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The establishment success of a population is a function of abiotic and biotic factors and introduction dynamics. Understanding how these factors interact has direct consequences for understanding and managing biological invasions and for applied ecology more generally. Here we use a mesocosm approach to explore how the size of founding populations and the number of introduction events interact with environmental conditions (temperature) to determine the establishment success of laboratory-reared Drosophila melanogaster. We found that temperature played the biggest role in establishment success, eclipsing the role of the other experimental factors when viewed overall. Under optimal temperature conditions propagule pressure was of negligible importance to establishment success. At adverse temperatures, however, establishment success increased with the total founding population size. This effect was considerably stronger at the cold than at the hot extreme. Whether the population was introduced all at once or by increments (changing the number of introduction events) had a negligible global effect. However, once again, a stronger effect of increasing number of introduction events was seen at adverse temperatures, with hot and cold extremes revealing opposite effects: adding flies incrementally decreased their establishment success at the hot extreme, but increased it at the cold extreme. These differing effects at hot and cold thermal extremes implies that different establishment mechanisms are at play at either extreme. These results suggest that the effort required to prevent (or conversely, to facilitate) the establishment of populations varies with the environment in ways that can be complicated but predictable.

Quantifying intraspecific variation in heat tolerance is critical to understand how species respond to climate change. In a previous study, we recorded variability in critical thermal maxima (CT) by 3 °C among populations of small Iberian lizard species, which could substantially influence predictions of climate-driven activity restriction. Here, we undertake experiments to examine whether we could reproduce similar levels of heat-tolerance variability in response to water deficit. We hypothesized that deprivation of drinking water should increase variability in CT between populations more than deprivation of food under the theoretical expectation that the variation of the more limiting resource must trigger stronger variation in physiological performance. We measured CT after manipulating availability of live prey and drinking water in two populations of an arid and a mesic lizard species from the Iberian Peninsula. We quantified a mean CT across all studied lizards of 44.2 °C ± 0.2 SE for the arid species and 41.7 °C ± 0.3 SE for the mesic species. Using multimodel inference, we found that water deprivation (combined with food supply) caused population differences in CT by 3 to 4 °C which were two to three times wider than population differences due to food deprivation (combined with water supply) or to food and water provision. To highlight the need for more thermo-hydroregulatory research, we examined bias in research effort towards thermal versus hydric environmental effects on heat tolerance through a systematic literature review. We show that environmental temperature has been used five times more frequently than precipitation in ecological studies of heat tolerance of terrestrial species. Studies linking thermal tolerance of ectotherms to the interplay of air temperature and water availability are needed in the face of projected increases in aridity and drought in the 21st century, because the balance of body temperature and water resources are functionally interlinked., Manuscript development funded through British Ecological Society ‘Research Grant’ 4496-5470 to SHP, and Spanish Ministry of Science grants CGL2011–26852 to MBA and SHP and CGL2017–89898-R to DRV.

Many factors influence gas exchange patterns in insects and are generally treated in isolation from one another. Here, we provide a review of the current state of knowledge on the physics of gas exchange, insect respiratory chemoreceptors, the diversity and the methods typically used in the characterisation of respiratory pattern types, briefly covering some of the new tools and techniques that are being incorporated into this field. We then discuss the functional significance of insect gas exchange pattern variation, and possible evolutionary explanations of discontinuous gas exchange as a derived control mechanism for effecting physiological change in the context of (a) adaptive hypotheses, (b) non-adaptive hypotheses and (c) mathematical modelling of gas exchange. The lack of consensus in the literature for all proposed adaptive or mechanistic hypotheses suggests that multiple factors influence which gas exchange pattern is displayed by any particular insect during a given experiment. Thus, while the primary function of a breathing pattern is to meet an animal's gas exchange requirements, it is an interacting hierarchy of constraints that most likely determines how this demand may be met. We conclude the review with a brief discussion of future directions for the field.

Publisher Summary This chapter discusses the modern ecological and evolutionary contexts of the evolutionary physiology in insects and provides a survey of sources of environmental variability and their effects on insect populations. The chapter explores environmental variation and the various ways in which it may be quantified. Some environmental variables are relatively simple and straightforward, both to measure and to control, whereas others pose substantially greater problems from both perspectives. Even variables that are seemingly easy to measure might act in ways that are difficult to identify. The chapter examines insect responses to the thermal environment over a variety of spatial and temporal scales, focusing on recent developments in the field. The importance of water availability for insect survival and the determination of distribution and abundance patterns have been widely demonstrated. The chapter considers the question of what lessons insect evolutionary physiologists might have to offer ecology and conservation biology. In particular, how evolutionary physiology can offer ecologists a set of useful general rules in some cases and can unveil the nature of local contingency in others.