Before the end of this century, tropical rainforests will be subject to climatic conditions that have not existed anywhere on Earth for millions of years. These forests are the most species-rich ecosystems in the world and play a crucial role in regulating carbon and water feedbacks in the global climate system; therefore, it is important that the probable impacts of anthropogenic climate change are understood. However, the recent literature shows a striking range of views on the vulnerability of tropical rainforests, from least to most concern among major ecosystems. This review, which focuses on the impact of rising temperatures, examines the evidence for and against high vulnerability, identifies key research needs for resolving current differences and suggests ways of mitigating or adapting to potential impacts.

Impacts of warming on tropical lowland rainforests

Correlative analyses predict that anthropogenic climate warming will cause widespread extinction but the nature and generality of the underlying mechanisms is unclear. Warming-induced activity restriction has been proposed as a general explanatory mechanism for recent population extinctions in lizards, and has been used to forecast future extinction. Here, I test this hypothesis using globally applied biophysical calculations of the effects of warming and shade reduction on potential activity time and whole-life-cycle energy budgets. These 'thermodynamic niche' analyses show that activity restriction from climate warming is unlikely to provide a general explanation of recent extinctions, and that loss of shade is viable alternative explanation. Climate warming could cause population declines, even under increased activity potential, through joint impacts on fecundity and mortality rates. However, such responses depend strongly on behaviour, habitat (shade, food) and life history, all of which should be explicitly incorporated in mechanistic forecasts of extinction risk under climate change.

Activity restriction and the mechanistic basis for extinctions under climate warming

Can temperate insects take the heat? A case study of the physiological and behavioural responses in a common ant, Iridomyrmex purpureus (Formicidae), with potential climate change

Summary
Modelling thermal environments at high resolution becomes simpler when using operative temperature, which condenses microclimate and morphology into an index of thermal stress. Operative temperature can be mapped using large numbers of ‘operative temperature thermometers’, hollow models that duplicate external properties of the animal.
As climatologists predict that air will warm by 2–4 °C by 2100, biologists must be able to distinguish climate change from systematic errors in operative temperature of the same magnitude.
A systematic error in operative temperature of 2 °C or a similar amount of climate warming can change predicted surface activity and indices of habitat quality, thermoregulatory precision and predation risk by 5–12%, and in some cases more than 30%.
As construction details of operative temperature thermometers can affect their accuracy by 2 °C or more, biologists should use detailed physical models calibrated against living animals over potential ranges of postures, orientations and microclimates.
Water-filled models do not measure operative temperature correctly, fail to capture thermal extremes and are an unnecessary complication as one can easily compute the body temperature of moving or stationary animals from body mass and the spatio-temporal distribution of operative temperatures.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12149

How to avoid errors when quantifying thermal environments

Uncertainty in projections of global change impacts on biodiversity over the 21st century is high. Improved predictive accuracy is needed, highlighting the importance of using different types of models when predicting species range shifts. However, this is still rarely done. Our approach integrates the outputs of a spatially-explicit physiologically inspired model of extinction and correlative species distribution models to assess climate-change induced range shifts of three European reptile species (Lacerta lepida, Iberolacerta monticola, and Hemidactylus turcicus) in the coming decades. We integrated the two types of models by mapping and quantifying agreement and disagreement between their projections. We analyzed the relationships between climate change and projected range shifts. Agreement between model projections varied greatly between species and depended on whether or not they consider dispersal ability. Under our approach, the reliability of predictions is greatest where the predictions of these different types of models converge, and in this way uncertainty is reduced; sites where this convergence occurs are characterized by both current high temperatures and significant future temperature increase, suggesting they may become hotspots of local extinctions. Moreover, this approach can be readily implemented with other types of models.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0587.2013.00600.x

Integrating ecophysiological models into species distribution projections of European reptile range shifts in response to climate change

We derived physiological models that accurately predicted extinctions of Mexican and other lizards. Clusella-Trullas and Chown argue that global forecasts are unreliable without incorporating variance in microenvironmental temperatures, Te. Here, we show that Te variance is small relative to Te increases from climate warming. Thus, extinction forecasts are reliable ( R ¯ 2 = 0.72 ) even without Te variance data.

http://www.diapsida.org/img/Sinervoetal_2011_Science.pdf

Response to Comment on “Erosion of Lizard Diversity by Climate Change and Altered Thermal Niches”

We conducted a 5 year demographic study in one population of the viviparous lizard Sceloporus grammicus Wiegmann, 1828 in central Mexico. The population was structured in three size classes (juveni...

http://repositorio.fciencias.unam.mx:8080/xmlui/bitstream/handle/11154/949/Demography%20lizard.pdf?sequence=2

Demography of the lizard Sceloporus grammicus: exploring temporal variation in population dynamics

We conducted an analysis of the body growth pattern of the viviparous lizard Sceloporus grammicus in one of its montane populations in Central Mexico. We calculated 177 individual growth rates for the period comprised between June 1991 and June 1997. Von Bertalanffy growth model provided the best fit to our data in comparison with logistic models. No intersexual differences were found in the growth pattern. The constructed growth curve estimated an age at maturity of 12 and a half months for females and 14 months for males. In spite of marked seasonality in the region, growth rates were not significantly different between seasons. Our results, together with previous studies on the growth ecology of other populations of S. grammicus , suggest that in the volcanic mountains of Central Mexico body growth, and therefore age and size at maturity, are relatively more limited during the whole year in comparison with populations inhabiting northern or lower-altitude localities.

FR Méndez-de la Cruz

Papers

Response to Comment on “Erosion of Lizard Diversity by Climate Change and Altered Thermal Niches”

Demography of the lizard Sceloporus grammicus: exploring temporal variation in population dynamics

Body growth in one montane population of Sceloporus grammicus (Sauria, Phrynosomatidae) in Central México