Chapter 5: Stochasticity in Growth Rates Flashcards
discrete (geometric) growth rate λ
the ratio of abundance in year t+1 (Nt+1) to abundance in year t (Nt)
λ =
Nt+1 / Nt
NT =
N0 * λ^T
continuous (exponential) growth rate
the instantaneous per capita growth rate
discrete (geometric) growth rate equations
λ = Nt+1 / Nt
NT = N0 * λ^T
r =
ln(λ)
λ =
e^r
continuous (exponential) growth rate equations
r = ln(λ)
λ = e^r
when use an exponential growth model for wild populations?
- in newly established populations
- populations recovering from catastrophic declines
- invasive, pest outbreaks
population growth is often variable
stochastic
2 population growth variances
- sample variance
- process variance
which variance is visualized with error bars?
sample variance
what causes stochasticity in growth rate over time?
- sample variance
- process variance
stochasticity
variation or bounce
sample variance
- aka observational error
- nature isn’t varying, but our estimation error makes it seem like it is
process variance definition
- the one actually affecting changes in abundance and the one we care about
process variance: internal drivers
- age structure
- sex ratios
- density dependence
- connectivity
process variance: changes due to interacting species
- predation
- competition
- parasitism
- human harvest
process variance: stochastic factors
- environmental stochasticity
- demographic stochasticity
process variance factors
- internal drivers
- changes due to interacting species
- stochastic (random) factors
environmental stochasticity
due to extrinsic factors that cause mean vital rates to change randomly over time
example of an extrinsic factor
weather
forms of environmental stochasticity
- drought
- early springs
- warmer winters
- summers
- hurricanes
- forest fires
are the effects of environmental stochasticity more or less dependent on population size?
less
