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Chapter 53

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

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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

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Population Dispersion

• Randomly spaced• Uniformly spaced - competition for resources• Clumped spacing - unequal resources

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Population Dispersion

• Human effect• Dispersal mechanisms

– light seeds (wind)– hooks and hairs (animal fur)– fruits (animal digestive systems)

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Demography

• Demography - statistical study of populations• Survivorship curvesSurvivorship 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

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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

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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.

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Biotic Potential

• Exponential growth model - J curve– Rate at which a population will increase

when no limits are placed on the rate of growth.

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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

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Population Growth

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

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Linked Population Cycles

Population cyclessnowshoe hares

Food plants (willows) and predators (lynx) both control the population.

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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