9/16/2011 1 INTRODUCTION TO POPULATIONS Definitions • What is a population? – Ecological* – Statistical9/16/2011 2 Ecological Population • “a group of organisms of the same species occupying a particular space at a particular time” (Krebs 2001:116) …same species… • Populations are composed of interbreeding individuals • There is genetic proximity9/16/2011 3 …particular space… • Populations occupy a delimited geographic area • There is spatial proximity Genetic, Geography and… • Demographics – Reproductive rates – Survival – Composition (sex ratio, age structure, etc.) • These things should be similar within populations9/16/2011 4 Hierarchical Aggregations of Populations • According to this definition, populations can be grouped at many different levels of aggregation (Garton 2002) – Deme – Population – Metapopulation – Subspecies – Species Deme • “a group of organisms where breeding is random” (Emlen 1984:202) • “a panmictic population” (Ehrlich and Holm 1963)9/16/2011 5 Deme • Genetics – This smallest grouping of individuals should emphasize genetic objective of random breeding within the group – In reality, random breeding is constrained by the social system • Geography – Continuous distribution of individuals in one patch of habitat • Demographics – Smallest group where it is reasonable to estimate birth, death, immigration and emigration rates Red-winged Blackbird Deme (Orians study area) • A patch of emergent vegetation adjacent to or within ponds, streams or lakes9/16/2011 6 Population • A collection of demes with strong connections between adjacent demes • Genetics – Relatively high rates of dispersal among demes • Geography – A collection of patches without great expanses of non-habitat intervening • Demographics – High correlations in demographic rates between adjacent demes Red-winged Blackbird Population • Patches of emergent vegetation adjacent to or within ponds, streams or lakes in Columbia River National Wildlife Refuge9/16/2011 7 Metapopulation • A collection of populations with weak connections between adjacent populations • Genetics – Relatively low rates of dispersal among populations produces genetic differentiation • Geography – Separated by expanses of non-habitat • Demographics – Low correlations in demographic rates between adjacent populations Red-winged Blackbird Metapopulation • Populations along Columbia River and adjacent populations9/16/2011 8 Subspecies • A collection of metapopulations in a region • Genetics – Rare dispersals maintain genetic similarity • Geography – Separated by expanses of non-habitat or other semi-permeable barriers to dispersal • Demographics – Nearly complete independence Red-winged Blackbird Subspecies9/16/2011 9 Species • A collection of subspecies encompassing the entire distribution of the species • May encompass substantial differences in phenotypes (habitat, physiology, behavior) and genotypes • Genetics – Very rare dispersals maintain genetic similarity (at least for a while) • Geography – The entire distribution • Demographics – N/A Red-winged Blackbird Species Down through Central
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