Ecology: Climate, Biomes, Populations, Communities, and Ecosystems – Study Guide

Global Climate Patterns & Biomes

Abiotic Factors Influencing Distribution and Abundance

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

• Seasonality: Regular changes in climate (temperature and precipitation) throughout the year due to Earth's tilt and orbit.

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

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

• Ocean Currents: Influence coastal temperatures and precipitation by transporting warm or cold water across the globe.

Key Point: The distribution and abundance of organisms are controlled by both present and past abiotic factors, as well as biotic interactions.

Predicting Biomes

Biomes are large ecological areas on Earth’s surface, with flora and fauna adapting to their environment. The type of biome present in a region is primarily predicted by:

• Average Temperature

• Average Precipitation

• Variation in Temperature and Precipitation

Example: Tropical rainforests occur in regions with high, stable temperatures and high precipitation, while deserts occur where precipitation is low.

Biogeography

Theory of Island Biogeography

Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. The Theory of Island Biogeography explains how species richness on islands is determined by immigration and extinction rates, which are influenced by island size and distance from the mainland.

• Immigration Rate: Higher on islands closer to the mainland.

• Extinction Rate: Lower on larger islands due to more resources and habitats.

Key Point: Both present and past abiotic (e.g., climate, geography) and biotic factors (e.g., competition, predation) control the distribution and abundance of organisms.

Biomes & Biogeographic Regions

Biomes are classified based on climate and dominant vegetation, while biogeographic regions are large areas with distinct groups of species, often shaped by historical events like continental drift.

Population Ecology

Population Change and Growth Models

Population ecology studies how and why populations change over time. Key processes include:

• Birth and Death rates

• Immigration (movement into a population)

• Emigration (movement out of a population)

Population growth can be modeled mathematically:

• Exponential Growth: Occurs when resources are unlimited; growth rate is density-independent.

• Logistic Growth: Occurs when resources are limited; growth rate slows as population approaches carrying capacity (K), making it density-dependent.

Key Equations:

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

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

Where:

• N = population size

• r = per capita rate of increase

• K = carrying capacity

Fitness Trade-offs: Organisms allocate limited resources between growth, reproduction, and survival, leading to trade-offs that affect population dynamics.

Community Ecology

Species Interactions

Communities are shaped by interactions among species, which can affect the fitness of each participant. The main types of interactions are:

• 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.

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

Short-term and Long-term Impacts: Interactions can have immediate effects on population sizes and long-term effects on evolution and community structure.

Niche Concept

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

• Realized Niche: The actual conditions occupied, limited by interactions such as competition.

Competition for Resources:

• Symmetric Competition: Both species are equally affected.

• Asymmetric Competition: One species is more negatively affected than the other.

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

Niche Differentiation & Resource Partitioning: Natural selection can lead to character displacement, reducing competition by evolving differences in resource use.

Ecosystem Ecology

Energy Flow and Nutrient Cycling

Ecosystem ecology examines how energy and nutrients move through living communities and their physical environments.

• Energy Transformation: Solar energy is converted to chemical energy by photosynthesis, producing biomass (Net Primary Productivity, NPP).

• Trophic Structure: Includes producers (autotrophs), consumers (heterotrophs), and decomposers/detritivores.

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

• Nutrient Cycling: Nutrients cycle between biotic (living) and abiotic (non-living) components of ecosystems.

Biogeochemical Cycles: Nutrients such as carbon, nitrogen, and phosphorus move through reservoirs in ecosystems, spending time in both living organisms and the environment.

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

• Human Impacts: Activities such as agriculture and fossil fuel combustion can alter nutrient cycles, leading to environmental issues.

Food Webs

Food webs illustrate the complex feeding relationships in ecosystems, showing how energy and nutrients flow from producers to various levels of consumers and decomposers.

Summary Table: Types of Species Interactions (Adapted from Table 52.3)

Interaction Type	Effect on Species 1	Effect on Species 2	Example
Competition	-	-	Two bird species competing for the same seeds
Consumption	+	-	Wolf preying on deer
Mutualism	+	+	Bees pollinating flowers
Commensalism	+	0	Barnacles on whales
Amensalism	-	0	Trampling of grass by elephants

Additional info: This study guide covers key concepts in ecology, including climate and biomes, population and community dynamics, and ecosystem processes. Students should be able to interpret graphs, maps, and tables related to these topics for exam preparation.