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Ecological Gradients in Diversity and Abundance: A Search for Patterns and Processes in Small Mammal Communities
McCain, Christy M.
McCain, Christy M.
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Abstract
One of the most fundamental questions in ecology is: what are the patterns of
diversity and the mechanisms that produce them? Many biological theories have
been proposed to explain latitudinal and elevational diversity gradients, but no
accepted, general explanation for the distribution of biodiversity has surfaced. Two
necessities for establishing a general diversity theory are utilizing more rigorous
statistical methods to test hypotheses, and including more comparative analyses.
With these aims in mind, I examine the predictability of null models and biological
diversity hypotheses for latitudinal and elevational gradients in diversity and
abundance of small mammals. The unimodal distribution of diversity in North
American desert rodents was highly consistent with the mid-domain effect—a spatial
constraint null model incorporating the overlap of variably sized ranges within a
bounded region. Deviations from the null model demonstrated a localized pulse in
richness caused by a local hard boundary, the Baja peninsula. The small mammal
diversity along an elevational transect in Costa Rica was unimodal with species
richness highest between 1000-1300 m. The spatial constraints of montane
topography appear to influence the diversity pattern, although climatic conditions
including an intermediate rainfall and temperature regime, and distance from the
persistent cloud cap also are correlated with the pattern. The global analysis of
elevational diversity trends for non-volant small mammals revealed a ubiquitous
pattern of mid-elevational peaks in species richness. The mid-domain null model was
not generally predictive across all datasets. Diversity peaks occurred at higher
elevations on taller mountains (Massenerhebung effect), which is consistent with
climatic factors working in concert to produce elevationally correlated habitat bands.
Gamma diversity patterns demonstrated higher altitudinal peaks in species diversity
as latitude increased. An examination of replicates in alpha diversity studies along
elevational transects found high variability both temporally and spatially,
emphasizing the necessity of replication in well-designed studies of diversity
gradients. In an examination of range size-abundance trends no strong relationship
was found between abundance or body size with elevational range size. Local and
regional abundances across elevational ranges generally revealed a trend toward
higher abundances at mid-range, although usually not centered at the range midpoint.
Description
The University of Kansas has long historical connections with Central America and the many Central
Americans who have earned graduate degrees at KU. This work is part of the Central American Theses
and Dissertations collection in KU ScholarWorks and is being made freely available with permission of the
author through the efforts of Professor Emeritus Charles Stansifer of the History department and the staff of
the Scholarly Communications program at the University of Kansas Libraries’ Center for Digital Scholarship.
Date
2003
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University of Kansas