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Community Ecology - General Biology

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  • Competition
    A āˆ’/āˆ’ interspecific interaction where both species are harmed by sharing limited resources. Can lead to competitive exclusion or niche partitioning.
  • Competitive exclusion
    Gause's principle: two species with identical niches cannot coexist permanently ā€” the better competitor will eliminate the other.
  • Ecological niche
    The full set of biotic and abiotic resources an organism uses in its environment ā€” its ecological role, including food, habitat, temperature range, and timing of activity.
  • Fundamental niche
    The full range of conditions and resources a species could potentially occupy in the absence of competitors.
  • Realized niche
    The portion of the fundamental niche a species actually occupies after competition limits it. Always smaller than or equal to the fundamental niche.
  • Resource partitioning
    Differentiation of niches that allows similar species to coexist by using different resources in space, time, or diet. Example: Anolis lizards using different perch heights.
  • Character displacement
    The tendency for traits to diverge more in sympatric populations of two competing species than in allopatric populations. Example: Galapagos finch beak depths diverge where species overlap.
  • Predation
    A +/- interspecific interaction where the predator kills and eats the prey. Drives evolution of offense adaptations (venom, speed) and defense adaptations (camouflage, toxins, mimicry).
  • Herbivory
    A +/- interaction where an herbivore eats part of a plant or alga, benefiting while harming but usually not killing the plant. Plants evolved chemical (nicotine, tannins) and structural defenses (thorns).
  • Parasitism
    A +/- interaction where the parasite derives nourishment from the host, harming it. Endoparasites live inside (tapeworms); ectoparasites live outside (ticks, lice).
  • Mutualism
    A +/+ interaction that benefits individuals of both species. Example: acacia trees provide food and shelter to ants that protect the tree from herbivores and competitors.
  • Commensalism
    A +/0 interaction that benefits one species while leaving the other unaffected. Example: cattle egrets following buffalo to catch insects flushed out of the grass.
  • Aposematic coloration
    Bright warning coloration in prey signaling toxicity or unpalatability. Example: poison dart frogs' vivid colors.
  • Cryptic coloration
    Camouflage that makes prey difficult to see against their background. Example: canyon tree frog blending into rocks.
  • Batesian mimicry
    A harmless or palatable species mimics a harmful or unpalatable species. Only the mimic is safe and free-rides on the harmful model's reputation. Example: hawkmoth larva mimics a venomous snake.
  • Mullerian mimicry
    Two or more genuinely harmful or unpalatable species resemble each other, causing predators to learn faster to avoid their shared warning pattern. Example: yellow jacket and cuckoo bee.
  • Species diversity
    A measure of community composition including species richness (number of species) and relative abundance (evenness of individuals among species).
  • Species richness
    The number of different species in a community or ecosystem. One component of species diversity.
  • Relative abundance
    The proportion of each species among all individuals in a community. Dominance by one species lowers diversity even if richness is the same.
  • Shannon diversity index (H)
    A mathematical index of community diversity accounting for species richness and relative abundance. Higher \(H\) means more diversity.
  • Food chain
    A linear sequence showing transfer of chemical energy from one trophic level to the next through feeding relationships.
  • Food web
    A network of interconnected food chains in a community. More realistic because species eat at multiple trophic levels and are eaten by multiple species.
  • Trophic level
    The feeding position an organism occupies in a food chain: primary producer, primary consumer, secondary consumer, tertiary consumer, etc.
  • Trophic efficiency
    The percentage of production transferred from one trophic level to the next, averaging ~10%. The other 90% is lost to respiration, feces, and uneaten biomass.
  • Energetic hypothesis
    Explains why food chains are short (~4-5 links): energy transfer is inefficient, so too little energy remains at higher levels to support another trophic level.
  • Keystone species
    A species with a disproportionately large effect on community structure through its ecological role, not necessarily abundant. Example: Pisaster sea star controls mussels.
  • Foundation species
    A species with strong effects on community structure due to large size or high abundance, providing habitat or food. Example: American chestnut, kelp, corals.
  • Ecosystem engineer
    A species that creates, modifies, or destroys habitat affecting other species and community structure. Example: beavers building dams.
  • Bottom-up control
    Community organization where abundance at each trophic level is limited by food or nutrients availability at lower levels.
  • Top-down control
    Community organization where predators limit herbivores, releasing plants or algae, creating a trophic cascade of alternating +/- effects down the food web.
  • Trophic cascade
    Indirect effects through a food web when a top predator is added or removed, causing alternating increases and decreases at each lower trophic level.
  • Disturbance (ecological)
    An event like storm, fire, or human activity that changes a community by removing organisms or altering resource availability.
  • Invasive species
    A non-native species introduced to a new region, free from natural predators and competitors, that spreads and disrupts native communities.