Measurements of whole-organism performance traits have been useful in studies of adaptation and phenotypeenvironment correlations. Bite force capacities may be tightly linked to both the type and magnitude of the ecological challenges of food acquisition, mate acquisition, and antipredation in vertebrates. In the present study, we present technical details on bite meters and on measuring bite forces. The ability to take reliable measurements depends on specific features of the measuring device and on where in the mouth the bite is applied. Using both previously available and original data, we demonstrate several ecologically and evolutionarily relevant features of bite force measurements. First, maximal bite forces are repeatable among individuals across all vertebrates studied to date. Second, in ectotherms such as lizards, maximal bite forces are affected by body temperature and motivational states. Third, bite forces are strongly correlated with head size and shape. Fourth, bite forces correlate with features of prey of vertebrates. Finally, bite forces are linked to male dominance and correlated with social-display structures. Thus, bite force performance measures can be used as 'traits', and thus be used in integrative studies at multiple levels of organismal biology. Accordingly, bite force data will help our understanding of the functions, capacities, and evolution of jaw-cranial musculoskeletal systems. Moreover, a plethora of opportunities exist for the use of bite force measurements, and if methods are carefully applied, several levels of organismal and ecological organization can be integrated to aid our understanding of the ecology and evolution of vertebrate taxa. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 709-720. ADDITIONAL KEYWORDS: diet -male-male combat -sexual dimorphism. INTRODUCTIONMulticellular organisms are the sum of integrated form-function complexes (Bock & von Wahlert, 1965). Comparisons among animals varying in formfunction complexes for their relative abilities to perform ecologically relevant tasks (e.g. evading predators and capturing prey, sensu Huey & Stevenson, 1979) enhance our understanding of the evolution of the enormous morphological diversity of animals (Arnold, 1983;Wainwright, 1991). Locomotor performance traits, for example, have been useful tools for analysing the design, function, and evolution of locomotor systems in vertebrates (Irschick & Garland, 2001). Furthermore, analyses of locomotor performance traits have provided insights into our understanding of evolutionary and functional tradeoffs and their roles in the evolution of phenotypic variation (Vanhooydonck, Van Damme & Aerts, 2001;Van Damme et al., 2002).Similarly, performance measures associated with the vertebrate jaw system provide insights with respect to vertebrate ecology and evolution. The jawcranial musculoskeletal system is a hallmark formfunction complex of vertebrates, used to capture, subdue, and orally process prey, and to obtain mates (Motta & ...

The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.

Daily energy metabolism and water flux were measured with doubly labeled water in the free-living insectivorous lizards Cnemidophorus tigris (mean body mass 15.7 g) and Callisaurus draconoides (8.6 g) in June 1979 in the Colorado Desert of California. C. tigris was an active forager; it spent 91% of its 5-h daily activity period in movement. C. draconoides was a sit-and-wait predator; it spent less than 2% of its 10-h activity period in movement. C. tigris had significantly higher rates of field energy metabolism and water influx (210 Jg day, 36.8 ul HO g day, N=19) than C. draconoides (136, 17.1, N=18). There were no significant differences between the sexes within either species.The extra costs of free existence were calculated from differences between field metabolic rates and maintenance costs estimated from laboratory respirometry. Rates of energy metabolism during the field activity period were about 1.5x resting levels at 40° C (∼field active body temperature) for C. draconoides and 3.3 x resting levels at 40° C (∼field active body temperature) for the more active C. tigris. Feeding rates calculated from water influx data were 13.3 mg g day for C. tigris and 5.8 mg g day for C. draconoides. Though C. tigris had a high rate of energy expenditure, its foraging efficiency [Formula: see text] was higher than C. draconoides'.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract. Cnemidophorus hyperythrus, a small (z4-g) teiid lizard, occurs along an elevational thorn scrub-thorn woodland-thorn forest habitat gradient in the cape region of Baja California. We compared body size, daily energy expenditure (DEE, measured with doubly labeled water), relative feeding rate (as reflected by H20 influx rate), behavior, and abundance of this species at two sites along the gradient. At the inland thorn woodland site C. hyperythrus were more abundant (; 100 lizards/ha) than at the thorn scrub site near the ocean (I 50 lizards/ha). Mean body mass of woodland site lizards was 13% greater than that of scrub lizards. The DEE of the thorn woodland lizards, 330 J g-1 ld-l, and their H20 influx, 99 mm3 g-l d-, were also higher than the thorn scrub lizards', 219 J g-l d-I and 52 mm3 g-l dl. Diets at the two sites were similar. There were no differences between sexes in diet, DEE, or H20 influx.Daily maintenance energy costs were calculated based upon laboratory measures of 02 consumption of resting lizards at a series of temperatures that represented the daily range of body temperatures experienced by lizards in the field. Activity costs (=DEE minus maintenance) were three times higher in the woodland lizards. Behavioral observations showed that woodland lizards were active most of the day (z9 h/d) whereas scrub lizards were active primarily in the morning (z3.5 h/d). Thus, the higher activity cost, DEE, and feeding rate of woodland lizards can be explained by their longer daily activity period. We suggest causal factors for the difference in daily activity period, and discuss implications of length of daily foraging period for adult body size, population density, and various life history parameters of lizards.

Energy budgets for the wide-foraging "arthropodivorous" lizard Cnemidophorus tigris were constructed for the reproductive season using doubly labeled water measurements of field metabolic rate (FMR). Rates ofbody mass change, clutch sizes, and clutch intervals were also investigated. FMRs ofboth sexes (males, 298 J ·g-1 ·d-1 ; females, 24 7 J · g-1 • d -1 ) were greater in the reproductive season than during the postreproductive season. This was not due to differences in resting metabolism, but, instead, was due to higher activity costs during the reproductive season. Although males had signficantly higher FMR than females, males and females had similar feeding rates (as reflected by water influx rates). The ratio of energy intake to expenditure was higher in females than in males. Females produced eggs but did not grow. Large males did not grow, but smalllst-yr males similar in size to females did grow. Females laid at least two consecutive clutches during a single reproductive season; clutch interval was ~25 d. Clutch size varied with time of laying (first or second clutch), female body size, and year.We compare the reproductive energetics of C. tigris and other wide-foraging Cnemidophorus with the energetics of ambush iguanids. The wide forager C. tigris and the ambusher Uta stansburiana apparently do not differ in the proportion of the energy budget devoted to reproductive production (reproductive effort, REP). But total reproductive effort, RE., which includes metabolism associated with reproduction, is much lower in Cnemidophorus tigris.Review of the literature indicates Cnemidophorus tend to lay smaller clutches and larger eggs than iguanids, but the number of eggs laid per unit time generally equals that of most iguanids. Cnemidophorus also deposit energy into their eggs at rates almost 60% higher than ambush iguanids. We consider higher rates of production in wide foragers to be permitted by their higher rates of net energy intake while foraging, compared with most ambushers. These higher rates of production in Cnemidophorus apparently allow them either to reach a larger size than iguanids of similar age at first reproduction or to be younger than iguanids of the same size at first reproduction. Life history characters may be influenced by differences in rates of production associated with different food-acquisition modes.