Global Climate Patterns & Biomes

Abiotic Factors Influencing Organism Distribution

Abiotic factors are non-living components of the environment that influence where organisms can live and how abundant they are. Understanding these factors is essential for interpreting global climate patterns and the distribution of biomes.

• Latitudinal Variation: Temperature and seasonality change with latitude, affecting the types of organisms that can survive in different regions.

• Temperature & Precipitation: The average values and variability of these factors predict the type of biome present in a region.

• Geological Influences: Mountain ranges and landforms can alter precipitation patterns (e.g., rain shadows).

• Ocean Currents: Influence coastal temperatures and precipitation, affecting nearby terrestrial biomes.

Example: Tropical rainforests are found near the equator where temperatures are high and precipitation is abundant year-round.

Biomes and Their Determinants

Biomes are large ecological areas on Earth's surface, with flora and fauna adapted to their environment. The main predictors of biome type are temperature, precipitation, and their seasonal variation.

• Temperature: Determines the metabolic rates and physiological tolerances of organisms.

• Precipitation: Influences water availability for plants and animals.

• Variation: Seasonal changes can create distinct wet/dry or warm/cold periods, shaping the adaptations of resident species.

Biogeography

Distribution and Abundance of Organisms

Biogeography studies the spatial distribution of organisms, considering both present and historical factors.

• Abiotic Factors: Climate, soil, water, and physical barriers.

• Biotic Factors: Interactions with other organisms (competition, predation, mutualism).

• Historical Factors: Past climate changes, continental drift, and evolutionary history.

Theory of Island Biogeography

This theory explains species richness on islands as a balance between immigration and extinction rates, influenced by island size and distance from the mainland.

• Larger islands: Support more species due to more resources and habitats.

• Closer islands: Have higher immigration rates from the mainland.

Example: A small, remote island will have fewer species than a large, nearby island.

Population Ecology

Population Change and Growth Models

Population ecology examines how and why populations change over time, focusing on birth, death, immigration, and emigration.

• Population Change Equation:

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

Quantifying Population Growth

• Intrinsic Rate of Increase (r): The per capita rate at which a population increases in size under ideal conditions.

• Maximum r (rmax): The highest possible value of r for a species.

Exponential Growth (Density Independent)

Occurs when resources are unlimited and population grows at a constant rate.

• Density Independent: Growth rate does not depend on population size.

Logistic Growth (Density Dependent)

Growth slows as population approaches carrying capacity (K).

• Carrying Capacity (K): Maximum population size that the environment can sustain.

• Density Dependent: Growth rate decreases as population size increases.

Community Ecology

Species Interactions

Species interact in various ways, affecting each other's fitness. These interactions shape community structure and dynamics.

• 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 benefits, the other is unaffected.

• Amensalism (-/0): One is harmed, the other is unaffected.

Niche Concept

• Fundamental Niche: The full range of environmental conditions a species can use.

• Realized Niche: The actual conditions used, limited by competition and other interactions.

Competition for Resources: Can be symmetric (equal impact) or asymmetric (one species is more affected).

• Competitive Exclusion Principle: Two species competing for the same resource cannot coexist indefinitely.

• Niche Differentiation: Evolutionary change in resource use to reduce competition (character displacement).

Ecosystem Ecology

Energy Flow and Nutrient Cycling

Ecosystem ecology focuses on the movement of energy and nutrients through living (biotic) and non-living (abiotic) components.

• Food Webs: Diagrams showing feeding relationships among organisms.

• Trophic Structure: Levels include producers (autotrophs), consumers (herbivores, carnivores), and decomposers/detritivores.

• Photosynthesis: Converts solar energy to chemical energy (sugars).

• Net Primary Productivity (NPP): The amount of biomass produced by producers minus the energy used in respiration.

• Energy Flow: Energy moves through the food web and is lost as heat at each trophic level (pyramid of productivity).

• Nutrient Cycling: Nutrients move between biotic and abiotic reservoirs in biogeochemical cycles (e.g., carbon, nitrogen cycles).

• Human Impacts: Activities such as agriculture and fossil fuel use alter nutrient cycles and ecosystem function.

Example: In a forest ecosystem, trees (producers) are eaten by deer (primary consumers), which are preyed upon by wolves (secondary consumers). Dead organisms are decomposed by fungi and bacteria, returning nutrients to the soil.

Additional info: The "pyramid of productivity" illustrates that only about 10% of energy is transferred from one trophic level to the next, with the rest lost as heat.