Effects of the invasive plant spotted knapweed (Centaurea stoebe L.) on grassland arthropod communities: Use of genomic barcoding tools for ecosystems reclamation management

British Columbia’s (BC) grasslands are home to 30 percent of the province’s species at risk and are one of Canada’s most endangered ecosystems. In BC’s Southern interior, human activities such as mining, recreation, and in certain instances, heavy livestock grazing, are altering grassland ecosystems; the increased soil disturbance may leave them susceptible to the colonization of invasive species. Invasive species can cause changes to native plant communities and nutrient cycling, and by doing so, may alter the amount and quality of habitat available for animals such as arthropods. Arthropods are diverse and contribute to energy flow and nutrient cycling, and are therefore an important group to study as a way of determining the effects of changes to ecosystem function. Spotted knapweed (Centaurea stoebe L.), a perennial forb native to Eastern Europe, is considered one of the most ecologically harmful invasive species in Western North America. The objectives of this study were (1) to determine if spotted knapweed is altering arthropod community structure and density in grassland habitats; and (2) to DNA metabarcode all arthropod specimens collected using methodology that could be implemented to expedite site restoration efforts. To address these objectives, pitfall traps were installed at sites that were colonized, in differing densities, by spotted knapweed, and DNA metabarcoding was conducted on specimens collected. The results suggest that spotted knapweed density indirectly correlates with arthropod functional groups through changes in plant community composition. These indirect effects show different correlations between the functional groups; suggesting that both top down and bottom up control is at play upon the introduction of spotted knapweed. Decreases in herbivore and detritivore biomass was associated with increasing spotted knapweed density. Omnivore, predator, and parasite biomass had more intricate interactions. DNA metabarcoding results indicated a more complex interaction between Orthoptera and spotted knapweed density than suggested by a simple positive correlation. All other arthropod orders sampled were not obviously influenced by spotted knapweed. This study describes a relatively rapid and inexpensive technique for monitoring arthropod biodiversity with a DNA metabarcoding methodology applicable to both invasive species conservation efforts and for guiding remediation work in disturbed grassland sites.