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Inter-annual variation in abundances calculated as the area under the curve (AUC) resulting from a generalized additive model (GAM), for each species summed across all habitats. Species are represented by four different families of spiders. Dictynidae: Emblyna borealis, Linyphiidae: Erigone arctica, Erigone psychrophila, Collinsia thulensis, Hilaira vexatrix, Mecynargus borealis; Lycosidae: Pardosa glacialis; Thomisidae: Xysticus deichmanni. Only significant regression lines are shown (α = 0.05). Statistics are shown in Table 3
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Understanding how species abundances vary in space and time is a central theme in ecology, yet there are few long-term field studies of terrestrial invertebrate abundances and the determinants of their dynamics. This is particularly relevant in the context of rapid climate change occurring in the Arctic. Arthropods can serve as strong indicators of...
Citations
... Color ranking of sites is based on average June and July daily air temperature (from cooler to warmer; see Table 1 for temperature) and species shades were attributed randomly. shown negative or heterogeneous responses of some arctic arthropods to rising temperatures (Bowden et al., 2018;Høye et al., 2021;Loboda et al., 2017). Above a temperature threshold, the positive effects of temperature on biomass and activity rate of some surfaceactive and low-flying arthropods could thus be counterbalanced by the negative effects on other taxa, leading to the observed null effect of temperature increase on arthropod availability (see also Høye et al., 2021;Koltz et al., 2018). ...
... of freeze-thaw events or reductions in insulation due to less snow cover during winter(Ávila-Jiménez et al., 2010;Everatt et al., 2015;Høye et al., 2021). Changes in water availability induced by changes in patterns of precipitation, melting of permafrost, or higher evaporation rates, can in turn negatively affect the abundance of some arthropod species(Ávila-Jiménez et al., 2010;Bowden et al., 2018). ...
Seasonally abundant arthropods are a crucial food source for many migratory birds that breed in the Arctic. In cold environments, the growth and emergence of arthropods are particularly tied to temperature. Thus, the phenology of arthropods is anticipated to undergo a rapid change in response to a warming climate, potentially leading to a trophic mismatch between migratory insectivorous birds and their prey. Using data from 19 sites spanning a wide temperature gradient from the Subarctic to the High Arctic, we investigated the effects of temperature on the phenology and biomass of arthropods available to shorebirds during their short breeding season at high latitudes. We hypothesized that prolonged exposure to warmer summer temperatures would generate earlier peaks in arthropod biomass, as well as higher peak and seasonal biomass. Across the temperature gradient encompassed by our study sites (>10°C in average summer temperatures), we found a 3‐day shift in average peak date for every increment of 80 cumulative thawing degree‐days. Interestingly, we found a linear relationship between temperature and arthropod biomass only below temperature thresholds. Higher temperatures were associated with higher peak and seasonal biomass below 106 and 177 cumulative thawing degree‐days, respectively, between June 5 and July 15. Beyond these thresholds, no relationship was observed between temperature and arthropod biomass. Our results suggest that prolonged exposure to elevated temperatures can positively influence prey availability for some arctic birds. This positive effect could, in part, stem from changes in arthropod assemblages and may reduce the risk of trophic mismatch.
... Lister and Garcia 2018;Outhwaite et al. 2020), indicating that spiders may have declined as well. In arctic Greenland, Bowden et al. (2018) found that some species had declined over 18 years while none increased. Samu et al. (2023) compared the spider fauna of an agricultural field and its margin area 23 years apart and found numerical declines of 45 and 59%, respectively; no changes in species richness or ecological traits could be detected, however. ...
Arthropod faunas have become impoverished in recent years in abundance as well as in diversity, but so far little evidence exists concerning spiders. In 2022, we repeated pitfall trap collections of spider assemblages completed 25 years previously in coastal dune habitats of the Hanstholm Reserve of National Park Thy, Denmark. Traps were placed approximately at the same spots, i.e. the habitats (white dune, grey dune, dry dune heathland, wet dune heathland, low pine plantation) were represented approximately as before. Contrary to most previous reports of insect decline, we found only weak evidence of reduction in abundance, but strong indications of reductions in faunistic value based on changes in ecological traits. Within the same period of spring and with the same number of traps, we collected 12% fewer spider individuals and 13% fewer species; rarefaction indicated that the lowered species richness was real. Species diversity had decreased and dominance increased. Changes in indices of ecological traits showed that the fauna had changed into decreased contribution of habitat specialists and species of restricted Danish distribution; the proportion of aeronauts had increased; the average body size had decreased. Indices of assemblage microclimatic niche positions and niche widths showed increased representation of shade and humidity loving species. Most of these changes were repeated in each of the habitats. Finally, we found evidence of a phenological shift towards activity earlier in spring in some species.
Implications for insect conservation
We discuss possible management measures to counteract the observed trend towards reduced faunistic value.
... Our previous work in the region has shown considerable heterogeneity in long-term changes and links to climate across invertebrate orders (28). For example, a subset of families exhibited declines in total abundance between 1996 and 2016 for all habitats studied (13), with habitat type playing an important role mediating the strength of species abundance trends for both spiders (Araneae) and muscid flies (Diptera) (13,25,29), while links to climate variables were taxon-specific and thus did not show a strong, consistent pattern. Conversely, we documented strong effects of climate on body size (30,31), phenology (32)(33)(34), community composition (25,28), and species interactions (35,36). ...
Arthropods respond to climate change by shifting their phenology in the spring and summer seasons. These phenological shifts are rarely uniform, and taxa show distinct variation in the direction and magnitude of phenological responses to climate drivers. To gain insights into the most climate-sensitive taxa and forecast the implications of climate change on community-wide activity and biotic interactions, it is important to understand how the climate affects the timing of activity of different taxa in local sites within a community. Here, we examined the temporal trends of arthropod phenology, and associations between arthropod phenological responses and climate predictors using arthropod monitoring data from five different habitats in high-Arctic Greenland covering a 25-year period. We found that, for most taxa, advanced arthropod phenology was associated with earlier snowmelt, and, to a lesser extent, warmer temperatures. However, the magnitude of advanced activity varied considerably between arthropod taxa and local habitats. Our study also revealed that pollinators were the most climate-sensitive group, with advanced and, in some habitats, shortened seasonal activities. Late active taxa and late snow melting habitats advanced phenology at greater magnitudes than early active taxa and early snow melting habitats. The magnitude of phenological shifts of arthropod taxa was dependent on habitat, highlighting the substantial spatial variation in phenological responses. Overall, our results demonstrate that high-Arctic arthropods are capable of tracking local climate drivers of phenology well, but the phenological responses of arthropod taxa to global climate change are complex, and community-wide trends may mask the variation in direction and magnitude of phenological shifts in different taxa and locally adapted populations.
... www.nature.com/scientificreports/ also found in an arctic survey of spiders, where during a monitoring period of 18 years the number of species did not change, but in some species abundances declined and no species increased 28 . In our case species responses were more varied. ...
... A manipulative field-scale experiment that intended to study the simultaneous and separate effects of land-use intensification and climate change, found parallel overall effects of the two factors, manifesting mainly in abundance reduction of arthropods in the manipulated grassland plots 49 . Climate change alone have been documented to dramatically influence arthropod communities, including spiders, in natural biotopes 18,50 and in especially vulnerable climatic regions, such as in the tropics 43 and under arctic climate 28,51 . www.nature.com/scientificreports/ ...
There is widespread evidence for a worldwide trend of insect decline, but we have much fewer data about recent temporal trends in other arthropod groups, including spiders. Spiders can be hypothesised to similarly decline because of trophic dependence on insects and being equally sensitive to local and global environmental changes. Background trends in arthropod populations can be verified if we decouple large-scale environmental transitions, such as climate change, from local factors. To provide a case study on baseline spider community trends, we observed changes in the spider community of an unsprayed alfalfa field and its margin 23 years apart under largely unchanged local conditions. We aimed to determine whether there are changes in spider abundance, species richness and mean species characteristics. Spider abundance per unit effort decreased dramatically, by 45% in alfalfa and by 59% in the margin, but species richness and most characteristics remained unchanged. Community composition in both habitats shifted and became more similar by the current study period. The population decline was especially marked in certain farmland species. We propose that in the absence of local causative factors, spider abundance decline in our study indicates a reduction of spider populations at landscape and regional scales.
... Because amphibian populations naturally fluctuate, short-term monitoring can provide insight into how amphibian communities respond to proximate changes in weather conditions, which is helpful for predicting long-term responses to climate change (Beranek et al., 2022). As extreme weather events become more variable and frequent, ecological communities are expected to have increased variation in seasonal activity patterns (Bowden et al., 2018); therefore, it is important to assess how communities and individual species respond to environmental variables (temperature, e.g.) from year to year. To that end, we used pitfall trapping to examine interannual variation of the amphibian community at Powdermill Nature Reserve (PNR) in Westmoreland County, Pennsylvania, U.S.A. during 2020-2021. ...
Amphibians are a highly vulnerable taxonomic group that have suffered population declines worldwide. As amphibians serve critical links between trophic levels and facilitate nutrient recycling, it is critical to understand how their species richness, abundance, and phenology shift over time. Because amphibian populations naturally fluctuate, short-term monitoring can provide insight into how amphibian communities respond to proximate changes in weather conditions, which is helpful for predicting long-term responses to climate change. We used pitfall traps to examine interannual variation of the amphibian community at Powdermill Nature Reserve (PNR) in Pennsylvania during 20202021 to provide critical details for future long-term monitoring. Mean monthly temperature and precipitation did not vary significantly between years, but monthly captures per sampling effort declined and monthly biomass per sampling effort increased from 2020 to 2021. Despite a lack of significant relationships between total amphibian captures and temperature and precipitation, peak abundance shifted earlier, and individuals were larger in 2021 compared to 2020. Interestingly, individual species biomass was predicted by an interaction between temperature and precipitation, suggesting individual species will vary in vulnerability to climate change, but the amphibian community as a whole at PNR is resilient to minor fluctuations in temperature and precipitation.
... Whilst global warming is particularly strong in the Arctic (IPCC 2022), transform tundra landscapes (e.g. Frost et al. 2013;Rich et al. 2013;Hobbie et al. 2017;Bowden et al. 2018), and is becoming a concerning threat to arthropods (Høye 2020; see also Halsch et al. 2021), a need for more insights about the Arctic biodiversity from a wide range of locations is needed Taylor et al. 2020). In this study, based on three consecutive years of sampling, we investigate habitat selection of two common Arctic wolf spider species, Pardosa hyperborea (Thorell 1872) and Pardosa furcifera (Thorell 1875), and we analyse the interacting effects of habitat and elevation on two life-history traits, i.e. body size and clutch size. ...
The Arctic tundra is characterised by harsh conditions and environmental gradients are especially pronounced. Variation in functional traits along such gradients provide insights into the drivers of species abundance and distribution and are particularly valuable in this region currently experiencing strong climate warming. Over three consecutive years, we analysed the interacting effect of two environmental factors, habitat and elevation, on the abundance, body size, and clutch size in two common Low-Arctic invertebrate predators (Lycosidae, Araneae), Pardosa furcifera (Thorell 1875) and Pardosa hyperbo-rea (Thorell 1872). Using generalised linear models, we firstly showed a habitat partitioning between P. furcifera, which dominated wet habitats, like fens, and P. hyperborea, which was more associated with drier habitats, like shrubs. Secondly, we found smaller body sizes at high elevation in P. hyperborea, a species that has a southern distribution in Greenland, and we identified season length as a major driver of the development in this species. In P. furcifera, a species likely more cold adapted, we found no body size difference between elevations, suggesting that local conditions (e.g. prey availability or snowmelt timing) are more important in explaining body size variations. Finally, body size and clutch size were strongly correlated in both species, but clutch size was not affected by habitat or elevation. We argue that fecundity is likely influenced by trade-offs and that considering additional complementary trait measurements would allow for a better understanding of the mechanisms underlying patterns in species life-history traits along environmental gradients.
... Arctic drying and an associated decrease in the abundance of emerging aquatic insects may have impacts on predator populations that rely on this aquatic subsidy. Wolf spiders (Araneae: Lycosidae) are dominant terrestrial arthropod predators in Arctic tundra (Bowden and Buddle 2010;Wyant et al. 2011;Bowden et al. 2018;Gillespie et al. 2020) that often reside in wet tundra habitats (Böcher et al. 2015;Bowden et al. 2018) and are known to consume aquatic Diptera (Wirta et al. 2015a, b;Eitzinger et al. 2019). Their growth, survival, and reproduction are being impacted by climate change in various ways. ...
... Arctic drying and an associated decrease in the abundance of emerging aquatic insects may have impacts on predator populations that rely on this aquatic subsidy. Wolf spiders (Araneae: Lycosidae) are dominant terrestrial arthropod predators in Arctic tundra (Bowden and Buddle 2010;Wyant et al. 2011;Bowden et al. 2018;Gillespie et al. 2020) that often reside in wet tundra habitats (Böcher et al. 2015;Bowden et al. 2018) and are known to consume aquatic Diptera (Wirta et al. 2015a, b;Eitzinger et al. 2019). Their growth, survival, and reproduction are being impacted by climate change in various ways. ...
Aquatic insects are often consumed by terrestrial predators in Arctic tundra. However, this aquatic-terrestrial linkage may be disrupted by rapid warming that is causing a decrease in freshwater habitats across large areas of the Arctic. In this study, we investigated emerging mosquitoes (Diptera: Culicidae) as a resource subsidy for wolf spiders (Araneae: Lycosidae) in western Greenland, an area where significant pond drying has occurred in recent decades. We used pitfall trapping to compare the abundance, size, and fecundity of wolf spiders collected near (< 1 m) versus far (75–100 m) from the margins of three tundra ponds before, during, and after mosquito emergence. Nearly 90% of the wolf spiders collected in our study were Pardosa glacialis, the species that subsequently became the focus of our analyses. P. glacialis abundances, sizes, and the proportion of females with an egg sac were similar throughout the season both near and far from ponds. However, females near ponds produced about 20% more eggs per egg sac. Stable isotope analyses and a laboratory experiment confirmed mosquito consumption by P. glacialis and demonstrated that individuals collected near tundra ponds were significantly depleted in 13C relative to those in upland habitats, indicating differences in food resources among habitats. Our evidence indicates that mosquitoes do indeed serve as a subsidy to wolf spiders in western Greenland, but the demographic effects on spiders appear to be modest. Thus, P. glacialis abundance in the landscape may be relatively robust to pond drying and associated biotic and abiotic changes. Further studies will be needed to assess the broader effects for tundra ecosystems of disruptions to this and other aquatic-terrestrial linkages via the drying of ponds.
... Among soil and foliage-dwelling arctic arthropods, herbivores (Hemiptera and Lepidoptera) and parasitoids (Hymenoptera) have increased locally in abundance, whereas detritivores (Collembola and Acari) have decreased (Koltz et al. 2018a). While spider communities (Araneae) seem not to have experienced drastic changes overall, individual species have declined in abundance (Bowden et al. 2018). Among flower-visiting arctic arthropods, muscid flies (Diptera) have drastically decreased in abundance (Loboda et al. 2018). ...
Species interactions are known to structure ecological communities. Still, the influence of climate change on biodiversity has primarily been evaluated by correlating individual species distributions with local climatic descriptors, then extrapolating into future climate scenarios. We ask whether predictions on arctic arthropod response to climate change can be improved by accounting for species interactions. For this, we use a 14‐year‐long, weekly time series from Greenland, resolved to the species level by mitogenome mapping. During the study period, temperature increased by 2°C and arthropod species richness halved. We show that with abiotic variables alone, we are essentially unable to predict species responses, but with species interactions included, the predictive power of the models improves considerably. Cascading trophic effects thereby emerge as important in structuring biodiversity response to climate change. Given the need to scale up from species‐level to community‐level projections of biodiversity change, these results represent a major step forward for predictive ecology.
... The timing and order in which species appear during the early community assembly phase in spring will in turn affect their competitive ability and abundance throughout their active season (Bokhorst et al., 2016;Clements et al., 2013;Louette & Meester, 2007). In High-Arctic Greenland, for example, abundances of some spider species have declined over the past 18 years in response to rising temperatures and altered timing of snowmelt (Bowden et al., 2018). Since spiders often play an important role as the first predators to emerge or colonise, shifts in their presence, abundance or behaviour are likely to alter community structure during the assembly phase (Dahl et al., 2018). ...
... There was no effect of temperature on total abundance at the first sampling time-point here, however, indicating that warming instead may structure communities through changes in dominance hierarchies and relative abundances of species, as observed in High-Arctic plants (Kapfer & Grytnes, 2017), flies (Loboda et al., 2018) and spiders (Bowden et al., 2018). ...
Climate warming is predicted to have major impacts on the structure of terrestrial communities, particularly in high latitude ecosystems where growing seasons are short. Higher temperatures may dampen seasonal dynamics in community composition as a consequence of earlier snowmelt, with potentially cascading effects across all levels of biological organisation.
Here, we examined changes in community assembly and structure along a natural soil temperature gradient in the Hengill geothermal valley, Iceland, during the summer of 2015. Sample collection over several time points within a season allowed us to assess whether temperature alters temporal variance in terrestrial communities and compositional turnover.
We found that seasonal fluctuations in species richness, diversity and evenness were dampened as soil temperature increased, whereas invertebrate biomass varied more. Body mass was found to be a good predictor of species occurrence, with smaller species found at higher soil temperatures and emerging earlier in the season.
Our results provide more in‐depth understanding of the temporal nature of community and population‐level responses to temperature, and indicate that climate warming will likely dampen the seasonal turnover of community structure that is characteristic of high latitude invertebrate communities.
... Our previous work in the region has shown considerable heterogeneity in long-term changes and links to climate across invertebrate orders (28). For example, a subset of families exhibited declines in total abundance between 1996 and 2016 for all habitats studied (13), with habitat type playing an important role mediating the strength of species abundance trends for both spiders (Araneae) and muscid flies (Diptera) (13,25,29), while links to climate variables were taxon-specific and thus did not show a strong, consistent pattern. Conversely, we documented strong effects of climate on body size (30,31), phenology (32)(33)(34), community composition (25,28), and species interactions (35,36). ...
Significance
Arthropods are excellent indicators for studying global change in the rapidly changing climate of the Arctic. We used the most comprehensive standardized dataset on Arctic arthropods to quantify diversity and abundance variation over 24 y in an area that is warming rapidly. Overall arthropod abundance and diversity showed opposing nonlinear trends, with a sharp increase in overall abundance in recent years. However, trends varied substantially among taxa and habitats and several groups declined in abundance. We found strong evidence of conditions outside the growing season and density-dependent feedbacks affecting abundance. Our results emphasize the need for a more integrated approach to investigating arthropod responses to environmental stressors at finer taxonomic resolution and by incorporating time-lagged effects.
