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Demography, life tables and survivorship curves Population demography Populations can be described by vital statistics or demographics Size Change in size over time (growth) Age Structure Density Distribution Rates of dispersal between populations Sex ratio Population size Number of individuals that contribute to a population’s gene pool Can be determined by Capture-Recapture Method for mobile species Capture-recapture method Sample small number and extrapolate Capture, mark, and release individuals Return later and capture second sample Count the number of marked individuals and use this to estimate total population Capture-recapture equation Marked individuals Marked Individuals in sampling 2 = in sampling 1 Total capture Total population size in sampling 2 Factors that increase populations Natality - Production of new individuals - (births, germination, etc.) Fertility - Measure of actual number of offspring produced Immigration - Organisms introduced into new ecosystems Factors that decrease populations Mortality - Death Rate Survivorship - Percentage of cohort surviving to a certain age Life expectancy - Probable number of years of survival for an individual of a given age Life span - Longest period of life reached by a given type of organism Emigration - Movement of individuals out of a population Life history patterns Patterns of timing of reproduction and survivorship vary by species Summarized in survivorship curves and life tables Life table Follows the fate of a given cohort of individuals A cohort is a group of individuals born in the same designated time interval Tracks age-specific patterns Population is divided into age categories Birth rates and mortality risks are calculated for each age category Survivorship curve Can be created from life tables Follows survival of a given cohort of individuals over time Graphs survival per 1000 individuals versus age on a logarithmic scale Survivorship curves Survivorship curves Log(lx) Shows risk of mortality Survivorship curve for Poa annua Survivorship curves Four general patterns: Full physiological life span Probability of death unrelated to age Mortality peaks both early and late in life Mortality peaks early in life Survivorship curves Crowding Annual plant Erophila verna Varied planting density Found shift in survivorship curves Intraspecific competition Density can affect all BIDE factors Life expectancy