Ecology: Population Regulation, Niches, and Interactions

Posted on Apr 1, 2025 in Biology

  • r-selection is selection for life history traits that maximize reproductive success at low density.
  • In density-independent population regulation, birth rate and death rate do not change with population density.
    • Environmental factors that occur randomly, regardless of population size.
  • In density-dependent population regulation, birth rates fall and death rates increase with rising population density.
    • Population density is maintained at or near carrying capacity (K).
  • Density-independent factors are usually abiotic.
    • Sudden changes in precipitation or temperature.
    • Catastrophic events:
      • Volcanic eruption, hurricane, flood.
  • An ecological niche is the sum of an organism’s use of biotic and abiotic resources.
  • Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community.
  • Fundamental niche is the niche potentially occupied by that species.
  • Realized niche is the niche actually occupied by that species.
  • Character displacement is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species (typically involves changes in allele frequencies).
  • Exploitation refers to any +/– interaction in which one species benefits by feeding on the other species.
  • Exploitative interactions include predation, herbivory, and parasitism.
  • Predation (+/– interaction) refers to an interaction in which one species, the predator, kills and eats the other, the prey.
  • Mechanical and chemical defenses protect species such as porcupines and skunks.
  • Animals with effective chemical defenses often exhibit bright warning coloration, called aposematic coloration.
  • Cryptic coloration, or camouflage, makes prey difficult to spot.
  • Batesian mimicry: a palatable or harmless species mimics an unpalatable or harmful model.
  • In Müllerian mimicry, two or more unpalatable species resemble each other.
  • Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga.
    • Many herbivores have specialized teeth or digestive systems for processing vegetation.
  • Plants may produce toxic or distasteful chemicals or mechanical defenses, such as spines or thorns.
  • In parasitism (+/– interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process.
  • Parasites that live within the body of their host are called endoparasites.
  • Parasites that live on the external surface of a host are ectoparasites.
  • Ecological communities are heavily influenced by positive interactions, where at least one species benefits and neither is harmed.
  • Mutualism (+/+) and commensalism (+/0) are positive interactions.
  • Mutualism (+/+) is a common interspecific interaction that benefits both species.
  • In a mutualism, both species incur costs, but the benefits to each partner exceed the costs.
  • Commensalism (+/0 interaction) is another common interaction in which one species benefits and the other is neither harmed nor helped.
  • The species diversity of a community is the variety of organisms that make up the community.
    • Species richness is the number of different species in the community.
    • Relative abundance is the proportion each species represents of all individuals in the community.
  • Trophic structure is the feeding relationships between organisms in a community.
  • Food chains link trophic levels from producers (photosynthesis) to top carnivores.
  • The position an organism occupies in a food chain is called its trophic level.