Ecology: Biomes, Population, Community, and Ecosystem Ecology

Ch. 52: Biomes and Abiotic/Biotic Factors

Abiotic and Biotic Factors in Ecology

Ecological systems are influenced by both abiotic (non-living) and biotic (living) factors, which together determine the distribution and abundance of organisms.

• Abiotic factors: Non-living components such as temperature, precipitation, sunlight, and soil type.

• Biotic factors: Living components including other organisms (predators, competitors, symbionts).

• Seasonality: Regular changes in environmental conditions (e.g., temperature, precipitation) due to Earth's tilt and orbit.

• Latitudinal variation: Differences in climate and daylight hours at different latitudes, affecting temperature and precipitation.

• Geological influences: Mountains, oceans, and other landforms can alter local climate patterns.

• Ocean currents: Influence temperature and precipitation patterns near coasts.

• Biomes: Major ecological communities defined by predominant vegetation and climate (e.g., tundra, desert, rainforest).

Key Point: The type and distribution of biomes are determined by both temperature and precipitation, as well as their seasonal variation.

Ch. 52 section 4 – Biogeography

Distribution and Abundance of Organisms

Biogeography studies the spatial distribution of organisms and the factors that influence where species are found.

• Abiotic and Biotic Factors: Both present and past factors affect species distributions.

• Theory of Island Biogeography: Explains species richness on islands as a balance between immigration and extinction rates, influenced by island size and distance from the mainland.

• Latitudinal gradients: Biodiversity tends to be higher near the equator and decreases toward the poles.

Ch. 51 sections 1–5 – Population Ecology

Population Dynamics and Growth

Population ecology examines how and why populations change over time and space.

• Population change: Influenced by birth, death, immigration, and emigration rates.

• Fitness trade-offs: Organisms allocate resources between growth, reproduction, and survival.

• Exponential growth: Population increases by a constant proportion over time, assuming unlimited resources.

• Logistic growth: Population growth slows as it approaches carrying capacity due to limited resources.

• Carrying capacity (K): The maximum population size that an environment can sustain.

Key Equations:

• Exponential growth: $\frac{dN}{dt} = rN$

• Logistic growth: $\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$

Graphing: Population growth models can be visualized as J-shaped (exponential) or S-shaped (logistic) curves.

Ch. 52 Sections 1–3 – Community Ecology

Species Interactions and Community Structure

Community ecology focuses on interactions between species and how these shape community structure and dynamics.

• Types of interactions:

  • Competition (−/−): Both species are harmed by the interaction.

  • Consumption (+/−): One species benefits, the other is harmed (includes predation, herbivory, parasitism).

  • Mutualism (+/+): Both species benefit.

  • Commensalism (+/0): One species benefits, the other is unaffected.

• Short-term vs. long-term impacts: Interactions can have immediate effects or lead to evolutionary changes over time.

• Niche concept: The role and space an organism occupies in its environment. Includes the fundamental niche (potential) and realized niche (actual, after competition).

• Resource partitioning: Species evolve to use different resources or habitats to reduce competition.

• Competitive exclusion principle: Two species competing for the same limiting resource cannot coexist indefinitely.

• Character displacement: Evolutionary changes in species traits due to competition.

• Predator-prey dynamics: Natural selection can lead to adaptations in both predators and prey.

Table: Types of Species Interactions

Interaction Type	Effect on Species 1	Effect on Species 2	Example
Competition	−	−	Two bird species competing for seeds
Consumption	+	−	Wolf preying on deer
Mutualism	+	+	Bees pollinating flowers
Commensalism	+	0	Barnacles on whales

Ch. 53 sections 1–2 – Ecosystem Ecology

Energy Flow and Nutrient Cycling

Ecosystem ecology studies the movement of energy and nutrients through living communities and their physical environments.

• Energy flow: Energy enters ecosystems as sunlight and is converted by producers into chemical energy (biomass).

• Net primary productivity (NPP): The amount of energy captured by producers minus the energy they use for respiration.

• Trophic structure: The organization of ecosystems into feeding levels:

  • Producers (autotrophs)

  • Consumers (herbivores, carnivores, omnivores)

  • Decomposers (detritivores)

• Energy transfer: Only a fraction of energy is transferred from one trophic level to the next (usually ~10%).

• Biogeochemical cycles: Nutrients cycle between living organisms and the abiotic environment (e.g., carbon, nitrogen, phosphorus cycles).

• Reservoirs: Storage locations for nutrients within ecosystems (e.g., atmosphere, soil, water bodies).

Key Equation:

• Net primary productivity: $\text{NPP} = \text{GPP} - \text{R}$

• Where GPP = Gross Primary Productivity, R = Respiration by producers

Example: In a forest ecosystem, trees (producers) capture sunlight and convert it to chemical energy, which is then transferred to herbivores (primary consumers) and further to carnivores (secondary and tertiary consumers).