gross2009invisible
The invisible niche: Weakly density-dependent mortality and the coexistence of species
Thilo Gross, Andrew M. Edwards and Ulrike Feudel
Journal of Theoretical Biology 258, 148-155, 2009
Weakly density-dependent effects, characterized by fractional scaling exponents close to one, are rarely studied in the ecological literature. Here, we consider the effect of an additional weakly density-dependent term on a simple competition model. Our investigation reveals that weak density-dependence opens up an “invisible niche”. This niche does not constitute a new mechanism for coexistence, but is a previously unexplored consequence of known mechanisms. In the invisible niche a weaker competitor can survive at very low density. Coexistence thus requires large habitat size. Such niches, if found in nature, would have a direct impact on species-area laws and species-abundance curves and should therefore receive more attention.
Figure 1: Two competing species can coexist if they suffer from mortality of the form $$mX+rX^p$$. This is well known for $$p=2$$, but surprisingly coexistence is possible in a finite range even in the limit $$p\to 1$$.