Bio Ch 14 - Population dynamics over time and space

Population dynamics

variation in a population over time and space

all populations experience fluctuations due to factors such as availability of resources, predation, disease, competition, etc.

Overshoots

when a population grows beyond its carrying capacity

Die-offs

a substantial decline in density that typically goes well below carrying capacity

Population cycles

regular oscillation of population size over a long period of time. Some populations exhibit regular fluctuations in size

can be modeled by starting with the logistic growth model

Delayed density dependence

when density dependence occurs based on a population density at some time in the past

ex. moose breed in the fall- if carrying capacity is high, many parents will breed. but, reduced resources in the spring may not support all of the offspring

Damped oscillations

a pattern of population growth in which the population size initially oscillates, but the magnitude of the oscillations declines over time

Stable limit cycle

a pattern of population growth in which the population size continues to exhibit large oscillations over time

Energy reserves in causing population size cycling

delayed density dependence may occur because the organism can store energy and nutrient reserves

Extinction

smaller populations are more likely to go extinct, but growth models suggest that small populations should have more rapid growth and be resistant to extinction

this contradiction can be resolved by incorporating random variation of growth rates into growth models

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 events

Demographic stochasticity

variation in birth and death rates due to random differences among individuals

Environmental stochasticity

variation in birth and death rates due to random changes in environmental conditions

Metapopulation

a set of local subpopulations linked by dispersal

each subpopulation has its own independent birth and death rates

Habitat fragmentation

the process of breaking up large habitats into a number of smaller habitats

usually occurs as a result of human activities; some habitat fragments experience extinctions

Metapopulation dynamics

two sets of processes determine dynamics:

1. growth and regulation

2. colonization and extinction of subpopulations

Basic metapopulation model

a model that describes a scenario in which there are patches of suitable habitat embedded within a matrix of unsuitable habitat. Assumes all patches are of equal quality

p = the fraction of occupied habitat patches

e = the probability of each patch becoming unoccupied (going extinct)

c = the probability of a patch becoming colonized

assumptions:

1. ignores population growth, birth and death

2. ignores population regulation and environmental interaction

3. patches are all the same size

4. patches are equidistant from all patches (equal migration probability)

5. populations are assumed independent

Source-sink metapopulation model

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

is subpopulations frequently exchange individuals, the subpopulations will act as one large populations

if patches are connected, abundance in one subpopulation can affect the abundance of the connected subpopulation

Rescue effect

the phenomenon of dispersers supplementing a declining subpopulation that is headed toward extinction

The landscape metapopulation model

contains the most realistic conditions of habitat patches that differ in quality and a surrounding matrix that is variable in its suitability for dispersal and the presence of dispersal barriers

considers effects of differences in the habitat matrix:

• the quality of a habitat patch can be affected by the nature of the surrounding matrix

• some matrix habitats are more easily traversed than others