Macroecology

Although some ecological processes can be best understood by studying interactions among species at local scales, some patterns emerge only at broad spatial or temporal extents.  Macroecology (Brown and Maurer 1989) is an approach to ecology that explicitly examines broad-scale patterns in abundance, diversity, or distribution of species.

I’m interested in these broad-scale patterns, particularly those involving biodiversity, and whether they are driven by important biological processes or are statistical artifacts. 

Brown, J.H and B.A. Maurer.  1989.  Macroecology:  the division of food and space among species on continents.  Science 243:1145-1150.

Recent and ongoing projects:

·        Latitudinal gradients of species richness:  a test of the geographic area hypothesis

The geographic area hypothesis advances area as the primary cause of latitudinal gradients in diversity.  The greater area of tropical zones, it suggests, stimulates speciation, inhibits extinction, and leads to increased species richness compared to the situation in smaller temperate and boreal zones.  Dr. Michael Willig and I estimated species richness of New World bats in biogeographic zones at two spatial scales and evaluated the ability of area to account for latitudinal gradients in species richness.  Although the latitudinal gradient of species richness is strong and significant for New World bats at both ecogeographic scales, area does not drive the pattern.  In fact, area represents a source of noise rather than a dominant signal at the focal scale of biome types and provinces in the Western Hemisphere.

Willig, M.R., and C.P. Bloch.  2006.  Latitudinal gradients in species richness:  a test of the geographic area hypothesis for New World bats.  Oikos 112:163-173.

·        Macroecology of Caribbean bats

The Caribbean Basin is a hotspot of biodiversity and a significant challenge for conservation planning because of political, social, and geographic considerations, as well as because of the extent of habitat modification and fragmentation that characterizes most islands.  Bats are the dominant components of the native mammal fauna on islands of the Caribbean, and they may represent keystone species because of their role in seed dispersal and flower pollination, especially after disturbance.  Despite considerable variation in species richness among islands, bat assemblages in the Caribbean form distinct clusters based on species composition that correspond to the Bahamas, Greater Antilles, and Lesser Antilles.  Through a variety of statistical approaches, colleagues and I quantified the effect of a suite of environmental characteristics (i.e., island area, elevation, latitude, hurricane-related disturbance, and inter-island distances) on bat species richness and guild richness.  In general, island area and maximum elevation are confounded because of their positive correlation.  One or both consistently enhanced aspects of biodiversity, whereas latitude, hurricane-related disturbance, and inter-island distance had little effect on taxonomic or functional aspects of biodiversity.

Willig, M.R., S.J. Presley, C.P. Bloch, and H.H. Genoways.  2010.  Macroecology of Caribbean bats: effects of area, elevation, latitude, and hurricane-induced disturbance.  Pp. 216-264 in Island Bats:  Evolution, Ecology, and Conservation (T. Fleming and P. Racey, Eds.).  University of Chicago Press, Chicago, IL.

·        Biodiversity and ecosystem processes

Because biodiversity is imperiled worldwide, ecologists increasingly are interested in the factors that determine the diversity of particular systems.  Such questions are particularly important in arid ecosystems, where desertification is occurring at a rapid rate.  Several colleagues and I examined a 9-year data set from the Jornada LTER to evaluate how primary productivity influenced species richness of plants.  Productivity was a weak predictor of richness, suggesting that instead of determining diversity, productivity might merely set an upper limit on diversity.  The actual level of diversity attained at any given site, within this constraint, may depend on non-resource factors such as pH, soil salinity, soil type, and history.

Cox, S.B., C.P. Bloch, R.D. Stevens, and L.F. Huenneke.  2006.  Productivity and species richness in an arid ecosystem: a long-term perspective.  Plant Ecology 186:1-12.