A test of optimal foraging and the effects of predator experience in the lizards Sceloporus jarrovii and Sceloporus virgatus (original) (raw)
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Oecologia, 1993
Maximizing the average rate of energy intake (profitability) may not always be the optimal foraging strategy for ectotherms with relatively low energy requirements. To test this hypothesis, we studied the feeding behaviour of captive insectivorous lizards Psammodromus algirus, and we obtained experimental estimates of prey mass, handling time, profitability, and attack distance for several types of prey. Handling time increased linearly with prey mass and differed significantly among prey types when prey size differences were controlled for, and mean profitabilities differed among prey taxa, but profitability was independent of prey size. The attack distance increased with prey length and with the mobility of prey, but it was unrelated to profitability. Thus, lizards did not seem to take account of the rate of energy intake per second as a proximate cue eliciting predatory behavior. This information was combined with pitfall-trap censuses of prey (in late April, mid-June and late July) that allowed us to compare the mass of the prey captured in the environment with that of the arthropods found in the stomachs of sacrificed free-living lizards. In April, when food abundance was low and lizards were reproducing, profitability had a pronounced effect on size selection and lizards selected prey larger than average from all taxa except the least profitable ones. As the active season progressed, and with a higher availability of food, the number of prey per stomach decreased and their mean size increased. The effect of profitability on size selection decreased (June) and eventually vanished (July-August). This variation is probably related to seasonal changes in the ecology of lizards, e.g. time minimization in the breeding season as a means of saving time for nonforaging activities versus movement minimization by selecting fewer (but larger) prey in the postbreeding season. Thus, the hypothesis that maximizing profitability could be just an optional strategy for a terrestrial ectothermic vertebrate was supported by our data.
Prey processing in lizards: behavioral variation in sit-and-wait and widely foraging taxa
Canadian Journal of Zoology-revue Canadienne De Zoologie, 2002
We determined the degree to which lizards process (i.e., chew) and manipulate their prey, using a phylogenetically broad sample of 12 species. Two transport and two chewing behaviors were identified. The transport behaviors included side-to-side movements and lingually mediated posterior movements of the prey. Chewing behaviors included puncture crushing and a previously undescribed behavior we term palatal crushing. Iguanian lizards (sit-and-wait predators) engaged in more palatal-crushing behaviors than autarchoglossans (widely foraging predators) did. However, iguanians also engaged in fewer cycles of chewing and transport behaviors per feeding bout. Autarchoglossan lizards used puncture crushing extensively and exhibited more variability in the sequence of behaviors used within a bout (interspersion of transport behaviors among chewing behaviors). Three behaviors (puncture crushing, interspersion, total) were shown to be coevolving after the effects of phylogeny were removed. The variation in feeding behavior we observed between iguanian and autarchoglossan lizards parallels patterns in tongue morphology and foraging mode in these large groups. Thus, it seems likely that each represents a component of a highly integrated character complex linking feeding morphology, behavior, and ecology.
The effects of prey species on food conversion efficiency and growth of an insectivorous lizard
Zoo Biology, 2008
Little is known about the effects of different prey species on lizard growth. We conducted a 6-week study to determine the relative effects of prey species on growth parameters of hatchling western fence lizards, Sceloporus occidentalis. Lizards were fed house cricket nymphs, Acheta domesticus, or mealworm larvae, Tenebrio molitor. The effects of prey species on growth were determined by measuring prey consumption, gross conversion efficiency of food [gain in mass (g)/food consumed (g)], gain in mass, and gain in snout-vent length. Lizards grew well on both the prey species. However, lizards that fed on crickets consumed a significantly higher percentage of their body mass per day than those fed mealworms. Nevertheless, lizards that consumed mealworms ingested significantly more metabolizable energy, had significantly higher food conversion efficiencies, significantly higher daily gains in mass, and significantly greater total growth in mass than lizards that fed on crickets.
Sequential analyses of foraging behavior and attack speed in ambush and widely foraging lizards
Adaptive Behavior, 2012
Food acquisition mode in lizards (i.e., ambush vs. widely searching) has been intensely scrutinized for the past decade to identify correlations between food acquisition mode, diet, sprint speed, and other aspects of phenotypic diversity. To begin to understand these correlations, we studied foraging mode variation in natural foraging behavior and attack speed in three ambush predators and two widely foraging species in the field. Sequential analyses revealed considerable variation in the temporal structure of behavioral repertoires associated with acquiring food. Ambush and wide-foraging species use unique combinations of behaviors prior to prey attack with differences among and between food acquisition modes. Attack speeds were well below maximum sprint speed for these species. Thus, the widely demonstrated correlation between food acquisition mode and sprint speed is not related to prey capture per se. The striking variation in prey capture repertoires in these model ambush and wide foragers shows that we have a long way to go before we will understand the ecological relevance of many performance and phenotypic traits that are related to foraging mode in lizards.
Behavioral Ecology and Sociobiology, 1999
The grand skink, Oligosoma grande, is a diurnal rock-dwelling lizard from the tussock grasslands of Central Otago, New Zealand, whose diet includes a variety of arthropods and fruit. We conducted a ®eld experiment to examine the in¯uence of prey distribution on foraging behavior and spacing patterns. On sites where prey distribution was unaltered (control sites), males and females diered in diet and foraging behavior. Most male feeding attempts were directed at large strong-¯ying insects, and males used a saltatory search pattern that involved relatively infrequent moves of long duration. Females spent more eort catching small weak-¯ying insects and visiting fruiting plants. Their search behavior involved frequent moves of short duration. The placement of meat-bait on experimental sites led to a redistribution of large¯ies without in¯uencing other prey types. Experimental females switched foraging strategy by adopting a search pattern of relatively infrequent moves of long duration, increasing the frequency of attempts to capture large prey, and reducing the importance of fruit in their diet. The experimental manipulation appeared to in¯uence space use. On control sites, both sexes had comparably sized home ranges. On experimental sites, male home ranges were signi®cantly larger than female home ranges.
Journal of Herpetology, 2014
Foraging modes were described originally for insectivorous lizards, but many species are omnivorous or herbivorous. Because seeking and consuming plants might alter foraging, we studied foraging by the omnivorous Podarcis lilfordi at two sites: one where lizards licked nectar from flowers of Euphorbia paralias and the other where they sought insects. Movements per minute (MPM) did not differ among groups. Proportion of time spent moving (PTM) was similar in lizards that licked flowers and those that did not. Average speed (AS) was slower, and speed while moving (MS) was faster when foraging for nectar than for insects. Lizards foraging for nectar did not eat insects; those foraging for insects frequently ate them. For lizards foraging for prey, MPM increased as PTM, AS, and capture attempts increased and as PTM decreased. PTM increased as AS and capture attempts increased and decreased as MS increased. AS increased as MS increased. For lizards that licked, proportion of time licking (PTL) was unrelated to MPM, PTM, or AS but increased marginally as MS increased. Lizards foraging for nectar retained the PTM of lizards foraging for prey, but added a large PTL. The ancestral active foraging mode has been retained for hunting insects but modified to search for and lick nectar. While foraging for nectar, lizards greatly reduce attacks on insects, suggesting that, at a given time, an individual forages exclusively for nectar or prey. Reduced predation pressure on islands may have freed lizards to expand the diet by reducing risk during intervals exposed to view while climbing plants and licking nectar.
Disentangling the effects of predator body size and prey density on prey consumption in a lizard
Functional …, 2011
Studies often use functional response (density dependent) or allometric (mass dependent) models but approaches that consider multiple factors are critical to capture the complexity in predatorprey interactions. We present a novel comprehensive approach to understand predation rates based on field data obtained from a vertebrate predator. 2. Estimates of food consumption and prey abundance were obtained from 21 semi-natural populations of the lizard Zootoca vivipara. We identified the most parsimonious feeding rate function exploring allometric, simple functional response and allometric functional response models. Each group included effects of sex and weather conditions. 3. Allometric models reveal the importance of predator mass and sex: larger females have the highest natural feeding rates. Functional response models show that the effect of prey density is best represented by a Holling type II response model with a mass, sex and weather dependent attack rate and a constant handling time. However, the best functional response model only received moderate support compared to simpler allometric models based only on predator mass and sex. 4. Despite this limited effect of prey densities on feeding rates, we detected a significant negative relationship between an index of preferred prey biomass and lizard density. 5. Functional response models that ignore individual variation are likely to misrepresent trophic interactions. However, simpler models based on individual traits may be best supported by some data than complex allometric functional responses. These results illustrate the importance of considering individual, population and environmental effects while also exploring simple models.
Functional Ecology, 2002
Relationships between morphology, bite force capacity, prey handling efficiency and trophic niche were explored in two sympatric species of lacertid lizards, Podarcis melisellensis (Braun 1877) and Lacerta oxycephala Duméril & Bibron 1839. 2. Head shape showed little variation, but head size (absolute and relative to snoutvent length, SVL) differed between species and sexes. Males have larger heads than females, both absolute and relative to their SVL. In absolute terms, male P. melisellensis have larger heads than male L. oxycephala , but the reverse case was true for the females. Relative to SVL, L. oxycephala have larger heads than P. melisellensis . 3. Bite force capacity was estimated by having the lizards bite on two metal plates, connected to a piezoelectric force transducer. Differences in maximal bite force between species and sexes paralleled differences in absolute head size. Differences in body size and head size explain the higher bite force of males (compared with females), but not the higher bite force of P. melisellensis (compared with L. oxycephala ). Among individual lizards, bite force correlated with body size and head size. 4. Prey handling efficiency, estimated by the time and number of bites needed to subdue a cricket in experimental conditions, also showed intersexual and interspecific variation. This variation corresponded to the differences in maximal bite capacity, suggesting that bite force is a determining factor in prey handling. Among individual lizards, both estimates of handling efficiency correlated with maximal bite force capacity. 5. Faecal pellet analyses suggested that in field conditions, males of both sexes select larger and harder prey than females. There was no difference between the species. The proportion of hard-bodied and large-sized prey items found in a lizard's faeces correlated positively with its bite force capacity. 6. It is concluded that differences in head and body size, through their effect on bite force capacity, may affect prey selection, either directly, or via handling efficiency.
Costs of reproduction in lizards: escape tactics and susceptibility to predation
Behavioral Ecology and Sociobiology, 1992
Increased basking and reduced agility in gravid female southern water skinks (Eulamprus tympanum) suggest that they will be more vulnerable to predators. However, gravid females shift their anti-predator tactics towards crypsis, by allowing potential predators (such as a human observer) to approach more closely than do males and non-gravid females. Gravid females were taken no more frequently than were non-gravid females or males when exposed to two types of natural predators, birds (kookaburra, Dacelo gigas) or snakes (common blacksnakes, Pseudechis porphyriacus) in field enclosures. Both these results suggest that the vulnerability of potential prey in this system is determined by the predator's probability of detecting a potential prey item, not its probability of capturing the prey item after detection. Hence, laboratory-based measures of performance demonstrating reduced escape speed may sometimes have little relevance to actual fitness under field conditions, if the probability that an animal will be taken by a predator depends primarily on whether or not it is seen, rather than on how quickly it can escape.