Population Ecology Concepts and Dynamics

Population Ecology Concepts

• Carrying Capacity: The maximum sustainable population size an environment can support. Reduced food availability, as during a drought, decreases carrying capacity. A pond's fish population stabilizes near its carrying capacity due to limited resources (oxygen, food).

Population Dynamics

• Population Fluctuations: Population size changes over time, often influenced by environmental and biological factors—seasonal food availability, resources, climate. Lemmings experience boom-and-bust cycles. Migratory birds' populations fluctuate seasonally.

• Territoriality: Animals defend territories to secure resources (food, mates, shelter)—songbirds during breeding, penguins in colonies.

• Dispersion Patterns: How individuals are distributed in an area.

• Clumped: Individuals grouped together (elephants around waterholes).

• Uniform: Evenly spaced (penguins spacing nests).

• Random: Unpredictable distribution (wildflowers).

Factors Affecting Population Size

• Density-Dependent Factors: Factors influencing population size based on density, such as competition for resources (food, space). Deer populations facing limited grazing during growth. Disease spreads more easily in dense populations, reducing their numbers.

• Density-Independent Factors: Factors impacting populations regardless of density—natural disasters (volcanic eruptions, floods) impacting bird and lizard populations.

• Limiting Factors: Environmental factors that restrict population growth:

• Competition: Species vying for the same resources, such as trees competing for sunlight.

• Predation: Predators controlling prey populations—sharks and fish, or lions and zebras

• Space: Limited space impacting coral reef colony growth.

• Natural Disasters: Forest fires reducing squirrel populations.

• Predator-Prey Dynamics: Interaction where predators control prey, and vice-versa—lemmins and snowy owls' populations influence each other.

Population Growth Patterns

• Exponential Growth: Rapid population increase under ideal conditions. Bacteria in a lab with unlimited nutrients grow exponentially.

• Logistic Growth: Population growth slowing as it approaches carrying capacity due to limited resources (S-shaped curve). Deer population growth in a fenced forest eventually slows and stabilizes.

• Migration: Movement of individuals into (immigration) or out of (emigration) a population. Wildebeest migration across the Serengeti and monarch butterflies.

Population Regulation

• Top-Down Control: Predators controlling their prey leading to effects down the food chain. Sea otters and sea urchins, controlling kelp forest.

• Bottom-Up Control: Resource availability at the bottom of the food chain determines populations at higher levels. Drought impacting grass, thus affecting herbivores and then top predators in a grasslands ecosystem.

• Parasitism and Disease: Parasites and diseases influencing population regulation, weakening individuals or causing death. Ticks impacting moose populations.

• Competition: When individuals or species vie for resources. Trees in a dense forest competing for sunlight and nutrients resulting in weaker trees dying.

• Human Impact: Human activities altering ecosystems and populations. Habitat loss reducing orangutan populations.