Ecological Communities and Species Interactions

Collection of vocabulary based on ecological communities, neutral theory, island biogeography, competition types, mutualism, and predator-prey dynamics.

Ecological community

A system that examines how species interact with one another, such as through predation and competition, affecting community structure and organization.

Emergent properties

Characteristics unique to a specific community, including species diversity, trophic structure, and stability over time.

Species diversity

A measure of the difference in evenness, richness, and biodiversity indexes within a community.

Trophic structure

The feeding relationships within an ecological community.

Neutral theory

A theory based on six key assumptions: 1. Ecological equivalence, 2. No niches or selection at the community level, 3. Ecological drift (random birth, death, dispersal), 4. Dispersal Limitation, 5. Speciation as a source of new species, and 6. Zero-Sum community (Fixed Community Size).

Ecological drift

The component of neutral theory involving random birth, death, and dispersal events.

Zero-Sum community

A neutral theory assumption stating that the community size is fixed.

Equilibrium species richness

The point occurring precisely where the downward-sloping immigration curve intersects the upward-sloping extinction curve.

Island Biogeography Theory (IBT)

A theory predicting that species richness is determined by immigration and extinction rates, which scale with an island's size and its isolation from mainland source populations.

Single Large or Several Small (SLOSS)

A conservation debate concerning whether species can persist in small fragments versus single large areas, considering habitat heterogeneity and the risk of catastrophic events like disease.

Interspecific competition

An interaction that occurs when different species compete for a resource in short supply.

Inference competition

Direct aggressive encounters among individuals that shape resource access.

Exploitative (resource) competition

An indirect form of competition where individuals deplete resources by consuming them, leaving less available for others without directly harming them.

Fundamental niche

The niche potentially occupied by a species based on physiology, genetics, and abiotic factors in the absence of biotic constraints like predators or competitors.

Realized niche

The restricted set of conditions a species actually occupies after interacting with other species through factors like interspecific competition and predation.

Competitive exclusion principle

The rule that two related, sympatric species cannot stably occupy identical ecological niches if resources are strictly limited; the superior competitor will eventually monopolize the resource.

Resource partitioning

An evolutionary process, such as disruptive selection, by which competing species use the environment differently (micro-habitats, time, or resources) to facilitate coexistence.

Facilitation

A positive or commensal interaction where one species modifies the environment to benefit another species.

Spatial partitioning

The division of the physical environment where species occupy different micro-climates, vegetation layers, or hunt in different territories.

Temporal partitioning

The division of resource use by time, such as species being diurnal versus nocturnal or peaking at different temperature thresholds.

Dietary partitioning

The exploitation of different food resources, varying prey sizes, or feeding at different heights on the same plant to avoid competition.

Obligate mutualisms

Strict, necessary interdependent relationships where at least one species cannot survive or reproduce without the other.

Facultative mutualisms

Flexible interactions where both species benefit but each could potentially survive and reproduce independently.

Evolutionarily Stable Strategy (ESS)

A behavior or trait that, once adopted by most of a population, cannot be invaded by a rare, alternative strategy; it explains how mutualisms persist despite the potential for "cheaters."

Prisoner dilemma

A game theory concept where the highest individual payoff comes from accepting help without giving any (defecting), illustrating the challenge of maintaining cooperation.

Antagonistic exploitative interactions ($+/-$)

Ecological relationships refer to the inclusion of predation, herbivory, and parasitism, where one organism benefits (+) by utilizing another, causing harm to the victim's survival or reproduction.

Evolutionary arms race

Reciprocal adaptations where the evolution of a trait in one species (e.g., predator speed) reduces the fitness of an interacting species, driving rapid, continuous evolutionary change.

Consumptive effects (CEs)

Predator effects that occur when predators kill and eat prey, directly reducing their population density.

Non-consumptive effects (NCEs)

Indirect effects where the "fear" of predators alters prey traits, such as foraging behavior or physiology, which cascades through the ecosystem.

Landscape of fear

The mapped tension between an organism's need to maximize energy intake and its need to stay safe from predators, driving behavioral and habitat alterations.

Reef rugosity

Structural complexity of a reef; high levels provide refuges that allow herbivores to graze intensively, while low levels can lead to macroalgae outcompeting coral due to heightened predation risk.