Species Interactions and Ecological Communities: Competition, Symbiosis, and Succession

A comprehensive vocabulary collection covering competition types, symbiotic relationships, community assembly rules, ecological succession, and relevant Indigenous cultural terms from Lectures 28–30.

Competition

An interaction between individuals seeking a common resource in limited supply, in which both participants are harmed ($-/-$) because each reduces resource availability to the other.

Intraspecific competition

Competition between individuals of the same species, which is strongest at high population density and can reduce growth and reproduction.

Interspecific competition

Competition between individuals of different species that occurs where their resource requirements overlap, affecting population growth, persistence, and distribution.

Interference competition

A direct interaction in which one competitor actively prevents another from accessing a resource via fighting, aggression, territorial defence, dominance hierarchies, or chemical inhibition.

Exploitative competition

An indirect competitive interaction in which competitors deplete a shared resource simply by consuming it first or faster, without needing direct physical contact.

Dominance hierarchy

A social ranking of individuals (a 'pecking order') that determines priority of access to resources.

Kleptoparasitism

The act of stealing food or prey obtained by another individual (for example, black bears taking puma kills or frigatebirds harassing seabirds for regurgitated fish).

Competitive exclusion principle

The ecological principle stating that two species with identical (completely overlapping) niches cannot coexist indefinitely; one will outcompete the other, forcing local extinction or a niche shift.

Resource partitioning

The division of limited resources (such as food type, microhabitat, feeding height, or activity time) among species, which reduces niche overlap and allows coexistence.

Competitive coexistence

The long-term persistence of competing species within the same community, achieved by reducing niche overlap.

Adaptive radiation

The evolutionary diversification of an ancestral lineage into multiple distinct species filling different ecological niches (such as Caribbean Anolis lizards).

Allelopathy

A form of interference competition in which an organism releases chemicals (e.g., from leaf litter leaching into soil or modifying pH) that inhibit the growth of competing plants.

Symbiosis

Any close, long-term physical relationship between individuals of two or more different species, encompassing mutualism ($+/+$), commensalism ($+/0$), and parasitism ($+/-$).

Mutualism

A symbiotic interaction where both species benefit ($+/+$), often arising through reciprocal co-evolution.

Commensalism

A symbiotic interaction in which one species benefits while the other is neither helped nor harmed ($+/0$).

Obligate symbiosis

A symbiotic relationship in which the participating partners cannot survive or reproduce without each other (e.g., lichens, yucca and yucca moths).

Facultative symbiosis

A symbiotic relationship in which partners derive benefit from each other but are fully capable of surviving independently.

Specific symbiosis

A symbiotic association in which an organism relies on one particular partner species.

Diffuse symbiosis

A symbiotic interaction in which an organism can partner with many different species (e.g., mycorrhizal fungi associating with various plant species).

Endosymbiont

A symbiotic organism that lives inside the body, tissues, or cells of its host partner.

Ectosymbiont

A symbiotic organism that lives externally on the surface of its host partner.

Co-evolution

The reciprocal evolutionary change occurring across generations in two or more interacting species.

Zooxanthellae

Photosynthetic dinoflagellates that live as endosymbionts inside the tissues of reef-building corals, providing photosynthetic products in exchange for shelter and waste nutrients.

Coral bleaching

The process where heat-stressed corals expel their endosymbiotic zooxanthellae after temperatures exceed a threshold, leaving the coral skeleton white.

Domatia

Small hairy tufts or pocket-like chambers on plant leaves (often where veins meet) that shelter beneficial predatory or fungivorous mites.

Frugivore

A fruit-eating animal that often functions as an important mutualistic seed disperser for plants.

Coprophage

An organism that feeds on dung or faeces (e.g., moth larvae in sloth dung).

Epiphyte

A plant that grows harmlessly on the surface of another plant (such as a tree trunk) strictly for mechanical support, gaining access to light and space.

Sexual deception

A pollination mechanism in which a plant mimics the visual cues and sex pheromones of a female insect to trick male insects into attempting copulation and transferring pollen.

Stress gradient hypothesis

An ecological hypothesis predicting that positive interactions (mutualism and facilitation) become more common as environmental stress increases, while competition dominates in resource-rich environments.

Ecological community

All the populations of different species living and interacting in the same geographic place at the same time.

Regional species pool

The entire set of species existing in a broader geographical region that could potentially disperse into and colonise a local habitat.

Community assembly filters

The sequential filters—specifically dispersal, abiotic tolerances, and biotic interactions—that determine which species from the regional pool establish in a local community.

Relative abundance

The proportion or percentage representation of each individual species relative to the total number of individuals in a community.

Direct interaction

An ecological interaction where one species directly affects another without mediation through a third party (e.g., direct predation, interference competition).

Indirect interaction

An ecological interaction where species A affects species C via an intermediate mediating species B, without interacting with species C directly.

Trophic cascade

A top-down chain reaction in which an apex predator's ecological effects propagate down through successive trophic levels of a food web.

Functional redundancy

A community property where the loss of one species produces little detectable ecological change because other species perform the same ecological role.

Disturbance

A discrete event (either natural or anthropogenic) that changes community structure by removing organisms, altering resource availability, or changing abiotic conditions.

Ecological succession

The natural, directional change in community species composition and structure over time following an environmental disturbance.

Primary succession

Ecological succession initiating on newly formed or exposed substrates that completely lack soil or remnant biological communities (e.g., after volcanic eruptions or glacial retreat).

Secondary succession

Ecological succession taking place in areas where a disturbance has damaged the standing community, but biological remnants (such as soil, seeds, and root systems) remain.

Pioneer species

Fast-growing, hardy organisms with high dispersal ability that are the first to colonise disturbed or barren landscapes.

Climax community

The relatively stable, mature ecological community that forms the endpoint of a successional sequence in the absence of further disturbance.

Facilitation

A successional interaction in which early colonising species modify abiotic conditions (e.g., adding nitrogen, creating shade) in ways that make the habitat more suitable for later species.

Inhibition

A successional interaction in which early colonisers make it harder for later species to colonise and establish through space pre-emption, resource competition, or allelopathy.

Intermediate disturbance hypothesis

The ecological hypothesis proposing that local species diversity peaks at intermediate frequencies and intensities of disturbance.

Alternative stable states

Different stable community configurations that an ecosystem can occupy, where large disturbances push the community across a threshold into a new persistent state.

Bunjil

The wedge-tailed eagle (Aquila audax), serving as the creator figure for the Kulin peoples and one of two ancestral moieties in Wurundjeri kinship systems.

Waa

The crow or raven, described as a trickster figure and representing the complementary moiety to Bunjil in Wurundjeri kinship systems.

Warin

The Woi-wurrung name for the common wombat, which also designates 'Wombat Season,' a colder period when wombats sun themselves at the entrances of their burrows.