WLF 448: Fish & Wildlife Population Ecology

Fall 2004


Principle Involved: Age and sex ratios are important influences on the birth rate. Managers can manipulate these ratios and have profound effects.

A. Sex Ratios

1. Terms

a. Mayr (1939):

b.  Operational Sex Ratio = only reproductively active members used to calculate ratio

c. Expression

d. How to compute sex ratios

2. Mammalian and avian patterns

a. Basic tendency

b. Explanations

3. Examples: humans, birds, mammals, fish

a. Humans

b. Birds

c. Mammals

D. Fishes

4. Significance and applications

a. Depends on mating system

b. Component of herd management in mammals

c. Kelker method: using changes in sex ratio to estimate population size.

B. Age Distribution

1. Stable-age distribution

1. Definition:

2. Occurrence

2. Changing age distributions

a. Age distributions will strongly influence population processes, especially birth and death rates.

b. Summary

3. Interpretation of age ratios

a. Age-sex distribution pyramids

b. Must be cautious when using age-ratio data to make inferences on population growth or projected population changes (see Caughley 1974).

C. Age-specific Birth and Death Rates

1. Nature of birth and death rates

a. Natality patterns

b. Examples

2. Effects on age structure

D. References

Alexander, M. M. 1958. The place of aging in wildlife management. Amer. SCI. 46(2):123-137.

Caughley, G. 1974. Interpretation of age ratios. J. Wildlife Manage. 38(3):557-562.


Updated 05 August 1996