POPULATION BIOLOGY

Ecosystem  Communities  Populations  Organisms 4.1 Population Dynamics Ecology can viewed through several hierarchical "levels of organization. Ecosystem  Communities  Populations  Organisms

Groups of organisms of the same species that live within a given area Populations Groups of organisms of the same species that live within a given area Key characteristics: Dispersion patterns Population density Growth rate

Limiting factors—biotic or abiotic factor that prevents population growth A. Physical factors -- temperature, water, light, soil acidity B. Biological interactions --competition, predation, symbiosis C. Geographical barriers – Mountains, deserts, oceans (Humans sometimes transport species past these barriers)

Population Density Population density is total population size per unit of area. Population densities depend on: Interactions within the environment Quality of habitat Density dependent factors Density independent factors Carrying capacity is the maximum number of organisms that can be supported in a given habitat.

Limits on Population Growth Density Dependent Limits Food Water Shelter Disease Density Independent Limits Weather Climate Water and shelter are critical limiting factors in the desert. Fire is an example of a Density independent Limiting factor.

Density dependent factors – The effect increases as the population increases. a. Predation b. Disease c. Intrinsic influences · Physiological stress from overcrowding · Abnormal behavior (aggressive behavior, kill young, etc.) · Competition for resources

Density independent factors -- Affect populations regardless of size. a. Abiotic – Environmental factors that effect population size. (rainfall, temperature, hurricanes) b. Biotic – Biological factors. An organisms predator or prey species population changes.

Growth Rate is the change in population size over time. Birth rate--number of births Death rate--number of deaths Immigration & Emigration—numbers that leave or join the population

Logistic growth (S-shaped curve)—Has a carrying capacity (K)– maximum number of individuals that can survive due to limited resources (food, light, space, water). Logistic growth often has an "overshoot" phase, followed by fluctuations in population.

Exponential growth (J-shaped curve)-- Assumes no limitations on resources. Some species have brief periods of exponential growth, followed by population crashes.

Population Growth Exponential vs. Logistical Growth