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Climate and the evolution of group-living behaviour in the armadillo lizard ( Ouroborus cataphractus )

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Abstract

We evaluated the hypothesis that the regular use of the southern harvester termite, Microhodotermes viator, as food source by the armadillo lizard, Ouroborus cataphractus, originated as an adaptation to survive the summer dry season in a climatic regime where rainfall is highly seasonal. To do so, we determined the most important climatic predictors of the geographical range of this species. Climatic data were obtained for 130 localities where O. cataphractus is known to occur and 168 adjacent localities where it is known to be absent. For each locality, data for 10 climatic variables were extracted from the South African Atlas of Agrohydrology and Climatology database. We constructed a forward stepwise logistic regression model of the probability of O. cataphractus occurrence, based on the set of 10 climatic variables. The best model included, in order of importance, average monthly summer rainfall, mean annual precipitation, average monthly solar radiation, and the ratio of winter rainfall over summer rainfall as most significant predictors. The selected model predicted 88.80% of the presences correctly and 85.52% of the absences. In essence, O. cataphractus is restricted to the winter rainfall zone of South Africa, excluding the high-rainfall southwestern section. We postulate that the highly predictable seasonal rainfall and the ameliorating effect of the Atlantic Ocean on climates in the Namaqualand region, in particular, have provided a unique selective regime for the origin of group-living in O. cataphractus. Dependence on M. viator as food source developed to survive the summer-autumn period of low food availability and resulted in the evolution of heavy armour and group-living behaviour. The moderate winters and early spring temperatures allowed full capitalization on high arthropod abundance during winter–spring, thereby overriding the negative impacts of armour and group-living on foraging efficiency at the home crevice.

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... Most notable is the major interspecific variation in anti-predator morphology: K. polyzonus is a relatively fast, lightly armoured lizard, while O. cataphractus is a slow-moving heavily armoured lizard [32,33]. Heavy armour in O. cataphractus serves as protection against attacks from small terrestrial mammals [33] and most likely evolved to facilitate foraging excursions to termite nests away from the safety of the crevice [34,35]. Armour in cordylid lizards, however, is assumingly ineffective against the beaks and talons of aerial predators [34,36]. ...
... Moreover, the protective effect of heavy armour would diminish the terrestrial predation risk [33], thereby allowing individuals to exploit the abundance of arthropods away from the crevice during spring and build up energy reserves for summer [46]. In addition, the temporal overlap of mating [46] and intense foraging from midwinter to spring appears to be vital for the survival of O. cataphractus, as it would restrict overall exposure to aerial predation to an absolute minimum [34,35]. On the contrary, high ambient temperatures during summer would allow for maximal running capacity in the lightly armoured K. polyzonus [7,9]. ...
... Given that the species displays a sit-and-wait foraging strategy [28], intraspecific competition for similar food resources becomes a major cost for the group-living O. cataphractus, compared to a solitary K. polyzonus [34]. High intraspecific competition for food at the rock-crevice resulting from group-living behaviour and low food abundance during summer might thus be the main selective pressure driving inactivity in O. cataphractus [34,35]. In contrast and following the above-mentioned, favourable weather conditions would not only maximise running speed, but also prey capture speed [7][8][9], thereby allowing the lightly armoured K. polyzonus to chase and capture prey items, despite low abundance, without an increased risk of aerial predation. ...
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It is generally assumed that favourable weather conditions determine the activity levels of lizards, because of their temperature-dependent behavioural performance. Inactivity, however, might have a selective advantage over activity, as it could increase survival by reducing exposure to predators. Consequently, the effects of weather conditions on the activity patterns of lizards should be strongly influenced by the presence of predators. Using remote camera traps, we test the hypothesis that predator presence and weather conditions interact to modulate daily activity levels in two sedentary cordylid lizards, Karusasaurus polyzonus and Ouroborus cataphractus. While both species are closely related and have a fully overlapping distribution, the former is a fast-moving lightly armoured lizard, whereas the latter is a slow-moving heavily armoured lizard. The significant interspecific difference in antipredator morphology and consequently differential vulnerability to aerial and terrestrial predators, allowed us to unravel the effects of predation risk and weather conditions on activity levels. Our results demonstrate that K. polyzonus is predominantly active during summer, when ambient temperatures are favourable enough to permit activity. In contrast, a peak in activity during spring was observed in O. cataphractus, with individuals being inactive during most of summer. While favourable weather conditions had a strong effect on the activity levels of K. polyzonus, no such relationship was present in O. cataphractus. Contrary to our hypothesis, the presence of terrestrial predators does not seem to affect daily activity levels or alter the influence of weather conditions on activity levels. We conclude that inactivity in O. cataphractus appears to be related to seasonal differences in vulnerability to predators, rather than the presence of predators, and highlight the importance of additional selective pressures, such as food abundance, in determining the species' activity levels.
... One species in particular, the armadillo lizard, Ouroborus cataphractus, is a highly suitable model organism for understanding the proximate causes of variation in body armour . Armadillo lizards occur in the western parts of South Africa and their range falls within the semi-arid Succulent Karoo biome (Shuttleworth et al. 2013). They are termiteeating specialists (Shuttleworth et al. 2008, Mouton et al. 2000, Broeckhoven and Mouton 2013, Shuttleworth et al. 2013) that evolved heavy body armour, including long spines and thick imbricating osteoderms, as a defence mechanism against mongoose predators when exploiting termites away from the safety of their shelters . ...
... Armadillo lizards occur in the western parts of South Africa and their range falls within the semi-arid Succulent Karoo biome (Shuttleworth et al. 2013). They are termiteeating specialists (Shuttleworth et al. 2008, Mouton et al. 2000, Broeckhoven and Mouton 2013, Shuttleworth et al. 2013) that evolved heavy body armour, including long spines and thick imbricating osteoderms, as a defence mechanism against mongoose predators when exploiting termites away from the safety of their shelters . Although strongly linked, the relationship between dermal armour and predation is not a straightforward one, because significant variation in osteoderm thickness is present among populations . ...
... Nevertheless, differential exposure to predators, rather than predator species or densities, might have contributed, albeit weakly, to variation in body armour. Armadillo lizards rely on harvester termites Microhodotermes viator as a food source, especially during the dry season (Shuttleworth et al. 2008, Mouton 2011, Shuttleworth et al. 2013. Populations that inhabit more arid environments might have an increased dependency on termites and might be more frequently exposed to mammalian predators during foraging excursions. ...
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Although it is widely assumed that body armour in animals evolved to thwart predator attacks, assessing the role that predators may play in shaping defensive morphologies has proven to be difficult. Recent studies suggest that body armour might be influenced by additional factors besides predation, and/or even by sexual selection. We investigated variation in dermal armour in 13 populations of armadillo lizards Ouroborus cataphractus, spanning the entire distribution range of the species. We obtained thickness measurements of osteoderms – bony plates embedded in dermal layer of the skin – using micro‐ and nano‐computed tomography. Using these data, we examined the effects of predation pressure/risk and climatic variables on dermal armour variation and addressed sexual and ontogenetic influence. Our results show that climate is the only factor affecting variation in dermal armour. Populations inhabiting more arid environments, characterized by low summer precipitation and mild winter temperatures, are relatively more armoured than those present in less arid environments. In contrast to our expectations, predation pressure or perceived predation risk was not associated with osteoderm thickness. The results of our study support the idea that the evolution of defensive traits might not be driven exclusively by predator‐prey interactions, but could be moulded by environmental factors. In particular, we highlight the role of dermal armour as a potentially important mechanism to reduce evaporative water loss in arid environments. This article is protected by copyright. All rights reserved.
... Although all members of the family possess (to varying degrees) spines and osteoderms, elaborated body armor evolved convergently in only two species, namely O. cataphractus and S. giganteus (Broeckhoven et al. Succulent Karoo biome in the western parts of South Africa (Shuttleworth et al. 2013). While most Cordylidae have a generalist insectivorous diet, O. cataphractus has specialized in exploiting harvester termites (Microhodotermes viator) at the foraging ports of termite nests, considerable distances away from the safety of the rock-crevice. ...
... Thermal quality is a function of T p , and the low T p of O. cataphractus therefore minimizes thermoregulatory costs for the species during spring and late winter, a critical time for energy acquisition, and furthermore enables accurate thermoregulation (Hertz, Huey and Stevenson, 1993) within crevices during summer and autumn when vitellogenesis, spermatogenesis and gestation take place (Flemming and Mouton, 2002). The permanent group-living behaviour of O. cataphractus constrains food availability at the individual level (Mouton, 2011;Shuttleworth, Mouton and Van Niekerk, 2013). In fact, seasonal analyses of both stomach contents (Mouton, Geertsema and Visagie, 2000) and bone histology (Curtin, Mouton and Chinsamy, 2005) confirm periods of extreme food stress in the species (Mouton, 2011). ...
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ENGLISH ABSTRACT: Thermal ecology is a central theme in reptilian biology because of the thermodynamic rate dependence of virtually all biological processes in these ectothermic animals. Thermoregulation includes active processes (with associated energetic costs related to altered behaviour and physiology) functioning to maintain body temperatures within a preferred temperature range, so that the majority of physiological functions occurs optimally, despite natural variation in the animal’s thermal habitat. The recent development of quantitative thermal indices now allows researchers to describe the thermal habitat and thermoregulatory functioning of an ectotherm within its environment from a cost-benefit perspective. The use of such quantitative biophysical approaches to reptile thermal ecology studies is however limited in the African context. Cordylus cataphractus is one of the best studied cordylids, and exhibits various characteristics atypical for the family, such as permanent group-living, seasonally lowered surface activity, a low resting metabolic rate and large fat bodies. These characteristics are generally thought to be associated with groupliving in a semi-arid habitat, yet, the possible links to thermal ecology remains unexplored. The objectives of the current study was: firstly, to characterize the preferred temperature range (Tp) of C. cataphractus through the use of ecologically realistic laboratory thermal gradients; secondly, to explore seasonal and geographical variation in thermal preference, by comparing Tp among individuals captured from a coastal and inland population and during different seasons (autumn and spring); thirdly, to describe the thermal habitat of a C. cataphractus population during summer, autumn, winter and spring and to then relate these findings to the seasonal activity patterns reported in literature for the species; fourthly, to describe the seasonal patterns of thermoregulation (during summer, autumn, winter and spring) in a C. cataphractus population through quantitative thermoregulatory indices; fifthly, to assess geographic variation in the thermal habitat and IV associated patterns of thermoregulation in C. cataphractus among a coastal population (western range limit) and an inland population (eastern range limit). The thermal habitat of C. cataphractus was described by measuring operative environmental temperatures (Te) with hollow copper lizard models placed around rocks according to the natural surface movement patterns of the species. Variation in thermal habitat quality was subsequently calculated (de = |Te – Tp|) and averaged. Field body temperatures (Tb) of lizards were measured with dorsally attached miniature temperature loggers. Thermoregulatory indices were calculated from Te, Tb and Tp, describing: thermoregulatory accuracy, the effectiveness of thermoregulation and thermal exploitation for each population (coastal and inland) for the respective sampling periods. The preferred body temperature range of C. cataphractus is the lowest recorded among cordylids to date (mean Tp = 29.8oC) and was conserved among different populations and within these populations among seasons, despite the fact that environmental temperatures are known to vary geographically and seasonally. Thermal habitat quality varied significantly at micro spatial scale around rocks in the coastal population. Since C. cataphractus males are territorial, competition for thermal habitat quality around rocks may therefore occur. Such effects will be a function of the time of year since the variability in thermal habitat quality among rock aspects (around rocks) varied seasonally. Thermal habitat quality of crevices varied among seasons and was typically higher in the open, outside rock crevices, during the cooler winter and spring periods, whereas in summer and autumn the crevice environments were more favourable. Thermal habitat quality was high in crevices during autumn, suggesting that the observed repressed surface activity of C. cataphractus described for the time is not necessarily, as previously thought, only due to food constraints. Moreover, in contrast to earlier reports, the current results (Tb versus Te) indicate that individuals emerged from crevices in summer. The geographical assessment indicated that lizards from the coastal population, with generally larger groups, thermoregulated more successfully than those from the inland population. The higher thermoregulatory success in the coastal population occurred in spite of the fact that thermal habitat quality was significantly lower at the coastal locality. The higher thermoregulatory success in the coastal population was likely due to reduced predation risk associated with increased group-size. The seasonal trends in thermoregulation at the coastal and inland population corresponded to the patterns predicted by the cost-benefit model of thermoregulation, accuracy of thermoregulation and the effectiveness of thermal exploitation being higher during the thermally more favourable autumn. AFRIKAANSE OPSOMMING: Uittreksel Termiese ekologie is ‘n sentrale tema in reptiel-biologie as gevolg van die termodinamies tempo-afhanklikheid van feitlik alle biologiese prosesse in hierdie ektotermiese diere. Termoregulering sluit aktiewe prosesse (wat lei tot energie-koste in terme van gedrag en fisiologie) in om liggaamstemperature binne ‘n vasgestelde voorkeurtemperatuur-reeks te handhaaf sodat fisiologiese prosesse optimaal kan geskied te midde van natuurlike variasie in die dier se termiese omgewing. Die onlangse ontwikkeling van kwantitatiewe funksionele termiese indekse stel navorsers nou in staat om die werklike termiese omgewing en die funksionering van die ektoterm binne sy omgewing te beskryf en uit ‘n koste (energie)- voordeel oogpunt te verstaan. Die gebruik van hierdie biofisiese koste-voordeel benadering in reptiel termoreguleringstudies is egter beperk in die Afrika-konteks. Cordylus cataphractus is een van die bes bestudeerde lede van familie Cordylidae, en vertoon verskeie eienskappe ongewoon vir hierdie groep akkedisse, soos groeplewendheid, beperkte seisoenale aktiwiteit buite hul skeure, ‘n relatiewe lae rustende metaboliese tempo en relatiewe groot vetliggame. Hierdie unieke eienskappe is al deur navorsers gekoppel aan die groeplewe lewensstrategie. Die potensiële koppeling van die termiese ekologie en die spesifieke lewensstrategie van C. cataphractus benodig verdere studie. Die doelwitte van hierdie studie was eerstens: om die voorkeurtemperatuur-reeks (Tp) van C. cataphractus te bepaal deur van ekologies-realistiese termiese gradiënte in die laboratorium gebruik te maak; tweedens: om geografiese en seisoenale variasie in Tp te ondersoek deur individue te gebruik wat uit binnelandse en kus-populasies, tydens verskillende seisoene, herfs en lente versamel is; derdens: om die termiese omgewing, meer spesifiek die variasie in termiese kwaliteit, binne die habitat van C. cataphractus populasie in verskillende seisoene, somer, herfs, winter en lente, te moduleer en met die gedokumenteerde aktiwiteitspatrone in verband te bring; vierdens: om die seisoenale temoreguleringspatrone (tydens somer, herfs, winter en lente) van C. cataphractus populasie te beskryf; vyfdens: om geografiese variasie in die termiese habitat en geassosieerde termoreguleringspatrone tussen kus-populasie (westelike VII verspreidingsgrens) en binneland-populasie (oostelike verspreidingsgrens) te bestudeer. Die kwaliteit van die termiese habitat van C. cataphractus is bepaal deur hol koper-modelle van akkedisse (operatiewe temperatuur modelle (Te)) te plaas rondom rotse in ooreenstemming met die natuurlike bewegingspatrone van die akkedisse. Die termiese kwaliteit is gevolglik afgelei (de = |Te – Tp|) en gemiddeldes bereken. Die liggaamstemperature (Tb) van vrylopende akkedisse in die veld is met dorsaal-gemonteerde miniatuur temperatuur “data-loggers” gemeet. Termiese indekse (deur Te, Tb en Tp te gebruik) is bereken om die akkuraatheid en effektiwiteit van termoregulering, sowel as termiese benutting van die omgewing vir beide populasies (kus en binneland) tydens verskillende seisoene te beraam. Die voorkeurtemperatuur-reeks van C. cataphractus is die laagste gedokumenteerde temperature vir enige lid van die familie Cordylidae tot op hede bestudeer (gemiddeld van Tp = 29.8oC), en het ten spyte van die feit dat omgewingstemperature wissel op geografiese en seisoenale vlakke, min gevarieer tussen die twee populasies asook tydens verskillende seisoene binne die populasies. Die termiese kwaliteit het beduidend gevarieer tussen seisoene en binne die mikroruimtelike omgewing rondom rotse in die kus-populasie. Aangesien C. cataphractus mannetjies territoriaal is, word die aanname gemaak dat kompetisie vir ‘n ruimtelike posisie ook ‘n termiese koste mag hê aangesien daar beduidende variasie in de om die rotse was. Variasie in termiese kwaliteit rondom rotse was verder ook funksie van die tyd van die jaar (seisoene). Die termiese kwaliteit van skeure het gevarieer tussen seisoene, en termiese kondisies/toestande was oor die algemeen meer gunstig buite die rots-skeure tydens die koeler winter en lente tydperke, terwyl skeure termies meer gunstig was in die somer en herfs maande. Termiese habitat kwaliteit van skeure was besonders hoog gedurende die herfs, en die voorspelling is dus dat die verlaagde oppervlak-aktiwiteit wat gedurende hierdie tyd van die jaar vir C. cataphractus gedokumenteer is nie noodwendig funksie van beperkte voedselbeskikbaarheid is nie. Teenstrydig met gepubliseerde aktiwiteitsrekords dui die resultate (Tb teenoor Te) verder daarop dat individue wel uit skeure kom tydens die warm somer seisoen. Die geografiese ondersoek het gewys dat akkedisse van die kus-populasie (wat gewoonlik uit groter groepe bestaan), meer akkuraat getermoreguleer het as akkedisse van die binneland-populasie. Die hoër akkuraatheid van termoregulering in die kus-populasie is bewerkstellig ten spyte van die feit dat die termiese kwaliteit beduidend laer was as die van die binneland-populasie. Die hoër termoreguleringsakkuraatheid in die kus-populasie kan waarskynlik toegeskryf word aan laer predasie-risiko geassosieer met groter groepe. Die seisoenale variasie-patroon van termoregulering kan verklaar word deur die koste-voordeel model van termoregulering, waarvolgens die akkuraatheid van termoregulering sowel as termiese benutting hoër is tydens periodes van hoë termiese kwaliteit (i.e. herfs). Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2011. Includes bibliography.
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Desert lizards are typically either widely foraging or sit-and-wait predators, and these foraging modes are correlated with major differences in ecology. Foraging mode is related to the type of prey eaten by lizards. Widely foraging lizards in the Kalahari desert, the Western Australian desert, and the North American desert generally eat more prey that are sedentary, unpredictably distributed, and clumped (e.g., termites) or that are large and inaccessible (inactive scorpions) than do sit-and-wait lizards. In contrast, sit-and-wait lizards eat more prey that are active. Foraging mode also appears to influence the types of predators that in turn eat the lizards. For example, a sit-and-wait snake eats predominately widely foraging lizards. Crossovers in foraging mode thus exist between trophic levels. Widely foraging lizards may also encounter predators more frequently, as suggested by analyses of relative tail lengths; but tail break frequencies are ambiguous. Daily maintenance energetic expenditures of widely foraging lizards appear to be about 1.3-1.5 times greater than those of sit-and-wait lizards in the same habitats, but gross food gains are about 1.3-2.1 times greater. Widely foraging species also have lower relative clutch volumes, apparently in response to enhanced risks of predation. Foraging mode within one species varies with changes in food availability. Physiology, morphology, and risk of predation might generally restrict the flexibility of foraging mode. Because foraging mode constrains numerous important aspects of ecology, any general model of foraging velocity must be complex.
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Cordylus cataphractus is a group-living lizard endemic to the dry western regions of southern Africa. Groups of up to 30 individuals are regularly encountered and, if this species is a sit-and-wait forager like other members of its family, competition for food among group members could be high. Three criteria were used to infer foraging mode in this species: 1) the number and duration of movements related to foraging, quantified as movements per minute (MPM) and percentage of time spent moving (PTM); 2) the amount of tongue-flicking directed at cotton applicators labelled with prey chemicals as a measure of prey chemical discrimination; and 3) the stomach contents of individuals as an indication of the natural diet. We selected a study site in the Graafwater district in the Western Cape Province, South Africa, and 15 individuals were observed in the field for 10 min periods to determine MPM and PTM. Low MPM and PTM values of 0.23 ± 0.08 and 2.20 ± 0.71, respectively, were recorded indicating that this species is a sit-and-wait forager like other members of the family Cordylidae. In the laboratory, nine lizards were tested for their ability to discriminate among three different odours, including a prey odour, by counting the number of tongue-flicks directed at the odours presented to them on cotton applicators. Only one lizard tongue-flicked once and there was no indication that C. cataphractus can discriminate prey chemicals. Most of the invertebrate prey species identified in the stomach contents were diurnal species. The stomach contents included a wide range of food items, from plant material to scorpions and millipedes. The southern harvester termite, Microhodotermes viator, is possibly the most important prey species of this lizard. An analysis of the stomach contents of 122 C. cataphractus specimens revealed a significantly higher proportion with empty stomachs among group-living than among solitary ones.
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Seasonal activity of snakes was investigated in northeastern Chihuahua, Mexico, from 1975 to 1977. The effect of rainfall patterns on seasonal snake activity was studied for 20 species collected along Mexico Highway 16 from Villa Aldama to El Pastor. A positive correlation exists between the number of snakes collected and the amount of precipitation, which in this region is highest in July. The greatest number of snakes was taken in August, about 1 month after the peak in rainfall. The relationship between rainfall, and its effects on vegetation and ultimately on seed and insect production, is discussed in relation to the prey available to snakes. Summer rain is the ultimate factor regulating food supply for snakes in Chihuahua and snake activity is greatest when prey items are most abundant.
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The possession of armour may affect escape behaviour in two ways. On one hand, by decreasing vulnerability to predators, armour may permit individuals to use habitats and behaviours that are too risky for unarmoured individuals. Alternatively, the possession of armour may have negative trade-offs on other traits involved in antipredator behaviour, such as sprint speed, thus constraining antipredator options relative to those available to unarmoured individuals. To examine these contrasting predictions, we examined species in the lizard family Cordylidae, which contains remarkable morphological diversity, ranging from completely unarmoured to heavily defended species. Moreover, phylogenetic analysis indicates that armour has been an evolutionarily labile trait. We found support for the second prediction. Degree of body armature was inversely correlated with distance run from a predator: heavily armoured species always entered refuges after short distances, whereas many unarmoured lizards continued to flee and could not be induced to enter a refuge. Possession of armour was also negatively related to use of vertical surfaces during escape behavour. These results were unchanged when analysed in a phylogenetic context. Thus, we conclude that the morphological requirements for active flight and armoured defence are incompatible. Heavily armoured species are bulky, have short legs and run more slowly than less armoured species. Rather than constituting an alternative to behavioural antipredator tactics, we conclude that the possession of armour is part of an antipredator syndrome that includes habitat use and behaviour as well as morphology. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
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We investigated possible differences in the consumption of termites (Microhodotermes viator) by individuals in different sized groups of Cordylus cataphractus during different times of the year. Scats, collected once a month from small (2-3 individuals), medium (4-10 individuals) and large C. cataphractus groups (more than 10 individuals), from January to December 2005, were analysed for the presence of termite head material. We found termite consumption to be generally greater in larger than smaller groups throughout the year, but only significantly so during the dry months, March and April. Individuals in all group categories utilized termites throughout the year, but consumption was low at the end of winter, a time when general insect abundance is high. We conclude that termitophagy is important to individuals living in large groups, particularly during the dry period of the year, most probably to reduce intragroup competition for food.
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Variations in the nature and extent of southern Africa's winter rainfall zone (WRZ) have the potential to provide important information concerning the nature of long-term climate change at both regional and hemispheric scales. Positioned at the interface between tropical and temperate systems, southern Africa's climate is influenced by shifts in the Intertropical Convergence Zone, the westerlies, and the development and position of continental and oceanic anticyclones. Over the last glacial–interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems. Central to this discussion has been the extent to which the region's glacial climates would have been affected by expansions of Antarctic sea-ice, equatorward migrations of the westerlies, more frequent/intense winter storms and an expanded WRZ. This paper reviews the developing body of evidence pertaining to shifts in the WRZ, and the evolution of ideas that have been presented to explain the patterns observed. Dividing the region into three separate axes, along the western and southern margins of the continent and across the interior into the Karoo and the Kalahari, a range of evidence from both terrestrial sites and marine cores is considered, and potential expansions of the WRZ expansions are explored. Despite the limitations of many of the region's proxy records, a coherent pattern has begun to develop of a significantly expanded WRZ during phases of the last glacial period, with the best-documented being between 32–17 ka. While more detailed inferences will require the recovery and analysis of longer and better-dated records, this synthesis provides a new baseline for further research in this key region.
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The Australian gidgee skink Egernia stokesii is unusual among lizards in that it maintains stable social aggregations of related individuals. Experiments were conducted to investigate whether lizards living in groups gained benefits from the collective detection of approaching threats. In captive colonies, lizards living in a group detected an approaching threat earlier than lizards alone, and lizards basking in a group spent more time in a non-vigilant, eyes-closed, state than lizards alone. These results imply that individuals in this species gain from the enhanced vigilance associated with group membership. Since many juveniles remain within their natal groups, group vigilance may enhance inclusive fitness.
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Examination of eroded and intact earth mounds in the Clanwilliam district, South Africa, indicates that they are well-established active termitaria of the harvester termite Microhodotermes viator. Unoccupied lower portions of the mounds contain ubiquitous trace-fossil evidence of earlier inhabitation by the same species. Previous studies indicating that fossorial molerats played a major role in the formation of the mounds are not supported by the observations presented here. Calcretization of the basal parts of the earth mounds has been caused by groundwater interaction with the more alkaline mound soil. 14C dating of this calcrete indicates that the earth mounds have been in existence for at least 4000 years, an order of magnitude greater than any previously recorded longevity for termitarium inhabitation.
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Predicting the distribution of endangered species from habitat data is frequently perceived to be a useful technique. Models that predict the presence or absence of a species are normally judged by the number of prediction errors. These may be of two types: false positives and false negatives. Many of the prediction errors can be traced to ecological processes such as unsaturated habitat and species interactions. Consequently, if prediction errors are not placed in an ecological context the results of the model may be misleading. The simplest, and most widely used, measure of prediction accuracy is the number of correctly classified cases. There are other measures of prediction success that may be more appropriate. Strategies for assessing the causes and costs of these errors are discussed. A range of techniques for measuring error in presence/absence models, including some that are seldom used by ecologists (e.g. ROC plots and cost matrices), are described. A new approach to estimating prediction error, which is based on the spatial characteristics of the errors, is proposed. Thirteen recommendations are made to enable the objective selection of an error assessment technique for ecological presence/absence models.
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(1) Light trap data, covering over 3 years, are discussed for some groups of insects in the lowland tropical monsoon forest on Barro Colorado Island. The groups concerned are Homoptera, Tettigoniidae and Mantidae. (2) The data are compared with information on rainfall and leaf production. It is shown that, especially for those groups of Homoptera that have nymphs feeding on the foliage, there is a good relation between leaf production and the demography of the species concerned. (3) In all cases the data are discussed in general terms although data per species are available. (4) In some cases anomalies in the rainfall pattern, such as an inch or so of rain in early March, the mid dry season, has a strong positive effect on the populations through increasing leaf production, in other cases it may actually have a negative effect.
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Thesis (MSc)--University of Stellenbosch, 2004. Bibliography.
Online at: http//www.addinsoft. com AKAIKE, H. 1974. A new look at the statistical model identification
  • Addinsoft Inc
ADDINSOFT INC. 2013. XLSTAT: Statistical and data analysis software. Online at: http//www.addinsoft. com AKAIKE, H. 1974. A new look at the statistical model identification. IEEE Transactions on Automatic Control 19: 716-723.
  • A F Bennett
  • W R Dawson
BENNETT, A.F. & DAWSON, W.R. 1976. Metabolism. In: Biology of the Reptilia (eds) C. Gans & W.R. Dawson, vol. 5, pp. 127-224. Academic Press, New York.
Spaceuse in a multi-male group of the group-living lizard, Cordylus cataphractus
  • E Effenberger
  • P Lef N Mouton
EFFENBERGER, E. & MOUTON, P.leF.N. 2007. Spaceuse in a multi-male group of the group-living lizard, Cordylus cataphractus. Journal of Zoology, London 272: 202-208.
Group dynamics and anti-predatory advantages of group-living in the armadillo lizard
  • J Hayward
HAYWARD, J. 2007. Group dynamics and anti-predatory advantages of group-living in the armadillo lizard, Cordylus cataphractus. M.Sc. thesis, Stellenbosch University, Stellenbosch, South Africa.
Osteoderm function in the lizard family Cordylidae
  • P Lef N Mouton
  • A F Flemming
MOUTON, P.leF.N. & FLEMMING, A.F. 2001. Osteoderm function in the lizard family Cordylidae. Proceedings of the Sixth International Congress of Vertebrate Morphology, Jena, Germany, July 21-26, 2001. Journal of Morphology 248: 264.
Oxygen consumption in two cordylid lizards
  • P Lef N Mouton
  • D Fourie
  • A F Flemming
MOUTON, P.leF.N., FOURIE, D. & FLEMMING, A.F. 2000b. Oxygen consumption in two cordylid lizards. Amphibia-Reptilia 21: 502-507.
Mediterranian environments
  • H D Allen
ALLEN, H.D. 1996. Mediterranian environments. In: The Physical Geography of Africa, (eds) W.M. Adams, A.S. Goudie & A.R. Orme, pp. 307-325. Oxford University Press, Oxford.
Grouping behaviour in Cordylus cataphractus
  • L Visagie
VISAGIE, L. 2001. Grouping behaviour in Cordylus cataphractus. M.Sc. thesis, Stellenbosch University, Stellenbosch, South Africa.
Thermoregulation in a group-living lizard, a temporal and spatial analysis
  • J C Truter
XLSTAT: Statistical and data analysis software
  • Addinsoft Inc
Selective regime and time
  • H J Deacon
  • M R Jury
  • F Ellis