Ecology - Ch 12

Population dynamics

Variation in population over space and time

How does population size increase?

Immigration and natality

How does population size decrease?

Emigration and mortality 

Overshoot 

When population grows beyond carrying capacity 

Die-off

Substantial decline in density that typically goes well below carrying capacity

What can cause an overshoot?

→ Carrying capacity decreases

→ Population increases by large amount in single breeding season

Populations show cyclic behavior due to: 

Density dependence with time delays 

Population size

Regular oscillation of population size over long periods of time

Delayed density dependence

When density dependence occurs based on population density at some time in past

Damped oscillation 

Pattern of population growth in which population size initially oscillates but magnitude of oscillation declines over time 

Stable limit cycle

Pattern of population growth in which population size continues to exhibit large oscillations over time

What does is mean when r x time passed is less than 0.37

Population approaches carrying capacity without oscillations

What does it mean when r x time passed has a value between 0.37 - 1.57? 

Population exhibits damped oscillations 

What does it mean when r x time passed has a value greater than 1.57?

Population oscillates time as stable limit cycle

What happens when organisms who can store energy reach carrying capacity?

Reach carrying capacity → run off food stores → experience massive die-off

What happens when organisms who can’t store energy reach carrying capacity? 

Reach carrying capacity → possible small die-off → continutes to fluctuate at carrying capacity 

Are small or large populations more at risk of going extinct?

Small populations

Deterministic model

Model designed to predict result without accounting for random variation in population growth rate

Stochastic model 

Model that incorporates random variation in population growth rate

Demographic stochasticity 

Variation in birth/death rates due to random differences among individuals 

Environmental stochasticity

Variation in birth/death rates due to random changes in environmental conditions

Metapopulations 

Collection of subpopulations that live in isolated patches connected by dispersal 

Habitat fragmentation

Process of breaking up large habitats into number of small habitats

Basic metapopulation model

Scenario in which patches of suitable habitat embedded in matric of unsuitable habitat

Source-sink metapopulation model 

Builds on basic → adds how patches aren’t equal quality 

Landscape metapopulation model

Builds on source-sink → adds how surrounding matrix varies in regards to ease of dispersal

Source populations

Subpopulations that serve as source of dispersers within metapopulation

Where do source subpopulations occur? 

In high-quality habitats 

What type of patch are organisms least likely to inhabit?

Small, isolated patches

Rescue effect

Phenomenon of dispersers supplementing declining subpopulation headed towards extinction