Warming conditions boost reproductive output for a northern gopher tortoise population

Abstract

The effects of climate change on at-risk species will depend on how life history processes respond to climate and whether the seasonal timing of local climate changes overlaps with species-specific windows of climate sensitivity. For long-lived, iteroparous species like gopher tortoises Gopherus polyphemus, climate likely has a greater influence on reproduction than on adult survival. Our objective was to estimate the timing, magnitude, and direction of climate-driven effects on gopher tortoise reproductive output using a 25 yr dataset collected in southeastern Georgia, USA, near the northern edge of the species’ range. We assessed the timing of climate effects on reproductive output (both probability of reproduction and clutch size) by fitting models with climate covariates (maximum temperature, precipitation, and temperature range) summarized at all possible time intervals (in 1 mo increments) within the 24 mo period prior to the summer census date. We then fit a final model of reproductive output as a function of the identified climate variables and time windows using a Bayesian mixture model. Probability of reproduction was positively correlated with the prior year’s April-May maximum temperature, and clutch size was positively correlated with the prior year’s June maximum temperature. April-May and June maximum temperatures have increased over the past 3 decades at the study site, which likely led to an increase in clutch size of approximately 1 egg (15% increase over a mean of 6.5 eggs). However, the net effect of climate change on gopher tortoise population dynamics will depend on whether there are opposing or reinforcing climate responses for other demographic rates.

Direct and indirect pathways for environmental drivers of hatching success in the loggerhead sea turtle

“…Therefore, a warming climate may make nest incubation conditions more conducive for higher hatching success, potentially leading to larger annual cohorts. Improved reproductive success at the leading edge of geographic ranges with increasing temperatures have been demonstrated for plants (Dangremond & Feller 2016, Ordoñez-Salanueva et al 2021) and invertebrates (Ling et al 2008) and recently observed in gopher tortoises Gopherus polyphemus (Hunter et al 2021). However, warming temperatures could influence hatchling sex ratios, skewing to ward a female bias (Hawkes et al 2007, Reneker & Kamel 2016, Jensen et al 2018, although turtles may compensate by choosing different elevations or digging deeper nests (Hays et al 2001), and temperatures could also be modulated by changes in precipitation and nest moisture (Lolavar & Wyneken 2015).…”