Populations 4: Population dynamics in variable environments Flashcards
What is wrong with the simple deterministic models
They neglect
-> Density dependence
-> Environmental dependence
-> Individual heterogeneity
Incorporating Density dependence into the MPM
The survival of juveniles and adults and fertility can be made a function of how many adults there were in the previous time step and how many juveniles there were in the previous time step.
The vital rates will change at each time stap as population size changes
Example: grey wolf population
- model used to predict grey old population recovery in the upper peninsula of Michigan
- Predicted population would reach 929 by end of 2013
- predicted to be 631 in 2021
Incorporating Environmental stochasticity into the MPM
The survival of juveniles and adults and fertility can be made a function of conditions during the year before (e.g. precipitation)
Different types of environmental change
Constant conditions
White noise: fully stochastic
Red noise: positive autocorrelation (if a condition occurred in one year it is more likely to occur in the next)
Blue noise: negative autocorrelation (If a condition occurred in one year it is less likely to occur in the next)
What value of used to track the growth rate
a is used instead of lambda as lambda assumes constant conditions
a=log(lambda s) and varies around 0 rather than 1.
Example of the use of MPM in natural population models
You can evaluate the degree of environmental stochasticity that will drive a population extinct through modelling by looking at a populations elasticity and sensitivity.
Vital rates will vary depending on the population density and environmental stochasticity
South African Sea lion and management using the MPM
The South African sea lion is endangered as they are hunted for fur and food.
A population matrix model was used to predict the effect of culling and climate change on the species, taking into consideration that the population switches between good and bad years.
These factors affect the vital rates, which can be multiplied by the population size to calculate the rate of change.
Results: climate change and culling will drive the population to extinction.
Overview
MPM are able to take into consideration density dependence, Environmental dependence and individual heterogeneity through by making vital rates a function of these factors.
The population rate of change is a rather than lambda in stochastic environments.
These models can be used to create forecasts to predict how populations will respond to environmental change and population change (e.g. culling)
Cactus management using MPM
Columnar cactus
- endemic to a small regionin central Mexico
- Population growth rate reached values above 1 only when either fecundity or seedling survival probability were increased 10-fold
- management practices aimed to increase germination and seedling establishment success
