r=
intrinsic growth rate
N=
current population size at time t
k=
carrying capacity
Delayed density dependence
when density dependence occurs based on a population density at some time in the past.
As the time delay increases, density dependence is ___________ and the population is more prone to both ___________ and ___________ K.
delayed; overshooting and undershooting
When rτ < 0.37…
the population approaches carrying capacity without oscillations.
When 0.37 < rτ < 1.57…
the population exhibits damped oscillations.
Damped oscillations
a pattern of population growth in which the population initially oscillates but the magnitude of the oscillations declines over time.
When rτ > 1.57…
the population will exhibit a stable limit cycle.
Stable limit cycle
a pattern of population growth in which the population continues to exhibit large oscillations over time.
Why may delayed density dependence occur?
the organism can store energy and nutrient reserves.
Delayed density dependence can occur when there is a time delay in development from one life stage to another.
Example:
When populations are low and food is abundant, the water flea Daphnia galeata stores surplus energy as lipid droplets.
When resources are less abundant, adults use this stored energy to reproduce.
Small or larger populations are more vulnerable to extinction than larger populations.
smaller populations
Deterministic model
a model that is designed to predict a result without accounting for random variation in population growth rate.
Stochastic model
a model that incorporates random variation in population growth rate; assumes that variation in birth and death rates is due to random chance.
Demographic stochasticity
variation in birth rates and death rates due to random differences among individuals.
Environmental stochasticity
variation in birth rates and death rates due to random changes in the environmental conditions (e.g., changes in the weather).
Habitat fragmentation
the process of breaking up large habitats into a number of smaller habitats.
Sources
high-quality patches that produce a large number of individuals that disperse to other patches.
Sinks
low-quality patches that produce few individuals and rely on dispersers to keep the sink population from going extinct.
If subpopulations rarely exchange individuals…
fluctuations in abundance will be independent among subpopulations.
If subpopulations frequently exchange individuals…
the subpopulations will act as one large population.
p=
the fraction of habitat patches that are occupied
e=
the probability of each patch becoming unoccupied (i.e. going extinct)
c=
the probability of a patch becoming colonized
We can increase the number of occupied habitat patches by…
providing corridors between patches to increase the rate of colonization (c).
We can also increase the number of occupied patches by…
decreasing rates of extinction (e).
Species may be preserved by…
protecting large fragments of habitat that reduce extinction risk, or by ensuring that individuals can disperse to and from patches.
Rescue effect
when dispersers supplement a declining subpopulation and thereby prevent it from going extinct.
Less isolated patches are more likely to be rescued and are also more likely to be colonized.
