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Population Ecology - General Biology

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  • What defines a population in biology?
    A population is a group of individuals of a single species living in the same general area, experiencing the same environment, capable of interbreeding, and often defined by boundaries.
  • What are the 3Ds of population ecology?
    Density (number of individuals per unit area/volume), Dispersion (pattern of spacing among individuals), and Demographics (how population characteristics change over time).
  • How is population density measured?
    Density can be measured by direct counts, sampling and extrapolation, mark-recapture methods, or counting indicators like nests, burrows, tracks, or feces.
  • What assumptions are made in mark-recapture studies?
    Marked and unmarked animals have the same capture likelihood, marked animals remix into the population, and no births, deaths, immigration, or emigration occur between samplings.
  • What are the three main dispersion patterns in populations?
    Clumped (aggregated in patches), Uniform (evenly spaced, often due to competition), and Random (independent positions, usually when resources are evenly distributed).
  • Why do populations show clumped dispersion?
    Individuals aggregate in areas with high resources or favorable conditions such as water, food, mates, or predator avoidance.
  • What causes uniform dispersion in populations?
    Uniform spacing often results from antagonistic interactions like territoriality or allelopathy (chemical competition).
  • What does random dispersion indicate about resource distribution?
    Random dispersion suggests resources and conditions are evenly distributed or equally good for survival.
  • What information does a life table provide in population ecology?
    A life table summarizes age-specific survival and reproduction data, often following a cohort from birth to death.
  • What are survivorship curves and their types?
    Survivorship curves plot the percentage of a cohort alive at each age. Types: I (low death rate early, high late), II (constant death rate), III (high early death rate).
  • What factors influence reproductive rate in populations?
    Age, frequency of reproduction, access to mates, clutch size, and parental care all influence reproductive rate.
  • What is the exponential growth model in population ecology?
    It describes population growth under ideal, unlimited conditions with \(\frac{dN}{dt} = rN\), where r is per capita growth rate.
  • What shape does exponential population growth produce on a graph?
    Exponential growth produces a J-shaped curve when population size is plotted over time.
  • What is carrying capacity (K)?
    Carrying capacity is the maximum population size an environment can support based on limiting resources like food, water, shelter, and nutrients.
  • How does carrying capacity affect population growth rate (r)?
    As population nears carrying capacity, resource limitation causes per capita birth rates to decline and death rates to increase, reducing r.
  • What is the logistic growth model formula?
    Logistic growth is modeled as \(\frac{dN}{dt} = rN \left(\frac{K-N}{K}\right)\), where growth slows as population approaches K.
  • What are life history traits?
    Life history traits include age at first reproduction, frequency of reproduction (semelparity vs iteroparity), and number of offspring per reproductive event.
  • What factors cause changes in population growth rates?
    Direct causes: birth rate, death rate, immigration, emigration. Indirect causes: biotic factors (competition, disease), abiotic factors (resource availability, climate).
  • How do predator-prey interactions affect population dynamics?
    Predator-prey cycles can cause population fluctuations; for example, snowshoe hare populations cycle due to predator pressure rather than food supply alone.
  • Why is exponential growth often unrealistic in natural populations?
    Because resources are limited and environmental conditions vary, populations usually experience slowed growth near carrying capacity, not unlimited exponential growth.