Lecture 15: Species Interactions - Competition and Coexistence

Vocabulary practice flashcards covering competitive exclusion, Lotka-Volterra dynamics, modes of competition, niches, and evolutionary character displacement from Lecture 15.

Competition

The use or defense of a resource by one individual that reduces the availability of that resource for another organism, resulting in a consumer-consumer interaction with -/- consequences.

Exploitation Competition

An indirect form of competition occurring without direct physical contact between consumers, often described as a 'race to the bottom' to deplete a shared resource.

Interference Competition

A direct form of competition involving physical contact, aggressive behavior, chemical inhibition, or active constraint to restrict another consumer's access to a contested resource.

Resource

Any substance, physical structure, or environmental space consumed or occupied by an organism that supports increased population growth as its availability increases (e.g., food, water, light, space, shelter).

Intraspecific Competition

Competition that takes place among individuals belonging to the same species, serving as a primary driver of density-dependent population dynamics.

Interspecific Competition

Competition among individuals of different species that can depress the population growth of both species and dictate species coexistence or local extinction.

Competitive Exclusion Principle

The ecological principle stating that two species competing for the exact same limiting resource cannot coexist indefinitely; the species capable of surviving at the lowest resource concentration will competitively exclude the other.

Lotka-Volterra Competition Model

A mathematical framework expanding on the logistic growth model to predict the population dynamics and outcomes of two species competing for shared resources.

Competition Coefficients ($\alpha$ and $\beta$)

Conversion factors in the Lotka-Volterra competition equations that translate individuals of one species into an equivalent per-capita competitive impact on the other species.

Zero Population Growth Isocline

A boundary line on a phase-plane diagram representing all combinations of population sizes ($N_1$ and $N_2$) at which a given species experiences zero net growth ($\frac{dN}{dt} = 0$).

Coexistence Criterion (Lotka-Volterra)

The condition where two competing species can stably coexist, which occurs when interspecific competition is weaker than intraspecific competition for both species.

Context-Dependent Outcomes

Ecological outcomes where the persistence, dominance, or exclusion of competing species changes depending on external environmental variables, multiple resource ratios, disturbance, or predation.

Resource Ratio Coexistence

Coexistence achieved when two species trade off in their limiting resource requirements, such as diatoms coexisting at an intermediate silicon-to-phosphorus ratio ($Si/P = 38$).

Asymmetrical Competition

Competition in which one species possesses an inherent advantage in acquiring a shared resource under specific environmental conditions, but loses that advantage under different conditions.

Intertidal Barnacle Zonation

An ecological pattern demonstrating asymmetrical competition: Rock barnacles competitively exclude Poli's stellate barnacles in the lower submerged intertidal zone, but Poli's stellate barnacles persist in the upper intertidal zone due to higher desiccation tolerance.

Allelopathy

A mechanism of interference competition in plants involving the chemical production and release of secondary compounds (such as polyacetylenes) that inhibit competitor germination or growth.

Fundamental Niche

The complete range of physical and abiotic environmental conditions under which a species can survive, grow, and reproduce in the absence of biotic interactions.

Realized Niche

The actual range of environmental conditions and resources occupied by a species in the presence of competitors, predators, and other biotic interactions; typically narrower than the fundamental niche.

Predator-Mediated Coexistence

A community dynamic in which an external predator preferentially consumes or suppresses a dominant competitor, allowing competitively inferior species (e.g., spring peepers) to persist.

Niche Partitioning

An evolved divergence in resource utilization patterns among coexisting species that reduces niche overlap and mitigates competitive intensity.

Character Displacement

An evolutionary divergence of morphological, physiological, or behavioral traits between two competing species driven by natural selection in regions where their geographic ranges overlap.

Allopatric

Referring to the geographic distribution condition where the ranges of two or more related species do not overlap.

Sympatric

Referring to the geographic distribution condition where the ranges of two or more related species overlap, enabling direct interactions and selection.

Galápagos Finch Character Displacement

The morphological divergence of beak depths in ground finches (Geospiza fuliginosa, G. fortis, G. magnirostris) when sharing islands to partition food resources, compared to intermediate beak depths on allopatric islands.