Aphid–willow interactions in a high Arctic ecosystem: responses to raised temperature and goose disturbance

Abstract

Recently, there have been several studies using open top chambers (OTCs) or cloches to examine the response of Arctic plant communities to artificially elevated temperatures. Few, however, have investigated multitrophic systems, or the effects of both temperature and vertebrate grazing treatments on invertebrates. This study investigated trophic interactions between an herbivorous insect (Sitobion calvulum, Aphididae), a woody perennial host plant (Salix polaris) and a selective vertebrate grazer (barnacle geese, Branta leucopsis). In a factorial experiment, the responses of the insect and its host to elevated temperatures using open top chambers (OTCs) and to three levels of goose grazing pressure were assessed over two summer growing seasons (2004 and 2005). OTCs significantly enhanced the leaf phenology of Salix in both years and there was a significant OTC by goose presence interaction in 2004. Salix leaf number was unaffected by treatments in both years, but OTCs increased leaf size and mass in 2005. Salix reproduction and the phenology of flowers were unaffected by both treatments. Aphid densities were increased by OTCs but unaffected by goose presence in both years. While goose presence had little effect on aphid density or host plant phenology in this system, the OTC effects provide interesting insights into the possibility of phenological synchrony disruption. The advanced phenology of Salix effectively lengthens the growing season for the plant, but despite a close association with leaf maturity, the population dynamics of the aphid appeared to lack a similar phenological response, except for the increased population observed.

Peak season carbon exchange shifts from a sink to a source following 50+ years of herbivore exclusion in an Arctic tundra ecosystem

“…; Gillespie et al . ). It is conceivable that such high‐intensity geese grazing may decrease high quality forage consumed by lemmings and further drive down lemming populations, which according to the nutrient recovery hypothesis may increase above‐ground standing dead, soil insulation, and reduce thaw depth, potentially altering landscape‐level carbon exchange (Fig.…”

“…) and insect herbivory (Rinnan, Stark & Tolvanen ; Gillespie et al . ). In some cases, herbivory has facilitated plant community transitions from moss‐ to graminoid‐dominated ecosystems in Siberia and Svalbard, respectively (Zimov ; Gornall et al .…”

“…; Gillespie et al . ), rodent (Olofsson, Tommervik & Callaghan ; Olofsson et al . ) and insect herbivory (Rinnan, Stark & Tolvanen ; Gillespie et al .…”

Warming the tundra: reciprocal responses of invertebrate herbivores and plants

“…Responses through leaf area in D. octopetala have been reported for long‐term warming (Hudson et al ) and fertilization manipulations (Wookey et al ). Indirect effects of herbivores have been long recognized for vertebrate herbivores in the tundra (Hik and Jefferies , Van der Wal et al ); herbivore faeces return nutrients to the ecosystem by providing highly decomposable resources that are rich in labile nutrients, and can enhance compensation mechanisms in plants (Gillespie et al ). Faeces of invertebrate herbivores (frass) are rapidly decomposed (Kagata and Ohgushi ) and, even small frass additions, can have a relevant impact on nutrient cycling (Frost and Hunter ).…”

“…Studies quantifying invertebrate herbivory in experimental warming treatments have reported neutral (Richardson et al ) or increased herbivory in warmed plots in the field (Roy et al , Liu et al , Hasle ) and in the lab (Kukal and Dawson , O'Connor ). In most field studies, however, increases in leaf damage reflect an increase in herbivore abundance (Dollery et al , Gillespie et al ), not necessarily an increase in per capita consumption rates (but see Liu et al ).…”