What is a population? a group of conspecific individuals within a single area arbitrary boundaries

Populations exist within the geographic and ecological range of a species. example: European starlings introduced in 1890; geographic range expanded westward Starling geographic range.

Populations exist within the geographic and ecological range of a species. example: European starlings introduced in 1890; geographic range expanded westward local densities are influenced by species’ ecological range Starling population densities.

Populations exist within the geographic and ecological range of a species. example: the cobra lily pitcher plant, Darlingtonia californica –endemic to northern CA and southern OR –patchy distribution: locally dense populations when conditions are appropriate Darlingtonia californica

Populations exist within the geographic and ecological range of a species.

Clematis fremontii var. riehlii restricted to limestone glades in Jefferson Co. Missouri

Other aspects of population structure: density –the number of individuals per unit area –ecological density dependence –source habitats produce excess densities –sink habitats absorb excess individuals but produce fewer

Other aspects of population structure: density spatial dispersion –aggregated –random –regular Variance/mean ratio: m = mean density per unit area v = variance in mean density

Other aspects of population structure: density spatial dispersion –aggregated dispersions are likely the most common –often reflect distribution of resources

Other aspects of population structure: density spatial dispersion –aggregated dispersions are likely the most common –often reflect distribution of resources –measuring dispersion is often scale dependent Regular on leaves Random within trees Aggregated throughout forest

Other aspects of population structure: density spatial dispersion genetic structure –phenotypic differences influence fecundity and survivorship

Other aspects of population structure: density spatial dispersion genetic structure –phenotypic differences influence fecundity and survivorship

Other aspects of population structure: density spatial dispersion genetic structure –phenotypic differences influence fecundity and survivorship –genetic events influence population evolution –clines and ecotypes Channel island fox

Other aspects of population structure: density spatial dispersion genetic structure age structure –influences the effective population size and demographic processes Emperor penguin

Other aspects of population structure: density spatial dispersion genetic structure age structure social structure –also influences effective population size and demographics Tule elk

Effective population size: determined by the actual numbers of breeding members and the number of offspring they produce

Minimum viable population: the smallest population capable of long term survival –large populations are buffered against extinction focus of conservation refuge planning California condor

Life tables summarize age-specific demographic attributes.

Survivorship curves describe life- history mortality patterns.

Populations can grow two ways: Continuous reproduction –less common then discrete reproduction –overlapping generations

Continuous reproduction –less common then discrete reproduction –overlapping generations –exponential population growth

Exponential population growth: Continuous reproduction –less common then discrete reproduction –overlapping generations –exponential population growth instantaneous growth –r is the intrinsic rate of population increase –r = b – d in closed populations

Populations can grow two ways: Discrete reproduction –most plants and animals –discrete generations

Discrete reproduction –most plants and animals –discrete generations –geometric population growth N(t) = N(0) t where

Discrete reproduction: Discrete reproduction –most plants and animals –discrete generations –geometric population growth N(t) = N(0) t where

Discrete reproduction: Discrete reproduction –most plants and animals –discrete generations –geometric population growth N(t) = N(0) t requires consistent annual population measurements

Discrete and continuous reproduction curves overlap one another.

Exponential and geometric growth models are unlimited. “the passion between the sexes….” N 14.7 = 1× = 10,434,068 assuming a 50/50 sex ratio, 20,868,136 elephants in 750 years

Population structure, e.g. age structure, affects population dynamics.

Are birth and death rates constant? b and d reflect relationships between populations and their environment environments are rarely constant the assumption of constant b and d becomes increasingly unrealistic

Are birth and death rates constant? b and d reflect relationships between populations and their environment environments are rarely constant the assumption of constant b and d becomes increasingly unrealistic

Some important questions: Why might population size and genetic structure be considered important conservation ecology issues? How can recognizing the spatial dispersion of a population contribute to broader understanding of its ecology? Why are scale independent random population dispersions relatively rare?

Some important questions: What are the ecological assumptions underlying the exponential and geometric growth models? Why might each of those assumptions not be met in real populations? Give examples. If growth models oversimplify the dynamics of real populations, why are they still useful tools for studying population growth?