Chapter 20

Basic Definition of Community
- Understand the term "community" in ecological context.
Types of Interactions within Communities
- Familiarize with three major interaction types: competition, symbiosis, and predation.
Niche Definition
- Grasp the concept of a niche and the impact of competition on species' niches.
Coevolution
- Understand coevolution and its role in symbiotic relationships.
Predator/Prey Relationships
- Learn about predator-prey interactions and coevolutionary dynamics.
Ecological Succession
- Recognize how succession contributes to biodiversity in communities.

Population:
- Refers to all members of a single species that live together in a specified geographic region.
Community:
- Encompasses all species living in a particular geographic area.
Ecosystem:
- The combination of a community and all its nonliving elements interacting with it.
Biosphere:
- The global ecological system integrating all ecosystems.

Interactions between populations within communities influence both ecological and evolutionary processes.
These interactions shape the community's structure and function.
Individualistic View:
- Suggests that a community is merely a collection of species coexisting in one location.
Holistic View:
- Views a community as a superorganism, with species functioning collectively as an integrated whole.
Assessing interactions within a community can be complex; biologists prioritize measurable interactions.
The concept that the whole is greater than the sum of its parts is fundamental in ecological studies.

Competition:
- Occurs when two or more populations utilize the same limited resource.
Symbiosis:
- Involves two or more species existing in close association, forming various types of relationships.
Predation:
- Describes the process where members of one species consume those of another species.

Habitat:
- The physical location where organisms reside.
Niche:
- Represents all the ways an organism utilizes its habitat; it describes the organism's role within its environment.
Similar organisms often compete for resources in a habitat but can coexist by dividing their niches.

Fundamental Niche:
- The total niche an organism can potentially occupy.
Realized Niche:
- The specific niche an organism occupies in the presence of competitors.

Gause's Principle:
- States that no two species can occupy the same niche indefinitely under competition for limited resources.
- Coexistence requires niche differentiation in one or more attributes. Lack of differentiation may lead to competitive exclusion, causing one species to become locally extinct.

Conducted experiments with three Paramecium species to demonstrate competitive exclusion and niche differentiation.
When grown alone, all species flourished, but together, P. aurelia outcompeted P. caudatum. P. caudatum and P. bursaria coexisted by adjusting their realized niches.

Describes how similar species avoid competition through utilizing resources differently (changing their realized niches).
Sympatric Species:
- Closely related species in the same geographical area, avoiding competition through resource partitioning.
Allopatric Species:
- Closely related species that avoid competition by existing in different geographical areas.

Example of Anolis lizards in the Caribbean partitioning resources based on microhabitat use.
Study of Geospiza finches on the Galapagos Islands showing phenotypic differences in beak size as a method of reducing competition for food.

Describes the evolutionary adaptations of two or more species in response to one another.
Three primary forms of symbiosis include:
1. Mutualism:
  - Both species benefit from the relationship.
2. Commensalism:
  - One species benefits while the other is neither helped nor harmed.
3. Parasitism:
  - One species benefits at the expense of the other.

Predator and prey populations exhibit cyclical dynamics, often depicted graphically (e.g., snowshoe hare and lynx populations over time).

When predator and prey are mutually dependent (often through an arms race dynamic), they influence each other's evolution.
Defensive adaptations:
- Plants may develop thorns or toxic chemicals, while animals may evolve coloration, mimicry, or behavioral strategies.

Müllerian Mimicry:
- Two harmful species resemble each other, enhancing predator avoidance.
Batesian Mimicry:
- A harmless species imitates a harmful species to deter predators.
Self Mimicry:
- An organism's body part resembles another part within the same organism, aiding in deception or defense.

Defined as predators crucial for maintaining species diversity in an ecosystem by controlling the populations of competitively dominant species.

Refers to a sequential process of community member replacement leading to a stable final ecological state.
Primary Succession:
- Occurs in lifeless areas where soil has yet to form.
Secondary Succession:
- Takes place in areas where disturbances have occurred but soil and some organisms remain.

Initial colonizers that modify the environment, facilitating further succession toward a climax community.

Natural events may reduce dominant populations, allowing for new communal dynamics.

Non-native species that can hinder native biodiversity and disrupt successional processes.
Restoration efforts often focus on controlling invasives to promote native plant recolonization and habitats.

The progression of ecological succession continues, occasionally reverting to earlier stages due to further disturbances, reinforcing the dynamic nature of ecosystems.