Carolina Block

Nonnative Vegetation Induces Changes in Predation Pressure and Escape Behavior of Two Sand Lizards (Liolaemidae: Liolaemus)

Abstract:  The introduction of nonnative plant species might generate habitat modifications that, in turn, increase the predation risk for animals, either by making prey species more conspicuous, limiting the availability of refuges, or by offering vantage points to potential predators. We compared predation pressure and escape behavior of two sympatric species (Liolaemus wiegmannii and Liolaemus multimaculatus) of Sand Lizards inhabiting forested and nonforested grasslands of the pampasic coastal sand dunes of Argentina. Predation pressure was evaluated by measuring the predation rate on plasticine replicas of lizards and the abundance of avian predators. We also recorded flight initiation distance (FID) of lizards in the different habitat types and the microhabitat used as refuge. Both lizard species prefer refuges in native plants but, when they are scarce, the nonnative Acacia longifolia is selected as alternative refuge. In forested habitats, sand-burying behavior is a complementary strategy used by L. multimaculatus to avoid predation. The FID of L. wiegmannii was greater in forested habitats than in nonforested ones. In contrast, L. multimaculatus exhibited a short FID in forested habitats, mostly because sand-burying behavior appears to reduce the risks typically associated with exposed areas. Plasticity in antipredatory behavior suggests that these lizards could recognize predators and develop a suitable antipredatory behavior. We conclude that increased predation pressure and structural alterations of the habitat in the presence of nonnative A. longifolia affect the decisions that determine how, when, and where these lizards flee.

Responses of two sympatric sand lizards to exotic forestations in the coastal dunes of Argentina: some implications for conservation

Abstract Context. Exotic forestations may modify habitat quality, affecting native animal populations that require specific microhabitats to remain viable. Aims. We determined whether abundances and body condition of the lizard species Liolaemus wiegmannii and L. multimaculatus differed between forested and non-forested dunes. We also examined what environmental attributes are important in explaining the potential differences. Methods. We sampled six sites of 300 ha each. Three of these sites had original vegetation and three were forested with exotic Acacia longifolia. We traced 120 transects per site searching for lizards. Key results. Lizards were two times more abundant in non-forested sites than in sites covered by acacia trees (even as low as a fourth of the area). Sites with high densities of acacia (≥78% of coverage) had the lowest abundance of lizards. In forested sites, the snout–vent length of L. wiegmannii was 10% smaller and relative body mass 22% lower than in non-forested sites. We found no differences in the body size of L. multimaculatus. Conclusions. The replacement of the native vegetation by A. longifolia has negative effects on lizard species, representing a substantial threat to L. wiegmannii and particularly to L. multimaculatus, a threatened status species. Structural and thermal characteristics of the non-forested sites seemed to be more favourable for the abundance and body condition, whereas the dense vegetation and the low temperatures on the forested sites might explain the lower presence of lizards. Implications. We recommend that before the implementation of future forestation plans in the pampasic coastal dunes, the deleterious consequences that this practice generates on native lizard fauna must be considered. When necessary, we recommend that A. longifolia be planted so that the coverage does not exceed a quarter of the total area, so as to prevent the formation of continuous (or closed) forest patches and to maintain the structural heterogeneity of the habitat that these lizards need to survive. In the most affected areas, eradication and control strategies may help reduce the advancement of this exotic plant over the areas intended for conservation.

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

Abstract 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. Resumen Los refugios naturales constituyen un recurso fundamental del hábitat de una especie. En consecuencia, el conocimiento de aquellos elementos utilizados como protección ante los depredadores, constituye una medida prioritaria para su conservación. Estudiamos los mecanismos antidepredatorios en un ensamble de lagartijas arenícolas, explorando si el uso de los refugios es al azar o si hay una selección de determinados tipos dependiendo de su disponibilidad. También se comparó la frecuencia de uso de sitios de refugio con los sitios de percha donde los individuos fueron detectados inicialmente. Liolaemus multimaculatus utilizó los sitios bajo roca, ya sea como refugio o como percha y sólo como refugio a sitios bajo subarbustos (Senecio bergii) e hierbas en mata (Spartina ciliata). Liolaemus gracilis utilizó más frecuentemente a lo esperado como sitios de refugio y percha a aquellos bajo hierbas rastreras (casi exclusivamente Panicum racemosum) y subarbustos (Senecio bergii). Liolaemus wiegmannii sólo utilizó subarbustos, tanto como sitios de refugio como de percha (principalmente Melilotus indicus pero también Achyrocline satureioides y Senecio bergii). Este trabajo demuestra que las lagartijas de Costa Bonita seleccionan determinados tipos de plantas del pastizal psamofítico nativo para reducir los riesgos de ser capturadas. La mayoría de estas plantas son sus principales sitios de percha.

Behavioral compensation buffers body temperatures of two Liolaemus lizards under contrasting environments from the temperate Pampas: a Bogert effect?

Postural adjustments and microhabitat selection are two behavioral mechanisms that lizards extensively use to regulate their body temperatures. The Bogert effect occurs when behavioral thermoregulation buffers potential changes in body temperatures of congeneric organisms due to environmental variation, in turn precluding physiological evolution. We compared field body temperatures (Tb) and behavioral thermoregulation traits between two Liolaemus lizards: the saxicolous Liolaemus tandiliensis and the arenicolous Liolaemus wiegmannii. These species are spatially segregated in two thermally contrasting environments from the SE of the temperate Pampas of Argentina. During summer, the mean operative temperature (Te) of the coastal sand dunes occupied by L. wiegmannii was 9 ºC higher than that of the Tandilia mountains inhabited by L. tandiliensis. Despite the contrasting thermal conditions of both habitats, the mean Tb of L. tandiliensis (34.72 °C) was similar to that of L. wiegmannii (35.01 °C). The behavioral thermoregulation mechanisms varied considerably between both species. Liolaemus tandiliensis combined static body posture with displacements towards sunlit areas. In contrast, L. wiegmannii combined elevated and prostrated body postures with movements towards full and filtered sun patches. Environmental gradients offer diverse challenges impelling lizards to find different behavioral thermoregulation adaptations in order to partially cope with environmental constraints. This occurs in many species of Liolaemus that are thermoregulatory efficient despite of the climatic adversities. In this study, two species of Liolaemus used different postural and microhabitat path-selection strategies according to climate, allowing them to buffer changes in Tb, thus suggesting that the Bogert effect may be occurring in these two species.

Scale dependency of Liolaemus lizards' home range in response to different environmental variables

Animal habitat-use patterns cannot be isolated from scale issues. Consequently, multi-scale studies provide a complete characterization of ecological patterns that can further explain the observed variation. Liolaemus constitutes the world’s second most speciose lizard genus. In this study, we assessed the relationships between home range size and environmental variables at 3 different spatial scales. The study at a local and regional scale was focused on the habitat specialist Liolaemus multimaculatus. The lizard’s home range was calculated using the minimum convex polygon method in populations from grassland sites of the coastal sand dunes of the Argentinean Pampas under 2 different conditions, with or without forestations of Acacia longifolia. On the other hand, at a geographical scale we considered the evolutionary implications of 20 species of Liolaemus. Home range size, phylogeny, ecological, environmental, and climatic data were obtained from the literature and remote sensing. L. multimaculatus home range varied from 12.66 to 570.00 m. Regionally, this species had smaller home ranges in forested habitats (X¯: 94.02 m2) compared with the non-forested sites (X¯: 219.78 m2). Habitat structure, vegetation types, and food availability would explain the space use at finer scales. When the 20 species of Liolaemus were considered, high mean air temperature and broad thermal amplitudes showed an inverse relationship with home range size. Neither net primary productivity nor phylogeny was good predictors for home range variation at geographical scale. This study highlights the scale dependence of the explicative capability of a set of environmental and intrinsic variables on home range patterns.