Editing Ecological niche (section)

== Coexistence without niche differentiation: exceptions to the rule ==
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 [[Cassidinae|hispine beetle]] species.<ref name=Strong82/>  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.

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.<ref>{{cite journal |author=Shmida, A., Ellner, S. |title=Coexistence of plant species with similar niches |journal=Vegetatio |volume=58 |pages=29–55 |year=1984 |doi=10.1007/BF00044894 |s2cid=22861648 }}</ref> 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]].

Research using mathematical modelling is indeed demonstrating that predation can indeed stabilize lumps of very similar species. [[Willow warbler]] and [[common chiffchaff|chiffchaff]] and other very similar warblers can serve as an example. The idea is that it is also a good strategy to be very similar to a successful species or have enough dissimilarity. Other examples of nearly identical species clusters occupying the same niche were water beetles, prairie birds and algae. The basic idea is that there can be clusters of very similar species all applying the same successful strategy and between them open spaces. Here the species cluster takes the place of a single species in the classical ecological models.<ref name=Scheffer>{{cite journal |doi=10.1073/pnas.0508024103 |pmid=16585519 |pmc=1458860 |bibcode=2006PNAS..103.6230S |title=Self-organized similarity, the evolutionary emergence of groups of similar species |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=16 |pages=6230–5 |year=2006 |last1=Scheffer |first1=Marten |last2=van Nes |first2=Egbert H. |doi-access=free }}</ref>