The Arctic is currently receiving increased attention across many research fields, because of observed and anticipated dramatic climate change (Serreze and Francis Reference Serreze and Francis2006; Post et al. Reference Post, Forchhammer, Bret-Harte, Callaghan, Christensen and Elberling2009). The ongoing melting of ice in the Polar Sea will have dramatic consequences for abiotic conditions in marine as well as freshwater and terrestrial environments (Post et al. Reference Post, Forchhammer, Bret-Harte, Callaghan, Christensen and Elberling2009; Screen and Simmonds Reference Screen and Simmonds2010; Wassmann et al. Reference Wassmann, Duarte, Agusti and Sejr2011). In terrestrial environments, warming will likely lead to a deepening of the active layer and the expansion of shrubs with profound effects on the ecology and biodiversity of the Arctic (Callaghan et al. Reference Callaghan, Chapin, Chernov, Christensen, Huntley and Ims2005). Arthropods form a major part of the terrestrial species diversity in the Arctic, and are particularly sensitive to changes in the abiotic environment (Høye et al. Reference Høye, Post, Meltofte, Schmidt and Forchhammer2007; Høye and Forchhammer Reference Høye and Forchhammer2008b). Hence, increased knowledge about the ecology, diversity, and distributions of these animals would fill an important gap in our understanding of how to conserve Arctic biodiversity. This special issue of The Canadian Entomologist is timely in this respect because each paper adds important knowledge about Arctic arthropods and because it highlights the large scientific potential for using Arctic arthropods as models in global change studies. Here, we outline ways in which Arctic entomology could take advantage of recent developments in other research fields and place the contributions to the special issue in a broader context.
It is acknowledged that trophic interactions play an important role in ecosystem feedbacks to the climate system (Callaghan et al. Reference Callaghan, Johansson, Key, Prowse, Ananicheva and Klepikov2011). In Arctic ecosystems, recent studies have demonstrated the importance of mammalian herbivores in carbon budgets (Cahoon et al. Reference Cahoon, Sullivan, Post and Welker2012). It is possible, however, that arthropod herbivores such as larvae of noctuid moths (Lepidoptera: Noctuidae) also play a similar role through periodic outbreaks, causing vegetation die-backs extending across large spatial scales in the boreal and recently also in the Arctic zone (Jepsen et al. Reference Jepsen, Hagen, Ims and Yoccoz2008). Similarly, it has been shown from temperate ecosystems that manipulating arthropod predators can cause trophic cascades ultimately influencing plant composition (Schmitz Reference Schmitz2006). Although Arctic arthropod food webs are more complex than previously believed, there may be limited functional redundancy among Arctic species (Hodkinson and Coulson Reference Hodkinson and Coulson2004). Hence, range shifts, extirpations, or invasions of species could have stronger repercussions in Arctic food webs compared with food webs at lower latitudes with higher functional redundancy. Trophic interactions could, therefore, play an important role in affecting primary productivity and decomposition, but more research is needed on such possible biological feedbacks to the global climate cycle through effects on the large carbon stocks stored in tundra soils (Tarnocai et al. Reference Tarnocai, Canadell, Schuur, Kuhry, Mazhitova and Zimov2009).
The strong seasonality and harsh environmental conditions of the Arctic suggests that climate change will likely have particularly strong effects on arthropods there. The life cycles and phenology of Arctic arthropods are probably adapted to time resource demands with periods of high resource availability or low risk of predation or parasitism (Danks Reference Danks2004). With a changing climate, such a temporal match may no longer occur if trophically linked organisms respond to different cues or at a different rate to the same cues (Miller-Rushing et al. Reference Miller-Rushing, Høye, Inouye and Post2010). The current pace of climate change is likely to affect species and communities to very different degrees possibly resulting in communities that are compositionally unlike any found today (Williams and Jackson Reference Williams and Jackson2007).
In order to meet the dual challenge of conserving Arctic arthropod biodiversity and understanding the role of arthropods in ecosystem functioning, there is an urgent need for taxonomic revisions of poorly described groups, high resolution distributional data on individual species, as well as a better understanding of the role of trophic interactions in shaping community composition and population dynamics of individual species. In this special issue of The Canadian Entomologist, experts on Arctic entomology provide examples of work being done to gauge the consequences of ongoing and future climate change in the Arctic. The papers are structured under three headings: trophic interactions in the Arctic, Arctic biodiversity, and taxonomic revisions. The background and major findings of these papers are briefly presented and placed in context of the three headings below.
Trophic interactions in the Arctic
Millions of birds migrate to Arctic breeding grounds every year. Shorebirds are dependent on energy sources on their breeding grounds for egg production and incubation (Klaassen et al. Reference Klaassen, Lindstrom, Meltofte and Piersma2001; Meltofte et al. Reference Meltofte, Høye, Schmidt and Forchhammer2007). Terrestrial invertebrates and insects in particular make up the majority of their food supply on the breeding grounds and may determine local densities of breeding birds. The drivers of seasonal and interannual variation in insect biomass are therefore likely to indirectly affect both breeding densities and breeding performance of insectivorous birds in the Arctic (Meltofte et al. Reference Meltofte, Høye and Schmidt2008). The paper by Bolduc et al. (Reference Bolduc, Casajus, Legagneux, McKinnon, Gilchrist and Leung2013) presents the results of trapping arthropods throughout the growing season on a near-daily basis across multiple years at four sites along a latitudinal gradient in the Canadian Arctic. Both near-daily and seasonal aspects of temperature were important predictors of arthropod biomass although models of arthropod families with synchronised emergence had a better fit to data.
Another prominent feature of boreal and Arctic ecosystems is the interannual variation in populations of herbivorous insects like defoliating caterpillars. Such outbreaks exhibit distinct spatial structures suggesting that trophic interactions could be regulating insect herbivore densities in some vegetation types and not in others. Schott et al. (Reference Schott, Kapari, Hagen, Vindstad, Jepsen and Ims2013) set out to test the hypothesis that moth outbreaks are the result of release from generalist arthropod predators such as harvestmen (Opiliones), spiders (Araneae), rove beetles (Coleoptera: Staphylinidae), and carabid beetles (Coleoptera: Carabidae) along altitudinal transects at two sites in northern Norway. Using a thorough multiannual sampling protocol across years with varying insect herbivore densities, they provide strong evidence against a role of generalist predators in regulating insect herbivore densities. Taken together, these two important papers illustrate the importance of space and time in the dynamics of Arctic arthropod communities, which is an understudied yet key feature of northern ecosystems.
Arctic biodiversity
Biodiversity assessments are relatively scarce for Arctic arthropods and some of the most extensive sampling efforts across multiple years have limited information about the composition of individual species (Tulp and Schekkerman Reference Tulp and Schekkerman2006; Høye and Forchhammer Reference Høye and Forchhammer2008a, Reference Høye and Forchhammer2008b; McKinnon et al. Reference McKinnon, Picotin, Bolduc, Juillet and Bety2012, but see Høye et al. Reference Høye, Hammel, Fuchs and Toft2009). Moreover, typically larger efforts to sample a broad spectrum of arthropods have relied on pitfall trapping as the sole collection technique. Sikes et al. (Reference Sikes, Draney and Fleshman2013) present results of applying a range of sampling techniques for collection of spider species from the Toolik Field station on the North Slope of Alaska, United States of America. The authors report a surprisingly high diversity of this group and demonstrate that none of the sampling techniques would have yielded such richness alone. By comparing their richness estimates to a recent study from the same area using only pitfall trapping (Wyant et al. Reference Wyant, Draney and Moore2011), the authors argue that richness estimates of many groups of Arctic arthropods may be substantially underestimated. The study by Ernst and Buddle (Reference Ernst and Buddle2013) confirm this notion by a study of the epigeic beetle fauna at Kugluktuk, Nunavut, Canada, demonstrating not only high species richness but also high functional diversity of this group. Also, assemblages from their two sites exhibited distinct seasonal turnover in function.
Várkonyi and Roslin (Reference Várkonyi and Roslin2013) describe a high Arctic host–parasitoid food web in northeast Greenland based on three years of sampling with a variety of methods. Their rich description of this community provides data to test predictions such as “the species diversity of Arctic parasitoids is low”. In so doing they also address the very important concern of sampling methods and their limitations. Despite the Arctic's reputation for being species poor, sufficient sampling effort using adequate sampling methods is still required to allow for robust conclusions on species richness. Using a careful assessment of the thoroughness of their methods, they conclude that the trophic interactions they described should represent 96% of those in the entire community but conclude that even at 74°N more species remain to be found. Overall, their effort provides an excellent baseline for future work and describes a diverse and complex and typically poorly studied community in the Arctic (Fernandez-Triana et al. Reference Fernandez-Triana, Smith, Boudreault, Goulet, Hebert and Smith2011).
Leung and Reid (Reference Leung and Reid2013) compare modern to historic butterfly records for Herschel Island, Yukon, Canada, adding more critical baseline data for future studies on the impacts of climate change. Their results indicated that changes are already detectable with both additions to, and apparent losses from, the studied fauna. Butterflies are a well-studied insect group and as such, have a richer historic data set than most, making them an ideal indicator taxon for studies focussed on climate change. Leung and Reid's documentation of northward range shifts nicely complements recent reports from lower latitudes (Hickling et al. Reference Hickling, Roy, Hill, Fox and Thomas2006; Pöyry et al. Reference Pöyry, Luoto, Heikkinen, Kuussaari and Saarinen2009).
Coulson (Reference Coulson2013) reviews the history of terrestrial invertebrate research in the Svalbard archipelago, well known for its vertebrate fossil research, but now possibly among the best known Arctic arthropod study sites. His review describes that research on Svalbard invertebrates has been increasing in frequency and due to the relative ease of logistics could help the archipelago become a centre for future studies. Given that the region is experiencing recent industrialisation and climate change, Coulson's review is timely and valuable in maintaining momentum in efforts to understand the biological consequences of these changes. This suite of papers about Arctic arthropod biodiversity have increased our knowledge of the fauna considerably, and provided important baselines against which the effects of ongoing climatic changes can be evaluated.
Taxonomic revisions
George Barrowclough eloquently stated “A prerequisite to making any decisions concerning the preservation of populations, species, or higher taxa is knowledge of their existence” (p. 124, Eldredge Reference Eldredge1992). As an example of such important baseline work, Dubatolov and Philipp (Reference Dubatolov and Philipp2013) have determined that a tiger moth species previously thought to be restricted to the Old World, is also found in North America and begin the work of untangling the taxonomy of a complex of closely related species. Valuable ecological studies such as those highlighted in this issue (e.g., Ernst and Buddle Reference Ernst and Buddle2013; Várkonyi and Roslin Reference Várkonyi and Roslin2013), cannot be conducted without a solid taxonomy for the target organisms. With such a taxonomic basis, the names of species correspond one-to-one to actual units of nature and tools exist to allow confident identifications. Unfortunately, the majority of Earth's species remain unknown to science (Mora et al. Reference Mora, Tittensor, Adl, Simpson and Worm2011) and of the estimated <20% that have been named, the majority of these remain unrevised taxonomically, incompletely documented geographically, and their precise location on the evolutionary tree of life is unknown. It is taxonomic work, of which Dubatolov and Philipp (Reference Dubatolov and Philipp2013) is one small but important example, that is required to solve these problems and make these species accessible for ecological or other studies (Wheeler et al. Reference Wheeler, Knapp, Stevenson, Stevenson, Blum and Boom2012). We hope this work inspires continued interest in the taxonomy of Arctic arthropods as this provides the foundation for understanding arthropod ecology and evolution.
Concluding remarks
This special issue of The Canadian Entomologist provides many examples of how our knowledge of Arctic entomology is still relatively limited. In light of the dramatic changes expected for this region in the 21st century, further advances in this field will be of great importance for northern societies. Although conditions for performing baseline studies are constrained by competition for funding, there is still a need for descriptive studies of arthropod communities. Such studies are the prerequisite for framing more general hypotheses: for example, about the role of arthropods in ecosystem functioning and stability. It is also clear from many of the studies of this issue that the conception of the Arctic as a species poor and simple ecosystem needs revision. It will be an important future achievement to assess the functional redundancy of different compartments of the arthropod food web in order to determine the relationship between biodiversity and ecosystem functioning.
Although the future scientific challenges are many, new tools and interdisciplinary collaborations are emerging. Barcoding libraries are growing rapidly (http://ibol.org), tools to infer species composition directly from soil (eDNA) are constantly being refined (Yoccoz Reference Yoccoz2012), and there is much potential for next-generation sequencing (Hajibabaei et al. Reference Hajibabaei, Shokralla, Zhou, Singer and Baird2011). Such tools could revolutionise future species inventories, long-term monitoring, and food web studies on arthropods in the Arctic and elsewhere. However, these tools first require sound ecology and taxonomy, including examples from the papers within this special issue. Also, web-based citizen science tools and smart phone applications for recording observations of species in the field are being developed and could provide a rapid increase in observational records for charismatic species like butterflies from remote areas like most of the Arctic (e.g., http://ebutterfly.ca). Finally, international collaborations among natural history museums (e.g., SYNTHESYS an European Union-funded network of natural history museums, http://www.synthesys.info), field stations (e.g., INTERACT an European Union-funded network of field stations, http://www.eu-interact.org), and stakeholder networks (e.g., the Circumpolar Biodiversity Monitoring Program [CBMP], http://caff.is/monitoring) are also facilitating easier access to databases, sites, and networks and provide new opportunities for entomological research in the Arctic.
In sum, although the Arctic will be facing immense pressures in the future, we remain optimistic that high-quality science can help guide sustainable interactions between humans and the natural resources of the Arctic. Arthropods form ideal model organisms in global change studies because of their sensitivity to environmental change and there is a particular need for such studies from the dramatically changing Arctic. It is our hope that the papers within this special issue will be a valuable source of inspiration and may stimulate novel insights and achievements in Arctic entomology during the 21st century.
Acknowledgements
The authors sincerely thank the Editor-in-Chief of The Canadian Entomologist, Christopher M. Buddle, for taking the initiative on the production of this special issue on Arctic entomology in the 21st century and editorial assistant Andrew Smith for help and support during the editorial process.
