Competition

Georgii F. Gause

Paramecium

Competitive Exclusion Principle "Two competing species cannot coexist in a stable environment if both require the same limiting resource." - if two competing species do coexist in a stable environment, they do so because of niche differentiation - their realized niches are slightly different and thus competition between them is lessened

Robert MacArthur,

MacArthur’s Warblers

Caveats to Resource Utilization Curves 1) Are we examining right resource? Is something else really limiting? 2) Is there variation in when the resource is limiting? If it is only limiting occasionally, then it may not matter much. 3) How do we quantify resource use by species in nature? Do resource utilization curves have to be normal? Does competition change during life history changes in the species? 4) How does overlap really affect the species? Is overlap really only on 1 dimension?

Resource Utilization in Cattails Typha latifolia – shallow 0-60 cm water depth Typha angustifolia – deeper cm water depth

Resource Utilization – Spiny Mice Aconomys cahirinus nocturnal Aconomys russatus dirunal but may become nocturnal

CyclotellaAsterionella Two species of competing Diatoms

Species can compete for two resources and can coexist when 2 conditions are met: 1) The habitat must be such that one species is more limited by one resource and the other species is more limited by the other resource. 2) Each species must consume more of the resource that more limits its own growth.