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Clayton J, Gardner MG, Fenner AL, Bull M. Co‐occupancy of spider‐engineered burrows within a grassland community changes temporally. AUSTRAL ECOL 2020. [DOI: 10.1111/aec.12714] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Jessica Clayton
- College of Science and Engineering Flinders University of South Australia GPO Box 2100 Bedford Park South Australia 5001 Australia
| | - Michael G. Gardner
- College of Science and Engineering Flinders University of South Australia GPO Box 2100 Bedford Park South Australia 5001 Australia
- Evolutionary Biology Unit South Australian Museum Adelaide South Australia Australia
| | - Aaron L. Fenner
- College of Science and Engineering Flinders University of South Australia GPO Box 2100 Bedford Park South Australia 5001 Australia
| | - Michael Bull
- College of Science and Engineering Flinders University of South Australia GPO Box 2100 Bedford Park South Australia 5001 Australia
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Nielsen TP, Bull CM. Effects of grazing regime on the relative body mass of the endangered pygmy bluetongue lizard (Tiliqua adelaidensis
). AUSTRAL ECOL 2019. [DOI: 10.1111/aec.12816] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Torben Peiter Nielsen
- School of Biological Sciences; Flinders University; Adelaide South Australia 5001 Australia
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Nielsen TP, Bull CM. The impact of sheep grazing on the fecundity and timing of reproduction in the endangered pygmy bluetongue lizard, Tiliqua adelaidensis. AMPHIBIA-REPTILIA 2017. [DOI: 10.1163/15685381-00003119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The endangered pygmy bluetongue lizard (Tiliqua adelaidensis) is found only in a few remaining patches of South Australian native grassland, most of which are used for live stock grazing. The lizards occupy spider burrows, they mate in October-November and females produce litters of one to four live born neonates in mid-January-mid-March. In this study we use ultrasound scans of females and observations of neonates in their maternal burrows to investigate how grazing affects the fecundity of the pygmy bluetongue lizard. We predicted that lizards in moderately grazed paddocks would have a higher reproductive output than lizards in hard grazed paddocks. Ultrasound scans indicated that this hypothesis was correct by showing a higher mean number of yolk sacs in females from moderately than from hard grazed paddocks. Females from moderately grazed paddocks also gave birth significantly earlier than females in hard grazed paddocks. The higher number of yolk sacs did not result in a significantly higher number of neonates observed in the burrows, which indicates that the weekly burrow observations used in this study may underestimate true fecundity. Understanding how grazing affects the fecundity of the pygmy bluetongue lizard is essential to the future management of this endangered species. This is not only because grazing is used to manage the habitat of all currently known lizard populations, but also because successful reproduction will be needed in those populations to supply the “surplus” individuals predicted to be essential for relocation programs to ensure the survival of the species.
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Affiliation(s)
- Torben P. Nielsen
- School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide 5001, South Australia
| | - C. Michael Bull
- School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide 5001, South Australia
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Clayton J, Bull M. The impact of sheep grazing on the depth of spider burrows and of burrows selected by the pygmy bluetongue lizard (Tiliqua adelaidensis). WILDLIFE RESEARCH 2016. [DOI: 10.1071/wr16138] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context
Grazing by domestic stock can potentially influence ecosystems positively or negatively, depending on the grazing regime and intensity. The pygmy bluetongue lizard (Tiliqua adelaidensis) is an endangered species, restricted to fragmented grasslands in the Mid North region of South Australia, predominantly grazed by sheep. These lizards refuge in vertical burrows. They do not dig their own burrows, instead relying on co-existing spiders for this essential resource.
Aims
We investigated how sheep grazing influenced spider burrows, and predicted the following: that grazing sheep might trample and destroy shallow burrows; that burrows in grazed habitat with less vegetative cover would have higher temperatures in summer; and that, by way of compensation, spiders would dig deeper burrows in grazed habitat.
Methods
We monitored 12 30m×30m plots monthly, over two austral spring/summer periods (September–March 2012–14). We recorded the number, depth and occupant of all spider burrows in those plots in each survey. We also measured temperatures inside artificial burrows in grazed and ungrazed habitat over a 3-day period in September 2014.
Key results
Mean burrow depth increased with grazing. This was not because individual burrows became deeper, but because the shallowest burrows were lost where there were sheep. Burrows were significantly hotter in grazed habitat, but lizards consistently chose deeper, cooler burrows. In the subset of burrows that were occupied by lizards, there was no difference in depth between grazed and ungrazed treatments. We detected no difference in spider digging activity between grazed and ungrazed plots.
Conclusions
Sheep grazing can destroy shallow burrows, probably through trampling, and because sheep produce burrow filling debris. However, grazing did not affect deeper burrows occupied by pygmy bluetongue lizards.
Implications
This short study indicated that moderate levels of grazing have low impact on deeper burrows suitable for pygmy bluetongue lizards and for lizard persistence. It explains how sheep and lizards have co-occurred for so long, but leaves open the question of how the loss of shallow burrows affects populations of the burrow-digging spiders that are an essential component of the lizard environment.
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Nielsen TP, Bull CM. Winter durability of pygmy bluetongue lizard burrows is higher for occupied than for unoccupied burrows and for those in less-grazed neighbourhoods. WILDLIFE RESEARCH 2016. [DOI: 10.1071/wr16109] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context Many ectothermic animals survive winter by hibernating, either buried or in burrows. During their hibernation these animals are vulnerable to changes in soil structure and temperature caused by the activity of grazing mammals. This may be a particular risk to ectotherms living in native grassland, as this habitat is often used for livestock grazing. The endangered pygmy bluetongue lizard lives in burrows, in fragments of native grassland in South Australia, and these burrows are likely to be affected by sheep grazing during the lizards’ hibernation. Aims The current study aimed to determine the following effects on the persistence of burrows suitable to the pygmy bluetongue lizard: different levels of grazing, winter vegetation cover, burrow entrance size and whether a lizard was overwintering in the burrow. Methods During two winters, we applied different grazing treatments to six experimental paddocks and determined whether suitable lizard burrows located in autumn were still suitable to lizards in the following spring. For each burrow, we recorded whether a lizard was overwintering, the burrow entrance diameter and the vegetation cover around the burrow during the winter. Key results Increased grazing pressure led to decreased persistence of lizard burrows. We also found that burrows with an overwintering lizard had a greater chance of persisting, but found no direct effect of winter vegetation cover or entrance diameter. Conclusions The results show that although pygmy bluetongue lizards may be able to stabilise their own burrows, the more intense the grazing the lower the chance of lizard burrow persistence. Implications Management of sheep grazing is an important component in future conservation of the endangered pygmy bluetongue lizard. Grazing on grassland with a lizard population should be kept at a moderate level and hard grazing should be avoided.
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