Week 2: Macroecology before Macroecology - cont

Nick Freymueller

Paper for Tuesday – A theoretical ecological model of size distributions among species of animals (1959)

Commentary Author: Morgan Ernest @ University of Florida

            Morgan Ernest is a professor who specializes in researching how communities respond to fluctuations in climate, habitat, and dominant species. Like Ethan White, she received her Ph.D. from UNM, and was at Utah State until recently. Her main research interests lie in using datasets to answer the questions pertaining to large scale ecological disturbances.

Paper Author: G. Evelyn Hutchinson and Robert MacArthur

            G. Evelyn Hutchinson was an England-born ecologist who spent the majority of his career at Yale. He is considered the father of modern ecology. He is noted for building on, and expanding Charles Elton and Joseph Grinnell’s early ideas of niche theory, where be brought together fundamental and realized niches. He also began noting the threat of climate change three decades before it gained steam in the mainstream

            Robert MacArthur was Hutchinson’s doctoral student at Yale. He was one of the first people to study niche partitioning, and he also worked with E. O. Wilson on the 1967 book The Theory of Island Biogeography. He taught at the University of Pennsylvania for seven years, and then moved on to Princeton for seven more years, where he died of renal cancer at age 42.

Cliff Notes:

1.)   “How do size distributions vary by species?”

2.)   Hutchinson and MacArthur developed a mathematical model for how species of various sizes might use a varying number of ecological elements. They then applied the model to all sorts of taxa, but most notably mammals of Western Europe and the American Midwest.

3.)   They found that there are very few species that are very small. However, as body size increases, there is a rapid increase in the number of species as body size increases. After that, there is a long, asymptotic decline of the number of species in the function as body size continues to increase; leading to the body size distributions of species appearing to follow a positive-skewed, or right-tailed, distribution.

4.)   Hutchinson’s and MacArthur’s findings seem to mean that larger animals require a greater number of ecological elements to be successful. This is evidenced near the end of the opening paragraph, where Hutchinson and MacArthur state: “A large ungulate may require a water hole, a grazing area, and some degree of cover; the wet marginal area of the water hole, the grazing area, and the cover might provide specific biotypes for three species of rodents.”

5.)   This approach has since been applied to other clades of animals, and researchers have found that other groups (e.g. birds, plants, and others) also seem to fit this distribution reasonably well. The ecological origin of this distribution phenotype is still somewhat unclear, but it may have to do with size-specific extinction or speciation (see Fig. 2 from Dial & Marzluff 1988; cited in the commentary).