Short-Term Dispersal Response of an Endangered Australian Lizard Varies with Time of Year

Dispersal is an important component in the demography of animal populations. Many animals show seasonal changes in their tendency to disperse, reflecting changes in resource availability, mating opportunities, or in population age structure at the time when new offspring enter the population. Understanding when and why dispersal occurs can be important for the management of endangered species. The pygmy bluetongue lizard is an endangered Australian species that occupies and defends single burrow refuges for extended periods of time, rarely moving far from the burrow entrance. However, previous pitfall trapping data have suggested movement of adult males in spring and of juveniles in autumn of each year. In the current study we compared behaviours of adult lizards each month, over the spring-summer activity period over two consecutive field seasons, to provide deeper understanding of the seasonal dispersal pattern. We released adult pygmy bluetongue lizards into a central area, provided with artificial burrows, within large enclosures, and monitored the behaviour and movements of the released lizards over a four day period. There was a consistent decline in time spent basking, amount of movement around burrow entrances, and rates of dispersal from the central release area from early spring to late summer. Results could be relevant to understanding and managing natural populations and for any translocation attempts of this endangered lizard species.     

The Effects of Winter Burning and Grazing on Resources and Survival of Texas Horned Lizards in a Thornscrub Ecosystem

ABSTRACT The ecological effects of land-use practices on reptiles, especially endangered or threatened species, are of conservation and scientific interest. We describe the effects of rotational livestock grazing and prescribed winter burning on resources and survival of the Texas horned lizard (Phrynosoma cornutum) during the summers of 1998 to 2001 in southern Texas, USA. We evaluated survival rates of Texas horned lizards (n = 111) on 6 study sites encompassing 5 different burning and grazing treatments. We also measured indices of cover (i.e., vegetation) and food abundance (i.e., harvester ants [Pogonomyrmex rugosus]). We telemetered and relocated adult lizards daily. We divided the study into 2 seasons, spring (15 Apr–30 Jun) and summer (1 Jul–15 Aug), corresponding to the relative activity of horned lizards. Winter burning provided an increase in food resources and led to increased survival of Texas horned lizards in the second growing season after fire, but grazing-induced changes in vegetation cover reduced survival, likely by increasing lizard vulnerability. Fire and grazing reduced litter and increased bare ground and forb cover but did not affect woody vegetation. Ant activity was greater in burned sites and varied with grazing level, season, and year. Summer survival functions of horned lizards varied by burning treatment, with higher survival observed on burned sites in the second year after burning. Survival rates were ordered from highest in ungrazed sites to lowest in heavily grazed sites. We recognize the limitations of our work resulting from a lack of spatial replication of treatments. However, our mensurative study provides fertile ground for future hypothesis testing regarding the effects of land management on shrubland and grassland reptiles. We propose that future studies focus on the population consequences of variation in burn frequency, burn timing, and grazing intensity.     

Direct and indirect effects of grazing constrain shrub encroachment in semi‐arid Patagonian steppes

Question: What are the long‐term effects of grazing exclusion on the population structure and dynamics of, and interactions among, three dominant shrub species? Location: Grass‐shrub Patagonian steppe, Chubut, Argentina. Methods: Permanent plots were established in grazed paddocks and paddocks excluded from grazing in representative Patagonian rangelands. Shrub abundance, population size‐structure, short‐term (two 3‐yr periods) and long‐term (matrix models) population dynamics, and neighborhood interactions of three native and codominant shrub species (Mulinum spinosum, Senecio filaginoides and Adesmia volckmanni) were measured and analysed using different statistical approaches. Results: The total density of shrubs was 74% higher in paddocks excluded from grazing, owing mainly to increases in Mulinum (80%) and Senecio (68%) species. However, differences in size structure between ungrazed and grazed paddocks were only detected in Mulinum. Demographic rates differed between shrub species, time‐periods and grazing conditions. In particular, recruitment in the short term (especially in wet years) and population growth rate in the long term (λ) were higher in paddocks excluded from grazing only in Mulinum populations. Senecio populations showed a marginal increase in recruitment and mortality independent of the grazing condition in the wet and dry period. Grazing exclusion modified the balance of neighborhood interactions among the three shrub species. In grazing‐exclusion paddocks, there was a balance between positive and negative interspecific interactions, while in grazed paddocks there were more negative intraspecific and interspecific interactions, resulting in a net negative balance of neighborhood interactions. Conclusions: Our understanding of woody encroachment in arid rangelands can be informed through evaluation of direct and indirect effects of grazing exclusion on the abundance and demography of dominant woody species. In Patagonian arid steppes, the occurrence of woody encroachment in rangelands excluded from grazing can be explained by altered responses in plant‐animal and plant‐plant interactions among shrub species.     

Population augmentation had no effect on the abundance or body condition of conspecifics and co‐occurring lizard species in a native grassland community

Wildlife translocations have been historically plagued by failure. As more species gain endangered status, we must increase the success rate through use of pre‐emptive empirical, evidence‐based research. The main ecological risk is the potential for the relocated individuals to have competitive advantage at the recipient site, acting invasively and, potentially, outcompeting the native fauna for food, shelter or other resources. Here we investigated the ecological risk of increased population density, following a population augmentation of the pygmy bluetongue lizard (Tiliqua adelaidensis) an endangered lizard, endemic to South Australia. We experimentally increased T. adelaidensis density to ascertain if a sudden increase in T. adelaidensis density would negatively affect the abundance or body condition of the resident conspecifics and co‐existing lizard species found at the recipient site. Twenty‐four individuals, from two populations, were relocated into previously built enclosures at a recipient site in grassland habitat, north of Adelaide, South Australia. For one activity‐season pre and post the augmentation, co‐existing lizard species were sampled in an effort to detect any changes inabundance or body condition. Comparisons were also made between experimental enclosures, containing residents and translocated individuals and control enclosures, containing only residents. Using Menetia greyii as a proxy for all of the competing species, our results show there was no reduction in abundance or body condition post augmentation. Our lack of evidence indicating a negative impact of the T. adelaidensis translocation on the body condition and abundance of the resident lizard species is a positive outcome for future conservation of this species. This study provides a new way of approaching wildlife movements, through identification of potential risks using small‐scale translocations in an enclosed area before conducting large‐scale releases into unfenced areas; the results are intended to facilitate higher translocation success rates and limit the negative effects upon the wider ecological community at recipient sites.     

Spiders provide important resources for an endangered lizard

Conservation management requires knowledge of how a target species interacts with other species. Some relatively common species can modify the environment to the advantage of rarer, endangered species. Thus, local enhancement of those common species can positively influence remaining populations of the rarer species. The endangered pygmy bluetongue lizard Tiliqua adelaidensis inhabits burrows that are constructed by lycosid and mygalomorph spiders. We recorded 490 burrows in a 1 ha plot at the end of one season, and then observed at regular intervals the formation and loss of burrows, and the changes in occupancy status of each burrow over the next season. We found spiders in 94% of all newly constructed burrows and deduced that they had built the burrows. We found no evidence that lizards dug new burrows or deepened existing burrows. The numbers of both lizards and spiders in the burrows declined over the spring and summer, with lizards moving from their burrows more often early in the season than later. However, there was no strong trend for lizards to replace spiders in burrows. In fact, lizards tended to occupy deeper burrows than spiders, suggesting little negative impact of lizards on spiders. However, spiders had a positive impact on lizards by providing the refuge burrows central for lizard survival. Although lizards readily accept artificial burrows, long-term conservation for the lizards must include viable spider populations to maintain a supply of suitable burrow refuges.     

Food restriction affects maternal investment but not neonate phenotypes in a viviparous lizard

Food availability significantly affects an animal's energy metabolism,and thus its phenotype,survival,and reproduction.Maternal and offspring responses to food conditions are critical for understanding population dynamics and life-history evolution of a species.In this study,we conducted food manipulation experiments in field enclosures to identify the effect of food restriction on female reproductive traits and postpartum body condition,as well as on hatchling phenotypes,in a lacertid viviparous lizard from the Inner Mongolian desert steppe of China.Females under low-food availability treatment (LFT) had poorer immune function and body condition compared with those under high-food availability treatment (HFT).The food availability treatments significantly affected the litter size and litter mass of the females,but not their gestation period in captivity or brood success,or the body size,sprint speed,and sex ratio of the neonates.Females from the LFT group had smaller litter sizes and,therefore,lower litter mass than those from the HFT group.These results suggest that female racerunners facing food restriction lay fewer offspring with unchanged body size and locomotor performance,and incur a cost in the form of poor postpartum body condition and immune function.The flexibility of maternal responses to variable food availability represents an important life strategy that could enhance the resistance of lizards to unpredictable environmental change.     

Responses of the endangered pygmy bluetongue lizard to conspecific scats

Many animals use chemical signals for communication between conspecifics and for territory marking. The pygmy bluetongue lizard is normally solitary, focussing activity around the entrance of its burrow, from where it ambushes prey, and rarely contacts other individuals. In this paper we examined whether lizards in laboratory experiments alter their behaviour in the presence of scats from conspecifics. In the first experiment, when lizards were offered a choice of two vacant burrows with or without a scat close to the entrance, they tongue flicked more often at the burrow entrance when the scat was present, and more often chose to occupy the burrow with the scat. An interpretation is that lizards use scat signals to recognise burrows that may be suitable because they have previously been occupied by a conspecific, but that they approach those burrows cautiously in case a resident is still present and likely to resist a takeover. Scats from male lizards were inspected (by both sexes) for longer than scats of female lizards. In the second experiment, when resident lizards were presented with scats outside of their burrows, they inspected and tongue flicked at those scats more often if the scat came from a male than a female lizard, but there was no definitive evidence from our experiments that lizards differentiated in their response to scats from lizards that were found close to or far from the test lizard. The results were consistent with a communication system in which lizards use scats to advertise their presence, independent of any direct contact.     

Herbivore phenology can predict response to changes in plant quality by livestock grazing

Livestock grazing can have a strong impact on herbivore abundance, distribution and community. However, not all species of herbivores respond the same way to livestock grazing, and we still have a poor understanding of the underlying mechanisms driving these differential responses. Here, we investigate the effect of light intensity cattle grazing on the abundance of two grasshoppers (Euchorthippus cheui and E. unicolor) that co-occur in the same grasslands and feed on the same food plant (the dominant grass Leymus chinensis). The two grasshopper species differ in phenology so that their peak abundances are separated into early- and late-growing seasons. We used an exclosure experiment to monitor grasshopper abundance and food quality in the field under grazed and ungrazed conditions, and performed feeding trials to examine grasshopper preference for grazed or ungrazed food plants in the laboratory. We found that the nitrogen content of L. chinensis leaves continuously declined in the ungrazed areas, but was significantly enhanced by cattle grazing over the growing season. Cattle grazing facilitated the early-season grasshopper E. cheui, whereas it suppressed the late-season grasshopper E. unicolor. Moreover, feeding trials showed that E. cheui preferred L. chinensis from grazed plots, while E. unicolor preferred the leaves from ungrazed plots. We conclude that livestock grazing has opposite effects on the two grasshopper species, and that these effects may be driven by grazing-induced changes in plant nutrient content and the unique nutritional niches of the grasshoppers. These results suggest that insects that belong to the same guild can have opposite nutrient requirements, related to their distinct phenologies, and that this can ultimately affect their response to cattle grazing. Our results show that phenology may link insect physiological needs to local resource availabilities, and should be given more attention in future work on interactions between large herbivores and insects.     

划区轮牧中不同放牧利用时间对草地植被的影响

对比研究了划区轮牧中不同时间的放牧利用对各小区的植被状况的影响。结果表明 ,在固定放牧时间长度的情况下 ,早放牧小区的草群结构比晚放牧的小区受到的影响大。家畜对早放牧小区的牧草利用率高于晚放牧的小区 ,草地生产力则表现出相反的趋势。对于可利用牧草营养 ,早放牧的小区可提供较多的粗蛋白。在生产实践中 ,要灵活应用划区轮牧制度 ,对不同时间放牧利用的各小区要根据草地的实际情况来确定其具体的放牧时间长度 ,在不同的年度也要按不同的顺序来轮换放牧 ,兼顾到草地的可持续利用与家畜生产。     

Soil and plant water relations in a crested wheatgrass pasture: response to spring grazing by cattle

Summary Few field studies have attempted to relate effects of actual livestock grazing on soil and plant water status. The present study was initiated to determine the effects of periodic defoliations by cattle during spring on soil moisture and plant water status in a crested wheatgrass (Agropyron cristatum (L.) Gaertn. and A. desertorum (Fisch. ex Link) Schult.) pasture in central Utah. Soil moisture in the top 130 cm of the soil profile was depleted more rapidly in ungrazed plots than in grazed plots during spring and early summer. Soil moisture depletion was more rapid in grazed plots in one paddock after 1 July due to differential regrowth, but there was no difference in soil water depletion between plots in another paddock during the same period. This difference in soil water depletion between paddocks was related to a difference in date of grazing. Although more water had been extracted from the 60 cm to 130 cm depths in ungrazed plots by late September, cumulative soil moisture depletion over the entire 193 cm profile was similar in grazed and ungrazed plots. Prior to 1 July, grazing had no effect on predawn leaf water potentials as estimated by a pressure chamber technique; however, after 1 July, predawn leaf water potentials were lower for ungrazed plants. Midday leaf water potentials were lower for grazed plants before 1 July, but did not differ between grazed and ungrazed plants after 1 July. A 4- to 8-day difference in date of defoliation did not affect either predawn or midday leaf water potentials. The observed differences in water use patterns during spring and early-summer may be important in influencing growth and competitive interactions in crested wheatgrass communities that are subject to grazing by domestic livestock.     

Post-feeding thermophily in lizards (Lialis burtonis Gray,Pygopodidae): Laboratory studies can provide misleading results

Many ectothermic vertebrates raise their preferred body temperature after feeding, likely expediting digestion. However, most studies documenting this phenomenon have relied upon laboratory thermal gradients, which grossly oversimplify an animal's environment. We explored the validity of thermal gradient methodology by investigating post-prandial thermophily in an Australian pygopodid lizard (Lialis burtonis Gray). Mean body temperatures did not differ between fed and unfed lizards in field enclosures. Feeding influenced body temperature in a thermal gradient, but in opposite directions depending on details of the methodology. When we introduced L. burtonis into the gradient at the warmer end, fed lizards had higher body temperatures than unfed conspecifics. However, the opposite was true when lizards were introduced at the cooler end. These contrasting results indicate that lizards with food in their stomachs did not seek out higher temperatures, but instead were more sedentary than unfed lizards. Our study highlights the need for caution in interpreting thermal gradient results unaccompanied by field data, and it demonstrates how minor changes in equipment design or procedures can significantly alter conclusions from laboratory studies.     

The effects of sheep grazing on seedling establishment and survival in grassland

This paper examines the effects of sheep and insect grazing on the generation of natural gaps in turf and the establishment of seedlings therein. The site is on an old field on limestone. There were five sheep grazing treatments: ungrazed, and grazed briefly in spring, briefly in autumn, in autumn or in summer and autumn. The first three of these treatments also contained plots in which insecticide was applied regularly during the growing season. Pins of increasing size (1.6 mm–12.8 mm diameter) were lowered at grid intersections in permanent quadrats to record gap type and the occurrence of seedlings on seven dates over 15 months.Heavily-grazed plots had more bare ground in spring and more herb seedlings established in them. Seedlings of annual species of Bromus were able to establish in gaps (bare ground and litter) of smaller size than was required by herb seedlings (which had much smaller seeds). The use of an insecticide increased seedling establishment in October in ungrazed and in spring-grazed paddocks but decreased it in autumn-grazed paddocks. This may indicate the greater importance of insect herbivory in making gaps in the matted sward of autumn-grazed plots.Seedlings which established in October 1986 and March 1987 were more likely to die than those establishing earlier in 1986. This may be because of winter-kill and especially vigorous spring vegetation growth respectively. Seedling mortality was not affected by gap size or grazing treatment (unless such effects operated before we detected the seedlings).     

The impact of cattle grazing regimes on tropical savanna bird assemblages

Globally, agricultural land use is implicated in the decline of avifauna. In rangelands (areas used for livestock grazing), bird community responses to grazing can be complex, species‐specific and scale dependent. A greater understanding of bird responses to grazing will lead to more meaningful management recommendations. We tested the hypothesis that foraging height predicts bird species’ responses to grazing, such that species using lower vegetation strata are most likely to respond to the impacts of livestock grazing. We examined the response of a tropical savanna bird community to four grazing strategies at a long‐term grazing trial in northern Australia. We predicted that ground‐foraging guilds would be more responsive to grazing treatment than foliage‐ or aerial‐foraging guilds. We analysed the bird community assemblage using generalised linear mixed models and examined individual species’ abundance in relation to microhabitat variables. We found that while ground‐foraging guilds were more responsive to grazing treatment, individual species dynamics within a foraging guild could be contradictory. For example, the red‐backed fairy‐wren decreased in abundance with increased grazing and was positively associated with grass and shrub (Carissa ovata) cover, whereas Australian magpies increased in abundance in the most heavily grazed paddocks. In general, the responses of bird species to grazing were more pronounced in guilds that forage closer to the ground, but whether the responses were positive or negative was driven by bird species ecology. Measures examining the responses of individual species are more useful than assemblage measures (such as richness) to describe the impacts of anthropogenic disturbance such as grazing.     

Comparative ecology of Varanus in the Great Victoria Desert

Abstract The ecologies of seven desert species of monitor lizards (Varanus), which are very variable in size, are described and compared. Data are reported on abundance, anatomy, behaviour, body temperature relationships, daily activity patterns, diet, growth, habitat and microhabitat, prey size, reproduction, seasonal patterns of activity, sexual dimorphisms, and tracks. As many as six of the seven species occur together in sympatry at one study site. New results reported here are merged with extensive data collected over the past quarter of a century to provide a comprehensive and detailed overview of numerous aspects of the natural history and ecology of the seven species in the Great Victoria Desert. One species of pygmy monitor has evolved large clutch size for unknown reasons. A food web for 40 species of desert lizards is presented. Hutchinsonian ratios of head lengths (larger/smaller) are significantly greater in two observed assemblages of sympatric varanids than in a null model consisting of all possible pairs of species of all Australian varanids. Evolution of body size and the two adaptive radiations of Varanus in Australia are discussed.     

Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

Food availability and predation risk can have drastic impacts on animal behaviour and populations. The tradeoff between foraging and predator avoidance is crucial for animal survival and will strongly affect individual body mass, since large fat reserves are beneficial to reduce starvation but may increase predation risk. However, two‐factor experiments simultaneously investigating the interactive effects of food and predation risk, are still rare. We studied the effects of food supplementation and natural predation risk imposed by pygmy owls Glaucidium passerinum on the abundance and fat reserves of tit species in boreal forests of north Europe, from January to March in 2012 and in 2013. Food supplementation increased the number of individuals present in a given forest patch, whereas the level of predation risk had no clear impact on the abundance of tit species. The stronger impact of food supply respect to predation risk could be the consequence of the harsh winter conditions in north Europe, with constant below‐zero temperatures and only few (5–7 h) daylight hours available for foraging. Predation risk did not have obvious effects on tit abundance but influenced food consumption and, together with food supplementation, affected the deposition of subcutaneous fat in great tits Parus major. High owl predation risk had detrimental effects on body fat reserves, which may reduce over‐winter survival, but the costs imposed by pygmy owl risk were compensated when food was supplemented. The starvation–predation tradeoff faced by great tits in winter may thus be mediated through variation in body fat reserves. In small species living in harsh environment, this tradeoff appeared thus to be biased towards avoidance of starvation, at the cost of increasing predation risk.     

Frequent mowing is better than grazing for the conservation value of lowland tussock grasssland at Pontville,Tasmania

Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction.     

Translocation for conservation: Neonates are less suitable than adults

Animal behaviour can affect the outcome of conservation translocations. It is important to understand the behaviour of the species being considered for translocation and how its behaviour varies over life stages. There may be uncertainty about what life stages are best as founders for release back into wild populations. A technique called head‐starting whereby juvenile life stages are raised in captivity and then released is one potential pre‐release strategy. However, juveniles of many species have a dispersive role in the life cycle, potentially raising difficulties for establishing new populations due to dispersal from the intended habitat following release. For this study, we compared aspects of the behaviour of captive adult and neonate pygmy bluetongue lizards (Tiliqua adelaidensis) – an endangered species for which translocation is likely to be an important management strategy – to determine if neonate behavioural characteristics are appropriate for their translocation. We filmed adult and neonate pygmy bluetongue lizards and compared their behaviour. We also filmed adults over an activity season to compare seasonal behaviour. Behavioural parameters measured included basking time, burrow exits, burrows occupied and walking the perimeter wall. Neonates basked significantly more than adults in summer and autumn. Neonates are likely to be basking more than adults because they are in a stage of rapid growth and need to gain body mass before the winter inactivity period. Neonates exited burrows more often than adults and used a greater number of burrows. These results indicate neonate lizards are actively exploring their habitat. Neonates are unlikely to be as suitable for translocation as they are actively moving about and more likely to be predated upon or disperse from the translocation site. Our finding can be applied to other species that have active juvenile life stages and are at particular risk of predation due to their small size.     

Loss of body mass under predation risk: cost of antipredatory behaviour or adaptive fit-for-escape?

Predation risk may compromise the ability of animals to acquire and maintain body reserves by hindering foraging efficiency and increasing physiological stress. Locomotor performance may depend on body mass, so losing mass under predation risk could be an adaptive response of prey to improve escape ability. We studied individual variation in antipredatory behaviour, feeding rate, body mass and escape performance in the lacertid lizard Psammodromus algirus. Individuals were experimentally exposed to different levels of food availability (limited or abundant) and predation risk, represented by reduced refuge availability and simulated predator attacks. Predation risk induced lizards to reduce conspicuousness behaviourally and to avoid feeding in the presence of predators. If food was abundant, alarmed lizards reduced feeding rate, losing mass. Lizards supplied with limited food fed at near-maximum rates independently of predation risk but lost more mass when alarmed; thus, mass losses experienced under predation risk were higher than those expected from feeding interruption alone. Although body mass of lizards varied between treatments, no component of escape performance measured during predator attacks (endurance, speed, escape strategy) was affected by treatments or by variations in body mass. Thus, the body mass changes were consistent with a trade-off between gaining resources and avoiding predators, mediated by hampered foraging efficiency and physiological stress. However, improved escape efficiency is not required to explain mass reduction upon predator encounters beyond that expected from feeding interruption or predation-related stress. Therefore, the idea that animals may regulate body reserves in relation to performance demands should be reconsidered.     

Evolution and ecology of lizard body sizes

Aim Body size is instrumental in influencing animal physiology, morphology, ecology and evolution, as well as extinction risk. I examine several hypotheses regarding the influence of body size on lizard evolution and extinction risk, assessing whether body size influences, or is influenced by, species richness, herbivory, island dwelling and extinction risk. Location World‐wide. Methods I used literature data and measurements of museum and live specimens to estimate lizard body size distributions. Results I obtained body size data for 99% of the world's lizard species. The body size–frequency distribution is highly modal and right skewed and similar distributions characterize most lizard families and lizard assemblages across biogeographical realms. There is a strong negative correlation between mean body size within families and species richness. Herbivorous lizards are larger than omnivorous and carnivorous ones, and aquatic lizards are larger than non‐aquatic species. Diurnal activity is associated with small body size. Insular lizards tend towards both extremes of the size spectrum. Extinction risk increases with body size of species for which risk has been assessed. Main conclusions Small size seems to promote fast diversification of disparate body plans. The absence of mammalian predators allows insular lizards to attain larger body sizes by means of release from predation and allows them to evolve into the top predator niche. Island living also promotes a high frequency of herbivory, which is also associated with large size. Aquatic and nocturnal lizards probably evolve large size because of thermal constraints. The association between large size and high extinction risk, however, probably reflects a bias in the species in which risk has been studied.