Modelled incubation conditions indicate wider potential distributions based on thermal requirements for an oviparous lizard

Abstract

Aim Predicting the distribution of species relies increasingly on understanding the spatially explicit constraints of environmental conditions on an organism's physiological traits. We combined an empirical model of temperature‐dependent embryonic development with a mechanistic model of soil temperatures to examine potential thermal limitations on the distribution of a nocturnal, oviparous skink, Oligosoma suteri, a range‐restricted endemic. Location New Zealand. Methods We estimated a thermal requirement for successful embryonic development as 616 degree‐days above a threshold of 13.8°C. We then modelled soil temperatures at representative sites across New Zealand and predicted duration of incubation to map the distribution of potentially viable oviposition sites, given variation in the timing of egg‐laying under even temperature increases. Results Successful development of O. suteri embryos is possible in locations outside their current distribution. Increasing temperatures increased the species’ potential range, reducing incubation duration and lengthening the oviposition window. However, due to the disconnected nature of their rocky shore habitat, individuals may not be able to disperse to currently uninhabited sites within that extended range. Additionally, although locations may be thermally suitable for incubation, predation by introduced mammals, competition and habitat modification may prevent successful establishment of populations. Main conclusions Our models contribute to understanding fundamental physiological constraints on an important life history stage that will inform conservation management actions, including potential future translocations.

Current knowledge and potential impacts of climate change on New Zealand’s biological heritage

“…Declines in Archey's frog Leiopelma archeyi populations on the Coromandel Peninsula between 1996 and 2001 have been tied to disease and climatic factors (Bell et al 2004), consistent with climate impacts on frogs globally (Stuart et al 2004). Increasing temperature may also have an effect on the egg-laying skink Oligosoma suteri, with positive outcomes including increased range and shorter incubation periods, but these advantages may be counteracted by physiological factors and invasive predators (Stenhouse et al 2018).…”

Thermal and physical characteristics of the nesting habitat of New Zealand’s only endemic oviparous lizard

“…As nests of O. suteri at our study site appeared to be closely clustered, it is possible that we were unable to locate the core of nesting activity, and further investigation of suitable nesting locations is warranted. Similarly, it may be that we conducted our survey prior to the main nesting Figure 5 Predicted duration of incubation for eggs of Oligosoma suteri within natural and mock nests for a range of estimated oviposition dates in austral summer 2016-17 using an incubation 'duration' of 616 degree days (Stenhouse et al 2018). The longest known successful incubation time for O. suteri is 149 days and the shortest is 42 days (Hare unpubl.…”

“…Female O. suteri lay between one and five eggs (Towns 1975;Hare et al 2002) between mid-December and mid-January (Towns 1975) with hatching occurring between late-February and mid-April (Whitaker 1968;Towns 1975). Nesting sites in the wild have all been located beneath rocks and boulders above the high-tide line and below permanent (Whitaker 1968;Parrish & Gill 2003;Stenhouse et al 2018). Some females appear to use cues for selection of nest sites in the wild as communal nesting is common (Whitaker 1968).…”

“…Furthermore, the species' habitat is likely threatened by sealevel rise resulting from climate change (Ackerley et al 2013). With the increased investment in mainland sanctuaries, and the knowledge that successful development of embryos is possible in locations outside their current distribution (Stenhouse et al 2018), translocation may become an important tool in the conservation of this species. However, prior to management outside their current range, it is vital that further data on physiology are obtained .…”

“…This includes use of degreeday models which are useful for predicting timing of events based on temperature-dependent developmental processes (Hartley & Lester 2003;Schultze et al 2016). Stenhouse et al (2018) provide estimated thermal requirements for successful embryonic development at 616 degree-days above a threshold temperature of 13.8°C.…”