Population Ecology Chapter 52 Population characteristics Density of

Population Ecology Chapter 52

Population characteristics Density~ # of individuals per unit of area • counts • sample size estimate • indirect indicators • mark-recapture Figure 52. 17

Density is the result of a dynamic interplay ◦ Between processes that add individuals to a population and those that remove individuals from it Births and immigration add individuals to a population. Births Immigration Popu. Iation size Emigration Deaths Figure 52. 2 Deaths and emigration remove individuals from a population.

Population characteristics Dispersion~ pattern of spacing • random~ unpredictable, patternless spacing (a) • clumped~ patchy aggregation (b) • uniform~ even spacing (c)

Demography: factors that affect growth & decline of populations Birthrate (natality)~ # of offspring produced Death Age rate (mortality) structure~ relative number of individuals of each age

Demography: factors that affect growth & decline of populations Survivorship curve~ plot of numbers still alive at each age

The survivorship curve for Belding’s ground squirrels ◦ Shows that the death rate is relatively constant Number of survivors (log scale) 1000 100 Females 10 Males 1 Figure 52. 4 0 2 4 6 Age (years) 8 10

Population Growth Models Zero population growth ◦ Occurs when the birth rate equals the death rate The population growth equation can be expressed as d. N = r. N dt

Population Growth Models Exponential model (red) • idealized population in an unlimited environment (Jcurve) r-selected species (r=per capita growth rate)

The equation of exponential population growth is 2, 000 1, 500 Population size (N) ∆ N= ∆ t rmax. N d. N = 1. 0 N dt 1, 000 500 0 Figure 52. 9 d. N = 0. 5 N dt 0 10 5 Number of generations 15

Population Growth Models Logistic model (blue) • carrying capacity (K): maximum population size that a particular environment can support (Scurve) K-selected species

The logistic growth equation ◦ Includes K, the carrying capacity (K - N ) ∆N = rmax N ∆t K Figure 52. 13 a Number of Paramecium/ml 1, 000 800 600 400 200 0 0 5 10 Time (days) 15 (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.

Population life history “strategies” K-selection, or density-dependent selection ◦ Selects for life history traits that are sensitive to population density r-selection, selection or density-independent ◦ Selects for life history traits that maximize reproduction

r-selected K-selected Short Long (opportunistic) maturation & lifespan Many (small) offspring; usually 1 (early) reproduction; no parental care High death rate (equilibrial) maturation & lifespan Few (large) offspring; usually several (late) reproductions; extensive parental care Low death rate

Population limiting factors Density-dependent factors • competition • predation • stress/crowding • waste accumulation Density-independent factors • weather/climate • periodic disturbances