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

Cactus

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 Fig. 53-6 Number of survivors (log scale) 1,000 100 II Number of survivors (log scale) 10 Figure 53.6 Idealized survivorship curves: Types I, II, and III III 1 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.

POPULATION DENSITY

Births and immigration add individuals to a population. PopuIation size 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.

White Abalone

Bald Eagles

White-tailed deer

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 proportion marked 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