COS 139-8
Niche theory to everywhere: the mathematically sound approach
Ecological niche aims to characterize the different ecological opportunities, including adaptation to a given habitat and adaptation to an ecological role within a habitat/community. However, niche theory has had to contend with criticisms of vagueness, and the lack of any useful predictive power throughout its long history. We deal with three essential questions:
(1) What are the basic definitions? The exact notion of niche has never agreed upon.
(2) What is the mathematical basis? When mechanistic modeling of specific population interactions made Lotka-Volterra looking obsolete, the hope for an all-encompassing mathematical theory was lost.
(3) What are the basic predictions? The original hint that coexisting species must be separated by their niche-width has never been clearly established even in the Lotka-Volterra context.
We provide a precise formulation of a framework theory for ecological niche by careful consideration of the necessary mathematical commonalities of species interaction models. The key point is that the Lotka-Volterra model can be seen as a linerazation of other models; one has to pay attention to time-scaling and other complications.
Results/Conclusions
(1) Straightforward generalization of the classical concepts works. Notion of resources is replaced by the notion of regulating factors: the environmental factors through which populations interact. Niche space is defined as a set of all regulating factors. Resource utilization function is replaced by the differential descriptors of the two-way interactions between the populations and the regulating factors: the population’s impact and sensitivity.
(2) These generalizations lead to a unified treatment of different kinds of niche segregation through considering robustness of coexistence against external perturbations. In particular, we discuss niche description of an arbitrary trophic network, treatment of structured populations with ontogenetic niche shift, spatial and temporal niche segregation. Connection to Chesson’s theory is provided.
(3) By and large, the original expectation for a minimal separation between niche positions, determined by the niche widths, prevails. There is no continuity between neutral and niche-based coexistence: While neutral coexistence is a possibility for species with identical physiology, neutrality, or near neutrality, of unrelated species is prohibitively unlikely. There are no such things as self-organized similarity, or emergent neutrality.
The empirically relevant conclusion of the framework is that one should always be interested in the ways the populations are regulated in a community.