INTRODUCTION TO POPULATIONS
1. Ecological - A group of organisms of the same species occupying a particular space at a particular time (Krebs 2001:116).
2. Statistical – Group to which inferences are to be made from a sample of that group
B. Ecologically-based Hierarchical Aggregations of Individuals (Garton 2002)
1. Deme – A group of individuals were breeding is random. Continuous distribution geographically. Occupy one “patch” of habitat.
2. Population – A collection of demes with strong connections between adjacent demes. Geographically a collection of patches without great expanses of non-habitat intervening. Genetically closely related. High rates of dispersal between demes. High correlations in demographic rates between adjacent demes.
3. Metapopulation – A collection of populations. Possible low correlations in demographic rates (which produces high levels of independence). Moderate rates of dispersal among populations. Low rates of dispersal among metapopulations (which can produce genetic differences among metapopulations). Correlations and dispersal rates among groups within the metapopulation (i.e., populations) are high enough to matter but not so high as to constitute a "population".
4. Subspecies – A collection of metapopulations in a region. Very rare dispersals among metapopulations maintain genetic similarity. Demographic independence may be nearly complete (i.e., correlations among metapopulations = 0). Occupied patches may be separated by large areas of non-habitat.
5. Species - The collection of all individuals encompassing the entire distribution and geographic range of the species.
C. Other Terms for Groups of Individuals
1. Stock
Cushing (1981) noted that many fish do not disperse much
Stock - a group of fish spawning in a particular lake or stream at a particular season, which to a substantial degree do not interbreed with any other such group (i.e., dispersal rates among stocks are rare to very rare).
2. "Species" as defined by Endangered Species Act 1972
"any distinct population segment of any species of vertebrate fish or wildlife that breeds when mature"
3. Evolutionary Significant Unit (ESU)
Endangered Species Act assigns National Marine Fisheries Service (NMFS) responsibility for determining if anadromous fish species are endangered or threatened
NMFS established the Evolutionary Significant Unit to define a "distinct population segment" when identifying Pacific salmon stochs for listing under ESA.
ESU criteria:
Reproductively isolated from other conspecific population units
Represents an important component in the evolutionary history of a species
D. Methods to Determine Level of Aggregation
1. State objectives clearly
What level of aggregation is of interest?
Is demographic similarity more important that genetic similarity?
Is spatial proximity more important that biological similarity?
2. Determine distribution
Determine distribution of individuals or groups
Identify significant geographical structures that might restrict movement
3. Determine movement
Determine amount of movement between groups (i.e., dispersal rates) by marking individuals or genetic comparisons
4. Determine demographic similarity
Determine demographic rates and identify degree of correlations among different groups
5. Determine phenotypic similarity
Physiological/behavioral characters
Morphometric/meristic characters
6. Determine genetic similarity
Gene frequencies
7. Integrate 1-6 to outline most discrete unit(s) possible, which still meet objectives
Cushing, D. H. 1981. Fisheries biology. The University of Wisconsin Press, Madison, WI, USA.
Garton, E. O. 2002. Mapping a chimera? Pages 663-666 in J. M. Scott et al. editors. Predicting species occurrence. Island Press, Washington.
Return to LECTURE OUTLINE