Population A group of individuals of the same species that interact with each other in the same place at the same time Metapopulation A population of populations, linked by genetic exchange (immigration and emigration)

Describing a Population Distribution: total geographic range including gaps Density: number of individuals per area Dispersion: how individuals are dispersed

Fig. 9.8

Why Study a Population? Explain distributions Changes over time Absences from suitable habitats

European Starling: 160 released in NY Central Park in 1890

Zebra Mussel: larvae released in ship ballast in Great Lakes, 1988

Old growth piñon Only juniper occurs in the Gunnison Basin today

How to study populations? Select sample population and study growth over time Determine birth and death rates, average life span, and other demographic variables

Demography: the vital statistics of a population Reproduction semelparous iteroparous nonoverlapping generations overlapping generations

Usually, long-lived species are iteroparous with overlapping generations e.g., bear, humans, elephant Short-lived species are more often semelparous with nonoverlapping generations e.g., insects, weeds Exceptions include salmon, agave, bamboo -- all are long-lived, but breed once and die These categories are important to know when trying to determine r for a species

Importance of Age Structure in a Population Humans: 0-12 yr no births, r is – 13-25 r + and high 26-35 r + and low 36-45 r + and very low 46-80 r = 0 or - The proportion of individuals in each age class defines the age structure for the population

Age structure for three countries Fig. 9.14 If r for each age class remains constant, the shape of the diagram will not change. Then, it’s a stable age distribution.

r-selected r-selected r-selected K-selected K-selected K-selected high r short-lived small size short generation time large litters, >1 per yr unstable habitats Type III survivorship N variable below K r-selected high r short-lived small size short generation time large litters, >1 per yr unstable habitats Type III survivorship N variable below K r-selected high r short-lived small size short generation time large litters, >1 per yr unstable habitats Type III survivorship N variable below K K-selected low r long-lived large size long generation time small litters, 1 per year stable habitats Type I or II survivorship N at or near K K-selected low r long-lived large size long generation time small litters, 1 per year stable habitats Type I or II survivorship N at or near K K-selected low r long-lived large size long generation time small litters, 1 per year stable habitats Type I or II survivorship N at or near K

Species with mixture of r and K-selected traits http://www.bcsturgeon.com/sturgeon.htm http://www.worldagroforestrycentre.org/ Sturgeon lives ~100 yrs female produces 1 million eggs, more eggs as it ages Giant bamboo lives ~250 yrs flowers once, 1000s of seeds Species with mixture of r and K-selected traits

Robert MacArthur 1930-1972 Hypothetico-deductive method in ecology Competition and niche partitioning r and K selection in life history strategy Predator – prey theories Optimal foraging Island Biogeography Population growth and dynamics Generalist vs. specialist feeding Paper on reserve: Fretwell, S. 1975. The impact of Robert MacArthur on Ecology. Annual Review of Ecology and Systematics 6: 1-13.