Ecology: the interactions of an organism with other organisms and its environment. Two-species interactions: outcome when both organisms are present. Types of interactions: mutualism: org 1 benefits. Org 2 benefits: commensalism: org 1 benefits. Org 2 no effect: predation/parasitism: org 1 benefits. Org 2 harmed: amensalism: org 1 no effect. Org 2 harmed: neutralism: org 1 no effect. Paradigms of competition: competition is an interaction between two organisms or species that harms each of them, competition is over a limiting resource (food, water, light, nesting space, pollinators) Can be interspecific (between species) or intraspecific (within species) If inter < intra allows more species to coexist: competition reduces the growth, survival and/or reproduction of both species. One species, the superior competitor for the limited resource, will always win. Gause"s paramecium example (1934, the struggle for existence: theory of limiting similarity: species that are too similar (niche overlap) cannot coexist. Goal linear (o>t>a) or circular (o>t, t>a, a>o).