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opencc-zeroMay 2022View details →

Testing the reliability and ecological implications of ramping rates in the measurement of Critical Thermal maximum

Critical Thermal maximum (CTmax) is often used to characterize the upper thermal limits of organisms and represents a key trait for evaluating the fitness of ectotherms. The lack of standardization in CTmax assays has, however, introduced methodological problems in its measurement, which can lead to questionable estimates of species' upper thermal limits. Focusing on ants, which are model organisms for research on thermal ecology, we aim to obtain a reliable ramping rate that will yield the most rigorous measures of CTmax for the most species. After identifying three commonly used ramping rates (i.e., 0.2, 0.5 and 1.0 °C min-1) in the literature, we experimentally determine their effects on the CTmax values of 27 species measured using dynamic assays. Next, we use static assays to evaluate the accuracy of these values in function of the time of exposure. Finally, we use field observations of species' foraging activities across a wide range of ground temperatures to identify the most biologically relevant CTmax values and to develop a standardized method. Our results demonstrate that the use of a 1 °C min-1 ramping rate in dynamic assays yields the most reliable CTmax values for comparing ant species' upper thermal limits, which are further validated in static assays and field observations. We further illustrate how methodological biases in physiological trait measurements can affect subsequent analyses and conclusions on community comparisons between strata and habitats, and the detection of phylogenetic signal (Pagel's λ and Bloomberg's K). Overall, our study presents a methodological framework for identifying a reliable and standardized ramping rate to measure CTmax in ants, which can be applied to other ectotherms. Particular attention should be given to CTmax values obtained with less suitable ramping rates, and the potential biases they may introduce to trait-based research on global warming and habitat conversion, as well as inferences about phylogenetic conservatism.

opencc-zeroOct 2022View details →

Habitat heterogeneity affects the thermal ecology of the federally endangered blunt-nosed leopard lizard 2019 data

Global climate change is already contributing to the extirpation of numerous species worldwide, and sensitive species will continue to face challenges associated with rising temperatures throughout this century and beyond. It is especially important to evaluate the thermal ecology of endangered ectotherm species now so that mitigation measures can be taken as early as possible. A recent study of the thermal ecology of the federally endangered Blunt-Nosed Leopard Lizard (Gambelia sila) suggested that they face major activity restrictions due to thermal constraints in their desert habitat, but that large shade-providing shrubs act as thermal buffers to allow them to maintain surface activity without overheating. We replicated this study and also included a population of G. sila with no access to large shrubs to facilitate comparison of the thermal ecology of G. sila in shrubless and shrubbed populations. We found that G. sila without access to shrubs spent more time sheltering inside rodent burrows than lizards with access to shrubs, especially during the hot summer months. Lizards from a shrubbed population had higher midday body temperatures and therefore poorer thermoregulatory accuracy than G. sila from a shrubless population, suggesting that greater surface activity may represent a thermoregulatory tradeoff for G. sila. Lizards at both sites are currently constrained from using open, sunny microhabitats for much of the day during their short active seasons, and our projections suggest that climate change will exacerbate these restrictions and force G. sila to use rodent burrows for shelter even more than they do now, especially at sites without access to shrubs. The continued management of shrubs and of burrowing rodents at G. sila sites is therefore essential to the survival of this endangered species.

Fig. 2 a–c in Non-ecological speciation, niche conservatism and thermal adaptation: how are they connected?

Fig. 2 a–c. Strong sexual isolation between two congeneric species of demoiselles (Odonata: Calopteryx) in Europe. a These two species differ mainly in the male's secondary sexual character (amount of wing melanization, while females of both species are very similar. The banded demoiselle (C. splendens) has about 50 % of the wing covered with melanin, whereas the beautiful demoiselle (C. virgo) has almost the entire wing melanized. b At a sympatric locality in southern Sweden ("Klingavälsåns Naturreservat") these two species are strongly sexually isolated from each other and mate assortatively, although a few heterospecific pairs are found. c Experimental manipulation of

Fig. 5 a–c in Non-ecological speciation, niche conservatism and thermal adaptation: how are they connected?

Fig. 5 a–c. Mate preferences and species recognition is learned, rather than purely genetic among females of the banded demoiselle (C. splendens). a Female C. splendens discriminate between con- and hetero-specific males based on a visual cue: the amount of wing melanization (see also Fig. 2). Females (middle, below the two males) were allowed to choose and/or physically interact with either con- or hetero-specific males, and their mate responses were recorded (b, c). b Species discrimination is not present among sexually naïve C. splendens females that have been isolated since emergence from males of both species, but is present among sexually experienced females that have interacted with males in the field. Filled symbols Heterospecific

Fig. 4 a–c in Non-ecological speciation, niche conservatism and thermal adaptation: how are they connected?

Fig. 4 a–c. Sexual and natural selection on 12 morphological traits in the banded demoiselle (C. splendens), based on field observations of mating success of marked individuals. a Sexual selection is stronger than natural selection across all traits, irrespective over which time scale sexual selection is measured ("short" vs "long", referring to minutes and hours vs days). b Natural selection on the morphological

Fig. 3 a–c in Non-ecological speciation, niche conservatism and thermal adaptation: how are they connected?

Fig. 3 a–c. Weak interspecific thermal niche divergence between phenotypically and ecologically similar demoiselles (C. splendens and C. virgo). a Thermal images obtained from infrared (IR) photographs of demoiselles can be used to obtain accurate estimates of body temperatures, ambient temperatures and substrate temperatures. Here a copulating pair of C. virgo (pair in middle of figure). Note the white colour of the male, which reveals his substantially higher body temperature than the substrate (temperature scale on the right). b Interspecific niche divergence between C. splendens and C. virgo in minimum thorax temperature, substrate temperature, maximum substrate temperature and ambient temperature at a sympatric site ("Klingavälsåns Naturreservat" in southern Sweden). There is no

opencc-zeroDec 2018View details →

Data from: Reconstructing the mass and thermal ecology of North American Pleistocene tortoises

Researchers often interpret the presence of tortoises in Pleistocene assemblages as evidence of an interglacial age, based on an assumption that these fossils indicate thermic climates, as modern giant tortoises require. Since the Paleocene, tortoises have been common components of terrestrial fossil assemblages and have repeatedly evolved species of giant size. Whereas extant giant tortoises are found only on islands off the coasts of South America and Africa, at least two species persisted in North America until the terminal Pleistocene. These tortoises, Hesperotestudo crassiscutata and Gopherus 'hexagonatus,' both of which reached carapace lengths of >1m, were distributed across the southern United States. This study provides new metrics to derive quantitative weight estimates from measurements of the tortoise shell. The linear measurement of 69 anatomical features of the shell of 108 live tortoises indicate that the regression between straight carapace length and weight is most significant, with a maximum r2 > 0.99. This regression is useful for tortoises that weigh between 1.8 and 339 kg. This mass estimate coupled with a heat dissipation rate derived from thermoregulation modeling provides estimates of how long tortoises can maintain a viable body temperature at low ambient temperatures. Depending on size, a tortoise can survive a maximum of 2.3 to 33 hours of freezing temperatures, which corresponds to a mean annual temperature ≥ 22° C and a mean winter low temperature ≥ 7.5° C. This analysis infers warmer temperatures at Pleistocene sites with fossil tortoise occurrences than previous qualitative estimates.

opencc-by-4.0Jan 2023View details →

Early Triassic Thermal Maximum and its ecological impact on conodonts

Supporting Information for Early Triassic Thermal Maximum and its ecological impact on conodonts