Willow drives changes in arthropod communities of northwestern Alaska: ecological implications of shrub expansion

Abstract

Arthropods serve as complex linkages between plants and higher-level predators in Arctic ecosystems and provide key ecosystem services such as pollination and nutrient cycling. Arctic plant communities are changing as tall woody shrubs expand onto tundra, but potential effects on arthropod abundance and food web structure remain unclear. Changes in vegetation structure can alter the physical habitat, thermal environment, and food available to arthropods, thereby having the potential to induce cascading effects throughout the ecosystem. We evaluated relationships between the abundance, biomass, and community composition of arthropods and the cover of several shrub taxa across tundra-shrub gradients in northwestern Alaska. While previous research had found a general positive association between arthropod biomass and shrub cover, we found heterogeneity in this relationship with finer-scale examination of (1) shrub taxa, (2) arthropod taxa, and (3) arthropod guilds. Abundance and biomass of arthropods showed strong, positive associations with the amount of cover of willow (Salix spp.) but were not significantly influenced by shrub birch (Betula spp.) or ericaceous (Ericaceae) vegetation. Significant shifts in arthropod community composition were also associated with willows. Among trophic groups of arthropods, herbivores and pollinators were most positively associated with willow cover. Due to geographical variation in both dominant shrub taxa and their rates of expansion, effects on arthropod communities are likely to be heterogeneous across the Arctic. Taken together, our results suggest that shrub expansion could increase food availability for higher-level insectivores and shift Arctic food web structure.

Impact of Cover Crop Planting and Termination Dates on Arthropod Activity in the Following Corn

“…To determine if cover crop biomass impacted arthropod activity during each sampling period across all cover crop planting and termination date combinations, a nonmetric multidimensional scaling (NMDS) analysis using Bray-Curtis distances was performed, following Dunbar et al (2016) and McDermott et al (2021) . NMDS summarizes the relationship among all variables and displays the relationships in ordination space.…”

Wing lengths of three Arctic butterfly species decrease as summers warm in Alaska

“…In Alaska, there is a northward expansion of shrub habitat into the tundra, altering the composition and abundance of different types of arthropods within shrub and open tundra habitats (Boelman et al 2015, Asmus et al 2018). Patterns of arthropod abundances, diversity, and body size changes could have important implications for food webs, since arthropods are an essential food source for migrating breeding birds (McDermott et al 2021). Tundra invertebrates rely on both seasonal and diurnal cues, such as temperature and the resulting snowmelt timing (MacLean 1975).…”

Tree and shrub expansion at treeline drive contrasting responses in a subarctic passerine community

“…The widespread expansion of dwarf birch in the region ( Betula nana ; Tape et al, 2006) may constitute one example as willow ( Salix spp.) appears to support a higher biomass of arthropod prey (McDermott et al, 2021). Successional replacement of Salix shrublands by dwarf birch may occur on certain sites particularly with the deepening of the moss mat which results in cooler soils, thereby conferring an advantage to dwarf birch over less cold‐tolerant Salix species (Carl Roland, personal communication).…”