PARENT SESSION
Contributed Oral Session 14: Evolutionary Ecology: Theory; Modeling
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Competitive non-transitivity and species coexistence: A lattice-based simulation.

Laird, Robert¹, Schamp, Brandon^*,2, ¹ University of Calgary, Calgary, Alberta, Canada² Queen's University, Kingston, Ontario, Canada

ABSTRACT- Reconciling the notion of species coexistence with the generally recognized effects of interspecific competition is a longstanding challenge in ecology. While neutral theory proposes that all individuals (and therefore species) may be ecologically identical (i.e., having relatively equal competitive abilities), many who recognize the inherent differences between coexisting species find this difficult to accept. A relatively poorly studied alternative to the notion of neutral theory's 'equality' is that of non-transitive competitive relationships among coexisting species which stems from the concept that competing species cannot necessarily be listed in a strictly linear competitive hierarchy. While neutral theory proposes that all species are equivalent, non-transitivity proposes that pairs of species are different in competitive ability, but that higher order combinations of species may demonstrate emergent 'equivalence' in terms of their ability to successfully compete, and therefore to coexist. The game 'rock-paper-scissors', wherein the three competitive types do not form a competitive hierarchy and therefore have the potential to coexist, is a popular analogy for this type of competition. We investigated the relationship between non-transitivity and species coexistence using a spatial lattice model. We observed that even small amounts of non-transitivity in the competitive outcomes matrix can make a community more resistant to species extinctions. Species richness and species evenness tracked closely with the level of non-transitivity of the competitive outcomes matrix. Further, the rate of species loss from the system was sensitive to the number of species in the system at the time. Our results show that, in addition to factors such as predation and disturbance that can attenuate the effects of competitive dominance, competitive non-transitivity may be an important mechanism by which competition itself can help to maintain species coexistence. Just how common non-transitive relationships are in communities, represents an important avenue of future inquiry.

Key words: coexistence, non-transitive competition, spatial lattice-model