Where is the love? Experimental translocation of the threatened striped legless lizard (Delma impar) and an investigation of the habitat suitability of the invasive African lovegrass (Eragrostis curvula)

Abstract

Translocation of individuals to patches of suitable unoccupied habitat may be a useful conservation action for dispersal limited species occurring in isolated populations. Where populations of threatened species are certain to be lost due to habitat destruction, salvage and translocation of individuals to suitable unoccupied habitat may mitigate some of the loss if translocation is thoroughly planned and considers the species biology, habitat requirements and threats affecting it (Germano et al., 2015). The striped legless lizard (Delma impar) may benefit in both these cases as it occurs in isolated populations, is a grassland habitat specialist, dispersal limited and suffers from ongoing habitat loss. Where uncertainties occur in regards to the species biology, translocation can be used to experimentally test hypotheses, for example habitat preference. I investigated the use of translocation as a conservation measure for D. impar. The suitability of the translocation release site in grass structure, food availability and thermal conditions was investigated to ascertain if the translocation may be successful in the long term. The translocation was used to experimentally test the suitability of African lovegrass (Eragrostis curvula) and kangaroo grass (Themeda triandra) as D. impar habitat in the context of the widespread establishment of the invasive grass African lovegrass at the release site and in the Southern Tablelands. The effects of grass structure, food availability and thermal conditions on D. impar selection of microhabitat were investigated. Lastly, short term persistence of the released individuals was determined as a short term indication of the likelihood of translocation success. D. impar were translocated into four enclosures containing approximately equal sized areas of African lovegrass and kangaroo grass. Fine scale grass structure (1 m2 scale), food availability and thermal conditions were measured at the source and release site and in each grass type at the release site. D. impar occupancy and persistence were determined by conducting ten surveys of artificial refuges (tile grids) in release enclosures and modelling D. impar habitat use with generalised linear models. The translocation release site (Scottsdale Reserve) broadly matched the population source site in vegetation structure and D. impar food availability. Summer thermal conditions were cooler at the release site. There were significant differences in vegetation structure, food availability and thermal conditions between African lovegrass and kangaroo grass. African lovegrass provided an inferior feeding habitat than kangaroo grass but had greater structural complexity than kangaroo grass and ground temperatures rarely exceeded maximum lizard critical body temperature. D. impar selected complex grass structures in both grass species. As grass complexity increased, D. impar occupancy increased more rapidly in kangaroo grass than African lovegrass. D. impar appeared to occupy African lovegrass pastures, at least in the short two month time frame of this study concurring with previous research that grass structure not grass species is the most important factor for D. impar habitat. A cooler summer thermal environment allowing greater hours of activity time and possibly a reduction in predation risk (not tested in this study) are the most likely explanation for D. impar's habitat selection of high complexity grass. The increased D. impar occupancy in African lovegrass and in high complexity grass of both species was not due to higher food availability in either situation. The tall and dense characteristic of African lovegrass and relatively short characteristic of kangaroo grass at Scottsdale Reserve and the effect of grass height on the ground thermal conditions is likely to explain the higher D. impar capture rate in African lovegrass compared to kangaroo grass. At the release site, the ecotone between African lovegrass and kangaroo grass may be the highest quality D. impar habitat due to the combination of greater food availability in kangaroo grass but suboptimal (hot) thermal conditions and cool thermal conditions and high grass cover in African lovegrass. There was strong evidence of short term persistence during the two months after release, possibly indicating at least short term release site habitat suitability. The success of the translocation in the long term will only be known after detailed monitoring in the following years. Show more