Population Ecology

Learning Objectives

Population ecology is a branch of biology that studies the dynamics of populations of organisms, especially how and why their numbers change over time and space. The following objectives guide the study of population ecology:

• Define ecology and describe its scales of study.

• Distinguish between populations, species, and communities.

• Describe spatial distribution patterns of populations.

• Explain population change over time, including survivorship curves and life-history strategies.

• Identify parameters for population growth or decline, including the role of r and rmax.

• Compare growth rates among species.

• Draw and label exponential and logistic growth curves, explaining their conditions.

• Define carrying capacity (K) and discuss its variability.

• Contrast density-independent and density-dependent factors affecting growth.

• Describe factors impacting human population growth.

Biodiversity and Species Distribution

Why do some regions have more species than others?

Species richness varies globally due to ecological and evolutionary processes. The study of how organisms interact with their environment and each other is central to ecology. Biodiversity, the variety of life on Earth, results from evolutionary processes acting over changing ecological contexts across time and space.

• Biodiversity is highest in tropical regions and lowest near the poles, as shown in global distribution maps.

• Ecological interactions (e.g., competition, predation, mutualism) shape community structure and species diversity.

• Evolutionary history and environmental factors (climate, habitat availability) influence regional species richness.

Example: Tropical rainforests have high biodiversity due to stable climates and complex ecological interactions.

Levels of Ecological Study

Overview of Scales

Ecological studies are conducted at multiple levels, each focusing on different aspects of organismal interactions and environmental processes:

• Organismal Ecology: Investigates morphological, physiological, and behavioral adaptations of individuals to their environment.

• Population Ecology: Analyzes changes in the number and distribution of individuals over time, including birth rates, death rates, and geographic range.

• Community Ecology: Examines interactions among populations of different species within a shared environment, such as competition, predation, and symbiosis.

• Ecosystem Ecology: Studies how all organisms within an area interact with abiotic (non-living) factors, such as nutrient cycling and energy flow.

• Global Ecology: Investigates processes affecting all terrestrial and aquatic ecosystems, including climate change and biogeochemical cycles.

Organismal Ecology

Focuses on how individual organisms adapt to their environment through morphology, physiology, and behavior.

• Adaptations include physiological changes (e.g., osmoregulation in salmon migrating between saltwater and freshwater), behavioral strategies (e.g., migration, mating rituals), and morphological traits.

• Example: Salmon migrate from saltwater to freshwater environments to breed, demonstrating physiological and behavioral adaptation.

Population Ecology

Studies how and why populations change in size and distribution over time.

• Population: A group of organisms of the same species living in the same area at the same time.

• Key parameters: Birth rate, death rate, immigration, and emigration.

• Example: Female salmon produce thousands of eggs, but only a few survive to return to the same stream to breed.

Community Ecology

Explores how populations of different species interact within a community and the consequences of these interactions.

• Interactions include competition for resources, predation, and parasitism.

• Example: Salmon compete for food with other aquatic organisms and are prey for bears.

Ecosystem and Global Ecology

These levels examine the interactions between biotic (living) and abiotic (non-living) components of ecosystems and the global processes that affect all life.

• Ecosystem Ecology: Studies nutrient cycling, energy flow, and decomposition rates.

• Global Ecology: Focuses on large-scale processes such as climate change, droughts, and floods affecting habitats worldwide.

Summary Table: Levels of Ecological Study

Additional info: These notes synthesize and expand upon the provided slides, adding definitions, examples, and a summary table for clarity and completeness.