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Chapter 51

Chapter 51. Population Ecology. Ecology Basics. Terms to know… Ecology Branch of biology Relatively new science Biotic factors Abiotic factors Environmental science ecology + human interactions Population same species, same area, same time Population ecology numbers + changes.

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Chapter 51

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  1. Chapter 51 Population Ecology

  2. Ecology Basics • Terms to know… • Ecology • Branch of biology • Relatively new science • Biotic factors • Abiotic factors • Environmental science • ecology + human interactions • Population • same species, same area, same time • Population ecology • numbers + changes

  3. Features of populations • Properties that individuals lack: • Population density • Population dispersion • Birth/death rates • Growth rates • Survivorship rates • Age structure • Properties that communities lack: • Common gene pool • Reproductive success • Evolution • Economic importance (crops, forests, game animals…)

  4. Population dynamics • Density– the number of individuals per unit of area or volume at a given period of time • Affected by: • Habitat • Season • Other populations • Weather • Limiting factors: the number of individuals in a population is controlled by the ability of the environment to support it • Density-dependent factors – the effect increases as population density increases • Examples: • Density-independent factors – affects the size of a population but is not influenced by changes in population density; typically abiotic • Examples:

  5. Population dynamics… • Dispersion– spacing in relation to other members of the population • Three basic varieties: • Clumped (aggregated distribution, patchiness) • Individuals are concentrated in specific areas • Reasons: distribution of resources, social behavior of animals (herds, family groups), reproduction • Advantages: reduced chance of predation • Uniform • Individuals are fairly evenly spaced • Reasons: social behavior of animals (territories), high levels of competition between individuals • Advantages: reduced competition • Random • Individual spacing is unrelated to others in the population • Does not occur often in nature

  6. Changes in population size • Per capita – per individual • Natality– average per capita birth rate (b) • Mortality– average per capita death rate (d) • Immigration– individuals entering a local population (i) • Emigration – individuals leaving a local population (e) • Population growth rate (r): • r = (b + i) – (d + e) • If r = positive number  population is increasing • If r = negative number  population is decreasing • If r = zero  population is staying the same • Examples:

  7. Intrinsic rate of increase • Maximum rate of increase when: • Conditions are ideal • Resources are abundant • Population density is low • rmax • Factors which influence this: • Age at which reproduction begins • The fraction of the life span devoted to reproduction • The number of reproductive cycles • The number of offspring produced each cycle • Different species have different intrinsic rates… • Small organisms have high rates (bacteria); large species have low rates (elephants)

  8. Exponential population growth • Optimal conditions allow a constant per capita population growth (rmax) • The larger the population gets, the faster it grows • J shape curve: • Organisms cannot reproduce this way indefinitely because of increased: • competition, predation, disease, wastes

  9. Logistic population growth • Population growth rate nears zero • Occurs near the environment’s limits to support the population • Carrying capacity (K) – the largest population that an area can maintain indefinitely, assuming no changes in the environment • S shape curve:

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