Predicting climate warming effects on green turtle hatchling viability and dispersal performance

Abstract

Summary1. Ectotherms are taxa considered highly sensitive to rapid climate warming. This is because body temperature profoundly governs their performance, fitness and life history. Yet, while several modelling approaches currently predict thermal effects on some aspects of life history and demography, they do not consider how temperature simultaneously affects developmental success and offspring phenotypic performance, two additional key attributes that are needed to comprehensively understand species responses to climate warming. 2. Here, we developed a stepwise, individual-level modelling approach linking biophysical and developmental models with empirically derived performance functions to predict the effects of temperature-induced changes to offspring viability, phenotype and performance, using green sea turtle hatchlings as an ectotherm model. Climate warming is expected to particularly threaten sea turtles, as their life-history traits may preclude them from rapid adaptation. 3. Under conservative and extreme warming, our model predicted large effects on performance attributes key to dispersal, as well as a reduction in offspring viability. Forecast sand temperatures produced smaller, weaker hatchlings, which were up to 40% slower than at present, albeit with increased energy stores. Conversely, increases in sea surface temperatures aided swimming performance. 4. Our exploratory study points to the need for further development of integrative individualbased modelling frameworks to better understand the complex outcomes of climate change for ectotherm species. Such advances could better serve ecologists to highlight the most vulnerable species and populations, encouraging prioritization of conservation effort to the most threatened systems.

Direct Evidence of Swimming Demonstrates Active Dispersal in the Sea Turtle “Lost Years”

“…We suspect that while swimming ability increases as turtles grow [23], different environmental and endogenous factors influence swimming activity and thus the swim speeds inferred along the tracks of turtles. Surprisingly, one of the environmental factors most likely to influence swimming speed and activity, water temperature [32] (which ranged from 21 C to 31 C along the tracks of turtles), had limited predictive value (green Spearman R = 0.006, p = 0.917, n = 235 steps; Kemp's ridley Spearman R = 0.074, p = 0.190, n = 312 steps). It is possible that conditions associated with microhabitat (e.g., the presence of floating algae or the density of prey items) [6,8] might obscure a relationship between swimming speed and temperature that would otherwise be observed, or that physiological performance can be maintained over a relatively wide range of temperatures if changes are gradual and acclimation can occur [23,24,33].…”

Some like it hot: from individual to population responses of an arboreal arid‐zone gecko to local and distant climate

“…, Cavallo et al. ), with many species predicted to decline or even to become extinct (Araújo et al. , Wake , Sinervo et al.…”

Reptile embryos and climate change: Modelling limits of viability to inform translocation decisions

“…The mechanistic model used by Mitchell et al (2008), known as Niche Mapper™ (Porter and Mitchell, 2006), has since been applied in other studies of the embryonic stages of reptiles, especially those with a focus on modelling sex ratios (e.g. Fuentes and Porter, 2013;Stubbs et al, 2014;Cavallo et al, 2015).…”

“…The integration of these field data with a microclimate model then allows the prediction of nest temperatures under various climates and at different geographical locations. Such methodologies have been applied in several studies of the embryonic stages of reptiles, including Bynoe's gecko (Heteronotia binoei; Kearney and Porter, 2004), tuatara (Sphenodon guntheri; Mitchell et al, 2008;Carter, 2015), flatback turtles (Natator depressus; Stubbs et al, 2014) and green turtles (Chelonia mydas; Cavallo et al, 2015), all using the Niche Mapper™ framework. In this study we further aimed to integrate field and laboratory data to describe the sensitivity of P. umbrina embryos to the thermal environment, and to apply a customised mechanistic model to map locations within southwestern Australia where embryos would survive, and could potentially be translocated.…”