Population Ecology: Dispersion, Demography, and Growth

Posted on Mar 18, 2025 in Biology

Population Ecology: Key Concepts

• Dispersal is the movement of individuals or gametes away from centers of high population density or from their area of origin.
• Endemic species are those that are only found in a small, specific area.
• Species transplants include organisms that are intentionally or accidentally relocated from their original distribution.
• If a transplant is successful, it indicates that the potential range of a species is larger than its actual range.
  • Guppy populations evolve rapidly when predators are removed.
    • Color pattern changes
    • Smaller number of offspring
    • Large sized offspring
• Population ecology explores how biotic and abiotic factors influence the abundance, dispersion, and age structure of populations.
• The most common pattern of dispersion is clumped, in which individuals aggregate in patches.
• Clumped dispersions are influenced by resource availability.
• A uniform dispersion is one in which individuals are evenly distributed.
• It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals.
• In a random dispersion, the position of each individual is independent of other individuals.
• It occurs in the absence of strong attractions or repulsions among individuals.
• Demography is the study of these vital statistics of a population and how they change over time.
  • Birth rates, Death rates, Survivorship, Reproductive rate
• A survivorship curve is a graphic way of representing the data in a life table.
• Survivorship curves can be classified into three general types:
  • Type I: Low death rates during early and middle life and an increase in death rates among older age groups.
  • Type II: A constant death rate over the organism’s life span.
  • Type III: High death rates for the young and a lower death rate for survivors.
• dN/dt is the growth rate.
• N is population size.
• T is time.

where r is the intrinsic rate of increase, the per capita rate at which an exponentially growing population increases in size at each instant in time

• A more realistic population model limits growth by incorporating carrying capacity.

• Carrying capacity (K) is the maximum population size the environment can support.
• Carrying capacity varies with the abundance of limiting resources.
• In the logistic population growth model, the per capita rate of population growth approaches zero as the population size nears carrying capacity (K).
• When N is small compared to K, the term (K – N)/K is close to 1, and the per capita rate of population growth will be close to r.
• When N is large compared to K, the term (K – N)/K is close to 0, and the per capita rate of population growth is small.
• When N equals K, the population stops growing.
• The population growth rate decreases as N approaches K.
• Reproductive strategy is an important aspect of a species’ life history.
  • Species that exhibit semelparity, or big-bang reproduction, reproduce once and die.
    • Insects
  • Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly.
    • Mammals
• K-selection is selection for life history traits that are advantageous at high population densities.