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"Climate Change and Insectivore Ecology" In: Encyclopedia of Life

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k Climate Change and Advanced article Article Contents Insectivore Ecology • Introduction • Changes in Abundance of Insectivores Jim Vafidis, Faculty of Applied Sciences, University of the West of England, Bristol, • Changes in Distribution of Insectivores UK • Changes in the Phenology of Insectivores and Their Insect Prey Jeremy Smith, School of Biosciences, Cardiff University, Cardiff, UK • Conclusions Robert Thomas, School of Biosciences, Cardiff University, Cardiff, UK Online posting date: 16th January 2019 The impacts of climate change on natural pop- Introduction ulations are only beginning to be understood. Although some important changes are already Climate change is typically described in terms of long-term occurring, in the future these are predicted to increases (across multiple years or decades) in average global be more substantial and of greater ecological temperatures, but the overall warming of the planet is highly vari- significance. Insects are a key taxonomic group able across local and regional scales. Although climate change for understanding the ecological impacts of cli- has been well documented over the last century, the most signifi- mate change, due to their responsiveness to cant changes have mainly occurred over the last 40 years (Walther environmental change and importance as food et al., 2002). As well as rising temperatures, climate change includes disruptions in the patterns of other meteorological vari- for other organisms. Insects are highly sensitive ables including rainfall, humidity, solar radiation and wind, in to rising temperatures, changes in rainfall pat- which the changes are less predictable. Weather is the short-term terns and erratic weather conditions, driving rapid manifestation of climate on a scale of days to weeks; extreme short-term variations in their abundance, mobil- weather events such as heatwaves, droughts, storms and floods ity, distribution and phenology. Such variations k are also becoming more frequent and more intense. k represent changes in their availability as prey Inevitably, by varying abiotic conditions, climate change can to insectivores, a diverse range of insect-eating have substantial direct effects on the biotic components of ecosys- animals that include mammals, fish, amphib- tems. Insects are one such biotic component that, by being small ians, reptiles and birds. The impacts of these and having relatively rapid life-cycles, are strongly affected by changes on the ecology of insectivores are com- changes in temperature, rainfall and wind. Physiologically, their plex and include population increases or decreases, development, metabolism, activity and phenology are all strongly broad-scale shifts in distribution, and changes influenced by their local conditions. Increases in temperature are linked with higher rates of insect activity, higher survival, in behavioural traits such as foraging strategy, increases in fecundity, accelerated life cycles and greater rates investment in parental care, and the timing of of dispersal (Bale et al., 2002; Wilf, 2008). breeding and migration. Although some insectiv- Insects are the most abundant and diverse animal group on orous species are able to respond to – and even Earth and are present in practically all freshwater and terrestrial benefit from – climate change, those that fail to ecosystems. As such, changes in their abundance, activity, distri- respond appropriately may struggle to reproduce, bution and phenology will have important ramifications for their disperse and survive, leading to population decline roles as herbivores, detritivores, predators and parasitoids, but and ultimately, to extinction. also as prey to a carnivorous guild of mammals, amphibians, rep- tiles, birds, fish, other invertebrates and even plants. These are the insectivores, which rely on insects and other invertebrates as food, either as their primary diet across the annual cycle or as a protein supplement during the breeding season. Although climate change biology is an active area of research, the majority of the research on insectivores so far has focused on terrestrial vertebrates includ- ing birds, mammals and reptiles. Rather than attempt to describe eLS subject area: Ecology the reported impacts on all insectivorous taxa, we have focused this article upon these groups. How to cite: Vafidis, Jim; Smith, Jeremy; and Thomas, Robert (January 2019) Insectivores play an important regulatory role in their ecosys- Climate Change and Insectivore Ecology. In: eLS. John Wiley & tems by suppressing arthropod populations of ectoparasites, Sons, Ltd: Chichester. herbivores and predators. For example, the little brown bat DOI: 10.1002/9780470015902.a0028030 Myotis lucifugus can consume up to 1200 mosquitos (Culicidae) eLS © 2019, John Wiley & Sons, Ltd. www.els.net 1 k k Climate Change and Insectivore Ecology in one hour (Ducummon, 2000), and a colony of 150 big brown emergence are energetically costly if there is insufficient prey bats Eptesicus fuscus are capable of consuming 50 000 leafhop- for the bats to feed on. Starvation and dehydration are major pers (Cicadellidae), 38 000 cucumber beetles (Diabrotica and causes of mortality among early-emerging bats (Jones et al., Acalymma), 16 000 June bugs (Phyllophaga) and 19 000 stink 2009). Most temperate bat species mate in autumn or winter and bugs (Pentatomidae), over the course of one breeding season females delay fertilization by storing spermatozoa in their repro- (Whitaker, 1995). Climate-driven changes in the spatial and ductive tract until conditions are suitable for reproduction in late temporal availability of prey as well as other resources including spring (Racey and Entwistle, 2000). Stored sperm can quickly water and suitable foraging habitat can have important implica- die in active individuals if the conditions are not yet suitable tions for insectivore populations. The reported impacts include to initiate ovulation and pregnancy, compromising reproductive changes in abundance, geographical shifts towards the poles and success during the breeding season (Sherwin et al., 2013). towards higher elevations, and the timing of seasonal events. In Even during spring, summer and autumn, flying insects in tem- this article, we assess the evidence for such impacts, examine perate regions are less active when night temperatures drop below the mechanisms by which these impacts may be mediated, 10 ∘C (Jones et al., 2009). For many temperate-zone insects, and discuss the future conservation of insectivores in a rapidly this temperature is a thermal threshold for flight, below which, changing world. aerial-hawking bats struggle to find prey. Warmer and drier night temperatures improve foraging conditions for aerial hawking species of bat, by increasing the activity of flying insect prey Changes in Abundance (Sherwin et al., 2013). Consequently, warmer foraging condi- tions are associated with higher rates of pregnancy and lactation, of Insectivores faster juvenile development and population growth (Ransome and McOwat, 1994; Linton and Macdonald, 2018). There are several reported instances of changes in insectivore In high temperatures, bats are highly susceptible to evaporative abundance observed at the local and regional scales that have been water loss due to the large surface-to-volume ratio of their wing attributed to the effects of climate change, particularly increases membranes. Increasing frequency of drought conditions in arid in temperature, changes in rainfall patterns and higher frequency regions increases energetic costs for bats, which must make of extreme climatic events. Changes in these parameters can both, regular trips to drink at nearby water sources. This is particularly directly and indirectly, affect rates of insect survival and fecun- problematic for lactating females, which require large volumes dity, which together lead to changes in insect population size. of water (Webb et al., 1995). The reproductive success of Myotis k The direct physiological effects of rising temperatures are more bat species in arid regions is predicted to decline by 84% with k significant for ectothermic species such as reptiles and amphib- an increase in temperature of 5 ∘C and a reduction in water ians, which are less able to thermoregulate effectively compared availability (Figure 1, Adams and Hayes, 2008). to endotherms such as mammals and birds. Reptiles, in particular, The effects of changes in food availability are especially evi- are susceptible to very high temperatures, which force them to dent in species with high metabolic rates. Shrews (Sorex spp.) spend more time sheltering in the shade, rather than foraging for insects. For example, energetic shortfalls during hot spring weather prevent Mexican populations of Sceloporus lizards from 2000 breeding, leading to decreases in lizard population size and local Water availability extinction of several local populations (Sinervo et al., 2010). 1800 In some circumstances, the dynamics of insectivore popula- Number of successful 1600 lactating bats tions seem to be more strongly affected by minimum tempera- tures rather than average temperatures. Bats, as small endotherms 1400 occupying temperate regions, have to expend large amounts of 1200 energy on thermal regulation when ambient temperatures are low. During unfavourable conditions such as low temperatures or pro- 1000 longed wet and stormy conditions, bats can also use brief periods 800 of torpor or protracted hibernation, to reduce energy expendi- ture (Geiser and Turbill, 2009).
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