Elevational variation of body size and reproductive traits in high-latitude wolf spiders (Araneae: Lycosidae)

The relative importance of abiotic and biotic environmental conditions for taxonomic, phylogenetic, and functional diversity of spiders across spatial scales

Both abiotic and biotic conditions may be important for biodiversity. However, their relative importance may vary among different diversity dimensions as well as across spatial scales. Spiders (Araneae) offer an ecologically relevant system for evaluating variation in the relative strength abiotic and biotic biodiversity regulation. We quantified the relative importance of abiotic and biotic conditions for three diversity dimensions of spider communities quantified across two spatial scales. Spiders were surveyed along elevation gradients in northern Sweden. We focused our analysis on geomorphological and climatic conditions as well as vegetation characteristics, and quantified the relative importance of these conditions for the taxonomic, phylogenetic, and functional diversity of spider communities sampled across one intermediate (500 m) and one local (25 m) scale. There were stronger relationships among diversity dimensions at the local than the intermediate scale. There were also variation in the relative influence of abiotic and biotic conditions among diversity dimensions, but this variation was not consistent across spatial scales. Across both spatial scales, vegetation was related to all diversity dimensions whereas climate was important for phylogenetic and functional diversity. Our study does not fully support stronger abiotic regulation at coarser scales, and conversely stronger abiotic regulation at more local scales. Instead, our results indicate that community assembly is shaped by interactions between abiotic constrains in species distributions and biotic conditions, and that such interactions may be both scale and context dependent.

Early snow melt and diverging thermal constraints control body size in arctic–alpine spiders

To predict species’ responses to a rapidly changing environment, it is necessary to detect current clines of life-history traits and understand their drivers. We studied body size variation, a key trait in evolutionary biology, of two arctic–alpine lycosid spiders and underlying mechanisms controlling this variation. We used long time-series data of body size of spiders sampled in Norway, augmented with museum data. Individuals of both species sampled in areas and years with longer snow-free periods grew larger than individuals in areas and years with shorter snow-free periods. Interestingly, temperatures below 0 °C led to a larger body size in Pardosa palustris, while temperatures above 0 °C led to a larger body size in Pardosa hyperborea. We assume that P. palustris, as the generally larger species, is less sensitive to environmental variability and low temperatures, because it can retain more energy compared with a smaller species and, therefore, can invest more resources in its offspring. With rising temperatures, both species might profit from a higher resource availability. In a rapidly changing arctic–alpine environment, alterations in the life-history traits and adaptation strategies of spiders are expected, which, regarding body size, seem to be highly influenced by early snowmelt and diverging thermal constraints.

Biting insects in a rapidly changing Arctic

Biting insects have a long-standing reputation for being an extreme presence in the Arctic, but it is unclear how they are responding to the rapid environmental changes currently taking place in the region. We review recent advances in our understanding of climate change responses by several key groups of biting insects, including mosquitoes, blackflies, and warble/botflies, and we highlight the significant knowledge gaps on this topic. We also discuss how changes in biting insect populations could impact humans and wildlife, including disease transmission and the disruption of culturally and economically important activities. Future work should integrate scientific with local and traditional ecological knowledge to better understand global change responses by biting insects in the Arctic and the associated consequences for the environmental security of Arctic communities.

Biogeographic position and body size jointly set lower thermal limits of wandering spiders

Most species encounter large variations in abiotic conditions along their distribution range. The physiological responses of most terrestrial ectotherms (such as insects and spiders) to clinal gradients of climate, and in particular gradients of temperature, can be the product of both phenotypic plasticity and local adaptation. This study aimed to determine how the biogeographic position of populations and the body size of individuals set the limits of cold (freezing) resistance of Dolomedes fimbriatus. We compared D. fimbriatus to its sister species Dolomedes plantarius under harsher climatic conditions in their distribution range. Using an ad hoc design, we sampled individuals from four populations of Dolomedes fimbriatus originating from contrasting climatic areas (temperate and continental climate) and one population of the sister species D. plantarius from continental climate, and compared their supercooling ability as an indicator of cold resistance. Results for D. fimbriatus indicated that spiders from northern (continental) populations had higher cold resistance than spiders from southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red-listed and rarest D. plantarius was slightly less cold tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection. The lowest cold resistance might put D. plantarius at risk of extinction in the future, and this should be considered in conservation plan.

Prey identity but not prey quality affects spider performance

•

Prey identity affected the survival and body mass of a generalist spider predator.

•

Trophic level of the prey did not affect spider survival and body mass.

•

Prey identity and cordgrass quality had an interactive effect on spider body mass.

•

Greater spider body mass led to greater egg production.

•

In a literature review, female spider fitness increased with greater body size.

Increasing host plant quality affects higher trophic level predators, but whether such changes are simply a result of prey density or are also affected by changes in prey quality remain uncertain. Moreover, whether changes in prey quality affect measures of predator performance is understudied. Using a combination of field and greenhouse mesocosm experiments, we demonstrate that the survival and body size of a hunting spider (Pardosa littoralis Araneae: Lycosidae) is affected more by prey species identity than the trophic level of the prey. Furthermore, increasing host plant quality does not necessarily propagate through the food web by altering prey quality. While changes in plant quality affected spider body mass, they did so in opposite ways for spiders feeding on Prokelisia (Hemiptera: Delphacodes) herbivores relative to Tytthus (Hemiptera: Miridae) egg predators, and had no impact on spider body mass for two additional species of intraguild prey. These changes in body mass were important because greater body mass increased spider egg production. To examine the generality of this pattern, we reviewed the literature and found a consistent positive relationship between female body size and egg production for Pardosa species, indicating that body size is a reliable proxy for fitness. While many studies emphasize the importance of nitrogen to arthropod diets, this focus may be driven largely by our understanding of herbivore diets rather than predator diets. Thus, the positive impact of host plant quality on higher trophic level predators appears to be driven more by altering prey composition, density, and availability rather than simply providing predators with more nutritious prey.

Differences in Mobility and Dispersal Capacity Determine Body Size Clines in Two Common Alpine-Tundra Arthropods

The Arctic is projected to be severely impacted by changes in temperature and precipitation. Species react to these changes by shifts in ranges, phenology, and body size. In ectotherms, the patterns of body size clines and their underlying mechanisms are often hard to untangle. Mountains provide a space-for-time substitute to study these shifts along multiple spatial gradients. As such, mobility and dispersal capacity might conceal reactions with elevation. We test this influence on body size clines by comparing two common arthropods of the alpine tundra. We find that high mobility in the lycosid spider Pardosa palustris blurs elevational effects. Partially low mobility at least during development makes the carabid beetle Amara alpina more susceptible to elevational effects. Specific life-history mechanisms, such as brood care in lycosid spiders and holometabolic development in carabid beetles, are the possible cause.