Short answers, pulled from the story.
The three major mechanisms of biological competition are interference competition, exploitation competition, and apparent competition, arranged from most direct to least direct. Interference competition involves direct fighting over resources; exploitation competition occurs when organisms deplete a shared resource without direct contact; apparent competition occurs when two prey species indirectly harm each other through a shared predator.
Apparent competition is an indirect interaction in which two prey species negatively affect each other not by sharing a resource, but by sharing a food-limited predator. University of Florida ecologist Robert D. Holt coined the term in 1977, noting that field ecologists had been mistakenly attributing such negative interactions to niche partitioning rather than predator dynamics.
The competitive exclusion principle holds that species cannot coexist if they occupy identical ecological niches. Russian ecologist Georgii Gause proposed the principle in 1934 based on his laboratory studies of two Paramecium species, Paramecium aurelia and Paramecium caudatum, whose competition intensified when their niches overlapped.
Character displacement is the tendency for competing species to evolve more different traits when they share the same territory than when they live apart. On Galapagos Islands where both Geospiza fortis and Geospiza fuliginosa are present, G. fuliginosa evolves a smaller beak and G. fortis evolves a larger beak, reducing competition for intermediate-sized seeds.
Intraspecific competition occurs between members of the same species competing for the same resources, and it can regulate population size as crowding limits resource availability. Interspecific competition occurs between individuals of different species sharing a limiting resource, and it can alter population sizes, community structure, and the evolution of the species involved.
r/K selection theory, developed from work on island biogeography by Robert MacArthur and E. O. Wilson, describes how competitive pressure shapes life-history strategies. r-selected species exploit empty niches and produce many offspring with low individual survival rates, while K-selected species compete effectively in crowded environments by investing heavily in fewer offspring with higher survival rates.