When speciation is not driven by (or strongly correlated with) divergent natural selection, it can be said to be nonecological, [1] [2] to distinguish it from the typical definition of ecological speciation: "It is useful to consider ecological speciation as its own form of species formation because it focuses on an explicit mechanism of speciation: namely divergent natural selection. There are numerous ways other than via divergent natural selection in which populations might become genetically differentiated and reproductively isolated." [3] Many instances of non-ecological speciation are likely allopatric, especially when the organisms in question are poor dispersers (e.g., land snails, salamanders); however, sympatric non-ecological speciation may also be possible, especially when accompanied by an "instant" (at least in evolutionary time) loss of reproductive compatibility, as when polyploidization happens. [2] [4] Other potential mechanisms for non-ecological speciation include mutation-order speciation [5] and changes in chirality in gastropods. [6]
Non-ecological speciation might not be accompanied by strong morphological differentiation, so it might give rise to cryptic species; however, some species are difficult for humans to differentiate that are strongly differentiated concerning their resource use and so are likely a result of ecological speciation (e.g., host shifts in parasites or phytophagous insects). [7] [8] When species recognition/sexual selection plays a strong role in maintaining species boundaries, the species generated by non-ecological speciation might be straightforward for humans to differentiate, as in some odonates. [9]
