Annual variation in the body condition of a small, arid-zone tortoise, Homopus signatus signatus

Loehr, Victor J. T.; Hofmeyr, Margaretha D.; Henen, Brian T.

doi:10.1016/j.jaridenv.2007.04.011

Cited by 22 publications

(22 citation statements)

References 30 publications

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“…Regressions of BM on SV provide the best surrogate measure of body condition (BC) in chelonians (Hofmeyr et al 2005;Loehr et al 2007a). We used the mean BM per season for the relevant individual when doing seasonal analyses because we measured tortoises' BM more than once per season for radio-tracked and recaptured animals.…”

Section: Data and Statistical Analysesmentioning

confidence: 99%

“…Seasonal changes in temperature and rainfall can influence body condition (Nagy & Medica 1986;Henen 1997;Loehr et al 2007a) and hence fitness parameters such as reproductive output (Hofmeyr et al 2005;Loehr et al 2007a) and survival (Shine et al 2001). Geographic variation in environmental productivity can influence population density, with lower densities in arid than mesic regions (see Branch 1984;Mason et al 2000).…”

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confidence: 99%

“…Regular weighing allowed a consistent evaluation of seasonal changes in body condition of telemetered tortoises. We measured straight carapace length (SCL, mm), shell width at the middle (SWM, at the sixth marginal scute; mm) and shell height (SHM, at the apex of the highest dorsal scute; mm) for each tortoise with vernier callipers (9 0.01 mm; Kanon, Tokyo) to calculate shell volume (SV, cm 3 ) using a modified formula for an ellipsoid: SV =p * SCL * SHM * SW/6000 (Loehr et al 2004;Hofmeyr et al 2005;Loehr et al 2007a). Body mass and SV were used to calculate body condition as a ratio of mass to shell volume (Loehr et al 2004) and as mass scaled to shell volume (Loehr et al 2007a).…”

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confidence: 99%

“…We measured straight carapace length (SCL, mm), shell width at the middle (SWM, at the sixth marginal scute; mm) and shell height (SHM, at the apex of the highest dorsal scute; mm) for each tortoise with vernier callipers (9 0.01 mm; Kanon, Tokyo) to calculate shell volume (SV, cm 3 ) using a modified formula for an ellipsoid: SV =p * SCL * SHM * SW/6000 (Loehr et al 2004;Hofmeyr et al 2005;Loehr et al 2007a). Body mass and SV were used to calculate body condition as a ratio of mass to shell volume (Loehr et al 2004) and as mass scaled to shell volume (Loehr et al 2007a). Because scute ring counts often provide a reliable estimate of age in chelonians (Germano 1994;Germano & Bury 1998;Hellgren et al 2000), we used a hand lens to count scute rings (annuli) on the dorsal and ventral sides of all individuals.…”

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confidence: 99%

“…Despite using denser refuges than females did, the smaller males still had a higher mean body temperature than females (Keswick 2012). Thus low body condition in males could be associated with the effects of a high body temperature on metabolic rate and/or water loss (Loehr et al 2007a and references therein). Alternatively, the formula used to calculate SV might have overestimated male body size, which would have resulted in an apparent lower body condition for males relative to females.…”

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Population ecology ofPsammobates oculiferin a semi-arid environment

Keswick

Hofmeyr

2013

African Journal of Herpetology

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We studied the ecology of Psammobates oculifer over 13 months near Kimberley, South Africa, to ascertain if the population's life history traits conform to chelonian patterns in arid environments. Capture rates were highest in spring and lowest in winter when environmental conditions were respectively most and least favourable for tortoise activity. Body condition did not change from autumn to spring, but reached lower values during the summer drought. Capture effort averaged 5 hours/tortoise, which corresponds closely to that of species with low population densities in arid regions. Population size structure was skewed towards adults, indicative of low recruitment and/or low juvenile survivorship. Females were larger and heavier than males, confirming sexual dimorphism in this species. Body size of cohorts scaled to annuli counts, indicating a close correspondence between body size and age. Telemetered adults deposited one or no growth ring in the year of study; consequently, annuli counts could underestimate adult age. Regression analyses showed that male and female growth rates did not differ, but males matured at a smaller size and younger age than females. The smallest male showing reproductive behaviour had 12 annuli and a shell volume of 157 cm 3 , while similar measures for females were 14 annuli and 185 cm 3 . The sex ratio of the population did not differ from 1:1 but the bias towards males in spring, and towards females in autumn, indicates that studies limited to particular seasons can misrepresent life history traits of populations. We concluded that the life history of P. oculifer conforms to chelonian patterns in arid regions.

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Section: Data and Statistical Analysesmentioning

confidence: 99%

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confidence: 99%

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Population ecology ofPsammobates oculiferin a semi-arid environment

Keswick

Hofmeyr

2013

African Journal of Herpetology

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Unexpected decline in a population of speckled tortoises

Loehr¹

2017

J Wildl Manag

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Long‐lived, iteroparous species exhibit various mechanisms to overcome temporary unfavorable conditions and promote adult survival and population persistence. Consequently, populations may appear relatively stable while subtle and slow‐progressing threats cause their decline. The speckled tortoise (Homopus signatus) is a long‐lived, iteroparous species in South Africa that is thought to be secure in areas that meet the species’ known requirements. To verify its stability, I monitored a dense speckled tortoise population, integrating 2 mark‐recapture studies (2000–2004 and 2012–2015) in long‐term joint live and dead encounters and POPAN population models. From 2000 to 2015, the study site remained fenced, ungrazed, and was not modified in any way, yet the size‐class frequency distribution, sex ratio, and abundance of speckled tortoises drastically changed. Population numbers decreased 66%, mainly because of the disappearance of juveniles and males. Modeling results identified a reduction in the number of entrants into the population (via births and immigration) as the likely cause of population changes, whereas apparent survival remained high. Observations, in part anecdotal, of increasing numbers of pied crows (Corvus albus) on the study site suggest that increased predation on speckled tortoise hatchlings contributed to the population decline. Examination of rainfall data for 1990–2015 did not reveal evidence of aridification in the study area, a documented cause of reduced reproduction in speckled tortoises. The results of this study caution against the assumption that areas in the range of the speckled tortoise that meet its known requirements can maintain healthy populations. © 2017 The Wildlife Society

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Structure and projected decline of a Karoo dwarf tortoise population

Loehr

Keswick

2022

J Wildl Manag

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Inconspicuous, secretive, or sparsely distributed species receive relatively little research attention, potentially leading to uncertainty about their status and lack of efforts to conserve them. Karoo dwarf tortoises (Chersobius boulengeri) are endemic to South Africa, spend most of the time in retreats at remote arid locations, and are seldom seen. We conducted a 3‐year (2018–2020) mark‐recapture study to investigate the size and structure of the only Karoo dwarf tortoise population currently known to exist. The population in the 16‐ha core of our study site consisted primarily of adult males and females, at a density of 3.3 individuals/ha. Many individuals had severely worn shells and appeared old. Small individuals (straight carapace length <65 mm) represented just 8% of the population and were mostly recent hatchlings. Overall, tortoises had high estimated survival rates (0.77–0.95; lower 95% confidence limit for the smallest tortoises was 0.16), despite a 15‐month drought. The lack of small individuals may reflect low levels of recruitment and population decline. Predation by corvids was an obvious threat to all size classes. We estimated that the local population across the 250‐ha study area was 800–900 males and females, and recommend precautionary conservation measures focused on reducing human‐subsidized avian predation.

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Annual variation in the body condition of a small, arid-zone tortoise, Homopus signatus signatus

Cited by 22 publications

References 30 publications

Population ecology ofPsammobates oculiferin a semi-arid environment

Population ecology ofPsammobates oculiferin a semi-arid environment

Unexpected decline in a population of speckled tortoises

Structure and projected decline of a Karoo dwarf tortoise population

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