<P> Conditional differentiation (sometimes called temporal niche partitioning) occurs when species differ in their competitive abilities based on varying environmental conditions . For example, in the Sonoran Desert, some annual plants are more successful during wet years, while others are more successful during dry years . As a result, each species will have an advantage in some years, but not others . When environmental conditions are most favorable, individuals will tend to compete most strongly with member of the same species . For example, in a dry year, dry - adapted plants will tend to be most limited by other dry - adapted plants . This can help them to coexist through a storage effect . </P> <P> Species can differentiate their niche via a competition - predation trade - off if one species is a better competitor when predators are absent, and the other is better when predators are present . Defenses against predators, such as toxic compounds or hard shells, are often metabolically costly . As a result, species that produce such defenses are often poor competitors when predators are absent . Species can coexist through a competition - predation trade - off if predators are more abundant when the less defended species is common, and less abundant if the well - defended species is common . This effect has been criticized as being weak, because theoretical models suggest that only two species within a community can coexist because of this mechanism . </P> <P> Some competing species have been shown to coexist on the same resource with no observable evidence of niche differentiation and in "violation" of the competitive exclusion principle . One instance is in a group of hispine beetle species (Strong 1982). These beetle species, which eat the same food and occupy the same habitat, coexist without any evidence of segregation or exclusion . The beetles show no aggression either intra - or inter-specifically . Coexistence may be possible through a combination of non-limiting food and habitat resources and high rates of predation and parasitism, though this has not been demonstrated . </P> <P> This example illustrates that the evidence for niche differentiation is by no means universal . Niche differentiation is also not the only means by which coexistence is possible between two competing species (see Shmida and Ellner 1984). However, niche differentiation is a critically important ecological idea which explains species coexistence, thus promoting the high biodiversity often seen in many of the world's biomes . </P>

Describe how organisms that would occupy similar niches change their behaviour to avoid conflict