Space use of the spotted sand lizard (Pedioplanis l. lineoocellata) under different degradation states

Abstract

Although the effects of grazing-induced savannah degradation on animal diversity are well documented, knowledge of how they affect space use or responding behaviour remains poor. In this study, we analysed space use of the spotted sand lizard (Pedioplanis l. lineoocellata) in degraded versus nondegraded habitats of southern Kalahari savannah habitats. Lizards were radio tracked, daily movement distances recorded and home range sizes calculated. In degraded Kalahari savannah habitats where plant diversity and perennial grass cover are low but shrub cover high, P. lineoocellata moves larger distances (40.88 ± 6.42 m versus 27.43 ± 5.08 m) and occupies larger home ranges (646.64 ± 244.84 m 2 versus 209.15 ± 109.84 m 2 ) than in nondegraded habitats (high plant diversity, high perennial grass cover and low shrub cover). We assume that this increase in daily movement distances and home range sizes is a behavioural plasticity to limited food resources in degraded savannah habitats. Although P. lineoocellata is able to adjust to resource-poor savannah habitats, the increase in the lizard's movement activities is likely to result in a higher predation risk. This is supported by the lower availability of protective vegetation i.e. perennial grass cover. Hence, we conclude that despite behavioural plasticity of P. lineoocellata, overgrazing has a severe negative impact on the space use of P. lineoocellata. RésuméBien que les effets de la dégradation de la savane due au pâturage sur la diversité animale soient bien documentés, on sait toujours peu de choses sur la façon dont ils affectent l'utilisation de l'espace ou les comportements de réponse. Dans cette étude, nous avons analysé l'utilisation de l'espace du lézard des sables tacheté Pedioplanis l. lineoocellata, dans des habitats de savane dégradés ou non du sud du Kalahari. Des lézards furent suivis par radio, les distances parcourues par jour furent enregistrées, et l'on a calculé la taille des domaines vitaux. Dans les habitats de savane dégradés du Kalahari, où la diversité végétale et la couverture herbacée pérenne sont faibles mais la couverture arbustive élevée, Pedioplanis lineoocellata couvre de plus grandes distances (40.88 ± 6.42 m versus 27.43 ± 5.08 m) et occupe de plus vastes domaines vitaux (646.64 ± 244.84 m 2 versus 209.15 ± 109.84 m 2 ) que dans les habitats non dégradés (grande diversité végétale, forte couverture herbacée pérenne et faible couverture arbustive). Nous supposons que cette augmentation de la distance parcourue chaque jour et de la taille des domaines vitaux est le résultat d'une plasticité comportementale face à des ressources alimentaires limitées dans les habitats dégradés de savane. Bien que P. lineoocellata soit capable de s'adapter à des habitats de savane pauvres en ressources, l'augmentation des déplacements du lézard est susceptible d'entraîner un plus grand risque de prédation. Cette hypothèse est confortée par la faible disponibilité de végétation protectrice, c.-à-d. d'une couverture herbacée pérenne. Dès lors, nous concluons...

Behavioural flexibility in foraging mode of the spotted sand lizard (Pedioplanis l. lineoocellata) seems to buffer negative impacts of savanna degradation

“…Other captured individuals were released immediately. Transmitters showed no effect on movement behaviour (Wasiolka et al, 2010).…”

“…Each individual was temporarily marked (small blue dot of approx. 0.25 cm 2 ) with xylen-free non toxic paint, and transmitters attached at the backs using 100% silicone glue according to Wasiolka et al (2010). Before each observations, the lizards were once located with a RX 98 Televilt receiver (Televilt, Sweden).…”

“…food, sites for nesting) are major drivers for changes in abundance and diversity in degraded habitats, however, these changes are likely to affect also behavioural patterns. For example, lizards may change and enlarge their home ranges in degraded savannas (Wasiolka et al, 2010) due to lower insect prey availability Pianka, 1986). While food availability will determine overall abundance of lizards, it remains unclear whether prey availability alone can trigger such significant changes in space use and which specific movement properties are affected by habitat degradation.…”

“…The study is based on the results of Wasiolka et al (2010) who found that home range size of the spotted sand lizard is significantly larger in degraded Kalahari savanna habitats than in nondegraded habitats. The major aim of the experiment was to distinguish between the effects of changes in habitat structure and prey availability on the lizard's foraging behaviour.…”

Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari

“…Farmland sites showed typical signs of degradation caused by heavy livestock grazing: low plant and structural diversity (Blaum et al, 2007;Wasiolka et al, 2009;Wasiolka et al, 2010), low proportions of perennial grasses and herbaceous vegetation but high proportions of shrub cover (particularly A. mellifera and R. trichotomum) and bare ground (Wiegand et al, 2005). Indeed, the overall stocking rates for wild ungulates and domestic livestock (calculated as large stock units (LSU)/km 2 , according to Dean and Macdonald (1994) in the farmland was more than four times higher than in the KTP (KTP: 0.95 LSU/km 2 : SANParks 2004e2009; farmland: 4.16 LSU/km 2 : Blaum et al, 2009a).…”