Ecological Succession and Community Dynamics

This page explores the concept of ecological succession, the process by which the structure of a biological community evolves over time. It details different types of succession, factors influencing succession, and how human activities can affect this natural process.

Ecological succession is categorized into two main types:

1. Primary succession: Occurs in previously uninhabited environments
2. Secondary succession: Begins in disrupted ecosystems that were previously inhabited

Definition: Ecological succession is the gradual process by which ecosystems change and develop over time.

The page outlines three different starting points for succession, known as seres: • Psammosere (sand) • Hydrosere (water) • Lithosere (rock)

The process of succession follows a general pattern:

1. Pioneer species colonize the area, adapted to extreme conditions
2. These species alter the environment, making it suitable for other species
3. More complex species arrive, further changing the environment
4. Complex species outcompete and replace pioneer species
5. The process continues until a stable climax community is reached

Highlight: The climax community is the most stable stage of succession, remaining dominant until significant climate changes occur.

The page introduces the concept of deflected succession, which occurs when factors prevent succession from reaching the natural climax community. This can be due to grazing, abiotic factors, or human intervention.

Vocabulary: Plagioclimax refers to a community that is maintained at a particular stage of succession due to human intervention.

Human activities that can lead to a plagioclimax include: • Urban development • Agriculture • Mowing • Burning • Pollarding • Coppicing

Changes during succession are noted across various factors: • Biomass: Increases from low to high • Biodiversity: Generally increases from low to high • Temperature extremes: Decrease from high to low • Water availability: Becomes more reliable • Light levels: May decrease if shaded by taller plants • Nutrient availability: Increases from low to high • Rates of change: Slow down from rapid to slow

The page also mentions the index of diversity, a measure used to quantify the biodiversity of an ecosystem. This index takes into account both the number of species present and their relative abundances.

Example: The Shannon-Wiener index is a common measure of biodiversity that considers both species richness and evenness in a community.

Understanding succession is crucial for ecological restoration and conservation efforts, as it provides insights into how ecosystems naturally develop and recover from disturbances.

Carrying Capacity and Population Dynamics

The carrying capacity is a fundamental concept in ecology, defined as the maximum population size that a particular habitat can sustain indefinitely. This page explores the factors affecting carrying capacity and the phases of population growth.

Factors influencing carrying capacity include physical and chemical aspects of the environment such as pH, mineral nutrients, light intensity, temperature, water availability, aspect, topography, and oxygen and carbon dioxide concentrations. These elements collectively determine the resources available to a population.

Definition: Carrying capacity is the maximum population size for a species that can be sustained in a particular habitat.

The standard growth curve of a population consists of four distinct phases:

1. Lag phase: Characterized by a small population and acclimatization to the environment.
2. Log phase: Rapid growth with abundant resources and minimal competition.
3. Stationary phase: Population reaches carrying capacity, with some limiting factors emerging.
4. Death phase: Resources are depleted, and waste products become toxic, leading to population decline.

Highlight: Understanding the phases of population growth is crucial for managing ecosystems and predicting population dynamics.

Human activities can significantly impact carrying capacity. For instance, culling may be used to control invasive species or manage populations that have grown beyond sustainable levels.

Example: Culling programs might be implemented to replace a lost predator when prey populations grow out of control.

The page also introduces the concepts of r-selected and K-selected species, which represent different evolutionary strategies:

• r-selected species: Fast reproduction, early maturity, little parental care, shorter lifespans (e.g., insects, some fish) • K-selected species: Slow reproduction, late maturity, extended parental care, longer lifespans (e.g., elephants, humans)

Vocabulary: r-selected species are typically pioneer species that can quickly colonize new environments, while K-selected species are often found in more stable, established ecosystems.

Lastly, the page discusses density-dependent and density-independent factors affecting population dynamics. Density-dependent factors, such as food supply and intraspecific competition, become more significant as population density increases. Density-independent factors, like catastrophic environmental events, affect populations regardless of their density.