Why tropical forest lizards are vulnerable to climate warming

Biological impacts of climate warming are predicted to increase with latitude, paralleling increases in warming. However, the magnitude of impacts depends not only on the degree of warming but also on the number of species at risk, their physiological sensitivity to warming and their options for behavioural and physiological compensation. Lizards are useful for evaluating risks of warming because their thermal biology is well studied. We conducted macrophysiological analyses of diurnal lizards from diverse latitudes plus focal species analyses of Puerto Rican Anolis and Sphaerodactyus. Although tropical lowland lizards live in environments that are warm all year, macrophysiological analyses indicate that some tropical lineages (thermoconformers that live in forests) are active at low body temperature and are intolerant of warm temperatures. Focal species analyses show that some tropical forest lizards were already experiencing stressful body temperatures in summer when studied several decades ago. Simulations suggest that warming will not only further depress their physiological performance in summer, but will also enable warm-adapted, open-habitat competitors and predators to invade forests. Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low.     

Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees' abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).
2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.
3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.
4. Bumble-bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body-size differences, with small bees acting as thermal conformers.     

作物发育温度非线性效应Beta模型的特征分析

Beta模型在反映温度对作物发育非线性效应方面被广泛采用.为使该函数满足在设定的最适温度下函数值取值最大的条件,得到Beta模型的特殊形式.分析认为,该模型满足温度对作物发育影响的三基点规律、较好地反映发育速率对温度变化的响应特征、温度三基点在模型中应比较明确的3个规范性要求,具有较强的变化特征表达能力,可以近似表达二次函数、高斯函数等函数的变化.分析了Beta模型与积温法计算结果的关系.通过对Beta模型一阶和二阶导数的分析,明确了其变化特征,指出已有研究对参数P生物学意义解释的不妥之处,提出作物发育速度对温度的非线性响应是感温性的本质特征的观点,并从新的视角肯定了参数P在一定程度上可以作为作物感温性强弱的度量.     

A novel method of behavioural thermoregulation in butterflies

Abstract The requirement for efficient thermoregulation has directed the coevolution of specialized morphological and behavioural traits in ectotherms. Adult butterflies exhibit three thermoregulatory mechanisms, termed dorsal, lateral and reflectance basking. In this study, we investigate a potential fourth mechanism whereby individuals perch with their wings fully spread and angled downwards such that the margins are appressed to the substrate. We find that mate‐locating male Hypolimnas bolina (L.) (Nymphalidae) adopt this posture when operational thoracic temperatures are lowest (less than approximately 34 °C). As thoracic temperature increases, males perch with wings increasingly closed and ultimately select shaded microhabitats. Using thermocouple‐implanted dead models, we show that appressed posture individuals warm faster than those adopting the conventional dorsal‐basking (horizontal wing) posture. This thermal advantage is not mitigated by shading of the outer 60–70% of the wing area, which suggests that – as with the conventional dorsal posture – only the basal wing surfaces contribute to heat gain via the absorption of solar irradiation. These investigations suggest that appression represents a novel extension of conventional dorsal basking behaviour in butterflies.     

Control of body temperature in shuttling ectotherms

During the daily increase of ambient temperatures (T_a), a thermoregulating ectothermic animal enters three successive phases: a basking-foraging phase, a proportional control phase and a sun-shade shuttling phase. The first and third phase consist of shuttling between two different microclimates, and a model is developed describing the relation between mean body temperature (T_b) and the lower operative environmental temperature. It is shown to be a curvilinear function, not a linear one as often has been assumed. The conditions for relating T_bs of ectothermic animals to T_as in a meaningful way is discussed, and the daily course of T_bs in shuttling animals is described. The model provides a reasonable fit to empirical values of T_bs in the tiger beetle Cicindela hybrida L.     

Body Temperature Changes in Free-ranging Baboons (Papio hamadryas ursinus) in the Namib Desert, Namibia

We surgically implanted temperature sensitive telemeters intraperitonealy in free-ranging baboons. Thereafter, we recorded body temperature changes while the baboons were free-ranging and under visual observation. Two distinct patterns of daily body temperature fluctuations occurred; they were related to the availability of drinking water. Core body temperature fluctuated by as much as 5.3°C and regularly exceeded 41°C. Behavioral adaptations of the baboons, notably sandbathing, appeared to be associated with the regulation of body temperature.     

Behavioural thermoregulation in two species of robber flies occupying different grassland microhabitats

1. 1.|The robber flies Machimus occidentalis and Machimus formosus are ambush predators that occur sympatrically in grassland habitats of southwestern Montana, U.S.A., although the former occurs earlier in the season.

2. 2.|Early in daily foraging periods, when ambient temperatures are relatively low, the two species exhibited similar behaviours. They perched in a crouched posture on fully insolated bare soil surfaces and oriented their longitudinal and dorsoventral axes to maximize the incident solar radiation intercepted by the broad lateral surface of the thorax. Measurements of operative body temperature of flies in different locations, orientations, and postures indicate that such basking can significantly raise body temperature.

3. 3.|Their thermoregulatory tactics diverged as daily temperatures and solar radiation loads rise.

4. 4.|Like previous grassland species studied, M. occidentalis moved upward onto vegetation, where crouched postures and orientation to the sun disappeared.

5. 5.|Machimus formosus, on the other hand, took refuge in the shaded portions of ground squirrel (Citellus sp.) and badger (Taxidea taxus) burrows.

6. 6.|In both cases, the vertical movements resulted in lower body temperatures than would occur if flies remained on the fully insolated soil surfaces.

7. 7.|We compare the tactics of these two species with those of previous grassland species studied.

Thermoregulatory significance of basking behaviour in the raccoon dog (Nyctereutes procyonoides)

1. 1.|The raccoon dogs frequently basked in spring while keeping their dark chest area towards the sun. The importance of this behaviour for the thermal balance was examined by using a cylinder model, and the results were compared with that of the blue fox which has pale chest and no basking behaviour.

2. 2.|With no external radiation source, cooling rates of blue fox and racoon dog models were almost equal, while in the sunshine with the chest area towards the sun, raccoon dog gained and blue fox lost heat.

3. 3.|In the same sunshine, the raccoon dog lost heat if its back area was towards the sun in comparison with the situation when the chest area was towards the sun.

4. 4.|Temperatures at the skin level were much higher for sun-exposed raccoon dogs than blue foxes especially on the chest area.

5. 5.|It is concluded that the hair coat structure of the raccoon dog is especially favourable for trapping heat from the sun, and with postural adjustments the animal takes maximal advantage of this free heat.

Analysis of reciprocal-transfer experiments to estimate the length of phases having different responses to temperature

Background and Aims: The responsiveness of plant ontogeny to temperature may changewith plant age. These changes may best be identified by experimentsin which individual plants are transferred in a time seriesfrom low temperature (LT) to high temperature (HT), and viceversa. Any change in the value of the slope for a plot of theduration taken to complete a developmental phase against timeof transfer (either LT to HT or HT to LT) will indicate a changein the temperature responsiveness of development, and the timeat which this change occurs. The analysis of this type of reciprocal-transferexperiment is usually performed by regression for each of thevisually identified linear sub-phases, separately for the datafor LT-to-HT and for HT-to-LT transfers. Here, a mathematicalapproach is presented using a single curve-fitting procedure. Methods: Both LT-to-HT and HT-to-LT transfers are combined in a singlecurve-fitting procedure. This new, combined approach is illustratedusing a published data set for three rice (Oryza sativa) cultivars,where the pre-flowering duration is divided into three sub-phases,and temperature responsiveness is generally stronger duringthe second than the first and third sub-phases. Results and Conclusions: This new model approach provides an objective method, relativeto the separate analyses, for assigning data points to a particularsub-phase. Plausible parameter values can be obtained from capturingthe whole data of both sets of transfers, which otherwise couldnot be obtained from the separate-analysis method. Furthermore,the length of sub-phases identified from the LT-to-HT transfersis consistent, in terms of its response to temperature, withthat identified from the HT-to-LT transfers. Re-analysis ofthe published rice data using the new approach reveals thatin addition to temperature sensitivity, the optimum temperatureof pre-flowering development may vary with plant age. The newapproach gives rise to a generalized model for the analysisof reciprocal transfer experiments to quantify age-dependentchanges of response of plants (and potentially insects) to anyenvironmental variables that have a significant impact on theirdevelopment.     

Thermal biology of a colour‐dimorphic snake,Elaphe quadrivirgata,in a montane forest: do melanistic snakes enjoy thermal advantages?

The adaptive significance of colour polymorphisms in animals has received extensive scientific attention. In snakes, a generally accepted hypothesis is that melanistic individuals enjoy thermal advantages compared to normal coloured individuals. Elaphe quadrivirgata on Yakushima Island exhibits a distinct melanistic/striped colour dimorphism. To test this hypothesis, the thermal biology of free‐ranging E. quadrivirgata was investigated using temperature‐sensitive radio transmitters. The thermal quality of habitats was also evaluated using physical models of the snake. In addition, the species' set‐point range (T_set) was estimated using a laboratory experiment. In July, thermal environments appear to be benign because snakes were able to maintain their body temperature (T_b) within T_set from the midday to evening by using average thermal habitats. By contrast, later months of the year were severe in thermoregulation, and snakes had difficulty maintaining their T_b within T_set by using average thermal habitats. There were no significant intermorph differences in thermoregulation indices in any months, whereas slight differences were detected in hourly comparisons. Most of these comparisons indicated active and precise thermoregulation (with respect to T_set) in striped individuals by using thermally favourable but rare microhabitats such as forest gap. Thus, the obtained values do not support the prediction that melanistic individuals are precise thermoregulators. Yet, melanistic individuals do modify their thermoregulation strategy with respect to the available thermal environments in contrast to striped individuals. Together with the fact that body heating is slower in striped individuals than in melanistic individuals under experimental conditions, it is concluded that melanistic individuals have the potential to enjoy thermal advantages but that this might be of no practical use in terms of T_b in the wild because of the greater thermoregulatory efforts of striped individuals, and because melanistic individuals may use forest gap rarely due to conspicuousness to visually orientated predators under the exposed habitat. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 309–322.     

中华鳖新孵幼体的热耐受性、体温昼夜变化和运动能力的热依赖性

研究中华鳖新孵幼体的热耐受性、体温及温度对运动能力的影响 .结果表明 ,在干燥和潮湿环境下 ,选择体温分别为 2 8.0℃和 30 .3℃ ;潮湿环境下 ,临界高温和低温分别为 40 .9℃和 7.8℃ .在缺乏温度梯度的热环境中 ,水温对幼鳖体温的影响比气温更直接 ,体温和环境温度的昼夜变化相一致 ,说明幼鳖生理调温能力很弱 .在有温度梯度的热环境中 ,幼鳖能通过行为调温将体温维持到较高且较恒定的水平 ,导致体温昼夜变化不明显 .幼鳖运动能力有显著的热依赖性 ,在一定温度范围内随体温升高而增强 .体温31.5℃时 ,幼鳖的运动表现最好 ,最大续跑距离、单位时间跑动距离和单位时间停顿次数分别为 1.87m、4 92m·min-1和 6 .2次·min-1.体温过高时 ,运动能力下降 .当体温为 33 .0℃时 ,最大续跑距离、单位时间跑动距离和单位时间停顿次数分别为 1.30m、4.2 8m·min-1和 7.7次·min-1.     

Flowering phenology in Solidago altissima: adaptive strategies against temporal variation in temperature

The evolution of flowering phenology is the result of a trade-off that balances many factors, including growth, reproductive capacity, and temporal overlap with pollinators. When there is large temporal variation in temperature, particularly in the onset of frost, the optimum flowering strategy will vary from year to year. In Duluth, MN, USA, the end of the growing season can vary by more than 30 days. In this study, we observed flowering phenology and pollinator abundance on 15 genotypes of Solidago altissima in Duluth, MN. We predicted that temporal variation in temperature would lead to a range of flowering strategies in the S. altissima population; some genotypes flower early and in synchrony, some ‘hedge their bets’ by flowering over a range of dates, and others have an intermediate strategy. Our results indicate that genotypes vary in mean flowering date and duration of flowering and, for the two observed years, pollinator abundance was highest for early-flowering genotypes.     

Impact of the 1998 El Niño event on a Lake Charr, Salvelinus Namaycush, Population Recovering from Acidification

This study provides a case history of the impact of the 1998 El Ni no event on a lake charr population in a shallow (maximum depth = 13m) lake in the southern boreal shield ecozone of Ontario. The lake lost its native charr population by acidification from air-borne pollutants in the 1950–1960s. A naturally reproducing population was re-established through hatchery stocking after the water quality improved in the 1980s. The warm years triggered by the El Ni no event exposed fish to bottom water temperatures of 20°C for several weeks and resulted in the loss of all hatchery-reared juveniles that were released in 1998. A few adults survived the warm years by making use of cold water refuge areas (groundwater seepage). This study shows how climate change can eliminate charr populations at the margins of their range. It also illustrates the potential confounding effects of climate warming on aquatic ecosystems already subject to other stressors.     

Life history adaptation along a latitudinal cline in the water strider Aquarius remigis (Heteroptera: Gerridae)

We addressed the general hypothesis that life history differences among eastern populations of the North American water strider, Aquarius remigis (Heteroptera: Gerridae), along a north-south gradient are manifestations of genetic differentiation due to natural selection. We raised offspring of two field-caught populations from each of three latitudes in a common laboratory environment at 20° C and two photoperiods. Nearly all Quebec (PQ) individuals (ca. 46° N) entered diapause to reproduce the following spring (univoltine life cycle), while intermediate proportions of New York (NY; ca. 43° N) and New Jersey (NJ; ca. 41° N) individuals reproduced directly, producing a second generation (bivoltine life cycle). PQ females were smaller, developed faster, and laid smaller eggs than NY and NJ individuals; NY and NJ populations differed little in these variables. NY females had longer life spans than either PQ or NJ females, but lower oviposition rates. Total reproductive output did not differ across latitudes. Photoperiod affected body length, development time, and reproductive pathway, resulting in a latitude by environmental interaction. PQ individuals reproduced directly under 15L : 9D (summer) conditions only, while the NY and NJ populations exhibited more direct reproduction under 13L : 11D (spring or fall) conditions. Some life history characters of the NY and NJ populations displayed the higher variability indicative of phenological transition zones. These results indicate local adaptation of populations to long-term climatic patterns. Water striders appear to adapt to longer seasons by extending development, growing larger, and breeding directly. Larger body size and extended or rapid development are associated with bivoltinism and increase in egg size, but not necessarily with higher fecundity or oviposition rate. The phenological transition zone appears to be unrelated to a transition zone a little further south established by allozyme data and morphology, as all populations studied here could be electrophoretically identified as northern "type".     

Too hot to die? The effects of vegetation shading on past,present, and future activity budgets of two diurnal skinks from arid Australia

Behavioral thermoregulation is an important mechanism allowing ectotherms to respond to thermal variations. Its efficiency might become imperative for securing activity budgets under future climate change. For diurnal lizards, thermal microhabitat variability appears to be of high importance, especially in hot deserts where vegetation is highly scattered and sensitive to climatic fluctuations. We investigated the effects of a shading gradient from vegetation on body temperatures and activity timing for two diurnal, terrestrial desert lizards, Ctenotus regius, and Morethia boulengeri, and analyzed their changes under past, present, and future climatic conditions. Both species’ body temperatures and activity timing strongly depended on the shading gradient provided by vegetation heterogeneity. At high temperatures, shaded locations provided cooling temperatures and increased diurnal activity. Conversely, bushes also buffered cold temperature by saving heat. According to future climate change scenarios, cooler microhabitats might become beneficial to warm‐adapted species, such as C. regius, by increasing the duration of daily activity. Contrarily, warmer microhabitats might become unsuitable for less warm‐adapted species such as M. boulengeri for which midsummers might result in a complete restriction of activity irrespective of vegetation. However, total annual activity would still increase provided that individuals would be able to shift their seasonal timing towards spring and autumn. Overall, we highlight the critical importance of thermoregulatory behavior to buffer temperatures and its dependence on vegetation heterogeneity. Whereas studies often neglect ecological processes when anticipating species’ responses to future climate change the strongest impact of a changing climate on terrestrial ectotherms in hot deserts is likely to be the loss of shaded microhabitats rather than the rise in temperature itself. We argue that conservation strategies aiming at addressing future climate changes should focus more on the cascading effects of vegetation rather than on shifts of species distributions predicted solely by climatic envelopes.