Population Ecology Chapter 53

turtles

Population Groups of individual of the same species that live in the same place Characteristics of populations 1. Population range –Area where it occurs 2. Spacing patterns –Spacing of individuals 3. Size

Population range No population is in all habitats No population is static 1. Changing environment (receding glaciers) 2. Expansion to new areas

Cattle egret Current

Population Density Dispersion Pattern of spacing

Spacing 1. Randomly spaced –Little interaction 2. Uniformly spaced –Competition for resources 3. Clumped spacing –Uneven distribution of resources –Social interactions (herd, flock, pride)

Dispersion (a) Clumped (b) Uniform (c) Random

Demography Statistical study of populations Grows: births outweigh deaths Shrinks: deaths outweigh births Sex ratios (females > males) Generation time (birth to reproduce) Reproduction Survivorship curves

Age structure Cohort Group of individuals that are of the same age Fecundity: Birth rate Mortality: Death rate Age structure # of individuals in a given cohort

Survivorship curve 1, II III Percentage of maximum life span Number of survivors (log scale) I

Factors regulate populations Cost of reproduction Age at first birth Semelparity: Single birth event Annuals/insects Iteroparity: Several births over several years

Factors regulate populations Carrying capacity K: Maximum population an environment can sustain Density-dependent effects Increase density decreased birth rates Light, water, space, food, disease Density-independent effects: Fire, volcano, cold

Carrying capacity Snowshoe hare Lynx Number of lynx (thousands) Number of hares (thousands) Year

Factors regulate populations K-selection: Density dependent selection r-selection: Density independent selection

Human growth

Density dependent factors Competition for resources Territoriality Intrinsic factors Disease Predation Toxic wastes 5 µm

Population pyramids

Fig Less indus- trialized countries Indus- trialized countries Life expectancy (years) Infant mortality (deaths per 1,000 births) Less indus- trialized countries Indus- trialized countries 60

Ecological footprint Log (g carbon/year) Not analyzed

Energy use (GJ): > 300 < 10150–300 50–150 10–50

Growth Population growth rate  N= change in population size  t = change in time B=birth rate D=death rate

Growth B=births during specified time D= deaths during specified time b= annual per capita birth rate m (mortality)= per capita death rate N is population size B  bN D  mN

Growth r = (per capita rate of increase) r  b – m NN tt  rN

Fig Number of generations ,000 1,500 2, N = dN dt 0.5N = dN dt Population size (N)

Fig ,000 6,000 4,000 2, Year Elephant population 1900

Table 53-3

Fig ,000 1,500 1, Number of generations Population size (N) Exponential growth 1.0N = dN dt 1.0N = dN dt K = 1,500 Logistic growth 1,500 – N 1,500

Fig , Time (days) Number of Paramecium/mL Number of Daphnia/50 mL Time (days) (b) A Daphnia population in the lab(a) A Paramecium population in the lab