Ecology 62(3). 1981, pp. 515-521 ( 1981 by the Ecological Society of America COMPENSATION FOR ALTITUDINAL CHANGES IN THE THERMAL ENVIRONMENT BY SOME ANOLIS LIZARDS ON HISPANIOLA' PAUL E. HERTZ2 AND RAYMOND B. HUEY 3 Museum of Comparativoe Zoology, Harvard University, Cambridge, Massachusetts 02138 USA Abstract. Populations of the Anolis cybotes species group on Hispaniola behaviorally compen- sate for changes in the thermal environment associated with altitude. Lizards occupy more open habitats, increase basking frequency, and restrict times of activity at high elevation: a result is that the change in mean cloacal temperature with elevation is very small relative to that known for other anoles. In contrast to this large behavioral variation among populations, physiological differences appear to be minor. In this regard, the evbotes group has several parallels with the well-studied cristatellus group of Anolis on Puerto Rico. However, the cybotes group has no equivalent to Anolis gundlcahi, which employs physiological adaptations to compensate for different thermal environ- ments. Kev ivords: altitudinal variation; Anolis lizards; basking; behavioral thermoregulation; body temperature; critical thermal maximum; habitat shift; Hispaniola. INTRODUCTION Thermal environments change dramatically with al- titude (McCullough and Porter 1971). Lizards can compensate for such changes in several ways: long- and short-term shifts in regulatory behaviors (habitat selection, basking frequency, restriction of time of ac- tivity), physiological acclimatization, and genetic dif- ferentiation among populations (see Slobodkin and Rapoport 1974). Behavioral shifts are believed to be the primary compensatory mechanism in most lizards (Bogert 1949, Huey and Slatkin 1976), but few studies have examined the magnitude of the other responses (Spellerberg 1972a, b, c, Hertz 1977, 1980b, Hertz et al. 1979). Many West Indian lizards of the iguanid genus An- olis are abundant over a broad elevational range. Thus they are well suited for a study of responses to altitu- dinal changes in the thermal environment. Moreover, independently derived species groups occur on each of the Greater Antilles (Williams 1976). Therefore, one can identify general patterns of both altitudinal distri- butions and associated responses. Here we consider the thermal biology of several populations of the Anolis cybotes species group along a 2200-m altitudinal transect in Hispaniola. We ex- amine changes in apparent thermoregulatory behav- iors and in physiology and find that behavior rather than physiology appears to be the primary compen- satory mechanism. (The extent of genetic differentia- tion, as estimated by morphological and electropho- ' Manuscript received 17 October 1979; revised I Septem- ber 1980; accepted 17 September 1980. 2 Present address: Department of Biological Sciences, Bar- nard College, Columbia University, New York, New York 10027 USA. : Present address: Department of Zoology NJ-15, Univer- sity of Washington, Seattle, Washington 98195 USA. retic studies, will be treated separately.) We also compare present results with similar data on other an- oles-in particular, the related A. cristatellus species group on Puerto Rico (Wyles and Gorman 1980)-to determine the general applicability of our findings for this lizard genus. Anoles of the cybotes species group are small liz- ards (maximum snout-to-vent length 65 mm) that perch on the lower parts of tree trunks and sometimes on rocks or on the ground. Most species have restrict- ed distributions (e.g., A. Iongitibialis in lowland desert scrub and A. shrevei in high mountain grasslands), but one, A. cybotes, occurs in diverse habitats and from sea level to 1200 m elevation (Schwartz and Thomas 1975). MATERIALS AND METHODS During visits to the Dominican Republic in the sum- mers of 1974 and 1976 (total work time = 10 observer wk), we collected data on 278 cybotes from three pri- mary localities: a relatively closed-canopy, xeric coastal forest (near Playa Saladilla, 2 km south of Bar- ahona, Barahona Province, 5 m elevation); a lush, mid- dle-elevation woodland (0.2 km northeast of Sabana Larga, Peravia Province, 550 m elevation); and a high- ly developed agricultural habitat (Palera, Valle Con- stanza, La Vega Province, 1150 m elevation); and on 42 shrevei from a mountaintop pine savanna (Valle Nuevo, Peravia Province, 2200 m elevation). We col- lected smaller secondary samples on cybotes from three disturbed habitats (near Jarabacoa, La Vega Province, 520 m elevation; the Hotel Montafia, La Vega Province, 660 m elevation; near Polo, Barahona Province, 700 m elevation) as well as a sample of lon- gitibialis from desert scrub (near Cabo Rojo, Peder- nales Province, 5 m elevation). To describe the diurnal thermal biology of the liz- ards in our primary samples, we captured active sub-