Delineating the ecological niche to predict competitive outcomes and the influence of evolution

Abstract

Concerns with global and localized environmental change have increased interest in the course and outcomes of evolution as populations adapt to changing resource availability. Interest in populations often focuses on competitive outcomes under forcing or subsequent changes of resource availability. Changes of resource availability may be the supply of one resource in contrast to another—implicitly a change of supply ratio—or explicitly a change in the supply ratio of a pair of resources. Existing models of populations’ contention for resources generally focus on development and competition over time assuming constant population characteristics, known initial states, and predictable future environmental states. We describe a simpler model to analyze evolution of populations’ resource response characteristics under specific constraints and to predict expected competitive outcomes under a wide range of potential subsequent resource supplies. We have developed, tested and applied a model of expected competitive outcomes in contention for multiple resources. We have analyzed changes of populations’ requirements niches resulting from evolution in resource-limited ecological regimes. We have shown that evolution in one ecological regime not only shifts a population’s requirements niche toward greater fitness in that regime but can also shift the niche toward unexpected greater or lesser fitness in other regimes. A population is formulated by its intrinsic growth response as a function of population-common and per-resource organismal growth response traits. The trait parameters are determined by curve fitting from demographic observations by a new Characterization Protocol. Competition is modeled in a Hutchinsonian space of resource supplies. Expected competitive outcomes are reported as per- and inter-population intrinsic growth rates throughout resource supply space. Results are displayed in qualitative and quantitative graphic forms and tabulated quantitative values of populations’ response parameters. We have applied our model to populations descended from a common ancestor in regimes of complementary restriction of two essential resources. Our model detects expected, unexpected and cryptic response trait changes and predicts intuitive and non-intuitive competitive relationships that can result from those changes in the event that any combination of ancestor, descendantsor any other characterized population should come into competition anywhere in the resource supply space.