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Chapter 52: Population Ecology

Chapter 52: Population Ecology. Population ecology Study of populations in relationship to the environment Includes environmental influences on population density, distribution, age structure, & size Population

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Chapter 52: Population Ecology

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  1. Chapter 52: Population Ecology Population ecology Study of populations in relationship to the environment Includes environmental influences on population density, distribution, age structure, & size Population Individuals of one species simultaneously occupying the same general area, utilizing the same resources, & influences by similar environmental factors

  2. Characteristics of populations • Population density • Number of individuals per unit area • Measuring density • Count all individuals in a representative sample area • Estimates based on indirect indicators such as nest, burrows, droppings, or tracks • Mark-recapture method • Population dispersion • The pattern of spacing among individuals within the designated geographic boundaries • Types • Clumped • Individuals are aggregated in patches • Most common • Uniform • Spacing of individuals is even • Rare but territoriality is often the reason • Random • Varies in an unpredictable way • Occurs in absence of strong attractions/repulsions of individuals • Rare • Ex. Windblown dandelions

  3. Demography • Study of factors that affect the growth & decline of populations • Age structure & sex ratio • Age structure • Relative number of individuals of each age in the population • Birth rate/fecundity • Death rate • Generation time • The average span of time between birth of individual & the birth of their offspring • Sex ratio • Proportion of individuals of each sex found in a population • Life Tables & survivorship curves • Type I • Death rate increases in elderly but is flat for other ages • Type II • Death rate constant throughout all age spans • Type III • Death rate high in young & elderly

  4. Life History • Traits affecting organism’s schedule of reproduction & survival • Life histories are highly diverse but exhibit patterns • Includes: • When reproduction begins • How often an individual reproduces • How many offspring an individual produces • Limited resources mandate tradeoffs between investment in reproduction vs. own survival • Semelparity • Organism invests most of their energy into growth & development then expends all energy into a single reproductive effort before dying • Ex. Annual plants, salmon, bamboo • Favored in highly variable, unpredictable environments with low offspring survival rates • Iteroparity • Organism produces fewer offspring at a time but over several reproductive seasons • Favored in dependable environments with high competition for resources

  5. Population Growth Models • Exponential model • Idealized population in an unlimited environment • Logistic model • Incorporates the concept of carrying capacity (K) • Carrying capacity= maximum population size an environment can support

  6. Regulation of Population Growth • Intra-specific competition • 2 or more individuals of the same species rely on a limited resource. • Density-dependant factors • intensify as the population increases • Competition for resources • Territoriality • Health (i.e. disease) • Predation • Toxic waste • Intrinsic factors (i.e. stress syndrome in white footed mice)

  7. Population Dynamics • Study of the interactions between biotic & abiotic factors that cause variations in population size • Some populations have regular boom & bust cycles • Small herbivores lemmings show a 3-5 year cycle • Large herbivores snowshoe hare shows a 9-11 year cycle • Insect Cicada show a 13-17 year cycle • In some species crowding effects the endocrine system=reduced fertility

  8. Human Population Growth • For centuries humans have appeared to grow exponentially… • Agricultural revolution increased birth rate & decreased death rate • Industrial revolution improved sanitation, nutrition, & health care • Can not grow indefinitely…. • Population ecologists do not agree on the human carrying capacity • Age structure within each country causes variations in population growth • Humans can consciously control reproduction through contraception or government sponsored family planning • Agricultural & industrial technology has increased carrying capacity • Social changes, individual choice, government intervention and/or increased mortality due to environmental limitations will cause the human population to stop growing

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