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IJsselstein, Netherlands

Loehr V.J.T.,Homopus Research Foundation
Journal of Herpetology | Year: 2015

In some herbivores, home range size is correlated negatively with the primary productivity of their environments. Although the South African Succulent Karoo is arid, it receives relatively predictable winter rainfall and therefore relatively predictable primary production toward the following spring. Lush springs may alternate with occasional drought years. Over five spring seasons with variable rainfall patterns, I studied home range size in 21 male and 31 female Namaqualand Speckled Tortoises (Homopus signatus) in the Succulent Karoo using opportunistic sightings, thread-trailing, and radio telemetry. In addition, daily movement distances were determined for 8 males and 28 females with the use of thread-trailing over three spring seasons. The average home range size for H. signatus was 3,470 m2, much smaller than home ranges for tortoises in other arid regions. Home range size did not differ between the sexes, but was negatively correlated with rainfall. Daily movement distances were also similar between sexes, but tortoises moved greater distances in a relatively warm spring. It appears that temporary mesic conditions in spring enable male and female H. signatus to meet their nutritional needs in a relatively small area, and the flexible response to variable environmental conditions may enhance tortoise survival during drought years. © 2015 Society for the Study of Amphibians and Reptiles. Source

Loehr V.J.T.,Homopus Research Foundation
African Journal of Herpetology | Year: 2016

The arrangement of scutes on the carapaces of extant chelonians is very similar among species, but intraspecific deviations from typical scute patterns are common. Because intraspecific variation may relate to inbreeding depression, unfavourable egg incubation conditions and the presence of environmental pollutants, investigations of carapacial scute patterns in natural populations can enhance insight into the ecologies and survival challenges of chelonians. A population of the tortoise Homopus signatus, inhabiting an arid range with substantial annual rainfall variation, was sampled to record carapacial scute patterns. The typical pattern of H. signatus consisted of five vertebral scutes, four pairs of costal scutes, a cervical and a supracaudal scute, and 12 pairs of marginal scutes. Although it was expected that size classes (i.e. representing tortoises born in different years) and sexes would have different percentages deviations from the typical scute pattern as a result of different egg incubation conditions, percentages were similar among size classes and sexes. A high percentage of 44% (25% if counts of the relatively variable marginal scutes were excluded) of all tortoises had deviant carapacial scute patterns. Since the study population was situated in a relatively pristine area and supernumerary carapacial scutes appear related to egg incubation conditions in other chelonians, the wide variation in carapacial scute patterns in wild H. signatus may be the result of frequently challenging incubation conditions in the species' harsh environment. © 2016 Herpetological Association of Africa. Source

Loehr V.J.T.,University of the Western Cape | Loehr V.J.T.,Homopus Research Foundation | Henen B.T.,University of the Western Cape | Henen B.T.,US Marine Corps | Hofmeyr M.D.,University of the Western Cape
Copeia | Year: 2011

Although many tortoise species inhabit drought-prone regions with potentially limiting resources, these species have long, iteroparous lives. To assess reproductive responses to variation in rainfall, and to understand interactions among egg size, body size, body condition, and rainfall, we studied egg production in the Namaqualand Speckled Padloper, Homopus signatus signatus, in Springbok, South Africa, in five consecutive spring seasons. Annual rainfall was low and varied substantially (131-226 mm). The percentage of females that were gravid (36-75%) differed among years and correlated with the amount of rain in the months prior to nesting. Gravid females had a higher body condition than that of non-gravid females, presumably because individual variation in resource acquisition caused some females to forfeit reproduction. The body condition of gravid and non-gravid females differed among years and was lowest in the year of lowest rainfall. In most years, egg size correlated to female size, but neither female size nor egg size differed among years. Egg size did not significantly correlate to maternal body size in dry years, when other determinants, such as body condition, seemed to outweigh the effect of body size. Egg volume represented up to 11.9% of female shell volume. The adult shell is somewhat flexible dorso-ventrally, which may help females accommodate the large egg, as indicated by the larger shell height and volume of gravid compared to non-gravid females. Large eggs may be advantageous for H. s. signatus, as larger hatchlings may survive better in arid environments. Since the range of H. s. signatus is threatened with aridification, the effects of drought on egg production may seriously challenge the long-term survival of populations. © 2011 by the American Society of Ichthyologists and Herpetologists. Source

Loehr V.J.T.,Homopus Research Foundation
Chelonian Conservation and Biology | Year: 2012

Road mortality of South African tortoises has not been evaluated. I recorded the number and distribution of remains of Homopus femoralis directly along 8.4 km of tar road with low traffic volume in the Karoo, South Africa. I identified 48 carcasses, with a relatively high number found along 1.5 km of road. Multiple dry culverts already present under this stretch of road provide an opportunity to reduce mortality by adding structures to guide tortoises to the underpasses. © 2012 Chelonian Research Foundation. Source

Loehr V.J.T.,Homopus Research Foundation
Journal of Arid Environments | Year: 2012

Herbivorous tortoises in arid, winter-rainfall regions need to forage in seasons that provide relatively little heat for their ectothermic metabolism. To help understand how tortoises exploit resources in winter-rainfall areas, I recorded ambient, soil, and body temperatures for Homopus signatus in four spring seasons, and in one summer, autumn, and winter. The spring thermal environment enabled H. signatus to maintain body temperatures that were high compared to other small tortoise species. Mature females had higher spring body temperatures than males and immature individuals, probably because mature females were developing eggs. In summer, autumn, and winter, body temperatures differed between males and females, relating to sexually different activities and retreat uses. The relatively high body temperatures of H. signatus in winter and spring, along with a non-isometric relationship between body temperature and soil temperature, suggest that tortoises thermoregulated and may need considerable time to gain heat. Additional studies should compare body temperatures of H. signatus to operative temperatures, and determine the vulnerability of the taxon to human interferences that affect behavioural time budgets and body temperatures. © 2012 Elsevier Ltd. Source

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