Population Ecology: Dynamics, Growth Strategies, and Succession

Population Dynamics and Carrying Capacity

Population dynamics refers to how populations change over time in response to environmental factors.

• The Carrying Capacity of a Habitat

  The carrying capacity (K) is the maximum number of individuals in a population that a specific environment can support sustainably.

• When the carrying capacity of a habitat is reached, the population size varies around that value due to two main causes:

  • Fluctuations: These are non-periodic changes caused by unpredictable environmental factors (e.g., disease, drought).
  • Cyclical Changes: These are predictable changes, such as seasonal variations (winter, spring) or the regular interaction between predators and prey populations.

Population Growth Strategies (K and R Selection)

Species employ different strategies for population growth and survival:

• K-Strategists (Equilibrium Species)

  These species have few offspring but invest significant resources caring for them, resulting in high survival rates for the young (represented by Survival Curve Type I).

• R-Strategists (Opportunistic Species)

  These species grow quickly, producing many offspring. However, many of them die during the first stages of life (represented by Survival Curve Type III).

Community Dynamics and Ecological Succession

• Ecological Succession Defined

  Ecological succession is the process of gradual changes that an environment experiences over time. Changes in communities can follow two directions:

  • To the Climax Stage: This is the most complex and stable stage in a mature ecosystem. The collection of similar climax communities that covers a large area, often found across multiple continents, is called a biome.

  • Into Regression: In this process, biodiversity decreases, and the ecosystem changes into a previous, less developed stage.

Types of Ecological Succession

• Primary Succession

  Primary succession takes place in virgin areas such as sand dunes, lava deposits, or the bare rock of a mountain after a glacier retreats.

• Secondary Succession

  Secondary succession takes place in ecosystems that have suffered a regression (e.g., after a fire or logging). The ecosystem will recover relatively quickly, provided that the soil, containing spores and seeds from the eliminated vegetation, is not eroded and lost.

Changes Observed During Succession

As an ecosystem progresses through succession toward the climax stage, several factors change:

• Factors That Increase:

  • Biodiversity
  • Biomass
  • Number of species
  • Number of trophic levels
  • The complexity of interactions between living things
  • The stability of the ecosystem

• Factors That Decrease:

  • The number of generalist species (they are replaced by better-adapted specialist species).
  • Productivity (Net Primary Productivity decreases as the ecosystem reaches maximum biomass and growth slows down).