BIO105 – Learning Guide Week 3: Communities

Vocabulary

Community: An assemblage of populations of different species interacting with one another in the same geographical area. Community ecology explores these interspecies interactions and their effects on population dynamics and ecosystem structure.
Biodiversity: The variety of life in the world or in a particular habitat or ecosystem. It encompasses species diversity (number and relative abundance of species), genetic diversity (variation within species), and ecosystem diversity (variety of habitats, communities, and ecological processes).
Evenness: A measure of the relative abundance of the different species in a community. High evenness means that all species are present in roughly equal numbers, while low evenness indicates that some species are much more abundant than others. Evenness is a component of biodiversity along with species richness.
Resistant vs. Resilient:
- Resistant: The ability of an ecosystem or community to remain unchanged in response to a disturbance.
- Resilient: The ability of an ecosystem or community to recover quickly after a disturbance, returning to its prior state or function.
Types of Species Interactions:
- Competition: An interaction between organisms or species in which both require a resource that is in limited supply, resulting in a negative impact on both (-/- interaction).
- Predation: An interaction where one organism, the predator, kills and eats another organism, its prey (+/ - interaction).
- Parasitism: An interaction where one organism, the parasite, lives on or in another organism, the host, deriving nutrients at the host's expense. The host is typically harmed but not immediately killed (+/ - interaction).
- Herbivory: An interaction where an animal (herbivore) feeds on plants or algae. Similar to predation from the plant's perspective (+/ - interaction).
- Consumption: A broad term that encompasses predation, herbivory, and parasitism, referring to any interaction where one organism eats or degrades another.
- Mutualism: An interaction between two species where both species benefit from the interaction (+/ + interaction).
- Commensalism: An interaction between two species where one species benefits and the other is neither helped nor harmed (+/ 0 interaction).
Competition: As discussed above, a -/- interaction.
- Intraspecific vs. Interspecific competition:
  - Intraspecific competition: Competition occurring between individuals of the same species for limited resources.
  - Interspecific competition: Competition occurring between individuals of different species for limited resources.
- Exploitation vs. Interference competition:
  - Exploitation competition: Indirect competition where individuals reduce the availability of a shared resource, impacting others who also rely on that resource (e.g., plants competing for soil nutrients).
  - Interference competition: Direct competition where individuals physically or chemically interact to prevent others from accessing resources (e.g., animals fighting over territory or mating partners, or allelopathy in plants).
Niche: The specific role an organism plays in its environment, encompassing its use of resources (food, water, space) and its interactions with other species. It describes where an organism lives and what it does.
Keystone Species: A species that has a disproportionately large effect on its environment relative to its abundance. The removal of a keystone species can lead to a cascade of negative effects on the ecosystem, significantly altering community structure (e.g., sea otters, wolves).
Coevolution: The process of reciprocal evolutionary change in two or more species that interact closely with one another. Each species acts as a selective force on the other, driving adaptations.
Adaptations: Traits that have evolved by natural selection and increase an organism's fitness (survival and reproduction) in its specific environment.
Mimicry: An adaptation where one species (the mimic) evolves to resemble another species (the model), often for protection from predators (Batesian mimicry: harmless mimic resembles harmful model; Mullerian mimicry: two or more harmful species resemble each other) or for hunting (aggressive mimicry).
Induced vs. Constitutive Defenses:
- Induced defenses: Defenses produced or increased by an organism only in response to specific threats or damage (e.g., a plant producing toxins after being eaten).
- Constitutive defenses: Defenses that are always present in an organism, regardless of the presence of a threat (e.g., thorns on a rose bush).

Concept Questions

1. What is a community? Why is community ecology sometimes seen as population ecology of multiple species?

A community is defined as an assemblage of populations of different species that are found in the same place at the same time and interact with each other. These interactions can be direct (e.g., predation, competition) or indirect (e.g., through shared resources).

Community ecology is often viewed as