Ch. 11 - Population Growth

Geometric population growth

population growth in which generations do not overlap and successive generations differ in size by a constant ratio.

What kinds of species experience geometric population growth?

Species with seasonal, pulsed reproduction:

• deer

• bison

• birds

Formula for geometric population growth

N_t = N₀lambda^t

Exponential population growth

population growth in which generations overlap and the per capita rate of increase (r) is constant.

What species experience exponential growth?

species experience exponential growth for short periods of time when resources are abundant:

• bacteria

• invasives: zebra mussels, privet

• insects: locusts

formula for exponential population growth

N_t = N₀e^rt

Logistic population growth

population growth that occurs when resources are limited.

Examples of species that experience logistic population growth

occurs in nature when population size exceeds the carrying capacity:

• sheep

• harbor seals

• elephants 

• fruit flies

formula for logistic population growth

dN/dt = r_maxN(1-N/K)

Density Dependent Factors

Biotic factors that limit population growth and are influenced by population density.

Examples of density dependent factors

• parasitism

• competition (mate selection)

• predation

• disease (aspergillus sydowii)

Density independent factors

abiotic factors that limit population growth and are not influenced by population density.

Examples of density independent factors

• natural disasters (hurricane)

• extreme weather (drought, flood)

• human activities (deforestation)

How do density dependent factors regulate a population?

Regulates population at a relatively constant size near K.

How do density independent factors regulate a population?

It affects population in unpredictable ways.

What kind of population growth is this?

Geometric population growth

What kind of population growth is this?

Exponential population growth

What kind of population growth is this?

Logistic population growth