11/5 Population Ecology 2

What are the 3 forms of population growth?

Exponential, Logistical, Cyclical

Exponential Growth (constant r)

A population's per individual growth rate (r) stays the same regardless of population size - Making the population grow faster and faster as it gets larger. Population size has no “stopping” point = keeps increasing.

Logistic Growth

Occurs when the growth rate (r) decreases as the population reaches carrying capacity 

Cyclical Growth

Both density dependent and density independent factors affect population growth, often on regular cycles

When do we expect the different types of population growth to be present? For example, why is exponential growth unrealistic for most populations? 

Because resources are not unlimited in real world environments.

What kind of populations might an exponential growth model be appropriate for?

Introduced populations (non-native species), catastrophically reduced populations that are now rebounding, new populations (ex. a new population on an island), lab populations

What is carrying capacity?

a species’ average population size in a particular habitat (K); most populations grow quickly at low densities, but growth rate slows down at high densities

What affects carrying capacity?

Limited by environmental factors like adequate food, shelter, water, and biotic factors

When N = 0,  (K-N)/K = 1, that is what kind of growth

Exponential

N = K,   (K-N)/K = 0, what kind of growth is that?

NO GROWTH (population has reached its carrying capacity)

What is density dependence?

When a population's growth rate is regulated by its own density; Usually as N increases b goes down and d goes up

What is density independence?

r may drop for reasons unrelated to density

What are Allee effects?

Density Dependent Factors

Competition for food, space, and shelter; increased predation; increased disease; waste build-up

Density Independent Factors

seasonal changes: weather/climate, light availability, and more and recurring catastrophes (often enough to regulate the population)

What is population age structure?

The distribution of individuals across different age groups

Why might we care about population age structure? What does it tell us?

It can tell us if the population is growing, stable, or declining.