Ecology: Key Concepts and Definitions

Posted on Feb 11, 2025 in Biology

Ecology: A Scientific Discipline

Ecology is the study of organisms in their environment and their relationship to each other.

Environmentalism: A Social and Political Movement

Environmentalism is distinct from ecology, representing a social and political movement.

Types of Interactions

  • Intraspecific: Interactions within the same species. Example: mating behavior.
  • Interspecific: Interactions with other species. Example: predation and mutualism.

Biotic and Abiotic Factors

  • Biotic: Living components. Example: plants and animals.
  • Abiotic: Nonliving components. Example: weather, sunlight, precipitation.

Levels of the Ecological Hierarchy

  1. Individual
  2. Population: All individuals of the same species in a given area, able to interbreed.
  3. Community: All species in an area interacting with each other.
  4. Ecosystem: Adding abiotic components to communities.
  5. Landscape: A patchwork of distinct communities linked by higher-order processes such as energy transfer.
  6. Biome: Large regions of Earth’s surface defined by plant life. Example: forests, grasslands, deserts, tundra.
  7. Biosphere: All biomes on Earth.

Keystone Species

Keystone species have a larger impact on the community than would be expected. Example: elephants as destructive feeders.

Food Webs

Food webs involve the transfer of energy on a trophic level, flowing from producers to consumers to top predators.

10% Rule

When energy is passed in an ecosystem from one trophic level to the next, only ten percent of the energy will be passed on. This can really only sustain about five levels.

Connectance (C)

Connectance is the ratio of the observed links in the web divided by the hypothetical maximum number of links. C= L/S2 (where L = number of links, S = number of species).

H2O Quality Index

H2O Quality Index = Sum (N x V) / Sum (N)

(N) = number of taxa, (V) = value, (N x V) = Taxon Score

H2O Quality Index Interpretation: Excellent (2.6-3.0), Good (2.0-2.5), Fair (1.5-1.9), Poor (1.0-1.4)

Zonation

Zonation is a change in biotic/abiotic components of a community as one moves across environmental gradients.

Measures of Biodiversity

Species Richness (S)

Species richness is the number of species in total.

Rank Abundance Diagram

Curves that plot rank abundance (x-axis) against relative abundance (y-axis). Pi = ni/N

Pi = proportion belonging to species “i”

ni = number of individuals of species “i”

N = number of all individuals of all species in a community

Simpson’s Index (D)

The probability that two individuals randomly selected will belong to the same species. D = ΣPi2

  • D equals the sum of the square of the proportions.
  • D ranges from 0-1 (as the number of species increases, the value of D decreases).
  • Simpson’s Index of Diversity = 1 – D
  • Simpson’s Reciprocal Index = 1/D
  • Species Evenness (ED) = (1/D)/S

Sorenson’s Coefficient of Community (CC)

Allows comparison of the species shared by two communities based on species presence or absence. CC = 2c/(s1+s2)

  • “c” is the number of species common to both communities.
  • s1 is the number of species in community 1.
  • s2 is the number of species in community 2.

Adaptations of Stream Organisms

  • Behavioral: They avoid the current, burrow into sediment, find shelter in logs/rocks/etc.
  • Morphological: Small body size, dorsoventral flattening (e.g., planarians), lateral flattening (e.g., fish), suckers/hook-like appendages (e.g., dobsonfly larvae), ballasting (e.g., stony cases of the caddisfly).

Drift

Drift is a nonrandom downstream movement that peaks at night.

Explanations of drift:

  1. Accidental dislodgment
  2. To escape predators
  3. In response to overpopulation/reduced foraging

Important Ecologists