Sand Dune Lizard Research Articles

The Contribution of Aquatic Plants to the Trophic Ecology of a Sand Dune Lizard in Southern Brazil

Trophic subsidy is an ecological process consisting in the transference of nutrients between adjacent habitats, allowing the occupancy of less productive habitats by several species. We tested for the existence of trophic subsidy provided by aquatic plants of temporary ponds in maintaining individuals of the sand dune lizard Liolaemus occipitalis in southern Brazil. This lizard is a sit-and-wait predator restricted to coastal sand dunes. As these sand dunes occur in a mosaic of temporary ponds, we hypothesized the existence of a nutritional/energetic dependence of lizards from adjacent aquatic habitats. Our evaluation was based on carbon and nitrogen stable isotope analysis in association with gut content analysis of lizards sampled along an entire inundation cycle. Stomach contents revealed no seasonal variation in consumed prey item composition. Nevertheless, we detected changes in prey group composition. The volumetric contribution of Diptera increased over inundation classes (increase = 5%; peak = 61%). Carbon and nitrogen stable isotope ratios indicated that the L. occipitalis trophic web is mainly maintained by terrestrial sources. Isotope ratios also indicated the existence of aquatic contributions to tissue formation, but, despite its tendency to increase over the inundation process (10.7–13.3%), this trend lacks statistical support. We conclude that the studied population of L. occipitalis partially depends on trophic subsidy from aquatic sources and that any conservation plan for this endangered lizard species should take into account the preservation of non-habitats like temporary ponds.

A management strategy for the long-term conservation of the Endangered sand-dune lizard Liolaemus multimaculatus in the Pampean coastal dunes of Argentina

AbstractThe sand-dune lizard Liolaemus multimaculatus is an Endangered species endemic to the Pampean coastal dunes of Argentina. To inform the development of a future Action Plan for this species, we investigated the demography and conservation status of all remaining populations, and we suggest management actions appropriate to local needs. We used population viability analysis to assess extinction risk in three inbreeding scenarios and estimate the minimum viable population and the minimum area requirement. To assess the current status of each local population, we used information related to population size, human pressure and connectivity. The results were then used to set and prioritize conservation management actions at local level. Our models indicated that populations of > 2,400 individuals would be viable in the long term and that inbreeding depression has a strong effect on extinction risk. The southern patches of coastal dune contain the largest populations of sand-dune lizards, and they are also better connected and less threatened. We suggest land protection as the priority management action for populations larger than the minimum viable population, whereas habitat recovery, when possible, should be the priority for patches of coastal dune smaller than the minimum area requirement. Supplementation with a small number of individuals could stabilize unviable populations but should be considered only in certain situations.The long-term conservation of the sand-dune lizard will be feasible only if a conservation action plan is developed and implemented.

The Influences of Habitat on Body Temperature Control in a Southern Population ofLiolaemus Occipitalis(Boulenger, 1885) in Brazil

This study aimed to estimate the degree of body temperature control of the sand dune lizard Liolaemus occipitalis in the subtem- perate climate region of southern Brazil. The data suggest more accurate thermoregulation in males than females. Sand substrate appears to be more important than air in serving as a heat source for the lizards. The high conductivity of sand might minimize the effects of the relatively low average air temperatures in southern Brazil. Nevertheless, the mean body temperature of L. occipitalis from southern Brazil was lower than that recorded in northern populations of L. occipitalis and other Liolaemus species in southern latitudes of South America. This suggests that maintenance of body temperature might be the limiting factor for the expansion of the southern limit of the species distribution.

Vegetation Refuges of a Sand Lizard Assemblage in Temperate Coastal Sand Dunes

Natural refuges constitute a fundamental resource in the habitat of any given species. Consequently, the knowledge of those elements that are used as protection from predators is a priority for conservation. We studied the antipredatory mechanisms of an assemblage of sand dune lizards, determining whether refuge sites are random or whether particular types are chosen depending on their availability. We also compared the frequencies of the use of refuge sites with the use of perch sites by individuals at initial detection. Liolaemus multimaculatus used sites under rocks, either as refuges or as perches, and sites under sub-shrubs (Senecio bergii) and clump herbs (Spartina ciliata) as refuge only. Liolaemus gracilis used sites under creeping herbs (almost exclusively Panicum racemosum) and sub-shrubs (Senecio bergii) as refuge and perch sites more frequently than expected. Liolaemus wiegmannii only used sub-shrubs (mainly Melilotus indicus but also Achyrocline satureioides and Senecio bergii) both as refuge and perch sites. We show that lizards of Costa Bonita select certain types of native psammophytic grassland plants as refuge. Most of the plants used as refuge are also used as perch sites.

Ampliación del conocimiento sobre uso de hábitat en Liolaemus multimaculatus, sitios de fuga

The knowledge about spatial preferences in animals represents the first stage to understand the interactions between the organisms and its environment. The sand dune lizard (Liolaemus multimaculatus) is a species highly adapted to live in the sand. The goal of this work was to study the habitat use in different moments/situation during its period of activity, in order to obtain a more understanding about spatial preferences in this species. Models based on the use vs availability criterion were applied in order to assess the preferences for sites used as refuge and to compare those sites with perch sites. The models shows differences between use and availability and also differences between perch sites and refuge sites were observed. Results shows that this species used a great diversity of microhabitats with a high reject for microhabitats without vegetation cover. The conservation of good habitats for this species must consider both kinds of microhabitats, those used for thermoregulation and feed and those others used for refuge.

Selection of key features of vegetation and escape behavior in the Sand Dune Lizard (Liolaemus multimaculatus)

Abstract Vegetation structure and cover are two of the main factors which determine microhabitat preferences in lizards. The Sand Dune Lizard (Liolaemus multimaculatus) is a vulnerable and endemic species of the pampean coastal habitats from Argentina. We hypothesized that: a) Sand Dune Lizard prefer to perch in microhabitats that offer a good balance between visibility and refuge, and; b) lizards prefer microhabitats in which plant types allow them to resort to sand burying behavior. We recorded data of microhabitat (bunch-grasses sizes and plant types) used by lizards (males, females and juveniles) in a population at the Mar Chiquita Provincial Nature Reserve. We applied the use-availability design to assess preferences. We evaluated differences between sex and relation between sizes of lizards. Lizards preferred bunch-grasses of intermediate size. Habitats conformed only by herbaceous species were the most preferred by lizards. We did not find differences between males and females, neither relations between size of lizards and the tested variables. Adult lizards of both sexes use bunch-grasses more frequently than juvenile individuals. The preferences for herbaceous species could be related to the sand-bury behavior that lizards use to escape from predators. More studies are necessary in order to assess the processes related with habitat preferences

Home Range Size and Overlap inLiolaemus multimaculatus(Squamata: Liolamidae) In Pampean Coastal Dunes of Argentina

The home range is the space used by individuals to carry out their life cycles. The Sand dune lizard (Liolaemus multimaculatus) is a vulnerable species, endemic to the pampas coasts of Buenos Aires and Río Negro Provinces in Argentina. The aim of this work was to assess home range size and overlap of the Sand dune lizard. The study was carried out at Mar Chiquita Provincial Reserve. Home range and overlap were calculated using the minimum convex polygon method. The mean ±SD home range size for all individuals was 45.90 ± 74.37 m2 and no differences were observed between males and females (p = 0.49). However, an analysis without outlier individuals showed more accurate values for females (21.31 ± 17.59 m2) and males (33.52 ± 24.62 m2), and differences between sex were observed (p = 0.04). The relationship between body size and home range size was not significant (p = 0.41). Home range overlap was high (22 to 58%; Fig. 2) and did not show differences between males and females (p > 0.05 in all cases). Our results showed some similarities with the Brazilian sand lizard (Liolaemus lutzae) in which home range value is only up to 1.5 units higher than in L. multimaculatus. Further studies about this species' social system are necessary to understand the observed patterns.

Methods for Assessing Population Size in Sand Dune Lizards (Liolaemus Multimaculatus)

Basic information, such as population size and density, is needed for conservation and management of many species, especially threatened species. Thus, well-designed population monitoring programs that use appropriate methods for estimating parameters of interest, including density and survival, are needed as well. Mark-recapture and distance-sampling are established methods for estimating density in wildlife surveys. The sand dune lizard (Liolaemus multimaculatus) is an endemic and vulnerable species that inhabits dune habitats in Argentina. At present, however, there are no accurate estimates of density of this species and no established monitoring programs. The objectives of this study were (1) to test the use of mark-recapture and distance-sampling methods and (2) to estimate density of this species in Mar Chiquita Reserve (37° 37′ S–57° 16′ W), an important area for the protection of this species. For distance-sampling surveys, we used a systematic line-transect design; for mark-recapture sampling, we performed exhaustive surveys and captured, marked, and recaptured lizards manually. Based on distance-sampling, populations were estimated at 3.6 and 5.4 individuals per ha in 2007 and 2008, respectively; corresponding estimates based on mark-recapture data were 5.2 and 4.1 individuals per ha in 2007 and 2008, respectively. Detection probabilities were 0.23 in both 2007 and 2008 distance-sampling analyses and capture probabilities were 0.02 and 0.05 in 2007 and 2008 mark-recapture analyses. Based on these estimates, the Mar Chiquita Reserve contains a population of at least 10,000 individuals. Both methods were adequate for estimating populations of sand dune lizards, given the facility with which individuals can be detected and captured. The distance-sampling method requires less effort, but the mark-recapture method allows estimates of survival as well as density. Results of this work provide the baseline for developing a monitoring program for this lizard, and we suggest that the distance-sampling method be used to monitor all populations of sand dune lizard.

Characterization of microsatellite markers for the endemic sand dune lizard, Sceloporus arenicolus

AbstractHere we characterize and report on the genetic variability of eight microsatellite loci for the endemic sand dune lizard, Sceloporus arenicolus, that amplified consistently for individuals throughout the species’ range. The number of alleles per locus was high (mean = 13.25) and observed heterozygosities ranged from 0.354 to 0.808. With the exception of a single locus, the loci did not deviate from Hardy–Weinberg expectations. This set of markers is currently being used to examine population structure and landscape genetics in S. arenicolus, a habitat specialist with a restricted range and patchy distribution.

Effects of Vegetation Loss on a Sand Dune Lizard

Habitat degradation in the form of vegetation loss often decreases the abundance of various species of reptiles (Fleischner 1994, Smith et al. 1996). Several reasons have been proposed for why vegetation loss should decrease abundance, including reduction of thermoregulatory patches, decreased prey availability, and increased predation from being in more exposed areas (Jones 1981, Norbury 2001). Vegetation loss could adversely affect lizards because they might be unable to escape lethal substrate temperatures (Adolph 1990, Carrascal et al. 1992). Vegetation loss may also decrease food availability, which could affect reptile abundance either directly or indirectly by affecting behavior. Individuals might compensate for reduced food availability by moving farther in search of prey or spending more time foraging, which might increase their susceptibility to predators (MacArthur and Pianka 1966, Hinsley 2000). Vegetation loss might additionally increase predation risk because fewer refuges are available. We examined the effects of vegetation loss by livestock grazing and agricultural practices on the abundance of the lizard Acanthodactylus longipes. To investigate the differences in abundance we found, we next compared body condition, thermoregulatory behavior, and activity patterns of lizards from unprotected and protected habitats. To test the hypothesis that vegetation loss affected thermoregulatory behavior, we compared the time that A. longipes spent thermoregulating by postural changes in unprotected and protected habitats. We expected that lizards in habitats with less vegetation might spend more time thermoregulating at higher temperatures by postural changes, while lizards in protected habitats might use vegetation more frequently. To test whether vegetation loss affected food availability or susceptibility to predation, we examined whether lizards in habitats experiencing vegetation loss moved greater distances or spent more time moving than in protected habitats. We assumed that if food availability were decreased, lizards would compensate by moving greater distances while foraging or spending more time foraging. This analysis also assumes that more active lizards are at higher risk of predation due to greater visibility. To provide an additional assessment of predation risk, we examined the distance from vegetation at which the lizard was observed. A. longipes is a common diurnal lizard that inhabits the sand dune deserts of North Africa and the Middle East; it thermoregulates by postural changes and by using vegetation (Attum 2004). A. longipes is ecologically and morphologically specialized for psammophile environments (Arnold 1981, Baha El Din 2001).

Thermoregulatory accuracy, precision, and effectiveness in two sand-dwelling lizards under mild environmental conditions

We investigated thermoregulation and habitat use in two sympatric lizard species of the family Phrynosomatidae (side-blotched lizards, Uta stansburiana, and sand-dune lizards, Sceloporus arenicolus) in southern New Mexico to determine whether thermoregulation was necessary and detectable under mild temperature conditions, and what behavioral mechanisms the lizards used to thermoregulate throughout their daily activity. We measured lizard temperature preference (Tsel) in a laboratory thermal gradient as well as field body temperature (Tb) at the study site. We then calculated several indices of thermoregulation to evaluate the effectiveness of thermoregulation for both species. In addition, we recorded and compared micro- and macro-habitat use for the two species; we also compared these habitats with randomly selected microsites. Uta stansburiana thermoregulated less precisely in a laboratory gradient than did S. arenicolus and had a slightly higher preferred temperature. Environmental thermal heterogeneity occurred at both micro- and macro-habitat spatial scales, allowing lizards to thermoregulate optimally for over 10 h/day. The two species maintained mean body temperatures within their selected temperature range throughout most of the day. Two indices of thermoregulatory effectiveness revealed that both species are effective thermoregulators, and thermoregulation was easily detectable throughout the day. Lizards used the behavioral mechanisms of microhabitat choice, posture, shuttling between sun and shade, and orientation to the sun to regulate Tb.

Water, Energy, and Electrolyte Balance in Captive Namib Sand-Dune Lizards (Angolosaurus skoogi)

Angolosaurus skoogi, were quantified in the laboratory. Both temporal and thermal acclimation of resting metabolic rate (measured by constant volume respirometry) were demonstrated. No significant difference could be detected in the metabolic or evaporative water loss (EWL) rates (measured gravimetrically) of animals resting above and below sand at 30 C. The ratio of active to resting (A/ R) metabolic rates increased with temperature, ranging from 2.5 at 15 C to 3.8 at 40 C. EWL A/R rates showed a similar increase with temperature. It is predicted that, under field conditions, activity would result in about an eightfold increase above both resting metabolic and EWL rates. Animals can, thus, conserve a considerable amount of energy and water by remaining submerged. Energy, water, and electrolyte intake were quantified in two separate feeding experiments. Energy intake showed a fivefold and water intake a fourfold increase between 23 and 37 C. Digestive efficiency averaged 63% in animals fed their natural diet (the cucurbit Acanthosicyos horrida and the grass Stipagrostis hermannii) and 80% in animals fed a diet of carrots. The difference is attributed to the higher fiber content of the natural diet. Digestive efficiency was independent of temperature, but the gut passage time of food ranged from 5.6 days at 23 C to 2.4 days at 37 C. By remaining submerged when ambient temperatures are lower than sand temperatures (e.g., at night), animals can, thus, improve their gross energy assimilation. Compared to the diets of other desert reptiles, the natural diet of A. skoogi has a high water content and a relatively low electrolyte load. The presence of a functional salt gland and an efficient urate excretory pathway suggests that this species is capable of handling a far greater electrolyte load than that ingested with its natural diet. This may be adaptive in times of feeding stress.