Bringing the Hutchinsonian niche into the 21st century: ecological and evolutionary perspectives

Abstract

G. Evelyn Hutchinson more than a half century ago proposed that one could characterize the ecological niche of a species as an abstract mapping of population dynamics onto an environmental space, the axes of which are abiotic and biotic factors that influence birth and death rates. If a habitat has conditions within a species' niche, a population should persist without immigration from external sources, whereas if conditions are outside the niche, it faces extinction. Analyses of species' niches are essential to understanding controls on species' geographical range limits and how these limits might shift in our rapidly changing world. Recent developments in ecology and evolutionary biology suggest it is time to revisit and refine Hutchinson's niche concept. After reviewing techniques for quantifying niches, I examine subtleties that arise because of impacts species have on their own environments, the density-dependent modulation of how individuals experience environments, and the interplay of dispersal and temporal heterogeneity in determining population persistence. Moreover, the evolutionary record over all time scales reveals a spectrum of rates of change in species' niches, from rapid niche evolution to profound niche conservatism. Substantial challenges revolving around the evolutionary dimension of the Hutchinsonian niche include quantifying the magnitude of evolved intraspecific and clade-level variation in niches and understanding the factors that govern where along the spectrum of potential evolutionary rates any given lineage lies. A growing body of theory provides elements of a conceptual framework for understanding niche conservatism and evolution, paving the way for an evolutionary theory of the niche.

Fig. 1.

The niche and population dynamics. (A) Experimental niche model for a beetle, Calandra oryzae (L): intrinsic growth rate at different temperature and moisture values (9). The isopleth r = 0 defines the niche boundary. Site X is in the niche; sites Y and Z are not. (B) Per-capita growth rate at three locations along a gradient, expressed as functions of local density. Growth is logistic; without movement, maximal growth rate is at n = 0, and equilibrium is at carrying capacity K (black dots). Sites 1 and 2 are within the range; site 3 is outside of the range. Adding constant dispersal shifts local abundances toward the white dots; high-K sites are lowered (site 1); low-K sites (e.g., site 2) are raised above K (growth rate is negative; such sites are called “pseudosinks”); and sites (e.g., site 3) outside the niche sustain sink populations. (C) Allee effects along gradient. At low N, per-capita growth rate increases with N (this could be direct density dependence or indirect density dependence with short time lags). Site 2 has a positive, locally stable equilibrium; a population can persist even if it cannot increase when rare. Site 2 is within the population persistence niche, but outside of the establishment niche. (D) (Upper) Alternative local dynamics with Allee effects. (Lower) Local dynamics given niche destruction.

Fig. 2.

Alternative niche concepts. (A) With Allee effects, the population persistence niche > the establishment niche. (B) With niche destruction, sites with a high initial growth rate are vulnerable to extinction, so lie outside of the population persistence niche, along these axes. In plant ecology, the term persistence niche is sometimes used to denote the role of individual adult survival through disturbances in permitting population persistence, for populations that have already established (90). I am using the term population persistence niche more broadly, to emphasize distinct aspects of the niche at the population rather than individual level. (C) The evolutionary niche. This figure (adapted from ref. 64) can describe many scenarios: (i) a species with geographic variation among niches of local populations; (ii) frames of a species over time, with niches wandering over its history within broad limits (bounded niche evolution); (iii) aggregate niche of a clade, with specialists descended from an ancestral generalist; and (iv) an adaptive radiation, where from an ancestral specialist (not shown) a clade collectively wanders through much more niche space than represented in any species.