Lizard Predators Research Articles

Lizard Abundance in an Exurban Southwestern Savanna, and the Possible Importance of Roadrunner Predation

Ranches are being converted to low density exurban housing developments in the southwestern United States, with potentially significant but little studied impacts on biological diversity. We counted lizards in a grassland and mesquite/oak savanna in southeastern Arizona, along 48 transects evenly divided among landscapes that were grazed by livestock, embedded in housing developments, both or neither. Terrestrial lizards as a group (mostly Aspidoscelis uniparens and Holbrookia maculata) were scarce in developed areas, especially where homeowners kept livestock. Combined counts of lizards (Sceloporus clarkii, Sceloporus undulatus and Urosaurus ornatus) associated with three dimensional substrates did not differ among landscape categories. Roadrunners (Geococcyx californianus), known predators of terrestrial lizards, were more common in developed areas, especially those that were grazed. These results are consistent with the hypothesis that the relative scarcity of terrestrial lizards in developed landscapes was due to increased predation by roadrunners, but predation by other species, especially domestic pets, may also have been important.

Island Biogeography of Populations: An Introduced Species Transforms Survival Patterns

Population phenomena, which provide much of the underlying basis for the theoretical structure of island biogeography, have received little direct study. We determined a key population trait-survival-in the Bahamian lizard Anolis sagrei on islands with an experimentally introduced predatory lizard and on neighboring unmanipulated islands. On unmanipulated islands, survival declined with several variables, most notably vegetation height: The island with the shortest vegetation had nearly the highest survival recorded for any lizard. On islands with the introduced predator, which forages mostly on the ground, A. sagrei shifted to taller vegetation; unlike on unmanipulated islands, its survival was very low on islands with the shortest vegetation but was higher on the others. Thus, species introduction radically changed a resident species' relation of survival to a key island-biogeographical variable.

Effects of long‐term fox baiting on species composition and abundance in an Australian lizard community

Abstract We report on the effects of almost a decade of 1080‐fox baiting on a lizard community in a mosaic Australian habitat. Replicated comparisons of baited versus non‐baited control areas with near‐identical histories of bush fires, grazing and climate showed a higher density of red fox tracks (Canis vulpes) in the non‐baited areas. Furthermore, the fox‐baited areas showed a more than five times higher density of sand goannas (Varanus gouldii), a species that strongly overlaps the red fox in food niche breadth and is itself a direct target of fox predation, in particular its eggs and young. Exclusion of predators from a natural habitat led to significant increases in the density of small lizards, suggesting that predation can drive lizard population dynamics in this ecosystem. Replicated pitfall‐trapping in three habitats in the control areas (with high fox and low goanna density) versus the baited areas (with low fox and high goanna density) showed that fox baiting had positive effects on the density of diurnal scincid lizards in open grassland, whereas the control areas showed higher density of nocturnal gecko lizards. Our interpretation is that fox removal may result in a shift in the top predator towards the sand goanna. Historically, this indigenous, endemic species was the natural top predator. It has co‐evolved with its prey and that may have moulded it into a more efficient lizard predator per encounter than the introduced fox.

AVERSIVE BEHAVIOR OF BEADED LIZARD, HELODERMA HORRIDUM, TO SYMPATRIC AND ALLOPATRIC PREDATOR SNAKES

Abstract Twenty-two beaded lizards (Heloderma horridum) showed their capacity to discriminate chemical cues of 9 sympatric snakes (potential predators of lizards) and 6 allopatric snakes. The study demonstrated a previously unknown ability to recognize and avoid dangerous snakes by this helodermatid. Experiments revealed differences among escape latency (ESC) in 60-s trials for this behavior. Mean number of seconds ±1 SD for Boa constrictor was 2.81 ± 1.68, Loxocemus bicolor was 9.41 ± 1.99, Crotalus basiliscus was 3.04 ± 1.59, Agkistrodon bilineatus was 3.54 ± 1.60, Drymarchon corais was 10.77 ± 2.31, and Masticophis mentovarius was 16.05 ± 2.17. Other sympatric snakes used as controls, such as Micrurus distans, Trimorphodon biscutatus, and Oxybelis aeneus, elicited no aversive behavior presumably because they do not feed on helodermatids. Experiments also showed antipredator behaviors were elicited by the allopatric snakes Charina trivirgata (16.27 ± 1.88 s), Crotalus molossus (6.36 ± 1.73 s), and C. tr...

Bottom-up effects of nutrient availability on flower production, pollinator visitation, and seed output in a high-Andean shrub

Soil nutrient availability directly enhances vegetative growth, flowering, and fruiting in alpine ecosystems. However, the impacts of nutrient addition on pollinator visitation, which could affect seed output indirectly, are unknown. In a nutrient addition experiment, we tested the hypothesis that seed output in the insect-pollinated, self-incompatible shrub, Chuquiraga oppositifolia (Asteraceae) of the Andes of central Chile, is enhanced by soil nitrogen (N) availability. We aimed to monitor total shrub floral display, size of flower heads (capitula), pollinator visitation patterns, and seed output during three growing seasons on control and N addition shrubs. N addition did not augment floral display, size of capitula, pollinator visitation, or seed output during the first growing season. Seed mass and viability were 25-40% lower in fertilised shrubs. During the second growing season only 33% of the N addition shrubs flowered compared to 71% of controls, and a significant (50%) enhancement in vegetative growth occurred in fertilised shrubs. During the third growing season, floral display in N addition shrubs was more than double that of controls, received more than twice the number of insect pollinator visits, and seed output was three- to four-fold higher compared to controls. A significant (50%) enhancement in vegetative growth again occurred in N addition shrubs. Results of this study strongly suggest that soil N availability produces strong positive bottom-up effects on the reproductive output of the alpine shrub C. oppositifolia. Despite taking considerably longer to be manifest in comparison to the previously reported top-down indirect negative effects of lizard predators in the same study system, our results suggest that both bottom-up and top-down forces are important in controlling the reproductive output of an alpine shrub.

Negative impacts of a vertebrate predator on insect pollinator visitation and seed output in Chuquiraga oppositifolia, a high Andean shrub.

Studies on plant-pollinator interactions have largely neglected the potential negative effects of the predators of pollinators on seed output, even though anti-predatory behaviour of pollinators may affect visitation patterns, pollen transfer, and therefore potentially, plant reproductive output. We tested the hypothesis that the presence of lizards and insectivorous birds, by reducing pollinator visitation, can have significant negative effects on seed output in the insect-pollinated, genetically self-incompatible lower alpine Andean shrub, Chuquiraga oppositifolia (Asteraceae). The lower alpine belt supports a high density of territorial Liolaemus (Tropiduridae) lizards and low shrubs interspersed among rocks of varying sizes, the latter inhabited by lizards and commonly used by flycatchers Muscisaxicola (Tyrannidae) as perching sites. In a 2x2 factorial predator-exclusion experiment, visitation rates of the most frequent pollinators of C. oppositifolia (the satyrid butterfly Cosmosatyrus chilensis and the syrphid fly Scaeva melanostoma), the duration of pollinator visits, and seed output, were 2-4 times greater when lizards were excluded, while birds had no effect. In a natural experiment, visits by S. melanostoma were 9 times shorter, and pollinator visitation rates of C. chilensis and S. melanostoma, and C. oppositifolia seed output were 2-3 times lower on shrubs growing adjacent to lizard-occupied rocks compared to those growing distant from rocks. Our results, verified for additional Andean sites, suggest that lizard predators can alter the behaviour of pollinators and elicit strong top-down indirect negative effects on seed output. Such effects may be especially important in high alpine plant communities, where pollinator activity can be low and erratic, and pollen limitation has been reported.

Size-based predation by kookaburras ( Dacelo novaeguineae ) on lizards ( Eulamprus tympanum : Scincidae): what determines prey vulnerability?

Lizards and birds are both popular ”model organisms” in behavioural ecology, but the interactions between them have attracted little study. Given the putative importance of birds as predators of diurnal lizards, it is of considerable interest to know which traits (of lizards as well as birds) influence the outcome of a predatory attempt. We studied predation by giant terrestrial kingfishers (kookaburras, Dacelo novaeguineae: Alcedinidae) on heliothermic diurnal lizards (highland water skinks, Eulamprus tympanum: Scincidae), with particular reference to the role of prey (lizard) size. Our approach was twofold: to gather direct evidence (sizes of lizards consumed in the field, compared to those available) and indirect evidence (size-related shifts in lizard behaviour). We quantified the size structure of a natural population of skinks (determined by an extensive mark-recapture program), and compared it to the sizes of wild lizards taken by kookaburras (determined by analysis of prey remains left at the birds’ nests). Kookaburras showed size-based predation: they preyed mainly on small and medium-sized rather than large lizards in the field. However, the mechanism producing this bias remains elusive. It is not due to any distinctive behavioural attributes (locomotor ability, activity level, habitat usage) of the lizards of the size class disproportionately taken by the kookaburras. The greater vulnerability of subadult lizards may reflect subtle ontogenetic shifts in ecological and behavioural traits, but our data suggest that great caution is needed in inferring patterns of vulnerability to predation from indirect measures based on either the prey or the predator alone. Instead, we need direct observations on the interaction between the two.

Lizards Reduce Spider Species Richness by excluding Rare Species

To assess the impact of lizards on species richness and properties of individual species of web spiders, we conducted a 4.5-yr field experiment on Staniel Cay, Exumas, Bahamas. Spider populations were censused at ∼2-mo intervals in lizard-removal enclosures and in control enclosures with lizards present at natural densities. Lizards reduced total number of individuals, species richness (number of species), and composite diversity of web spiders. The differential absence of rare species was primarily responsible for the lower species richness in controls than in lizard-removal enclosures. The impact of lizards on the abundance of Metepeira datona, the numerically dominant spider species, was weaker than the impact on the abundance of all rarer species combined. Mean body lengths of Argiope argentata, a large, rare spider, were larger in removals than in controls, whereas mean body lengths of M. datona, a small, common spider, did not differ significantly in removals and controls. A. argentata were closer to the ground than two commoner species and thereby were potentially more vulnerable to lizard predation. The present mainland-enclosure experiment and an island-introduction experiment both demonstrated the same general pattern of lizard predation: exclusion of rare spider species. However, the impact of lizards on spiders was more devastating in the island experiment. Other experimental field studies that had terrestrial animals as subjects and that separately analyzed at least all common species in a prey assemblage demonstrated that predators reduced or had no effect upon prey species diversity. Each study in which predators reduced diversity indicated that local extinction of rare species in experimental areas with predators was common.

LIZARDS REDUCE SPIDER SPECIES RICHNESS BY EXCLUDING RARE SPECIES

To assess the impact of lizards on species richness and properties of individual species of web spiders, we conducted a 4.5-yr field experiment on Staniel Cay, Exumas, Bahamas. Spider populations were censused at ∼2-mo intervals in lizard-removal enclosures and in control enclosures with lizards present at natural densities. Lizards reduced total number of individuals, species richness (number of species), and composite diversity of web spiders. The differential absence of rare species was primarily responsible for the lower species richness in controls than in lizard-removal enclosures. The impact of lizards on the abundance of Metepeira datona, the numerically dominant spider species, was weaker than the impact on the abundance of all rarer species combined. Mean body lengths of Argiope argentata, a large, rare spider, were larger in removals than in controls, whereas mean body lengths of M. datona, a small, common spider, did not differ significantly in removals and controls. A. argentata were closer to the ground than two commoner species and thereby were potentially more vulnerable to lizard predation. The present mainland-enclosure experiment and an island-introduction experiment both demonstrated the same general pattern of lizard predation: exclusion of rare spider species. However, the impact of lizards on spiders was more devastating in the island experiment. Other experimental field studies that had terrestrial animals as subjects and that separately analyzed at least all common species in a prey assemblage demonstrated that predators reduced or had no effect upon prey species diversity. Each study in which predators reduced diversity indicated that local extinction of rare species in experimental areas with predators was common.

Effects of movement and eating on chemosensory tongue-flicking and on labial-licking in the leopard gecko (Eublepharis macularius)

Two forms of lingual protrusion, tongueflicking and labial-licking, were differentially affected by combinations of movement and eating conditions in a eublepharid gecko (Eublepharis macularius). Tongue-flicking, in which the tongue contacts substrates beyond the lizard's body, occurred at increased rates during locomotion and during locomotion was significantly more frequent after eating than in a baseline condition. Labial-licking, in which a protruded portion of the tongue touches the labial, mental or rostral scales that surround the mouth, increased after eating. Unlike tongue-flick rates, by far the highest labial-lick rates were observed in stationary lizards after eating. The elevated tongue-flicking rates during movement after eating may be a manifestation of a postingestive chemosensory search for prey. In addition to grooming, several possible chemosensory functions of labial-licking are discussed, including gustatory sampling, sampling prey chemicals on the labials for transfer to the vomeronasal system, and redistribution of chemicals on the tongue to enhance transfer. It is suggested that labial-licking might help motionless lizards maintain vigilance for visual prey stimuli associated with the specific chemical prey cues. Another possible explanation for the increased labial-lick rate while motionless after eating is that prey chemicals induce tongue-flicking, but that the distance protruded is lessened and the tongue does not contact environmental substrates. Tongue-flicking while stationary is unlikely to lead to detection of additional prey and might incur detection by the lizard's predators or prey.

Activity and Habitat Use in a Population of Ameiva ameiva in Southeastern Columbia

The abundance, time of activity, time budget, and microhabitat selection of a population of Ameiva ameiva living in the Sierra of Chiribiquete (Southeastern Colombia) were studied. The area is isolated from the surrounding forest and has reduced trophic resources and few potential predators of lizards. The population is characterized by the small size of the lizards and by low density (22.1 indv/ha). Probably the special characteristics of the habitat make possible the lengthened daily activity pattern in both juvenile and adult individuals, but this pattern is also related to relative humidity. The juveniles showed a unimodal pattern with maximum frequency of sightings at midday, while the.adults preferred the morning and afternoon hours. Both age groups used open, sunny areas and spent most of their time in foraging and basking behaviors.

Defensive secretion of a flightless grasshopper: Failure to prevent lizard attack

We tested the role of a grasshopper defensive secretion in deterring lizard predation. Adults, but not young larvae, of the chemically defended lubber grasshopperRomalea guttata (=microptera) froth a volatile secretion when attacked by predators. The lizardAnolis carolinensis failed to strike juvenile lubbers (which lack secretion) in laboratory trials. Survivorship of palatable crickets loaded with secretion offered toA. carolinensis was not significantly different from survivorship of control crickets. In experiments designed to investigate if lizards learn an aversion to the secretion, striking times forSceloporus undulatus fed wax worms coated with secretion were not significantly different over three days of trials. Three primary conclusions are drawn from these data. First, the secretion may not be necessary for lubber protection from lizards. Second, lubber secretion does not appear to deter lizards from attacking or eating prey items. Third, lizards do not appear to develop an aversion to the secretion.

Effect of Predators and Area on Invasion: An Experiment with Island Spiders

To assay the effect of area and predators on invasion success, spiders were introduced onto islands that were large, with lizard predators; large, without lizard predators; or small, without lizard predators. Short-term survival was greater on islands without than with predators; area had no effect. Spiders initially increased substantially on both groups of islands without lizards, but after 5 years they nearly died off on small islands while persisting on most large islands; populations in the presence of predators never increased above initial sizes. Results show how predators as well as area are important in determining invasion success.

Predation of lizards and frogs by adult vipers, Vipera aspis, in the Bernese Prealpine region (West Switzerland)

Predation of lizards and frogs by adult vipers, Vipera aspis, in the Bernese Prealpine region (West Switzerland)

Skin mechanics and morphology of two species ofPachydactylus(Reptilia:Gekkonidae)

The southern African species Pachydactylus namaquensis is one of only a few mainland species of geckos that exhibits the escape strategy of regional integumentary loss. The skin morphology and mechanics of this species were compared to the same parameters in lhe sympatric congener P. bibronii. The tensile strength and modulus of elasticity of the skin of both species fall in the middle range of values for geckos as a whole. Skin of P. namaquensis, however, has approximately half of the tensile strength of that of P. bibronii. As in other skin-losing forms, the morphological basis for weakness lies in the bilayering of the dermis and the presence of zones of weakness within the upper layer of the dermis. Field experience suggests that P. namaquensis does not lose the skin as easily as most geckos exhibiting regional integumentary loss. In this species this escape strategy has probably evolved in response to the prey subjugation mode employed by rock-dwelling lizard predators.

Reproductive potential of colonies of desert harvester ants (Pogonomyrmex desertorum): effects of predation and food

To ascertain what factors affect reproductive output of colonies of the Desert Harvester Ant, Pogonomyrmex desertorum, colonies were subjected to two experiments. The first was a 3-way factorial design, which varied (i) artificial predation intensity, (ii) seed addition, and (iii) insect matter addition. The second experiment used fences to prevent horned lizards (Phrynosoma spp.) from foraging on concentrations of worker ants found at colony entrances. Increased artificial predation caused a decrease in alate production. The effect of predation was strongest in colonies also receiving insect matter. The treatments of adding seeds and adding insect matter by themselves did not have a measurable effect on alate production. Exclusion of horned lizard predators using fencing also had no effect on alate production. Although this study shows that predation has the potential to affect reproductive output (and therefore the potential to have been important in the evolutionary history of P. desertorum) the present study shows no evidence that either present levels of predation or scarcity of food limit reproductive output.

Tail injuries increase the risk of mortality in free-living lizards (Uta stansburiana).

Caudal autotomy is an effective anti-predator mechanism used by many lizard species. Fitness benefits of surviving a predatory attack are obvious, although lizards that autotomize their tails may be at greater risk during subsequent encounters with predators than lizards with complete tails. In previous laboratory studies, tail-less lizards were more vulnerable to capture by predators, but little is known about the relative survival of tailed versus tail-less lizards in nature. This study reports on significant associations between naturally incurred tail injuries and the subsequent risk of mortality in 7 populations of the lizard Uta stansburiana. I used standard mark-recapture techniques to document survival and quantified tail injuries by estimating tail completeness. I then used sampled randomization tests to compare intitial tail completeness values of surviving versus non-surviving lizards. I evaluated overall patterns by comparising the means of tail completeness values of survivors versus non-survivors among mark-recapture sequences. Lizards with incomplete tails suffered higher mortality in the field, although this was not true for every comparison considered (i.e., for every mark-recapture sequence analyzed), and the overall trend was much stronger for adult males than for either adult females or juveniles. Higher mortality among lizards with incomplete tails is presumably a consequence of increased vulnerability to capture by predators. Vulnerability to predation of tail-injured lizards may be confounded by reduced social status in this species, because social subordination can result in the occupation of an inferior home range.

Chemical detection of predators by a lizard, the broad‐headed skink (Eumeces laticeps)

AbstractThe scincid lizard Eumeces laticeps is shown experimentally 1) to be capable of detecting integumentary chemical stimuli from two congeneric species of snakes that are sympatric predators of lizards and 2) to discriminate these chemical stimuli from similar ones derived from a sympatric snake that does not eat lizards and from a common insect food species. The experimental technique employed in this study, i.e., presentation of odorants on cotton‐tipped applicators, allows rapid assessment of responses to predator odors and is suitable for a survey of these responses in a wide variety of lizards. The skinks showed significantly higher tongue‐flicking rates in response to odors of snake predators and food odors (cricket) than to odors of a snake that does not eat lizards and an odorless control. Tongue‐flick attack score, a measure of response strength to chemical stimuli from food, was much greater for cricket stimuli than for the predator stimuli. Significantly more lizards bit applicators bearing cricket stimuli than bit applicators bearing any of the other stimuli. After biting applicators bearing predator odors, the lizards quickly released. In contrast, they frequently maintained a grasp after biting applicators bearing cricket odors. A few preliminary speculations are made regarding ecological factors that may affect responsiveness by lizards to predator odors.

Ecology and Reproduction of a Parthenogenetic Lizard, Cnemidophorus sonorae

Cnemidophorus sonorae was studied in southeastern Arizona during the summer of 1978. Daily activity was bimodal, with cessation of aboveground activity during the hottest part of the day. Hatchlings exhibited extended seasonal activity, being quite common after the adults had entered brumation in mid August. Frequency of broken tails of 193 C. sonorae was 20 percent. Snout-vent length at maturity ranged from 61 to 68 mm. The reproductive season lasted from mid May until late July, and the lizards were capable of producing 2 to 3 clutches. Average clutch size was 3.7 ? 0.16 eggs, and showed a positive correlation to snout-vent length. Relative clutch mass was about .16, less than that reported for many lizards but consistent with that expected from actively foraging predatory lizards. The teiid genus Cnemidophorus con- tains 47 species, most of which are

Collared Lizard Predation: The Effects of Conspicuous Morphology and Movement

Collared Lizard Predation: The Effects of Conspicuous Morphology and Movement