I did my studying at Texas A&M in the USA (BS, MSc) and the University of Stellenbosch in South Africa (PhD). I started as a lecturer at the University of the Witwatersrand in Johannesburg and remained there for 10 years before taking up a position at Macquarie University in Sydney in late 2009. My research is in the realm of behavioural and evolutionary ecology. I currently focus on two main areas: animal signalling/sexual selection and cognition, using lizards as a model system.
Abstract: We studied spatial clustering and activity patterns in the common barking gecko (Ptenopus garrulus garrulus) over the course of a breeding season in southern Africa. Only some populations exhibited significant clustering (two of six plots), suggesting that social and spatial organization varies according to such factors as population density and habitat. Clustering at our largest study site was not influenced by soil temperature or prey availability, although burrow placement was significantly associated with vegetation coverage. We also examined the timing of the reproductive cycle by testing whether barking geckos exhibit protandry (male first emergence). More males than females were active early in the breeding season and male territories were established before female emergence. Peak activity for 235 barking geckos at our primary study site was late October, although males were significantly more active early in the season, consistent with the protandry model. The barking gecko mating system is most consistent with an iteroparous, harem polygynandry with an activity cycle that exhibits protandry. Our study highlights the importance of replicated spatial sampling for studies examining clustering and density effects on reproduction and mating system.
Abstract: In externally fertilizing animals in which females mate with multiple males at the same time (simultaneous polyandry), the
possibility that females accrue genetic benefits that improve offspring viability remains largely unexamined. Here, we investigate
whether simultaneous polyandry influences offspring fitness in a wild population of the Grey Foam Nest Treefrog Chiromantis
xerampelina. Simultaneous polyandry in this frog is the most extreme reported for any vertebrate, with more than 90% of females
mating with 10 or more males during the deposition of a single clutch. We compared growth (using age and size at metamorphosis
as proxies) and survival of offspring produced by females that naturally mated with either 1 male (monandrous
females) or 10–12 males (polyandrous females). Polyandry did not influence size or age at metamorphosis, but we found that
offspring from polyandrous matings had both significantly higher mean survival and reduced variance in offspring survival.
These findings implicate a genetic mechanism, but targeted cross-classified breeding experiments that control for both maternal
and material effects will be required to conclusively determine whether elevated offspring viability is linked to enhanced genetic
diversity, intrinsic sire effects, or genetic compatibility. Irrespective of the causation, the findings provide the first evidence that
naturally formed polyandrous matings have increased offspring viability in an anuran amphibian. Key words: anuran amphibian,
genetic benefits, offspring viability, polyandry, sexual selection.
Abstract: In South Africa, animals and plants are commonly used as traditional medicine for
both the healing of ailments and for symbolic purposes such as improving
relationships and attaining good fortune. The aim of this study was twofold: to
quantify the species richness and diversity of traded animal species and to assess
the trade in species of conservation concern. We surveyed the Faraday traditional
medicine market in Johannesburg and conducted 45 interviews of 32 traders
during 23 visits. We identified 147 vertebrate species representing about 9% of the
total number of vertebrate species in South Africa and about 63% of the total
number of documented species (excluding domestic animals) traded in all South
African traditional medicine markets. The vertebrates included 60 mammal
species, 33 reptile species, 53 bird species and one amphibian species. Overall,
species diversity in the Faraday market was moderately high and highest for
mammals and birds, respectively. Evenness values indicated that relatively few
species were dominant. Mammal body parts and bones were the most commonly
sold items (n=2453, excluding porcupine quills and pangolin scales), followed by
reptiles (n=394, excluding osteoderms), birds (n=193, excluding feathers and
ostrich eggs) and amphibians (n=6). Most (87.5%) species traded were of least
concern using IUCN criteria, although 17 species were of conservation concern.
However, a higher than expected proportion of traders (62.5%) were selling listed
species, which is a matter for concern and should be monitored in the future.
Abstract: Progress in developing animal communication theory is frequently constrained by a poor understanding
of sensory systems. For example, while lizards have been the focus of numerous studies in visual signalling,
we only have data on the spectral sensitivities of a few species clustered in two major clades (Iguania
and Gekkota). Using electroretinography and microspectrophotometry, we studied the visual system of
the cordylid lizard Platysaurus broadleyi because it represents an unstudied clade (Scinciformata) with
respect to visual systems and because UV signals feature prominently in its social behaviour. The
retina possessed four classes of single and one class of double cones. Sensitivity in the ultraviolet
region (UV) was approximately three times higher than previously reported for other lizards. We found
more colourless oil droplets (associated with UV-sensitive (UVS) and short wavelength-sensitive
(SWS) photoreceptors), suggesting that the increased sensitivity was owing to the presence of more
UVS photoreceptors. Using the Vorobyev–Osorio colour discrimination model, we demonstrated that
an increase in the number of UVS photoreceptors significantly enhances a lizard’s ability to discriminate
conspecific male throat colours. Visual systems in diurnal lizards appear to be broadly conserved, but data
from additional clades are needed to confirm this.
Abstract: Sandveld lizards (genus Nucras) are widespread in southern Africa, but are generally secretive and poorly known. We
examined 385 preserved specimens from five species of Nucras collected over a broad time span (104 years) and a
geographic area covering most of South Africa and Swaziland. We had three main objectives: to test for sexual size
dimorphism, to quantify male and female reproductive cycles, and to determine diet. In addition, we examined the
importance of scorpions in the diet of Nucras based on previous studies reporting an unusually high incidence of
scorpions in the diet of Kalahari N. tessellata. Males of all species except N. lalandii had significantly larger heads than
females of the same body size, although females had significantly greater snout–vent length than males in three of the
five species examined. The general reproductive pattern was for females to contain vitellogenic eggs during late spring
and early summer. No females simultaneously contained oviductal and vitellogenic eggs, which suggests that females
produce only one clutch per season. Clutch size was unrelated to female body size in all species examined. Female follicle
volume generally coincided with male testicular volume, indicating for the most part synchronized reproductive cycles
between the sexes. Testis volume was generally highest during spring–early summer, with only N. holubi showing a
second peak in autumn. We recorded 15 arthropod orders in the diet of Nucras. All species feed on invertebrates,
primarily insects, and, to a lesser degree, spiders and centipedes. Termites, grasshoppers, and beetles both numerically
and volumetrically dominated their diet. We found no evidence that scorpions form a major part of the diet of any of
these five species of Nucras, including N. tessellata from biomes outside the Kalahari Desert.
Abstract: Understanding what constrains signalling and maintains signal honesty is a central theme in animal communication. Clear cases of dishonest signalling, and the conditions under which they are used, represent an important avenue for improved understanding of animal communication systems. Female mimicry, when certain males take on the appearance of females, is most commonly a male alternative reproductive tactic that is condition-dependent. A number of adaptive explanations for female mimicry have been proposed including avoiding the costs of aggression, gaining an advantage in combat, sneaking copulations with females on the territories of other males, gaining physiological benefits and minimizing the risk of predation. Previous studies of female mimicry have focused on a single mode of communication, although most animals communicate using multiple signals. Male Augrabies flat lizards adopt alternative reproductive tactics in which some males (she-males) mimic the visual appearance of females. We experimentally tested in a wild population whether she-males are able to mimic females using both visual and chemical signals. We tested chemical recognition in the field by removing scent and relabelling females and she-males with either male or female scent. At a distance, typical males (he-males) could not distinguish she-males from females using visual signals, but during close encounters, he-males correctly determined the gender of she-males using chemical signals. She-males are therefore able to deceive he-males using visual but not chemical signals. To effectively deceive he-males, she-males avoid close contact with he-males during which chemical cues would reveal their deceit. This strategy is probably adaptive, because he-males are aggressive and territorial; by mimicking females, she-males are able to move about freely and gain access to females on the territories of resident males.
Notes: Whiting, Martin J. Webb, Jonathan K. Keogh, J. Scott
Abstract: A crucial problem for most animals is how to deal with multiple types of predator, which differ in their sensory capabilities and methods of prey detection. For animals capable of rapid colour change, one potential strategy is to change their appearance in relation to the threat posed by different predators. Here, we show that the dwarf chameleon, Bradypodion taeniabronchum, exhibits different colour responses to two predators that differ in their visual capabilities. Using a model of animal colour perception to gain a 'predator's eye view', we show that chameleons showed better background colour matching in response to birds than snakes, yet they appear significantly more camouflaged to the snake visual system because snakes have poorer colour discrimination.
Abstract: The Concho Water Snake (Nerodia harteri paucimaculata) is confined to the Concho-Colorado River valley of central Texas, thereby occupying one of the smallest geographic ranges of any North American snake. On 1986, N. h. paucimaculata was designated as a federally threatened species, in large part because of reservoir projects that were perceived to adversely affect the amount of habitat available to the snake. During a ten-year period (1987-1996), we conducted capture-recapture field studies to assess dynamics of five subpopulations of snakes in both natural (river) and man-made (reservoir) habitats. Because of differential sampling of subpopulations, we present separate results for all five subpopulations combined (including large reservoirs) and three of the five subpopulations (excluding large reservoirs). We used multistate capture-recapture models to deal with stochastic transitions between pre-reproductive and reproductive size classes and to allow for the possibility of different survival and capture probabilities for the two classes. We also estimated both the finite rate of increase (lambda) for a deterministic, stage-based, female-only matrix model using the average litter size, and the average rate of adult population change, (lambda) over cap, which describes changes in numbers of adult snakes, using a direct capture-recapture approach to estimation. Average annual adult survival was about 0.23 and similar for males and females. Average annual survival for subadults was about 0.14. The parameter estimates from the stage-based projection matrix analysis all yielded asymptotic values of lambda < 1, suggesting populations that are not viable. However, the direct estimates of average adult lambda for the three subpopulations excluding major reservoirs were <(lambda)over cap> = 1.26, Si((lambda) over cap) = 0.18 and (lambda) over cap = 0.99, S (E) over cap((lambda) over cap) = 0.79, based on two different models. Thus, the direct estimation approach did not provide strong evidence of population declines of the riverine subpopulations, but the estimates are characterized by substantial uncertainty.
Notes: Whiting, Martin J. Dixon, James R. Greene, Brian D. Mueller, James M. Thornton, Okla W., Jr. Hatfield, Jeff S. Nichols, James D. Hines, James E.
Abstract: Aggregations are a common feature of many species although for most taxa, the mechanisms underlying these aggregations are poorly understood. The Augrabies Flat Lizard (platysaums broadleyi) is a sexually dimorphic lizard that experiences intense conflict as a result of sexual selection. In the wild, P. broadleyi share communal crevices and aggregate in the presence of large insect plumes. We experimentally tested whether lizards aggregate as a result of social factors. We also tested whether aggregative behavior differed between the sexes and depends on density. We found no evidence that Augrabies Flat Lizards preferentially group for social reasons in the absence of resources or thermoregulatory benefits. This was true for both sexes and at both densities (two-lizard and four-lizard trials). Although social factors did not promote grouping, males sheltered alone significantly more often than expected by chance, suggesting that males actively avoid one another. Therefore, social factors may work to promote social isolation rather than aggregation, under certain circumstances.
Notes: Schutz, Luke Stuart-Fox, Devi Whiting, Martin J.
Abstract: 1. An organism's thermal tolerance to the environment may indicate a thermal limit to its geographical distribution. 2. We measured the lower critical minimum (CTMin) and lower lethal temperature in the lizard Pseudocordylus melanotus melanotus. 3. CTMin was 10.17 +/- 0.48 degrees C and the lower lethal temperature was -5.15 +/- 0.31 degrees C. 4. All lizards that froze did not survive. This suggests that these lizards are restricted to areas where the microclimate allows them to avoid freezing. 5. Pseudocordylus m. melanotus can allow their body temperatures to drop well below CTMin without any ill effect. (c) 2006 Elsevier Ltd. All rights reserved.
Notes: McConnachie, S. Alexander, G. J. Whiting, M. J.
Abstract: We examined 170 museum specimens of the southern African gekkonid lizard Homopholis wahlbergii, to quantify sexual dimorphism, male and female reproductive cycles and diet. The largest male and female we recorded were 116 and 119 mm snout-vent length (SVL) respectively. We compared SVL, tail length, head length, head width and eye diameter and found no evidence of sexual dimorphism in any of these characters. The smallest female with thickened muscular oviducts and follicles, indicating sexual maturity, was 59 mm SVL, but the smallest female we found with fully developed eggs was 85 mm SVL. Virtually all females larger than 59 mm appeared to be in some stage of reproduction, suggesting that females reproduce every year once they reach sexual maturity. Egg size ranged from 17-19 mm long. Egg size was not correlated with maternal SVL. We found adult females with ready-to-lay eggs during the warmer months of the year, but not during winter and spring. The smallest sexually mature male was 72 mm SVL. Virtually all males larger than this size displayed at least semi-turgid testes and most adult male testes were at least semi-turgid for much of the year. The only significant decrease in testicular activity was in mid-winter (June-August), thus, spermatogenesis is closely tied to female follicular development and ovulation. Velvet geckos are largely insectivorous (92%) and feed on a broad spectrum of prey. Their diet was dominated both numerically (34%) and volumetrically (22%) by beetles. Lepidoptera were the next most important prey category, suggesting that they exploit both terrestrial and flying invertebrates. They are unusual among lizards because they feed on millipedes. Males and females had very similar diets which may be explained by their lack of sexual dimorphism, although females tended to eat a greater volume of prey. Interestingly, less than half (37%) of the lizards examined contained prey items, suggesting that most individuals were not in positive energy balance. We also found evidence of prey size selection as a function of gape size, such that larger geckos took advantage of larger prey items.
Notes: Whiting, Martin J. Reaney, Leeann T. Keogh, J. Scott
Abstract: Whether general patterns of signal evolution can be explained by selection for signal efficacy (detectability) has yet to be established. To establish the importance of signal efficacy requires evidence that both signals and their detectability to receivers have evolved in response to habitat shifts in a predictable fashion. Here, we test whether habitat structure has predictable effects on the evolution of male and female display coloration in 21 lineages of African dwarf chameleon (Bradypodion), based on a phylogenetic comparative analysis. We used quantitative measures of display coloration and estimated signal detectability as the contrast of those colors among body regions or against the background vegetation as perceived by the chameleon visual system. Both male and female display colors varied predictably with different aspects of habitat structure. In several (but not all) instances, habitat-associated shifts in display coloration resulted in habitat-associated variation in detectability. While males exhibit a remarkable variety of colors and patterns, female display coloration is highly conserved, consisting in all populations of contrasting dark and light elements. This color pattern may maximize detectability across all habitat types, potentially explaining female conservatism. Overall, our results support the view that selection for signal efficacy plays an important role in the evolution of animal signals.
Notes: Stuart-Fox, Devi Moussalli, Adnan Whiting, Martin J.
Abstract: Many species possess multiple sexually dimorphic traits, which incorporate different sensory modalities (e.g., acoustic, olfactory and visual), although their relative roles in sexual selection and in determining reproductive success are still poorly understood for most taxa. We assessed the role of multiple male traits, including one acoustic (dominant call frequency) and one visual (yellow throat patch) trait, in residency advertisement, contest behavior, and breeding success in barking geckos (Ptenopus garrulus garrulus). We show that male barking geckos maintain largely exclusive home ranges, with a trend for larger males to maintain larger home ranges. We also show that larger males have a lower dominant calling frequency. When aggressive behavior was elicited in the field using a recorded call of average frequency, resident males with low frequency calls were more likely to respond aggressively and charge the speaker compared to males with high frequency calls. However, body size and small relative throat patch size, rather than call frequency, were the best predictors of overall aggressiveness. Body size was also the best predictor of whether males bred. We suggest that call frequency in this crepuscular species constitutes an effective long-range signal of body size, used by males for remote rival assessment and to advertise home range boundaries in low-light environments.
Notes: Hibbitts, Toby J. Whiting, Martin J. Stuart-Fox, Devi M.
Abstract: Some aspects of escape predicted by theoretical models are intended to apply universally. For example, flight initiation distance (distance between an approaching predator and prey when escape begins) is predicted from predation risk and the costs of escaping. Escape tactics and refuge selection are not currently predicted by theoretical models, but are expected to vary with structural features of the habitat. One way of studying such variation is to compare aspects of antipredatory behavior among sympatric species that differ in habitat or microhabitat use. In an assemblage of lizards in northwestern Namibia, we conducted experiments to test predictions of escape theory for three risk factors in representatives of three families and observed escape tactics in additional species. As predicted by escape theory, flight initiation distance increased with directness of a predator's approach and predator speed in Agama planiceps, Mabuya acutilabris, and Rhotropus boultoni, and with distance from refuge in M. acutilabris. As predicted by theory, the probability of entering refuge increased with risk in R. boultoni. All available data indicate that flight initiation distance and refuge entry by lizards conform to theoretical predictions. Escape tactics varied greatly as a function of habitat type: (1) arboreal species fled up and around trees and sometimes entered tree holes; (2) saxicolous species used rock crevices as refuges, but differed in tactics prior to entering refuges; and (3) terrestrial species fled into bushes or other vegetation, often to the far sides of them. Some M. acutilabris entered small animal burrows or buried themselves in sand beneath bushes. Escape tactics varied even among congeners in Mabuya, highlighting the important effect of habitat structure on them. Although habitat partitioning has traditionally been viewed as favoring species coexistence, an interesting by-product appears to be structuring of escape tactics in lizard communities.
Abstract: In lizards, pheromonal cues are important for mate recognition and are expected to diverge during the speciation process. We tested for divergence in pheromonal mate and species recognition between male flat lizards (Platysaurus broadleyi) belonging to the same population, a different population, and a sister species. Males were given a choice between two refuges, an odourless control and one of the following: a conspecific female from the same population (sympatric), a conspecific female from a distant population (allopatric), and a female from their sister species (heterospecific), P. capensis. Males chose refuges treated with the scent of a heterospecific over an odourless control refuge but showed no preference for refuges that were scented with female conspecific (allopatric or sympatric) cues over the control. These results were consistent in the breeding and non-breeding seasons. In a second experiment males were offered a choice of female scents between sympatric and allopatric conspecifics; an allopatric conspecific and a heterospecific; and a sympatric conspecific and a heterospecific. Males showed a trend of preferring heterospecific over conspecific refuges and allopatric over sympatric conspecific-scented refuges, but these results were not significant at alpha <0.05. Contrary to our original expectations, these experiments do not provide any evidence for a pheromonal pre-mating isolation mechanism within this species complex. However, our results suggest a preference for novel female scents by males, consistent with selection for genetic diversity.
Notes: Lewis, Belinda A. Whiting, Martin J. Stapley, Jessica
Abstract: Potential prey are often exposed to multiple predators that vary in their foraging tactics and ability to detect prey. For animals that rely on crypsis to avoid predators, one solution is to alter their behaviour or appearance to maximize crypsis in ways that are specific to different types of predator. We tested whether dwarf chameleons (Bradypodion transvaalense) showed different behavioural responses, including colour change, towards multiple predators (bird and snake models) that detect and capture prey in different ways, and whether these antipredator responses varied geographically. Chameleons consistently used the same body postures (lateral compression and flipping to the opposite side of the branch) and displayed similar chromatic (colour) contrast against the natural background in response to both predator types. However, they became significantly more achromatically contrasting (brighter) in the presence of the snake compared to the bird. This relative difference in achromatic contrast towards the two types of predator was consistent among populations. There were also significant differences in both absolute achromatic and chromatic contrast among populations despite very similar light environment, background coloration and habitat structure. Our results highlight facultative crypsis as one type of flexible antipredator tactic and emphasize the importance of visual ecology in understanding prey-predator interactions. (c) 2006 The Linnean Society of London.
Abstract: Traditionally, studies of intrasexual selection have focused on single traits that are more exaggerated in males. Relatively little is known about systems in which traits are larger in females or the role of multiple traits in male contests. We used a tournament design in which each male encounters a series of different opponents, in conjunction with the structured Bradley-Terry model, to examine the role of multiple male traits in contests between male Cape dwarf chameleons, Bradypodion pumilum. Females are larger but males have relatively longer tails, larger and more ornamented heads and a larger central flank patch, all of which are emphasized during agonistic displays. We found no evidence that larger body size confers an advantage in male contests, despite high levels of aggression and escalated encounters. However, both the height of the casque (head ornament) and relative area of the flank patch were positively associated with fighting ability, and not correlated with each other, suggesting that they may represent independent sources of information about an opponent's ability. We discuss these results in relation to the role of male contest competition in the evolution of multiple male signals and sexual dimorphism in dwarf chameleons. In addition, we show that the use of tournament designs, in conjunction with the structured Bradley-Terry model, has important advantages over traditional designs and methods of analysing animal contests. (c) 2006 The Association for the Study of Animal Behavioar. Published by Elsevier Ltd. All rights reserved.
Notes: Stuart-Fox, Devi M. Firth, David Moussalli, Adnan Whiting, Martin J. xD;Part 6
Abstract: Vertebrates that destroy or disturb habitats used by other animals may influence habitat selection by sympatric taxa. In south-east Australian forests, superb lyrebirds (Menura novaehollandiae) displace soil, leaf litter and rocks during their daily foraging activities. We investigated whether superb lyrebirds disturb small sandstone rocks that endangered broad-headed snakes Hoplocephalus bungaroides and common small-eyed snakes Cryptophis nigrescens use as diurnal thermoregulatory sites. To estimate the frequency of lyrebird rock disturbance, and to assess whether lyrebirds also attack small snakes, we placed 900 plasticine snake replicas under stones on rock and soil substrates along transects on three sandstone plateaux. Because juvenile snakes must select retreat sites that simultaneously allow them to thermoregulate and minimize predation risk, we quantified the thermal environments underneath stones on rock and soil substrates. During the 6-week experiment, animals disturbed rocks on soil substrates twice as often (16.9%) as rocks lying on rock substrates (8.2%). Disturbed rocks were significantly smaller and lighter than undisturbed rocks on both substrates. Lyrebirds were the major agents of disturbance, and attacked 40% of snake models under disturbed rocks. Rocks on soil substrates conferred the greatest thermal benefits to snakes, but both species of snake avoided these microhabitats in the field. Instead, juvenile snakes selected rocks on rock substrates, and sheltered under stones that were too heavy for superb lyrebirds to disturb. By disturbing rocks over millennia, superb lyrebirds not only have shaped the physical landscape, but also may have exerted strong selection on habitat selection by sympatric snakes.
Abstract: Understanding the role of multiple colour signals during sexual signalling is a central theme in animal communication. We quantified the role of multiple colour signals (including ultraviolet, UV), measures of body size and testosterone levels in settling disputes between male rivals in an elaborately ornamented, African lizard, played out in a large 'tournament' in the wild. The hue and brightness (total reflectance) of the UV throat in Augrabies flat lizards, Platysaurus broadleyi, as well as body size, were consistent and strong predictors of 'fighting ability'. Males with high fighting ability were larger and displayed a UV throat with low total reflectance. In contrast, males with low fighting ability were smaller and had violet throats with broader spectral reflectance curves (higher total reflectance). As fighting ability is associated with alternative reproductive tactics in this system (territorial versus floater), we also examined the role of colour signals in predicting male reproductive tactic. Territorial males had UV throats with higher chroma but had poorer body condition than floater males, probably because of the energetic costs of maintaining a territory. Although testosterone was not a significant predictor of fighting ability or reproductive tactic, it was correlated with the hue of the UV throat, suggesting that testosterone may impose some constraint on signal expression. Lastly, we show that within the context of the natural signalling environment, UV-reflective throats constitute a conspicuous, effective signal that male Augrabies flat lizards use to advertise their status honestly to rivals. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Notes: Whiting, Martin J. Stuart-Fox, Devi M. O'Connor, David Firth, David Bennett, Nigel C. Blomberg, Simon P. xD;Part 2
Abstract: Lizards frequently rely on chemical cues to detect the presence of a conspecific or a predator, or to sample and detect potential prey. Male lizards in particular, may chemically sample potential refuges to avoid rivals. We tested whether male common barking geckos (Ptenopus g. garrulus) that normally take refuge in burrows, avoid refuges scented with a rival male. Geckos were equally likely to use an artificial refuge scented by another male compared to a control. We conclude that scent is an unimportant cue for rival male recognition in P g. garrulus based on 1) the result of this experiment: 2) during 5 10 man hours of field work we did not observe a single gecko tongue-flick; and 3) males respond aggressively to recordings of rival males and this appears to be the primary mechanism maintaining male spatial patterns.
Abstract: Previous studies have suggested that most small Australian elapid snakes are nocturnal and rarely bask in the open because of the risk of predation by diurnal predatory birds. Because the physiology and behaviour of reptiles is temperature dependent, staying in refuges by day can entail high thermoregulatory costs, particularly for juveniles that must grow rapidly to maximise their chances of survival. We investigated whether the risk of predation deters juveniles of the endangered broad-headed snake (Hoplocephalus bungaroides) from basking, and if so, whether there are thermal costs associated with refuge use. To estimate avian attack rates on snakes, we placed 900 plasticine snake replicas in sunny locations and underneath small stones on three sandstone plateaus for 72 h. At the same time we quantified the thermal benefits of basking vs refuge use. On sunny days, juveniles could maintain preferred body temperatures for 4.7 h by basking but only for 2.0 h if they remained inside refuges. Our predation experiment showed that basking has high costs for juvenile snakes. Predators attacked a significantly higher proportion of exposed models (13.3%) than models under rocks (1.6%). Birds were the major predators of exposed models (75% of attacks), and avian predation did not vary across the landscape. By trading heat for safety, juvenile H. bungaroides decreased the potential time period that they could maintain preferred body temperatures by 57%. Thermal costs of refuge use may therefore contribute to the slow growth and late maturation of this endangered species. Our results support the hypothesis that nocturnal activity in elapid snakes has evolved to minimise the risk of avian predation.
Abstract: Conflict between the sexes has traditionally been studied in terms of costs of mating to females and female resistance. However, courting can also be costly to males, especially when females are larger and aggressively resist copulation attempts. We examined male display intensity towards females in the Cape dwarf chameleon, Bradypodion pumilum, in which females are larger than males and very aggressive. We assessed whether aggressive female rejection imposes potential costs on males and whether males vary their display behaviour with intensity of female rejection, female size or relative size differences. Males persisted in courtship after initial female rejection in 84% of trials, and were bitten in 28% of trials. Attempted mounts were positively associated with males being bitten. Males reduced courtship with increased intensity of female rejection. Male courtship behaviour also varied with female size: males were more likely to court and approach smaller females, consistent with the hypothesis that larger females can inflict more damage. These results suggest that, in addition to assessing female willingness to mate, male dwarf chameleons may use courtship displays to assess potential costs of persistence, including costs associated with aggressive female rejection, weighed against potential reproductive pay-offs associated with forced copulation.
Abstract: We examined museum specimens of the Common Barking Gecko (Ptenopus garrulus) from the Kalahari and Namib Deserts to assess sexual size dimorphism, reproductive status, and diet. Males had significantly wider heads than females of the same body size; however, P. garrulus showed no sexual dimorphism in any other morphological character. The smallest mature male was 36 mm snout-vent length, whereas the smallest female was 31 mm. Peak reproductive activity for both sexes was in September and October. Clutch size was fixed at one large egg (average size = 5.9 X 4.4 mm); all eggs were in the right ovary, but more than one clutch may be laid in a single breeding season. Ptenopus garrulus, when compared with other geckos, produces very large offspring and thereby invest heavily in a single offspring. We recorded 15 arthropod orders in the diet of P. garrulus. Termites dominated their diet both numerically and volumetrically. Males and females ate prey of similar taxa and sizes, suggesting that trophic partitioning is absent. Therefore, the evidence suggests that the evolution of head width differences is driven by male contest competition.
Abstract: Habitat degradation through over-grazing and wood collection is especially prevalent in developing countries such as South Africa. As human populations expand and the demand for land increases, the traditional idiom of setting aside protected areas for conservation is insufficient and assessment and protection of diversity outside these areas is needed. We assessed the impact of land use on lizard assemblages in communal rangelands in South Africa by comparing abundance, species richness and species diversity between degraded communal lands with a protected area. We first quantified vegetation differences between the study areas and found marked differences. Communal lands had significantly fewer large trees and less ground cover. Contrary to prediction, we found no evidence that any species of lizard was negatively affected by habitat disturbance. Some species were more common in communal lands, and species richness and diversity were also higher using certain sampling techniques. Terrestrial diversity was likely enhanced due to the preference of many terrestrial lizards for open, sparsely grassed areas. We discuss other reasons for increased diversity such as the intermediate disturbance hypothesis and/or reduced numbers of predators and competitors. We also conducted surveys of households and traditional healers to investigate the relationship between human uses of reptiles and abundance. The predominant users of reptiles were traditional healers. The most commonly used species were not encountered in our field surveys, and respondents indicated that they appeared to be declining. Our results emphasise the importance of integrating local knowledge into biodiversity assessment and conservation planning. Although we did not identify a negative impact of disturbance on lizard communities, community structure was different and this likely influenced ecosystem integrity and function in some way. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: The African flat lizard genus Platysaurus is widely distributed oil rock outcrops in southern Africa and is found both east and west of the Kalahari Desert and between major river drainage systems. We assembled a molecular phylogeny for the genus in order to test several biogeographic hypotheses. Sequence data were obtained from 29 specimens representing 14 taxa of Platyaurus that span the geographic range of the genus. We targeted a fragment of the mitochondrial genome comprising the 3' half of the ND4 gene and most of the flanking tRNA-HSL. cluster. The edited alignment comprised 864 characters, of which 479 (55%) were variable and 461 (96%) parsimony informative. Overall. the phylogeny was well resolved and supported by high bootstrap values. Four major clades were identified comprising two to seven species: P. mitchelli and P. maculatus maculatus from the north-eastern range of the genus; P. broadleyi and P. capensis from the western range; P. imperator. P. torquatus, and P. intermedius rhodesianus P. i. intermedius, P. monotropis, P. minor. P. i. nigrescens, P. lebomboensis. P. i. wilhelmi. and P. o. orientalis. Platysaurus has been suggested to represent a recent adaptive radiation where rapid speciation was fuelled by population fragmentation brought on by vicariant events and possibly divergent sexual selection. The traditional explanation for the radiation of the genus is that the eastern migration of the Kalahari sands fragmented populations in the Plio-Pleistocene, resulting in conditions favorable for speciation. Our genetic data strongly suggests that many of the speciation events in Platysaurus already had occurred prior to the Plio-Pleistocene. Moreover. vicariant events associated with the formation of the major river systems played an additional role in the evolution and distribution of Platysaurus species. Our topology displays long internodes and long terminal branches. suggesting that the radiation is much older than previously believed. (C) 2003 Elsevier Inc. All rights reserved.
Abstract: We studied tree agama (Acanthocercus a. atricollis) habitat use in the Magaliesberg mountain range in northern South Africa using sightings of marked individuals, and in a few cases, radio-telemetry. Acanthocercus a. atricollis preferentially selected thorn trees (46%; Acacia karroo), followed by common sugarbush (10%; Protect caffra) and dead trees (9%). The type of tree selected was unrelated to lizard age class or sex. Multivariate analysis failed to show any age class or sex effects for specific tree physical characteristics, but did reveal a preference for trees with greater diameter, canopy cover and incidence of parasitic plants. We suggest that more 'complex' trees may enhance crypsis, facilitate escape from predation, or provide a foraging advantage. Acanthocercus a. atricollis selected night-time perches higher than those used during the day, possibly further offsetting predation risk.
Abstract: Lizards that forage from ambush do not exhibit prey chemical discrimination, but might enhance foraging efficiency by staying longer at ambush posts bearing chemical prey cues. By presenting chemical stimuli to free-ranging lizards, we tested whether Platysaurus broadleyi had longer giving-up time (i.e., time at an ambush post) in the presence of insect prey stimuli. The lizards remained no longer at tiles labelled by prey chemicals than control substances, but giving-up times were greater at tiles labelled by a plant food (fig). Ambush foragers may not use prey chemicals to assess the quality of ambush posts.
Abstract: Flat lizards Platysaurus intermedius wilhelmi occur on small discrete rock outcrops in Mpumalanga Province, South Africa. These rock outcrops are structurally simple and this, combined with the lizard's behaviour (ambush foraging in the open), make them ideal for field studies of anti-predatory behaviour. Lizards were approached in the field and how escape behaviour was influenced by habitat and age-sex class was recorded. Juveniles (c. 4 months of age) responded quite differently to an approaching human 'predator' compared with adult males and females (which responded similarly). Compared to adults, juveniles allowed a closer approach by the investigator; took longer to find a refuge and therefore fled further; were more likely to remain visible in the open and maintain visual contact with the investigator; and more likely to flee into vegetation when given the opportunity to take refuge in a crevice. We suggest that because a greater suite of predators (including arthropods living in rock crevices) feed on small juvenile lizards, this may affect their choice of refuge and result in the avoidance of crevices when chased. Finally, because juveniles were frequently found on small rock outcrops, the influence of rock outcrop area on anti-predatory behaviour was tested. Escape behaviour (time to refuge) was independent of rock outcrop area.
Abstract: We examined the relative importance of male and home range quality on female-male spatial overlap in the tree agama, Acanthocercus atricollis atricollis. Specifically, we asked whether males in good condition had the greatest spatial overlap with females, whether these same males have the best home ranges, or whether females are simply occupying areas with the best habitat and highest food abundance. Tree structure and prey abundance were used as measures of male home range quality, and male snout-vent length and male body condition were used as indices of male quality. Males had significantly larger home ranges compared to females and female-male overlap was common, while male-male overlap was marginal in a few cases (n = 3). Contrary to prediction, larger males did not occupy larger areas and home range size was not influenced by prey abundance. However, there was significant variation in prey availability between male areas. Female-male overlap was linked to prey abundance in male home ranges, possibly because of the direct influence it has on female fitness. However, several high quality males with high spatial overlap With females also had relatively high prey abundance. Male quality may well be linked to resource availability, but small sample size requires a cautionary interpretation.
Abstract: Tail autotomy is a widespread method of escape among lizards and can be costly. Most studies on the effects of tail loss have focused on active foraging lizards, but few data exist for ambush foraging lizards. we investigated potential costs associated with tail autotomy in an extreme ambush foraging cordylid lizard, Cordylus melanotus melanotus. We induced tail autotomy in free-ranging male Cordylus m. melanotus and measured potential shifts in behaviour (movements, foraging behaviour, time exposed and average distance to a potential refuge), and responses to an approaching human compared to marked individuals with complete tails. Tailed and tailless lizards behaved in a similar fashion for all measured variables although power tests could not rule out the possibility of falsely accepting the null hypothesis in some cases. We also measured locomotory performance (maximum sprint speed) for tailed and tailless lizards in the lab. Locomotory performance was also not compromised by tail loss. Finally, we measured the energetic content of tails as a proportion of total energetic content using bomb calorimetry. The cost of tail autotomy was approximately 12% of the total body energy (wet weight). Our results suggest that the major cost of tail loss in Cordylus m. melanotus is energetic.
Abstract: Differences between sexes in physiological performance have received little attention in animals. We tested for sex differences in maximum sprint speed and maximal exertion over a range of temperatures in a population of Platysaurus intermedius wilhelmi lizards. We also examined sex-based differences in selected temperature range, mean field body temperatures (T-b), and thermal activity limits. Finally, we conducted field studies to quantify male and female responses to a potential predator, which may be affected by their respective performance capabilities. Males were faster than females at all temperatures, and body size had no significant effect on sprint speeds. Males and females also selected similar T-b's when placed in a thermal gradient, but in the field, male lizards' T-b's were different from those of the females. However, predicted sprint speeds for males and females at their field T-b's are similar. No significant differences were found between males and females with regard to maximal exertion. When approached in the field, adult male lizards took refuge significantly earlier than did adult females and also fled over shorter distances, suggesting that females rely on crypsis as an escape strategy.
Abstract: One hundred and sixty-four museum specimens of the tree agama Acanthocercus a. atricollis were measured and dissected to examine sexual size dimorphism, reproduction and diet. Foraging mode and behaviour were also quantified in a wild population to obtain a broader picture of their foraging ecology and to test the hypothesis that tree agamas are ambush foragers. Males and females did not differ significantly in snout-vent length (SVL) or tail length; however, mature males had larger heads than females of the same body size. The smallest female showing sexual maturity was 96 mm SVL and the smallest male was 82 mm SVL. Mean clutch size was 11.3 and was positively correlated with female body size. Reproduction was seasonal and male and female reproductive cycles were synchronous. Testicular volume was greatest during August September and females contained enlarged follicles during August-December and showed no evidence of multiple clutching. Tree agamas fed on a broad spectrum of arthropods (10 orders), including millipedes, which other lizard taxa have been reported to avoid. Gut contents were dominated numerically by ants (92%), followed by beetles (4%). Volumetrically, orthopterans (26.8%) were most important, followed by beetles (26.3%) and ants (17.9%). Compared to adults, juvenile diet by volume was dominated by ants and consisted of fewer large prey items (e.g. beetles and orthopterans). Seasonal effects in both prey diversity and volume were evident. Tree agamas are classic ambush foragers. They spent only 4% of their time moving and made few movements per minute (mean = 0.4). When stationary, adult tree agamas positioned themselves on tree trunks (34.7%), on lateral branches (41.8%) and occasionally, on the ground (23.4%). No evidence of trophic partitioning (intraspecific niche divergence hypothesis) was found and field observations revealed that males defend territories and engage in combat. This supports the idea that selection may be favouring larger head size in males, as an outcome of male contest competition.
Abstract: Foraging: methods of insectivorous lizards fall into two major modes, ambush foraging, in which the lizard waits immobile to detect prey and active foraging, in which the lizard mo ies through its habitat while searching for pre!: Both modes exhibit remarkable phylogenetic stability Ambush foraging is the sole mode of all iguanians examined to date, and active foraging is the only known mode in large scleroglossan clades such as Teiidae and Varanoidea. We present quantitative data on foraging behavior demonstrating the existence of intrageneric variation in foraging: mode in the scincid genus Mabuya in southern Africa. Like the large majority of skinks, Mabuya striata sparsa, M. sulcata, and M. variegata are active foragers that have high values of number of movements per minute (MPM), proportion of time spent moving (PTM), and mean speed (average speed including time spent immobile) but relatively low speed while moving. In contrast, M. acutilabris and M. spilogaster are ambush foragers having significantly lower MPM, PTM, and mean speed but higher avenge speed while moving than the other species. The importance of these findings is twofold. first, intrafamilial variation in foraging mode in Scincidae and intrageneric variation are verified for Mabuya. Second, because intrageneric variation in foraging mode was previously known from quantitative data only in the lacertid genera Acanthodactylus and Pedioplanis (and atypically in Meroles), an excellent opportunity is provided to test hypotheses about foraging mode without confounding interfamilial phylogenetic differences.
Abstract: In the Kalahari desert the tree skink Mabuya striata sparsa occupies Acacia trees separated by areas of open sand. On a single day in austral spring, the effects of tree size and structural complexity, presence of colonial nests of weavers, and fallen limbs on lizard abundance, and of time of day and air temperature on numbers of lizards active, location on trees, ground, or ground cover, and occupation of sunny, shaded, or partially shaded sites were examined. Multiple regression showed that the numbers of adult and total lizards increased with tree size, amount of ground cover, and air temperature. Neither number and size of sociable weaver nests nor complexity of tree shape affected lizard abundance. Proportions of lizards on trees and ground did not vary with time of day; neither did height above ground among individuals on trees. The proportions of lizards fully exposed to the sun was higher early and late in the day than at midday, when more lizards occupied shaded sites. (C) 2000 Academic Press.
Abstract: Lizards are not widely regarded as able to alter their foraging mode substantially in relation to the specific food source utilized. Rather, their foraging mode determines the food type that they utilize. We studied Platysaurus brondleyi, a lizard that utilizes food. resources differing in several fundamental characteristics. We found that they maintain this broad feeding niche by altering their foraging behavior. Adult lizards ambushed mobile insects but searched actively when feeding on stationary figs beneath trees. This flexibility in foraging behavior allowed P. broadleyi to utilize figs, a high energy but ephemeral resource. Lizards did not vary their foraging mode in response to insect-prey density, but attack distances were further at the site with lower insect density, as predicted by optimal foraging theory. Juveniles adopted an intermediate foraging mode irrespective of the resource utilized.
Abstract: Most lacertids are active foragers, but intrafamilial variation in foraging mode is greater than in most lizard families. We collected data on eight species of African lacertids to assess this variation. Both active and ambush foraging occurred within Pedioplanis and Meroles. Meroles ctenodactylus had a proportion of time moving and proportion of attacked prey detected while moving intermediate to those for actively foraging and ambushing Pedioplanis, but its number of movements per minute was exceptionally high. This species has a unique mixed foraging mode. Like active foragers, it seeks food by tongue-flicking while moving and spends a high percentage of the time moving. Like ambush foragers, it searches visually for prey during pauses between movements. Our findings confirm published data on four Kalahari lacertids. We discuss the history of foraging modes in advanced lacertids.
Abstract: The reproductive biology of the Concho water snake (Nerodia harteri paucimaculata) was studied from 1988 to 1992 in central Texas. Minimum snout-vent lengths (SVL) at maturity were 380 mm in males and 460 mm in females. Mating occurred primarily in late April and early May although rye observed some evidence of fall mating. Gestation was approximately three months. Parturition occurred predominantly in mid-August, ranging from 29 July to 22 September. Approximately 85% (range 79.5-88.8) of adult females were gravid each year with the proportion of reproductive females varying as a function of body size. Litter size averaged 11.1 (range 4-29) and varied both among and within study sites. Maternal SVL was correlated with litter size and mass but not offspring SVL or mass with litter size held constant. Litter size had no effect on offspring SVL or mass when female SVL was held constant. Relative clutch mass averaged 0.46 and was independent of female size. Mean offspring length and mass were 175 mm SVL and 3.8 g, respectively, showing no overall sexual differences. However, mean SVL was typically greater far females within litters.
Abstract: Two lizard foraging modes, ambush and active foraging, are usually quantified by the variables MPM (movements per minute) and PTM (proportion of time spent moving), but both variables may be affected by behaviors other than foraging. We introduce PAM, the proportion of attacks on prey discovered while lizards are moving (in relation to total attacks). PAM focuses exclusively on foraging behavior Preliminary data reveal a very high, significant rank correlation between PAM and PTM, and a fairly high, but nonsignificant correlation between PAM and MPM. Collection of PAM data can be very time-consuming. In the absence of PAM, PTM appears to be a superior index of foraging activity to MPM, but all three indices provide valuable information on different aspects of foraging. We additionally present data for four agamine and five gekkonid species from southern Africa. The first quantitative data for agamines (all for Agama) agree with previous qualitative assessments that members of several agamine genera are ambush foragers. All the gekkonids, including three species of Rhotropus and one each of Pachydactylus and Phyllodactylus, are ambush foragers, like most geckos studied to date.
Abstract: Flat lizards (Platysaurus broadleyi) at Augrabies Falls National Park, South Africa, are restricted to rocky terrain where the predominant tree is the Namaqua fig (Ficus cordata cordata). P. broadleyi readily feeds on Namaqua figs when they are available, and the lizards sometimes form large (maximum recorded = 134) congregations under fruiting fig trees. The distance lizards travel to fruiting trees also exceed normal daily foraging distances. Location of fruiting fig trees by a lizard can have a high pay-off because figs are energetically rich and trees fruit irregularly and asynchronously, resulting in a resource that is available, but unpredictable in time and space. The prediction that bird activity in fig trees provides a cue to the presence of ripe figs was tested experimentally. By placing cages containing birds and empty control cages in trees devoid of fruit, we demonstrated that P. broadleyi are drawn to fig trees with high bird congregations. We also tested if the presence of a fig tree was necessary to draw lizards to bird congregations by placing cages containing birds and empty control cages in a matched-pairs design on rock away from trees. Namaqua fig trees were not necessary to draw lizards to bird congregations.
Abstract: Differential treatment of neighbours and strangers (the dear enemy phenomenon) can reduce the costly effects of territory defence. Individual recognition, and by extension the dear enemy phenomenon, was examined in the cordylid lizard Platysaurus broadleyi. I had no knowledge of familiarity between individuals and therefore classed intruders as neighbours or non-neighbours and tested for differences in a,agonistic response consistent with the dear enemy phenomenon. In the dear enemy phenomenon, levels of aggression are inversely related to degree of familiarity such that residents are more tolerant of immediate neighbours than distant territory holders. A manipulative field experiment in conjunction with field observations of known territory holders revealed that resident males allowed neighbours to approach more closely than non-neighbours before challenging them, residents were more aggressive towards non-neighbours than neighbours, contests between neighbours were significantly longer than between neighbours and non-neighbours and contests between residents and non-neighbours were likely to result in a win for the resident. while neighbours frequently drew contests. These results suggest a level of recognition consistent with the dear enemy phenomenon. I also manipulated front leg colour to test the hypothesis that it alone could serve as a cue for individual recognition. I found no support for this hypothesis and suggest that multiple cues operate in individual recognition.
Abstract: Harvester ants, Pogonomyrmex barbatus (F. Smith), exerted an energetic cost on the dung beetle Canthon imitator Brown through behavioural interference, by causing brood ball abandonment. This was verified experimentally in eight independent trials. Significantly more C. imitator (87.5%) abandoned brood balls after encountering P. barbatus on ant mounds. No fatalities were recorded from trials although harl ester ants were observed to sting and bite dung beetles. Five transects revealed a mean of 10.8+/-1.11 (range: 9-15) ant mounds/200 m. For a total of 54 ant mounds, brood balls occured at a mean of 1.3+/-0.31 (range: 0-13)/mound. Compared to random points,brood balls occured significantly more often on ant mounds (48% Of mounds contained brood balls).
Abstract: The distribution, movements, activity range, and habitat use of the Concho water snake, Nerodia harteri paucimaculata, were studied by mark-recapture and radio telemetry in a large lake system, in central Texas, USA. Concho water snake emigration and distribution were largely driven by alteration of habitat availability caused by fluctuating water levels. Habitat characteristics associated with the presence of snakes at the study area were turbid water, minimal wave action, a gentle shoreline gradient, a silt substrate, and a rocky shoreline. Males and gravid females were equally vagile, and the likelihood of a snake undertaking an emigrational movement was independent of age and/or reproductive condition. However, males had significantly more movement days than gravid females. Radio-tagged males had detectable movements on 64% of monitored days, compared to 43% of monitored days for gravid females. Mean activity range length was 278 m for males, 219 m for gravid females, and 210 m for juveniles. Concho water snakes generally selected retreat sites within 3 m of water, although gravid females selected sites as far as 15 m from water. As a management procedure for lake populations, we advocate increasing the vertical distribution of rocky shoreline.
Abstract: A morphometric method of analysis is applied to specimens attributed to the same species, using museum collections of mammals, birds, reptiles and insects. We demonstrate a central tendency of the log-transformed standard error of the m-coefficient (log(10) s.e.(m)), derived from linear regression analyses associated with equations of the form y = mx + c, when measurements of one specimen are compared against corresponding measurements of another specimen attributed to the same species. As indicated previously, this approach has potential application in palaeontological contexts where there is uncertainty about arty two specimens being conspecific. We recommend that s.e.(m) statistics be used in exploratory studies to quantify probabilities of conspecificity when any two hominid specimens are compared.
Abstract: The first quantitative data on foraging mode in the cordyliform lizards reveal different foraging behaviours between and within families. All species of cordylids studied (four Cordylus, two Pseudocordylus, and one Platysaurus) are ambush foragers. However, the species of Cordylus and Pseudocordylus microlepidotus are the most extreme ambushers. These species spent a significantly lower per cent time moving than did all of the other species studied and made significantly fewer movements per minute than Platysaurus capensis and gerrhosaurids. In addition, P. microlepidotus made significantly fewer movements per minute than did its congener Pseudocordylus capensis. Possible reasons for the high number of movements per minute in Platysaurus capensis are discussed. Very limited observations of two gerrhosaurid species show that Cordylosaurus subtessellatus is an active forager and Gerrhosaurus validus forages actively at least some of the time. A tentative hypothesis of the evolution of cordyliform foraging behaviour based on very limited data hints that active foraging is plesiomorphic in the Gerrhosaurini and further that gerrhosaurids may have retained active foraging from the common ancestor of Scincidae and Cordyliformes. Somewhat stronger data suggest that ambush foraging arose in the common ancestor of Cordylidae or Cordylinae. Further study is needed to trace inter-and intrageneric changes in foraging mode in cordylids.
Abstract: Using captures in mist nets and monitoring echolocation calls, we quantified bat distribution and activity and measured insect abundance as numbers of insects attracted to black lights at 15-min intervals. These data were collected simultaneously at pairs of sites in riverine and dry woodland savannah along a transect of ca. 350 km from north to south in the Kruger National Park, South Africa. The sites were situated in the north, central, and south of the park and data were collected in January 1993. Our study involved 18 sites, three pairs each in the areas of the Luvuvhu, Letaba, and Sable rivers. Half of the sites were in riverine woodland, the others in dry woodland. No statistical association exists between bat captures and either bat activity or insect abundance. Bat activity, however, was related significantly to insect abundance. Although bats were significantly more abundant (captures) in riverine habitats than in dry woodland savannah, comparisons of bat diversity and evenness (rarefaction curves, species abundance curves, and Whittaker plots) showed no differences between these habitats. The data neither demonstrate a decline in bat diversity away from the equator nor suggest specific bat communities associated with riverine habitats. The data do demonstrate the important influence of insects on the activity patterns of insectivorous bats.
Abstract: The diet of the Concho water snake Nerodia harteri paucimaculata was investigated from 1987 to 1990 by palpation of stomach contents. Prey remains representing 304 prey items were recovered from 192 individual snakes. Concho water snakes were almost completely piscivorous, feeding on 19 species of fish from nine families with minnows (Cyprinidae) dominating numerically. Cricket frogs (Acris crepitans) represented the only non-piscine prey. Diet diversity increased ontogenetically according to snake body size. Observations of foraging snakes suggest an ontogenetic change in foraging sites concurrent with a change in diet composition. Prey size was positively correlated with snake body size although some snakes occasionally ingested numerous small prey, possibly due to opportunistic feeding on small prey aggregations. Snakes occasionally attempted to handle prey too large to be ingested. Feeding occurred from mid-March to early November. Gravid females fed throughout the spring into mid-July and resumed feeding after parturition. Neonate and juvenile riverine snakes ingested prey in proportion to apparent availability while adults consumed a disproportionate amount of larger prey species. Lacustrine snakes primarily consumed prey associated with benthic or shallow water habitats. However, few individuals of open water and top water species were ingested, suggesting that prey habitat preference strongly influences catchability in lake systems.
Abstract: The spatial distribution of a Texas horned lizard population was quantified with respect to habitat and prey. Horned lizard spatial distribution was clustered in three specific areas, whereas ant mounds belonging to their primary prey, Pogonomyrmex barbatus, were randomly distributed in the study area. An analysis of vegetation cover relative to horned lizard spatial distribution suggests that habitat, not prey, governed the spatial distribution of this population. In particular, horned lizards selected disturbed areas where ground cover was less dense. Horned lizards occurred at a density of one lizard/3,636 m2 or nearly three lizards/ha. Pogonomyrmex barbatus mounds occurred at a density of 15.9 mounds/ha, equivalent to about 196,492 ants/ha. Relative to harvester ants, horned lizards occurred at a ratio of one lizard per six ant mounds or one lizard per 74,148 ants. Compared with a previous study in New Mexico, harvester ant density was considerably greater, however, horned lizard density was less. This may be related to prey availability; although ants are less abundant at the New Mexico site, more individuals may be available for consumption due to habitat differences.
