NO. 3597 RODENT ETHOLOGY — EISENBERG 5 



adapted genera, Peroijnathus, Micvodipodops, and Dipodomys (Eiseii- 

 berg, 1963b). The results combined with the Pero)nyscus data sug- 

 gested that any limiting factors a desert environment may impose 

 concerning space reciuirements of a given individual rodent are not 

 necessarily limiting with respect to the particular species-specific form 

 of the social organization. 



To confirm this hypothesis, two Old World taxa of desert-adapted 

 rodents were studied, the Gerbillinae and the Dipodidae. Table 1 

 contains a list of the specimens included in this study with their 

 geographical origins. Exact capture localities for specimens trapped 

 by the author are uicluded in previous publications (Eisenberg, 

 1962a, 1963a, b). 



Adai)tation to an arid en^^ronment involves the solution of several 

 severe physical problems including (1) lack of ^^"ater, (2) widely spaced 

 food plants with concomitant loss of cover, (3) extremes of heat and 

 cold. The behavioral, morphological, and physiological solutions to 

 these problems are varied when the vertebrates are surveyed as a group 

 (Schmidt-Nielsen, 1964), but all mechanisms are geared to the same 

 ends: maintenance of a constant body temperature (at least during 

 active periods), conservation of body fluids, and procurement of suffi- 

 cient food. A number of small desert rodents have adapted in a simi- 

 lar fashion, providing typical instances of parallel physiological or 

 behavioral evolution. For example, some species of the gerbilline, 

 dipodid, and heteromyid rodents can recover metabolic water in the 

 kidney and live on dry foods alone (Burns, 1956; Kirmiz, 1962; 

 Schmidt-Nielsen, 1964). Furthermore, many desert rodents are 

 nocturnal, construct burrows that are plugged during the day, and 

 cache quantities of food. In several cases bipedal locomotion has 

 evolved (e.g., within the Heteromyidae and the Dipodidae). 



None of these behavioral attributes is confined to desert-dwelling 

 species, but the total complex of attributes is unique to a certain type 

 of desert-dwelling form (Eisenberg, 1963b). Within the genus 

 Peromyscus, desert adaptation has taken place without the evolution 

 of either bipedality or the ability to reuse metabolic water. The 

 family Heteromyidae exhibits a range of morphological adaptations to 

 a desert environment wherein only the genera Microdipodops and 

 Dipodomys culminate their evf)lution \\\\\\ both an extremely special- 

 ized gross mori^hology and the ability to live on metabolic water alone 

 (Eisenberg, 1963b). 



Confronted with such a range of adaptations to the same set of 

 ])roblems in the desert, any correlation between behavior and ecology 

 must take cognizance of the multiplicity of variables affecting the 

 overall adaptation pattern. For this reason, tables 2 tkrough 5 

 summarize the niajor similarities and divergences regarding reproduc- 



