Community and Ecosystem Ecology

Community and Ecosystem Ecology Part 1

Objectives for Today

  • Understand what communities are and the factors affecting community richness and diversity.

  • Compare and contrast different hypotheses for species richness spatial patterns.

  • Explore succession and influence factors.

  • Identify main factors determining species richness on islands.

  • Discuss influences on biomass production in terrestrial and aquatic ecosystems.

Community Ecology

Definition

  • Community: A group of populations (of different species) that inhabit the same area at the same time.

Focus

  • Community ecology: Study of factors influencing the number and abundance of species in a community.

Ecosystem Ecology

Definition

  • Ecosystem: The physical environment in conjunction with the communities of organisms living within it.

Focus

  • Ecosystem ecology: Study of interactions between biotic (living) and abiotic (non-living) components, including energy flow and chemical cycling.

Species Richness and Diversity

Definition

  • Species richness: The number of different species in a community, serving as a measure of diversity.

Influencing Factors

  • Latitude

  • Time

  • Area

  • Productivity (of producers)

Species Richness Patterns

Richness and Latitude

  • Species richness increases as one approaches the equator.

  • Contributing factors may include temperature, water availability, habitat age, and size.

Hypotheses Explaining Richness

Species-time Hypothesis

  • Suggests that temperate habitats have fewer species because they are younger and periodically disturbed by mechanisms such as glaciers.

  • Older tropical habitats have been undisturbed and thus contain more diverse species.

Evidence

  • Older tree species in Britain have more diverse insect communities.

Species-area Hypothesis

  • Larger habitats support more species due to resource availability and space.

  • Evidence supports that tree species with larger ranges in Britain host more diverse insect communities.

Species-productivity Hypothesis

  • Greater productivity by plants yields greater species richness.

  • Influenced by temperature and rainfall patterns.

  • Areas with higher plant diversity also show increased diversity of animal communities.

Interaction of Time and Productivity

  • Evolutionarily older areas with consistent temperature/rainfall have higher diversity compared to younger areas.

  • Example: Older temperate forests of Asia have more tree diversity than younger European or American forests.

Community and Ecosystem Ecology Part 2

Succession

Definition

  • Succession: Gradual and continuous change in a community post-disturbance.

Types

  • Primary succession: Colonization of pristine land by organisms.

  • Secondary succession: Re-colonization of previously occupied land after severe disturbance.

Climax Community

  • A stable, final community attained after succession.

  • Progressing from pioneer stages (like lichens) to climax communities (mature forest).

Succession Mechanisms

Facilitation Model

  • Early colonizers modify the environment, making it favorable for subsequent species.

  • Initial colonizers improve soil organic matter and provide food.

Example

  • After Mount St. Helens' eruption, fungi colonized and improved soil for other species leading to a return of forest.

Inhibition Model

  • Early colonists can prevent other species from establishing, by monopolizing resources.

  • They may actively eliminate competition through toxic secretions or spatial dominance.

Island Biogeography

Influencing Factors

  • Succession dynamics: Facility, inhibition.

  • Species' ability to colonize islands: Distance from mainland and size.

  • Extinction rates: Determine community structures.

Equilibrium Model

  • The number of species on an island achieves equilibrium based on immigration and extinction rates.

  • Initially high immigration diminishes as the species pool becomes saturated, leading to increasing extinction rates.

Predictions

  • Species number increases with island size and decreases with distance from mainland.

  • Expect species turnover as competition heightens and resources become limited.

Community and Ecosystem Ecology Part 3

Biomass Production in Ecosystems

Definition

  • Net Primary Production (NPP): The amount of energy produced by primary producers available to consumers, calculated as total energy fixed minus energy used for respiration.

Influencing Factors

Terrestrial Ecosystems

  • Primarily dependent on water and temperature.

  • Nutrient availability, specifically nitrogen, plays a critical role.

Aquatic Ecosystems

  • Relies on light and nutrient availability.

  • Upwelling brings nutrients to the surface enhancing productivity.

Overall Production Statistics

  • Primary production varies significantly across ecosystems, with specific productivity thresholds delineated for terrestrial and aquatic environments.

Consumption Dynamics

  • Most primary production is fueled by detritivores rather than primary consumers due to inefficient direct consumption by herbivores.