Field Energetics and Foraging Mode of Kalahari Lacertid Lizards (original) (raw)
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ENERGY EXPENDITURE IN FREE-RANGING LIZARDS
2000
Abstract. 8 8 were not different from those of 9 9 in spring or fall. Average daily field metabolic rates were 2.0 to 2.5 x resting laboratory rates measured on a simulated normal thermal cycle; estimated rates during the field activity period were 2.5 to 3.1 x resting levels measured at 35°C. Only 11 to 17% of total daily energy
1998
The study of variability over time within populations and between populations can provide insights into the range of phenotypic variation within individuals versus genotypic variation among individuals. Studies of variability help place bounds on rates of energy flow within ABSTRACT individuals and the rates of allocation of energy to mainte-The extent of variation in reptile field metabolism, and its causal nance, growth, and reproduction. These rates of energy flow bases, are poorly understood. We studied the energetics of the in individuals collectively determine rates of production in insectivorous lizard Callisaurus draconoides at a site in the Califorpopulations. Moreover, comparisons between sample sites and nia Desert (Desert Center) and at a site at the southern tip of the times focus attention on factors that cause variation in FMR, Baja Peninsula (Cabo San Lucas; hereafter, Cabo). Reproducing including changes in thermoregulation (Adolph and Porter Callisaurus were smaller at Cabo than at Desert Center. The 1993), amount of daily activity (Karasov and Anderson 1984), allometry of metabolism with body mass can account for most and intensity of daily activity (Brown and Perez-Mellado 1994). differences in whole-animal metabolism. There was no significant The ability to predict FMR accurately requires extensive knowleffect of sex or source population on mass-adjusted metabolic edge of the factors that compose and influence the rates of rate in the laboratory (resting metabolism, measured by closedenergy flow through individuals. Knowledge and understandsystem respirometry) or in the field (field metabolism, measured ing of the components of daily energy flow and the environwith doubly labeled water). The mass-adjusted resting metabolism mental factors that influence FMR will facilitate other kinds and field metabolism of gravid females and the field metabolism of studies that use energy as a currency in foraging, behavioral, of juvenile lizards were not significantly different from those of and life-history analyses (Congdon et al. 1982; Congdon 1989). nonreproductive adults. Temperature had a significant effect on We investigated RMRs and FMRs of free-living zebra-tailed resting metabolism (Q 10 Å 2.7); fed lizards had resting metabolism lizards (Callisaurus draconoides) during seasons of reproducthat was 22% higher than that of fasted lizards; field metabolism tion and/or growth at two sites (one in the tropical zone and was positively correlated with growth rate in juveniles; and field one in the temperate zone) in the arid southwest of North metabolism of adults increased from spring to late summer at America. Because we previously studied the RMR and FMR of Desert Center by 25%, probably because of longer activity period this species during a period of no production at one of these length and slightly higher activity period body temperature. We sites (Anderson and Karasov 1981), these studies together adcalculated from water influx and field metabolism that juveniles vance our knowledge of variation in lizard energetics. One allocated 18% of their metabolizable energy intake to growth and goal was to test for variation in FMR among populations and that most energy deposited into eggs was transferred from energy understand its proximal causes. A second goal was to characterstores rather than ingested in the weeks prior to laying. ize energy flow at different points in the life cycle of individuals within a population. For example, our comparisons permit an investigation into the total contribution of all components of the energy cost of production rather than simply the energy Introduction in a clutch or new tissue, such as energy allocated to courtship, It is axiomatic that measures of resting metabolic rate (RMR; competition for mates, nesting, acquisition of extra food en-Bennett and Dawson 1976; Andrews and Pough 1985) and ergy, and respiratory cost of production (Congdon et al. 1982; Nagy 1983a; Anderson and Karasov 1988). Comparisons within and between populations included measurements of
Locomotor capacity and foraging behaviour of kalahari lacertid lizards
Animal Behaviour, 1984
Closely related lacertid lizards (Eremias, Nucras) in the Kalahari desert differ in patterns of foraging behaviour. Some species are relatively sedentary ('sit-and-wait'), whereas others are more active ('widely-foraging') predators. We determined whether whole-animal locomotor capacities (cruising endurance on a treadmill, initial speed and maximum burst speed in a racetrack, and sprint endurance in a torus-shaped track) correlated with interspecific differences in foraging behaviour. Two of three widely-foraging species had greater cruising endurance, greater sprint endurance, but lower burst speed than did a sit-and-wait species. However, the two species that sprinted quickly also had limited endurance, and vice versa. Pre-feeding negatively influenced endurance but not sprint capacity.
LOCOMOTOR CAPACITY AND FORAGING BEHAWOUR OF KALAHARI LACERTIQ LIZARDS
1984
Closely related lacertid lizards (Eremias, Nucras) in the Kalahari desert differ in patterns of foraging behaviour. Some species are relatively sedentary ('sit-and-wait'), whereas others are more active ('widely-foraging') predators. We determined whether whole-animal locomotor capacities (cruising endurance on a treadmill, initial speed and maximum burst speed in a racetrack, and sprint endurance in a torus-shaped track) correlated with interspecific differences
Amphibia-Reptilia, 1995
The ecophysiology of the agamid lizard Ctenophorus nuchalis was studied near Shark Bay, Western Australia, during three seasons, over four years, in order to evaluate seasonal and year-to-year variation in energy and material balance, and to compare this agamid with similar-sized iguanid lizards. We measured water influx and efflux rates and field metabolic rates with doubly-labelled water, sodium fluxes with radiosodium, and osmotic status (plasma osmotic and ionic concentrations) in free-ranging adults of both sexes, as well as juveniles. Feeding rates were calculated from diet composition information in conjunction with rates of water and sodium intake, and body condition indices were also determined. There were marked seasonal and year-to-year differences in body condition, and in rates of body mass gain or loss, and these correlated with drought periods. Rates of resource use were highest in spring, and declined through summer and autumn, and rates were lowest during 1983, a year having unusually low winter rainfall. Hatchlings, which emerged in autumn, were able to find and capture food resources, even though adults were eating little during that season. The annual pattern of energy, water and salt balance in this agamid lizard is quite similar to that of an equivalent-sized iguanid lizard.
Foraging mode in lacertid lizards: variation and correlates
Amphibia-Reptilia, 1990
Foraging strategy was observed in five species of Israeli lacertid lizards in the field. Acanthodactylus scutellatus is a sit-and-wait strategist, whereas A. boskianus, A. schreiberi, Lacerta laevis and Mesalina guttulata forage widely. However, the actual values differed from those reported by Huey and Pianka (1981) for Kalahari lacertids, possibly indicating the existence of a continuum of foraging modes. Foraging intensity (proportion of time spent moving or frequency of moves) is positively correlated to relative tail length, and negatively correlated to relative clutch mass. Additional possible correlates are discussed, and some cautionary remarks added.
COVARIATION OF THERMAL BIOLOGY AND FORAGING MODE IN TWO MEDITERRANEAN LACERTID LIZARDS1
1996
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.
Covariation of Thermal Biology and Foraging Mode in Two Mediterranean Lacertid Lizards
Ecology, 1996
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).
Does foraging mode affect metabolic responses to feeding? A study of pygopodid lizards
Current Zoology
Foraging mode (ambush vs. active) profoundly affects many aspects of organismal biology, including metabolic rates and their relationship with food intake. Previous studies on snakes suggest that ambushers tend to have lower standard metabolic rates (SMR) and higher energetic costs of digestion and assimilation of prey (specific dynamic action, or SDA) than do active foragers. However, phylogenetic considerations may be at least partly responsible for such patterns, as foraging mode is strongly conserved evolutionarily and most SDA studies have focused on species from only two lineages of ambush foragers (pythonid and viperid snakes) and one lineage of active foragers (colubrid snakes). We sought to deconfound the effects of phylogeny and foraging mode, investigating SMR and SDA in two closely related pygopodid lizards, the common scaly-foot Pygopus lepidopodus (active forager) and Burton's legless lizard Lialis burtonis (ambush forager). Consistent with the pattern seen in snakes, L. burtonis exhibits a significantly lower SMR and a higher SDA than does P. lepidopodus. The magnitude of SDA in L. burtonis is comparable to that of some pythons and vipers, providing yet more evidence for the remarkable convergence between this species and ambush-foraging snakes [Current Zoology 59 (5): 618-625, 2013].
Foraging efficiency of predators can be evaluated by using optimality or profitability models which incorporate prey choice, handling time and pursuit or search time. Optimality of a diet could vary based on the age, sex, size, predation risk, or foraging experience of the predator. This study tested the effects of a predator's age and foraging experience by observing prey capture attempts and success rate, and by calculating diet profitability for adult and neonate Sceloporus jarrovii and adult Sceloporus virgatus. Prey availability was assessed in order to determine prey preference and profitability. Neonates showed an increased number of prey capture attempts, but success rate was similar for neonates and adults of both species. Total diet profitability of neonates was lower than adults of either species, which could be a result of poor prey choice or gape limitation (although body size showed no direct effect). Overall, the diets of all three groups were less profitable than would be expected based on the types of prey in the environment, although this is likely due to low availability (from the lizard's perspective) of highly profitable items. Lizards seem to be eating prey items in the same proportion as they are found in the environment.