Chapter 53

Ecology is the study of how organisms (biotic) interact with each other and their environment (abiotic)

Populations A population consists of individuals of a species living together at the same place at the same time. Most species have a limited geographic range. organism’s environment (abiotic) include: temperature water sunlight soil

Population Dispersion Randomly spaced Uniformly spaced - competition for resources Clumped spacing - unequal resources

Population Dispersion Human effect Dispersal mechanisms light seeds (wind) hooks and hairs (animal fur) fruits (animal digestive systems)

Demography - statistical study of populations Survivorship curves Survivorship is the percentage of an original population that survives to a given age. Type I - full life span Type II - mortality unrelated to age Type III - early susceptibility

Cost of Reproduction A life history is the complete life cycle of an organism. cost of reproduction Due to limited resources, increased reproduction may decrease survival Natural selection will favor the life history that maximizes reproductive success. number of offspring vs size size may affect chances of survival

Cost of Reproduction Reproductive events per lifetime semelparity - organisms focus all reproductive efforts on a single, large event iteroparity - organisms produce offspring several times over many seasons Age at first reproduction Longer-lived animals tend to reproduce later, and provide more parental care than shorter-lived animals.

Biotic Potential Exponential growth model - J curve Rate at which a population will increase when no limits are placed on the rate of growth.

Biotic Potential Carrying capacity Carrying capacity (K) is the maximum number of individuals the resources in a given area can support. Logistic growth As a population approaches carrying capacity, its growth rate slows as resources become depleted. sigmoidal (S curve) growth curve

Population Growth Density-dependent population controls As populations approach their carrying capacity, competition for resources can be severe, leading to decreased birth rate and increased risk of mortality.

Linked Population Cycles snowshoe hares Food plants (willows) and predators (lynx) both control the population.

Population Growth and Life History Models K-selected species tend to produce relatively few, large offspring. large investment in parental care r-selected species tend to produce many, small offspring. small investment in parental care