Conservation Biology and Restoration Ecology

Page
3

The small-population approach

The declining-population approach

Slide 18

Small-Population Approach

The small-population approach studies processes that can make small populations become extinct.

A small population is prone to positive-feedback loops that draw it down an extinction vortex.

The key factor driving the extinction vortex is loss of the genetic variation necessary to enable evolutionary responses to environmental change.

Slide 19

Processes culminating in an extinction vortex

Inbreeding

Small

population

Genetic

drift

Lower

reproduction

Higher

mortality

Smaller

population

Reduction in

individual

fitness and

population

adaptability

Loss of

genetic

variability

Slide 20

Minimum Viable Population Size

Minimum viable population MVP is the minimum population size at which a species can survive.

The MVP depends on factors that affect a population’s chances for survival over a particular time.

A meaningful estimate of MVP requires determining the effective population size, which is based on the population’s breeding potential.

Slide 21

Case Study: Analysis of Grizzly Bear Populations

One of the first population viability analyses was conducted as part of a long-term study of grizzly bears in Yellowstone National Park.

This grizzly population is about 400, but the Ne is about 100.

The Yellowstone grizzly population has low genetic variability compared with other grizzly populations.

Introducing individuals from other populations would increase the numbers and genetic variation.

Slide 22

Long-term monitoring of a grizzly bear population

Slide 23

Declining-Population Approach

The declining-population approach

Focuses on threatened and endangered populations that show a downward trend, regardless of population size.

Emphasizes the environmental factors that caused a population to decline.

Slide 24

Steps for Analysis and Intervention

The declining-population approach involves several steps:

Confirm that the population is in decline

Study the species’ natural history

Develop hypotheses for all possible causes of decline

Test the hypotheses in order of likeliness

Apply the results of the diagnosis to manage for recovery.