Ecologj, 77(4), 1996, pp. 1163-1 173 O 1996 by the Ecological Society of America COVARIATION OF THERMAL BIOLOGY AND FORAGING MODE IN TWO MEDITERRANEAN LACERTID LIZARDS1 JOSABEL BELLIURE AND LUIS M. CARRASCAL Museo Nacional de Ciencias Naturales, Departamento Ecología Evolutiva, José Gutiérrez Abascal, 2, E-28006 Madrid, Spain JosÉ A. D~AZ Departamento Biología. Animal I (Vertebradosj, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain Abstract. Body temperatures, heat exchange rates, behavioral thermoregulation, and movement behavior (as an index of foraging mode) were studied in two widely distributed, medium-sized lacertid lizards (Acanthodactylus erythrurus and Psammodromus algirus). P. algirus mainly inhabits broad-leaved forests, whereas A. erythrurus prefers open, sandy areas with sparsely distributed vegetation. These habitat preferences parallel differences between the areas in which both genera presumably originated: Eurosaharian xeric steppes with high operative temperatures (Te) for Acanthodactylus, and Mediterranean open forests with lower Te for Psammodromus. Field observations showed that percentage of time spent basking and basking rate (number of basks per minute) were negatively related to Te, although average bask duration was not. Percentage of time spent moving, moving rate (number of moves per minute), and the average duration of individual moves were inversely related to Te and were higher in P. algirus. The percentage of total locomotion time that was spent moving in the shade was also higher in P. algirus. Behavioral thermoregulation strategies differed in a laboratory thermogradient, where P. algirus basked more often and for shorter periods and selected warmer patches than did A. erythrurus. Selected body temperatures (T,) in a laboratory thermogradient were significantly higher in A. erythrurus than in P. algirus. Shade Seeking T, was higher in A. erythrurus, but Resume Basking T, did not differ significantly between the two species. Heating and cooling rates also differed in the two species: A. erythrurus warmed more slowly and cooled faster than did P. algirus. Our data support the existence of a complex syndrome that combines aspects of the behavior, physiology, and ecology of both species. The thermal consequences of inhabiting a certain type of habitat can be counterbalanced by behavioral and physiological means that, in turn, affect movement and, hence, foraging behavior. Thus, the more active species (P. algirus) heated faster, cooled more slowly, and basked more often but for shorter periods and at warmer patches than the less active species (A. erythrurus). Key words: Acanthodactylus erythrurus; basking behavior; foraging mode; heat exchange rates; lacertids; Psammodromus algirus; selected body temperature; thermoregulation; western Mediterra- nean. Foraging modes, usually classified as sit-and-wait vs. widely foraging (Pianka 1966, Huey and Pianka 1981), according to the mobility of predators, are correlated with major differences in ecological (Eckhardt 1979, Huey and Pianka 1981), physiological (Anderson and Karasov 1981, Huey et al. 1984), life history (Vitt and Congdon 1978), and morphological (Webb 1984) char- acters. Foraging modes of lizards fit well into this di- chotomous view of foraging strategies (Pietruszka 1986, McLaughlin 1989). Widely foraging lizards have higher rates of energy expenditure and higher rates of food intake than do sit-and-wait species (Anderson and ' Manuscript received 6 January 1995; revised 13 August 1995; accepted 25 August 1995; final version received 25 September 1995. Address al1 correspondence to Luis M. Carrascal. ' Authorship follows alphabetic order. Karasov 1981); they show greater endurance but lower burst speed (Huey et al. 1984); their relative clutch mass is often lower (Vitt and Congdon 1978, Mag- nusson et al. 1985); and they eat more prey that are sedentary and clumped (e.g., termites) and fewer prey that are active (Huey and Pianka 1981, Magnusson et al. 1985). Since the pioneer demonstration by Cowles and Bo- gert (1944) that desert lizards behaviorally regulate their body temperature (T,), thermoregulation has come to be seen as a major aspect of reptilian ecology (Huey and Stevenson 1979, Huey 1982), with crucial effects on locomotion and foraging performance (Bennett 1980, Avery et al. 1982). However, there is no agree- ment in the literature about the ways in which move- ment behaviors influence, and are restricted by, ther- moregulatory behavior (but see Hillman 1969, Ander- son and Karasov 1988). Whereas some authors have