Paper 31
Brown, J.H. 1984 On the relationship between abundance
and distribution of species. American Naturalist 124:255-279
Blog by Kaitlyn
Sullivan
Paper Author: James H. Brown
(Commentary by Christy M. McCain)
Christy M. McCain
· Ph.D. from University of Kansas
· Associate Professor and Curator of Vertebrates Dept.
of Ecology & Evolutionary Biology and University of Colorado Boulder
Natural History Museum
Research interests:
“I am interested in the mechanisms producing and
maintaining patterns of species distribution, abundance, and diversity. To
address these processes, I consider three levels of ecological organization to
be equally important: species-level autecology, population-level dynamics, and
community-level processes and interactions. My research so far has highlighted
small mammal range dynamics, abundance patterns across altitudinal ranges, and
species richness patterns along latitudinal and elevational gradients. I
particularly exploit mountain systems as natural experiments to look at how
evolutionary history, ecological processes, and future climate change influence
species populations. My overarching goal is to strive for quantitative, general
theories applicable to both the advancement of ecology and the improvement of
our conservation strategies. I use multiple tools at various spatial scales to
address research questions, including field studies, synthesis of collection
and historical data, comparative analyses, null models, GIS, and simulation modeling.”
James H. Brown
· Professor of Biology at the University of New Mexico
· Bachelor of Arts, Zoology, 1963, Cornell University
· Ph.D., Zoology, 1967, University of Michigan
Research Interests:
“Community ecology and biogeography, with special
projects on granivory in desert ecosystems; biogeography of insular habitats;
and structure of dynamics of geographic-scale assemblages of many species.”
Summary
His
paper examined the various patterns and theories surrounding “spatial variation
in abundance within species”. Using
various data, he demonstrates the greatest population density across a species
range occurs in the center and declines towards the range boundaries. He noted two assumptions in his explanation
for this.
1.
“a
species’ range corresponds to its environmental niche”
2.
“those
environmental niche variables are spatially autocorrelated.”
He
argued that for this to be true, then highest abundance should occur at the
center of the range as it provides optimal environmental conditions. He coined this the ‘abundant center’ pattern,
and claims it can be “defined by a normal probability density function”.
Secondly, his paper examined the
primary patterns and theories regarding positive correlation between abundance
and distribution of related species. He
argued that if species could gather enough resources to support a larger number
of individuals in an area, that species should also be able to sustain many
smaller populations in a large number of sites.
Species with similar niches, who are not able to gather as many
resources however, cannot support large populations and will be restricted to
fewer sites. His last assumption on
which his ideas were based, was that “similar and related species share
substantial portions of their niches”.
Brown poses his question: “Is there
any general pattern of spatial variation in abundance within the area in which
a species normally occurs?” Following this up with: “yes, density is greatest
near the center of the range and declines, usually gradually, toward the
boundaries”.
Questions:
-
In his summary, Brown argue that
“most exceptions to this predicted pattern can be explained as cases in which
assumptions of the model are clearly violated.”
What does he mean by this?
-
What implications has this had towards
other statistical models?
It's an interesting paper. I have a tendency whenever papers try to propose some sort of Grand Theory of Ecology (which seems to be a lot of macro papers) to gravitate towards the the exceptions. Both exceptions to the rule seem to be components of habitat fragmentation, which makes me think that today, with habitat loss being more severe now more than ever, that those exceptions aren't very exceptional. I don't know how this theory would work outside of the context of a null model.
ReplyDeleteVery interesting, especially in thinking about how important this paper was in framing current research in a wide variety of areas in ecology.
ReplyDeleteI think when Brown says that in his summary he means that any exceptions (or observations that deviate from the predicted pattern) are likely cases where an assumption in the model is being violated e.g. Brown mentions environmental patchiness as one exception, so perhaps an site that might have a variety of different habitat 'types' in an area?