Introduction to Ecology and the Distribution of Life

Introduction to Ecology

Definition and Scope

Ecology is the scientific study of how organisms interact with their environment, encompassing both biotic (living) and abiotic (non-living) components. The central goal of ecology is to understand the distribution and abundance of organisms. Ecology is inherently interdisciplinary, drawing from evolution, physiology, and other biological subfields.

• Key Point: Ecology investigates interactions at multiple biological scales, from individuals to the entire biosphere.

• Key Point: Ecological research helps address practical problems such as conservation, resource management, and understanding human impacts on the environment.

Five Main Levels of Ecological Study

• Organismal Ecology: Focuses on the adaptations (morphological, physiological, behavioral) that enable individual organisms to survive and reproduce in their environment.

• Population Ecology: Examines groups of individuals of the same species, analyzing how population size and structure change over time and space.

• Community Ecology: Studies interactions among species within a defined area, including competition, predation, and mutualism.

• Ecosystem Ecology: Investigates energy flow and nutrient cycling among organisms and their physical environment.

• Global Ecology (Biosphere Ecology): Explores ecological phenomena at the planetary scale, including human impacts on global processes.

Organismal Ecology

Adaptations and Interactions

Organismal ecology investigates how individual organisms' structure, physiology, and behavior help them meet environmental challenges. For example, studies on migration and resource allocation in mule deer reveal trade-offs between timing of birth and resource availability.

• Key Point: Adaptations can be behavioral (migration), physiological (water conservation), or morphological (body shape).

• Example: Mule deer in Wyoming adjust reproductive timing based on migration distance and resource availability.

Population Ecology

Population Dynamics

A population is a group of individuals of the same species living in the same area at the same time. Population ecology studies how and why population sizes change over time and space, considering factors like birth rates, death rates, immigration, and emigration.

• Key Point: Population growth rates and fluctuations affect both population size and evolutionary potential (effective population size).

• Example: Chinook salmon populations are influenced by eco-evolutionary dynamics, where fluctuations in growth rate impact long-term viability.

Community Ecology

Species Interactions

A community consists of all the species that interact within a particular area. Community ecology examines the nature and consequences of these interactions, such as predation, competition, and mutualism, and how communities assemble and change over time.

• Key Point: The structure and function of communities are shaped by both biotic and abiotic factors.

• Example: Predation risk for crabs and shrimp in eelgrass habitats is influenced by habitat complexity and location (edge vs. center).

Ecosystem and Global Ecology

Energy Flow and Nutrient Cycling

Ecosystem ecology focuses on the movement of energy and nutrients through living organisms and their physical environment. Global ecology (biosphere ecology) examines ecological processes at the largest scale, including the effects of human activities on the entire planet.

• Key Point: Ecosystem and global ecologists study processes such as coastal erosion, climate change, and the cycling of carbon and nutrients.

• Example: Mangrove forests reduce coastal erosion more effectively than salt marshes during hurricanes.

Determinants of Species Distribution and Abundance

Abiotic and Biotic Factors

The distribution of organisms is shaped by both abiotic (non-living) and biotic (living) factors. Biogeography is the study of how organisms are distributed geographically.

• Abiotic factors: Physical characteristics of the environment, such as temperature, moisture, sunlight, and soil type.

• Biotic factors: Interactions with other organisms, including competition, predation, and food availability.

• History: Past geological and climatic events (e.g., continental drift, glaciation) influence current distributions.

The Ecological Niche

A niche is the range of environmental conditions a species can tolerate and the resources it can use. The niche concept helps explain the geographic range of species.

• Example: Arctic microbes have a wide temperature tolerance, while hot springs microbes have a narrow, high-temperature tolerance.

Biotic Interactions

Biotic factors can limit species distributions. For example, the tsetse fly in Africa restricts the range of cattle by transmitting a fatal disease.

Dispersal and Historical Factors

Dispersal is the movement of individuals from their birthplace to where they live and breed as adults. Historical events, such as the formation of land bridges, have shaped species distributions by enabling or restricting dispersal.

Human Impacts on Species Distributions

Humans have dramatically altered species distributions through activities such as hunting, fishing, and the introduction of species to new areas.

• Exotic species: Non-native species introduced to new environments.

• Invasive species: Exotic species that spread rapidly and outcompete native species, often causing ecological harm.

Global Climate Patterns

Weather vs. Climate

• Weather: Short-term atmospheric conditions (e.g., temperature, precipitation, wind).

• Climate: Long-term average weather patterns in a region.

Why Does Climate Vary Around the Globe?

• Sunlight: The amount of solar energy received per unit area decreases from the equator to the poles due to the curvature of the Earth.

• Temperature: Regions near the equator are warmer because sunlight strikes more directly, while higher latitudes receive sunlight at a lower angle.

Why Are the Tropics Warm and Wet?

• Hadley cells: Large-scale atmospheric circulation patterns that transport warm, moist air from the equator toward higher latitudes, causing high rainfall near the equator and dry conditions at about 30° N and S.

What Causes Seasons?

• Earth's tilt: The 23.5° tilt of Earth's axis causes seasonal variation in temperature and precipitation as different regions receive varying amounts of sunlight throughout the year.

Other Climate Impacts

• Rain shadows: Mountains can create wet and dry areas by blocking the passage of moist air.

• Ocean currents: Transport heat and influence climate patterns, especially in coastal regions.

Biomes: Terrestrial and Aquatic

Definition and Classification

A biome is a large region characterized by distinct abiotic factors and dominant vegetation types. The prevailing climate determines which plants can grow, which in turn shapes the ecosystem.

• Key abiotic factors for terrestrial biomes: Average annual temperature and precipitation, and their annual variation.

• Net Primary Productivity (NPP): The total amount of biomass produced by photosynthesis minus the carbon lost through respiration.

Summary Table: Terrestrial Biomes by Temperature and Rainfall

Temperature	High Rainfall	Moderate Rainfall	Low Rainfall
High, steady	Tropical rainforest	Tropical seasonal forest	Tropical desert
High, variable	Tropical seasonal forest	Savannah
Moderate, variable	Temperate forest	Grasslands
Low	Boreal forest	Arctic tundra

Aquatic Biomes

• Salinity: Influences osmosis and water balance in organisms.

• Water depth: Affects light penetration and nutrient availability, dividing water bodies into photic (light) and aphotic (dark) zones.

• Water flow: Determines oxygen and nutrient distribution.

• Nutrient availability: Nutrients often sink, limiting productivity unless mechanisms like upwelling or turnover bring them to the surface.

Mechanisms Bringing Nutrients to Surface Waters

• Coastal runoff: Streams bring nutrients to oceans (e.g., estuaries).

• Ocean upwelling: Currents bring nutrient-rich water from the ocean bottom to the surface.

• Lake turnover: Seasonal temperature changes mix surface and deep waters in lakes.

Human Impacts on Biomes

Anthropogenic Biomes and Climate Change

• Humans have altered 75% of Earth's ice-free land, changing landscapes, climate, and ecological processes.

• Deforestation, urbanization, and agriculture reduce biodiversity and ecosystem services.

• Human-induced climate change is increasing global temperatures, altering precipitation patterns, and affecting species distributions.

Greenhouse Effect and Climate Change

• Greenhouse effect: Greenhouse gases (CO2, methane, water vapor) trap heat in the atmosphere, warming the planet.

• Human activities have increased greenhouse gas concentrations, leading to global warming.

Impacts on Ecosystems

• Climate change affects both terrestrial and aquatic ecosystems, altering species distributions, population dynamics, and ecosystem productivity.

• Humans have introduced invasive species, overexploited fisheries, polluted aquatic habitats, and contributed to ocean acidification.

Conservation and Restoration

• Efforts are underway globally to mitigate human impacts, restore habitats, and conserve biodiversity through science, policy, and community action.

Summary

• Ecology studies interactions between organisms and their environment at multiple scales.

• Abiotic and biotic factors, along with historical and human influences, determine the distribution and abundance of life on Earth.

• Global climate patterns and biomes are shaped by sunlight, atmospheric circulation, and geography.

• Human activities are fundamentally altering ecological processes and the biosphere, making ecological understanding crucial for sustainability.