Great Basin Naturalist Memoirs Volume 7 Biology of Desert Rodents Article 3 8-1-1983 Desert rodent adaptation and community structure Michael A. Mares Stovall Museum, University of Oklahoma, Norman, Oklahoma 73019 Follow this and additional works at: https://scholarsarchive.byu.edu/gbnm Recommended Citation Mares, Michael A. (1983) "Desert rodent adaptation and community structure," Great Basin Naturalist Memoirs: Vol. 7 , Article 3. Available at: https://scholarsarchive.byu.edu/gbnm/vol7/iss1/3 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist Memoirs by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. DESERT RODENT ADAPTATION AND COMMUNITY STRUCTURE' Michael A. Mares- Abstrac:t.— Desert rodent communities are compared for evidence of convergent evolution at various levels of or- ganization, including the systemic (physiological, anatomical, etc.), autecological, and synecological. Convergence is quite pronounced at the systemic level, less pronounced at the autecological level, and even less detectable at the svnecological level. This is not to imply that community convergence does not occur, but rather that our current abilities to quantify and detect convergence at the community level are nidimentary— and our data base is still far from adequate to the task of rigorously comparing community attributes. Most research on the ecology, behavior, physiology, and community structure of desert rodents has been conducted on North American species inhabiting deserts of the United States. The patterns of species coexistence that have been elucidated in these deserts are often presumed to apply in other deserts of the world. It has become apparent in recent years, however, that the complex North .American desert system is unique in many ways, perhaps especially in the biogeographic history of its habitats and faunas, from most of the other deserts of the world. The North American deserts offer an unusually diverse fauna of desert rodents (both alpha and beta diversity are high) which evidences patterns of distribution and coexistence that excite biologists working with the mechanisms of competitive interactions. Similar studies carried out in other deserts might very well lead to a different set of ideas concerning the ways in which desert rodents manage to coex- ist and how desert communities develop over time. The present paper is an attempt to compare community struc- ture and development as well as patterns of coexistence among the various faunas of desert rodents of the world. Al- though data are sketchy for many areas, sufficient information is available to allow a preliminary comparison of methods of adaptation and coexistence to be made. Research on desert rodents began over a dents to arid environments; this research was century ago in the United States. The earHest greatly stimulated by the studies of the studies examining desert rodents were those Schmidt-Nielsens (see Schmidt-Nielsen 1964, of Coues (e.g., 1868), Coues and Allen (1877), for a review), who showed convincingly that and C. Hart Merriani and his team of in- some small mammals were well adapted vestigators from the old Biological Survey. In physiologically to pronounced aridity. Later addition to the taxonomic investigations of research has allowed a finer resolution of the Merriam himself (e.g., Merriam 1889) and mechanisms of physiological adaptation to those of his subordinates (e.g., Osgood 1900, deserts (e.g., McNab and Morrison 1963, Goldman 1911, Howell 1938), there were MacMillen 1964a, 1964b, 1972, Hudson other .studies by contemporaries of the survey 1964a, Chew 1965, Carpenter 1966, Brown scientists (e.g., Grinnell 1932, Benson 1933, 1968, Brown and Bartholomew 1969, Mullen Blos.som 1933, Hall and Dale 1939). After the 1971, Abbott 1971, Whitford and Conley initial work had formed a rather firm tax- 1971, Maxson and Morton 1974, Baudinette onomic foundation, field research entered the 1974). stage of natural historical, ecological, and Within the last 15 years, desert research in biogeographical .studies (e.g., Taylor and Vor- the United States has centered on problems hies 1923, Bailey 1931, Benson 1935, Dice dealing with species coexistence. It has long and Blos.som 1937, Blair 1943, Monson and been remarked that the deserts of the United Ke.s-sler 1940, Tappe 1941, Fitch 1948). Al- States support a broad diversity of species, though ecological and taxonomic in- but only since the mid-1960s have research- vestigations continued during the mid- ers attempted both to understand the causa- twentieth century, much research was cen- tive agents of this diversity as well as the tered on the physiological adaptations of ro- mechanisms of species coexistence. Earlier 'From Ihc symposium "Biology of Desert Rodents," presented at the annual meeting of the American Society of Mammalogists. hosted In Brigham Young • » . University, 20-24 June 1982. at Snowbird. Utah. 'Stovall Museum, University of Oklahoma, Norman, Oklahoma 73019. 30 1983 Biology of Desert Rodents 31 studies of coexistence had examined the pos- Since ecologists tend to extrapolate the re- sible roles of abiotic factors on species distri- sults of research carried on in one biome to bution patterns (e.g., Hardy 1945), but later other areas supporting apparently similar research has focused on the role of inter- ecosystems, it is tempting to believe that as specific competition as a possible determi- we explain patterns of coexistence or adapta- nant of distributional patterns (see Brown et tion within the deserts of the United States al. 1979, for a review). Research emphasis we will have described these patterns for over the last decade has centered on the body deserts around the world. As MacArthur sizes of coexisting rodent species (e.g., Brown (1972:1) noted, "To do science is to search 1973, Brown 1975, Bowers and Brown 1982), for repeated patterns." In this brief essay I the sizes of seeds taken by granivorous ro- will characterize the patterns of adaptation dents (e.g.. Brown and Lieberman 1973, of desert rodents that have been described Mares and Williams 1977), the distribution of largely within the conterminous United the seed resource in the desert and whether States. Realizing full well that "natural selec or not clumped seeds are favored by bipedal tion depends for its effectiveness on a series of chances" (Leigh 1971:221), I believe it is species (e.g., Reichman and Oberstein 1977, important to local Wondolleck 1978, Price 1978, Hutto 1978, distinguish between pat- terns and those of a global nature. Perhaps all Trombulack and Kenagy 1980), and on the important questions regarding life in deserts importance of microhabitat selection in can be answered by studying intensively one maintaining coexistence (e.g., Rosenzweig particular geographic unit—then again, per- 1973, 1977, 1979, Rosenzweig et al. 1975, haps not. If all deserts are not equal, a very Schroder and Rosenzweig 1975, Lemen and real problem develops in discovering which Rosenzweig 1978). patterns are truly generalizable. Each of these areas of research is con- troversial. For example, Lemen (1978) has strongly criticized the proposed seed The Patterns size-body size relationship, and support for The first problem that presents itself is that his position can be garnered from Stamp and of scale—does one seek patterns at the level Ohmart (1978), M'Closkey (1978), and others. of biochemical reactions, organ systems, or Ekrly indications that bipedal rodents are communities? The second problem is that of able to travel greater distances more rapidly confounding causation. Does bipedality de- and at lower energetic costs than quad- velop, for example, because of intrinsic prob- rupedal species (e.g., Dawson 1976) have lems related to integrated locomotor design been shown to be in error (Thompson et al. (e.g., Alexander 1975), or do such seemingly 1980), thus casting doubt on the validity of a unrelated factors as seed distributions, gran- linchpin in the theory relating locomotor ivory, predator avoidance, and substrate all mode (bipedality) to the habit of foraging on play a part in the selection of a particular widely dispersed seed clumps (see also Frye type of movement? Although it is easy to be- and Rosenzweig 1980). Evidence for body come overwhelmed by the complexity of size differences among coexisting competitors desert rodent adaptations, I will limit my has been challenged by Conner and Sim- analysis to characteristics above the purely berloff (1979) and Rebar and Conley (in biochemical level. This broad brush approach press). Even the basic premise that com- will give an overview of adaptations of desert petition has helped mold desert rodent com- rodents from the United States and will com- munities (Brown Munger and Brown 1976, pare these with rodents from other parts of has hypothesis that 1981) been shown to be a the world that have also successfully made is testable only the greatest difficulty, if with the transition to desert life. I will in essence it can be unambiguously tested at all (e.g., be assessing the available literature on desert Rosenzweig 1981). rodent biology for examples of convergence, The many basic studies done in the arid "the strongest sort of evidence for the effi- portions of the United States have made this cacy of selection and for its adaptive orienta- region one of the best studied areas on earth. tion of evolution" (Simpson 1953:171). 32 Great Basin Naturalist Memoirs No. 7 Physiological Adaptations Not all rodents inhabiting North American arid areas are desert specialists (e.g., Lee Water Balance—North America 1963, Andersen 1973, MacMillen and Chris- topher 1975). Although it is clear that the Perhaps one of the most widely known ability to withstand water deprivation has a traits of small mammals in desert regions is strong phylogenetic component (e.g., Hudson the ability to withstand water deprivation.