Population & Community Ecology – Comprehensive Study Notes

Carrying Capacity (K) & Population Growth Models

• Carrying capacity = maximum number of individuals an environment can sustain long-term.

  • Determined by limiting resources essential to survival.

  • Plants → \text{water}, \text{sunlight}, \text{nutrients}, space.

  • Animals → \text{food}, \text{water}, \text{shelter}, nesting space.

• Scarcity of any key resource drives competition.

  • Intraspecific (within the same species).

  • Interspecific (between different species).

• Population-growth equations

  • Exponential model: \dfrac{dN}{dt}=rN (growth rate r constant, no limits).

  • Logistic model: \dfrac{dN}{dt}=rN\left(1-\dfrac{N}{K}\right)

  • Modifier \left(1-\dfrac{N}{K}\right) slows growth as N approaches K.

Community Ecology & Structure

• Community = multiple interacting populations in a defined area.

  • Example: a fallen log hosts bacteria, fungi, insects, worms, termites, etc.

• Community structure describes

  • Species present, their relative numbers, & interaction patterns.

  • Often visualised via biological networks (e.g.Afood webs).

• Key metrics

  • Species richness = count of different species.

  • Species evenness = how evenly individuals are distributed among species.

  • Species diversity integrates both (higher when richness & evenness are high).

Patterns of Richness & Diversity

• Highest richness near the equator (tropical rain forests, coral reefs).

  • Drivers: high solar energy, warm temperatures, abundant rainfall, minimal seasonality.

• Lowest richness toward the poles (cold, dry, low productivity).

• Illustrative comparisons

  • Forest A with 20 tree species vs Forest B with 5 → Forest A has greater richness.

  • Two forests each with 20 species but one has 90\% of individuals in a single species → lower evenness & therefore lower diversity.

Coral Reefs: A High-Diversity Hotspot in Crisis

• Among the planetAs most diverse habitats.

• Roughly 50\% already lost because of

  • Ocean warming.

  • Ocean acidification driven by excess CO_2.

• Major global CO_2 sinks

  • Atmosphere

  • Oceans

  • Living biomass (forests).

• Ocean carbonate buffer system: CO2 + H2O \leftrightarrow H2CO3 \leftrightarrow HCO_3^- + H^+

  • Extra CO_2 pushes equilibrium right → lower pH.

• Corals live in mutualism with dinoflagellate protists (zooxanthellae).

  • Heat/acid stress → corals expel symbionts → bleaching → death.

Climate Influences on Community Structure

• Global patterns determined by latitude & altitude → temperature + precipitation.

• Local/topographic effects (rain shadows, lake effects, etc.) fine-tune conditions.

• Monsoon climates (e.g.AIndia): short intense rainy season + prolonged drought.

• Southeastern U.S. forests: rainfall distributed year-round → lush, species-rich.

Disturbance & the Intermediate Disturbance Hypothesis (IDH)

• Disturbances = storms, wildfires, landslides, etc.

• IDH: species diversity peaks under intermediate disturbance frequency/intensity.

  • Too frequent → few species can persist.

  • Too rare → competitive dominants exclude others.

• Example: California chaparral

  • Fire-adapted native communities; periodic burns maintain plant diversity.

  • Building homes in chaparral while suppressing fire disrupts natural dynamics.

Environmental Heterogeneity

• More varied (heterogeneous) environments host more species.

  • Field with rock piles supports field specialists plus rock-dwelling specialists.

Species Interactions

• Competition: strong competitors may exclude others (Competitive Exclusion Principle).

• Predation: efficient predator can drive prey locally extinct.

• Symbiosis

  • Mutualism: gut microbiome assists digestion & immunity; host supplies habitat & food.

  • Coral–dinoflagellate mutualism (detailed above).

Habitat vs. Niche

• Habitat = physical place providing resources (forest, desert, single tree, etc.).

• Niche = organismAs functional role + resource use + interactions.

  • Beaver: ecosystem engineer; dams raise water tables, create ponds.

  • Garden spider: ambush predator among plants.

  • Oak tree: canopy dominant converting sunlight to biomass.

Conservation Ecology

• Goal: maintain biodiversity & ecosystem function, reduce human impacts.

• Strategies

  • In situ conservation: protect species within natural habitats (reserves, parks).

  • Ex situ conservation: protect outside natural setting (zoos, botanical gardens, seed banks).

  • Habitat restoration: repair degraded ecosystems.

  • Pollution reduction & climate mitigation.

  • Legal protection for endangered species.

• Example organisations: Upstate Forever (regional land & water conservation).

• Field successes: hundreds of species preserved via combined approaches.

Exam / Course Logistics (as stated)

• Final exam covers entire semester; worksheet packets will be used for review sessions.

• Deadlines

  • All coursework due by \text{Monday} at midnight (except character development assignment).

  • Character development due \text{Tuesday} at midnight.