Ecology and the Biosphere

Population Ecology

• Births and immigration add individuals to a population.
• Deaths and emigration remove individuals from a population.
• Population: A group of individuals of a single species living in the same general area.

Dispersion

• Clumped: Individuals aggregate in patches (most common).
• Uniform: Individuals are evenly distributed.
• Random: Pattern of each individual is independent of other individuals (uncommon).

Mark-Recapture Method

• Capture, tag, and release organisms.
• Recapture a 2nd sample; note how many are marked.
• Estimate population size: N = \frac{sn}{x}
  • Where:
    • s = number tagged and released
    • n = 2nd sample of individuals
    • x = number of marked in 2nd sample

Demography

• Study of birth/death/migration rates of a population over time.
• Life Tables:
  • Age-specific summary of survival and reproductive rates.
  • Follows the fate of a cohort (same-aged group from birth to death).

Survivorship Curves

• Type I: Low death rates early/mid-life, sharp increase in older age (large mammals).
• Type II: Constant death rate over lifespan (rodents, invertebrates).
• Type III: High death rates in young, lower death rate for survivors (high offspring numbers, little to no care).

Exponential Population Growth

• Describes population increase under idealized conditions.
• Equation: \frac{dN}{dt} = rN
  • where:
    • r = rate of increase
    • N = population size

Logistic Population Growth Model

• Incorporates carrying capacity (K) to limit growth.
• Equation: \frac{dN}{dt} = rN \frac{(K - N)}{K}
  • where:
    • K = Maximum population size the environment can support

Community Ecology

• Focuses on interactions between species.
• Community interactions:
  • Competition (-/-)
  • Predation (+/-)
  • Herbivory (+/-)
  • Parasitism (+/-)
  • Mutualism (+/+)
  • Commensalism (+/0)

Competitive Exclusion Theory

• Two species competing for the same limiting resources cannot coexist.

Ecological Niche

• Sum of a species’ use of abiotic and biotic resources in the environment.
• Fundamental Niche: Potential niche without competition.
• Realized Niche: Actual niche with competition.

Character Displacement

• Characteristics are more divergent in sympatric populations than in allopatric populations.

Defensive Adaptations

• Aposematic coloration (warning)
• Cryptic coloration (camouflage)
• Batesian mimicry (harmless mimics harmful)
• Müllerian mimicry (two unpalatable species mimic each other)

Species Diversity

• Trophic Structure: Feeding relationships between species.
• Dominant Species: Most abundant or highest biomass.
• Keystone Species: Not necessarily abundant, but exert strong control.
• Ecosystem Engineers: Create or maintain physical structure.

Ecological Succession

• Primary Succession: Occurs where no soil exists.
• Secondary Succession: Occurs where soil still exists.

Ecosystems

• Energy Flow: Energy enters as sunlight, is converted to chemical energy by autotrophs, then passes to heterotrophs as food and is dissipated as heat
• Chemical Cycling: Chemicals cycled amongst abiotic and biotic components (inorganic elements assimilated into organisms)

Trophic Levels

• Primary Producers: Autotrophs
• Primary Consumers: Herbivores
• Secondary, Tertiary, Quaternary Consumers: Carnivores
• Decomposers: Recycle nutrients from all levels

Aquatic Biomes # Major Terrestrial Biomes

• Lakes, Oceans, Intertidal Zones, Coral Reefs, Marine Benthic Zone, Wetlands, Streams & Rivers, Estuaries
  • Tropical Forest
  • Savanna
  • Desert
  • Chaparral
  • Temperate Grassland
  • Temperate Broadleaf Forest
  • Northern Coniferous Forest
  • Tundra
  • High Mountains
  • Polar Ice