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DEMOGRAPHY. The study of birth and death processes that determine growth and age structure of a population. Each age class of a population has an expected:. Mortality rate. Fecundity rate. Demographic characteristics can be represented in:. Life Tables summarize deaths and/or births
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DEMOGRAPHY The study of birth and death processes that determine growth and age structure of a population.
Each age class of a population has an expected: Mortality rate Fecundity rate
Demographic characteristics can be represented in: • Life Tables • summarize deaths and/or births • in different age classes of a population Conventional life table
Demographic characteristics can be represented in: • Life Tables • summarize deaths and/or births • in different age classes of a population Conventional life table Diagrammatic life table (flow diagram)
Diagrammatic Life Table # in each age class Fecundity Probability of survival (Assumes 50-50 sex ratio)
2) Survivorship Curves 1,000 I 100 II Number of survivors (log scale) 10 III 1 0 50 100 Percentage of maximum life span Fig. 53-6
Imagine that a species of fish used to be a broadcast spawner (producing many eggs that then get no subsequent parental care) but has evolved to be a mouth brooder (holding the eggs in the parent’s mouth until they hatch and then caring for the young for a while). We would expect the survivorship curve of this species to shift A) from Type I to Type II or III. B) from Type II to Type I. C) from Type III to Type I or II. D) from Type II to Type III. E) The survivorship type would vary unpredictably.
Births and immigration add individuals to a population. Immigration Births PopuIationsize Emigration Deaths Deaths and emigration remove individuals from a population. Population Dynamics
Population Density (Abundance): # of individuals of the same species that occur in a given area. Knowing the population density of a particular species is important for conservation and management decisions.
Density Estimation (“Sampling”) Techniques Census (direct counts) Indirect counts Sample plots or transects Mark-recapture
Mark-recapture Technique: • capture and mark several, then release all • soon after, capture more, SOME of which • have marks (“recaptured”)
Reasoning: Proportion of 2nd capture that are recaptured individuals represents the proportionmarked in entire population... R/C = M/N M = # caught and Marked in first trapping session C = # Caught in second trapping session R = # marked individuals Recaptured N = estimated Number in entire population
R/C = M/N So, N = M / (R/C) N = (M x C) / R
Assumptions of mark-recapture technique: • closed population (no immigration or emigration) • no births or deaths (in sampling period) • marked and unmarked individuals • equally likely to be caught in second trapping