Community Ecology

Community Ecology

What is a Community?

  • Definition: A community is an assemblage of populations of various species with the potential for interaction.

  • Communities involve populations of multiple species and their interactions.

  • Interspecific interactions refer to interactions between different species.

    • -specific: pertains to a particular species.

    • intra-: refers to interactions within a species.

    • inter: refers to interactions between species.

Species Interactions

Competition

  • Definition: Competition occurs when different species fight for limited resources.

  • Interspecific Competition:

    • Symbolized as (-/-), indicating that both species suffer from the interaction.

    • Can lead to Competitive Exclusion, where one species is completely eliminated from a locale.

  • Ecological Niche:

    • Defined as the set of biotic and abiotic resources a species uses.

Resource Partitioning

  • Concept: Similar species can coexist if their niches do not overlap.

  • Resource Partitioning:

    • Differentiation of niches that enables similar species to coexist.

    • If their niches overlap, two species cannot coexist permanently.

    • Can lead to Character Displacement, where traits become more divergent in sympatry (same area) than in allopatry (different areas).

Niches

  • A species' niche includes more than just where it is found:

    • Fundamental Niche: The potential niche of a species.

    • Realized Niche: The actual niche that a species occupies.

Predation

  • Definition: Predation occurs when one species kills another for food.

  • Symbolized as (+/-), indicating that the predator benefits while the prey is harmed.

  • Adaptations in Predators:

    • Examples include claws, stingers, and poisons for capturing or killing prey.

  • Adaptations in Prey:

    • Examples include camouflage, poison, and behavior or mimicry for defense.

Herbivory

  • Definition: Herbivory occurs when an herbivore eats parts of plants.

  • Symbolized as (+/-), indicating that herbivores benefit while plants are harmed.

  • Herbivore Adaptations:

    • Special stomachs/intestines and grinding teeth to digest plant material.

  • Plant Defenses:

    • Include chemical toxins and protective structures.

Parasitism

  • Definition: Parasitism is when parasites derive nourishment from hosts.

  • Symbolized as (+/-); parasites benefit while hosts are harmed.

  • Types of Parasites:

    • Ectoparasites: Live on the surface of the host.

    • Endoparasites: Live inside of the host.

  • Parasites often do not kill their hosts, but can spread diseases.

Mutualism

  • Definition: Mutualism benefits all species involved in the interaction.

  • Symbolized as (+/+), indicating that both species benefit.

  • Interacting species depend on each other for survival, leading to increased fitness.

  • Mutualism can drive coevolution of related adaptations.

  • If one species does not gain a benefit, resulting in a relationship of commensalism (+/0) where one species benefits and the other is neither helped nor harmed.

Characterizing Communities

Species Diversity

  • Species Diversity can be characterized in two ways: species richness and species abundance.

    • Species Richness: The number of different species present in a community.

    • Species Abundance: The proportion of each species in relation to the total number of individuals.

  • Importance: Diverse communities typically exhibit higher productivity, stability, and resistance to invasion.

The Three Sisters: Companion Planting

  • The Three Sisters refer to a traditional agricultural method used by the Iroquois since the 1300s that includes corn, beans, and squash.

    • Provides soil fertility and contributes to a healthy diet through a single planting structure.

    • Corn (planted in the center) supports the growth of pole beans.

    • Beans add nitrogen to the soil, enhancing its fertility and structure.

    • Squash leaves cool the soil and hinder weed growth.

Trophic Structure

  • Trophic Structure: The feeding relationships between organisms within a community.

    • Complex Interactions: These interactions are often illustrated in a food chain, showcasing how energy flows through an ecosystem.

Biogeographic Factors

Latitudinal Gradients

  • Species Richness Patterns: Exhibit a latitudinal gradient.

    • Species richness is generally high near the equator and decreases towards the poles.

    • Climate Factors:

    • Tropical growing seasons are noticeably longer.

    • Less variability in seasons compared to polar regions.

    • Biogeographical History: Tropical environments have existed for longer durations, particularly due to factors like glaciation.

Area Effects

  • Larger Areas tend to support higher species richness.

    • Related to the concept of a species-area curve.

    • This idea extends to islands and also includes lakes, mountain peaks, and other fragmented habitats.

    • Useful in predicting potential species decline in regards to habitat loss.

Disturbances

  • Definition: A disturbance is an event that changes a community by removing species or altering available resources (e.g., storms, fires, floods, droughts).

  • Moderate Disturbance Levels: Can increase species richness.

  • High Disturbance Levels: May prevent many species from surviving.

  • Low Disturbance Levels: Allow some dominant species to outcompete others in the community.

Ecological Succession

  • Definition: Ecological succession is a process where a variety of species colonize an area and are replaced by others over time, occurring in stages.

  • Areas experiencing significant disturbances have an ordered recovery process following this principle.