Peaks, plateaus, canyons, and craters: The complex geometry of simple mid-domain effect models
Research output: Contribution to journal › Journal article › Research › peer-review
Robert K. Colwell, Nicholas J. Gotelli, Carsten Rahbek, Gary L. Entsminger, Catherine Farrell, Gary R. Graves
Background: Geographic ranges, randomly located within a bounded geographical domain,Geographic ranges, randomly located within a bounded geographical domain,
produce a central hump of species richness (the mid-domain effect, MDE). The hump arises
from geometric constraints on the location of ranges, especially larger ones.
Questions: (1) How do patterns of species richness in one- and two-dimensional MDE(1) How do patterns of species richness in one- and two-dimensional MDE
models change as a function of range size? (2) How does dispersal affect these patterns?
Methods: We used a spreading dye algorithm to place assemblages of species of uniformWe used a spreading dye algorithm to place assemblages of species of uniform
range size in one-dimensional or two-dimensional bounded domains. In some models, we
allowed dispersal to introduce range discontinuity.
Results: As uniform range size increases from small to medium, a flat pattern of speciesAs uniform range size increases from small to medium, a flat pattern of species
richness is replaced by a pair of peripheral peaks, separated by a valley (one-dimensional
models), or by a cratered ring (two-dimensional models) of species richness. With large range
sizes, the peaks or rings fuse to form a central plateau (one-dimensional) or a flat-topped
mound (two-dimensional) of highest species richness. Adding dispersal to the two-dimensional
model weakens the peripheral ring and introduces complex patterns for long-distance dispersal.
Conclusions: Heterogeneous range size distributions (whether theoretical or empirical) usedHeterogeneous range size distributions (whether theoretical or empirical) used
in most MDE models produce species richness patterns dominated by wide-ranged species,
hiding complex patterns formed by small- to medium-ranged species. These patterns, which are
analogous for one and two dimensions, are complicated further by long-distance dispersal and
discontinuous ranges. Although geometric constraints lead to classic mid-domain effects for
large-ranged species and for mixed range-size frequency distributions, small- and medium-sized
ranges of a uniform size generate more complex patterns, including peaks, plateaus, canyons,
and craters of species richness.
|Journal||Evolutionary Ecology Research|
|Publication status||Published - 2009|
Keywords: biogeography, boundary effects, doughnut, geographical range, geometric
constraints, null models, spatial scale, species richness gradients, stochastic models.