POPULATION ECOLOGY

You Must Know: How density, dispersion, and demographics can describe a population. The differences between exponential and logistic models of population growth. How density-dependent and density-independent factors can control population growth.

Population = group of individuals of a single species living in same general area Density: # individuals / area Dispersion: pattern of spacing between individuals Introduction

Determining population size and density: Count every individual Random sampling Mark-recapture method

Patterns of Dispersal: 1.Clumped – humans in a city 2.Uniform – like trees in an orchard 3.Random – like trees in a forest

Additions occur through birth, and subtractions occur through death. Life table : age-specific summary of the survival pattern of a population Represent data with a survivorship curve. Plot # of individuals in a cohort still alive at each age. Demography: the study of vital statistics that affect population size

Survivorship Curves: Type I curve: low death rate early in life (humans) Type II curve: constant death rate over lifespan (squirrels) Type III curve: high death rate early in life (oysters)

The following contribute to the biotic potential of a species. 1.Age of sexual maturation 2.How often organism reproduces 3.# offspring during each event 4.Survivorship of offspring to reproductive age Note: These traits are evolutionary outcomes, not conscious decisions by organisms biotic Potential – the maximum growth rate of a population under idea conditions, with unlimited resources and without growth restrictions

 N/  t = B-D N = population size t = time Change in Population Size Change in population size during time interval Births during time interval Deaths during time interval = -

Zero population growth: B = D Exponential population growth: ideal conditions, population grows rapidly

Unlimited resources are rare Logistic model: incorporates carrying capacity (K) K = maximum stable population which can be sustained by environment dN/dt = r max ((K-N)/K) S-shaped curve

Laboratory Populations

Factors that limit population growth: Density-Dependent factors: population density matters i.e. Predation, disease, competition, territoriality, waste accumulation, physiological factors Density-Independent factors: population density not a factor i.e. Natural disasters: fire, flood, weather

K-selection: pop. close to carrying capacity r-selection: maximize reproductive success K-selectionr-selection Live around KExponential growth High prenatal careLittle or no care Low birth numbersHigh birth numbers Good survival of youngPoor survival of young Density-dependentDensity independent ie. Humansie. cockroaches

Populations fluctuate due to biotic and abiotic factors : peak in wolf numbers 1995: harsh winter weather (deep snow)

What do you notice about the population cycles of the showshoe hare and lynx?

Boom-and-bust cycles Predator-prey interactions Eg. lynx and snowshoe hare on 10-year cycle

Exponential and logistic growth patterns are associated with two kinds of life-history strategies R-selected species exhibits rapid growth (J shaped curve). This type of reproductive strategy is characterized by an opportunistic species. Opportunistic Species produce many offspring that are small, mature quickly, and require little to no parental care. K-Selected Species one whose population size remains relatively constant (at carrying capacity). They produce relatively large offspring that require extensive parental care.

Human Population Growth 2 configurations for a stable human population (zero population growth): A.High birth / high death B.Low birth / low death Demographic transition: occurs when population goes from A  B

Age-Structure Diagrams

Global Carrying Capacity UN predicts: 7.8 to 10.8 billion people by the year = 7 billion Estimated carrying capacity = billion? Ecological footprint: total land + water area needed for all the resources a person consumes in a pop. 1.7 hectares (ha)/person is sustainable U.S.: 10 ha/person  over K?? Limitations? Consequences? Solutions?

Map of ecological footprint of countries in the world (proportional sizes shown)