How Much Should the Hutchinson Ratio Be and Why?

• Published in: Oikos 1999-10, Vol.87 (1), p.201-203
• Main Authors: Ganeshaiah, K. N., Kumar, A. R. V., Chandrashekara, K.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Bats; Biological and medical sciences; Correlations; Ecological competition; Forum; Fundamental and applied biological sciences. Psychology; General aspects; Hawks; Insect morphology; Population ecology; Population growth; Synecology
• ISSN: 0030-1299; 1600-0706
• DOI: 10.2307/3547014

While addressing the question "Why are there so many kinds of animals?" Hutchinson suggested a process of how species competing for a common resource spectrum could co-exist (Hutchinson 1959). He proposed that a certain extent of morphological displacement in the harvesting organ (character displacement) of two closely competing species leads to a relatively, non-competitive sharing of their common resource pool facilitating their coexistence. Such a process obviously sets limits on the similarity among the characters of the closely competing species. Expressing these limits of similarity as the ratio of body size or of the trophic organs of the larger to that of the smaller of the competing species, he suggested that typically this ratio (HR for Hutchinson ratio, henceforth) could be 1:1.3. Although the flurry of literature that followed confirmed that these ratios occur within a certain range, they were not consistent across guilds and were not always 1:1.3 (Simberloff and Boecklen 1981). Several workers have developed arguments to show the dependence of HR on guild size and variance of resource use organs (reviewed by Schoener 1986, Yom-Tov 1993, Dayan and Simberloff 1994). In this paper, based on minimal assumptions, we show that HR is a function of a) the number of competing species in a community and b) the variances of their traits or characters involved in harvesting. We provide evidence in support of our argument.