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 PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Figure 52.2

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 rate (mortality) Age 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 Figure 52.4 1000 100 10 1 Number of survivors (log scale) 2 4 6 8 Age (years) Males Females

Population Growth Models Zero population growth Occurs when the birth rate equals the death rate The population growth equation can be expressed as dN dt = rN

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

∆ N = rmaxN ∆ t The equation of exponential population growth is Figure 52.9 5 10 15 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt = 1.0N 0.5N ∆ N ∆ t = rmaxN

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

∆N ∆t = K rmax N The logistic growth equation Includes K, the carrying capacity Figure 52.13a 800 600 400 200 Time (days) 5 10 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. 1,000 Number of Paramecium/ml ∆N ∆t = (K - N) K rmax N

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

r-selected (opportunistic) K-selected (equilibrial) Short maturation & lifespan Many (small) offspring; usually 1 (early) reproduction; no parental care High death rate K-selected (equilibrial) Long 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