Climatic severity and the response to temperature elevation of Arctic aphids

1  Theory suggests that any given rise in temperature resulting from climate change will have its greatest effect on high Arctic ecosystems where growing seasons are short and temperatures low. 2  A small temperature rise, similar to that predicted for the middle of the next century, has profound effects on a population of the high Arctic, Dryas-feeding aphid Acyrthosiphon svalbardicum on Spitsbergen (Strathdee et al. 1993a). 3  Here comparative experiments on a closely related Dryas-feeding species, A. brevicorne, at two contrasting sub-Arctic sites are described. Together with the results from Spitsbergen these sites represent two colder sites (high Arctic and upland sub-Arctic) and one warmer site (lowland sub-Arctic). 4  Differential responses in aphid population density and overwintering egg production to temperature elevation support the hypothesis that the ecological effects are greatest at sites with the most severe climates; however, there is no similar gradient in advancement of host plant phenology with warming

Effects of temperature elevation on a field population of Acyrthosiphon svalbardicum (Hemiptera: Aphididae) on Spitsbergen

A manipulation experiment was carried out on a field population of the aphid Acyrthosiphon svalbardicum near Ny Ålesund, on the high arctic island of Spitsbergen, using cloches to raise temperature. An average rise in temperature of 2.8 deg. C over the summer season markedly advanced the phenology of both the host plant Dryas octopetala and the aphid. Advanced aphid phenology, with concomitant increases in reproductive output and survival, and successful completion of the life-cycle led to an eleven-fold increase in the number of overwintering eggs. Thermal budget requirements in day degrees above 0°C were calculated for key life-cycle stages of the aphid. Temperature data from Ny Ålesund over the past 23 years were used to calculate thermal budgets for the field site over the same period and these were compared with the requirements of the aphid. Each estimated thermal budget was then adjusted to simulate the effect of a +2, +4, and −2deg. C change in average temperature on aphid performance. This retrospective analysis (i) confirms that the life-cycle of A. svalbardicum is well suited to exploit higher summer temperatures, (ii) indicates that the annual success of local populations are sensitive to small changes in temperature and (iii) suggests that the aphid is living at the limits of its thermal range at Ny Ålesund based on its summer thermal budget requirements

Identification of three previously unknown morphs of Acyrthosiphon svalbardicum Heikinheimo (Hemiptera: Aphididae) on Spitsbergen

Identification of three previously unknown morphs of Acyrthosiphon svalbardicum Heikinheimo (Hemiptera: Aphididae) on Spitsbergen

Feeding studies on Onychiurus arcticus (Tullberg) (Collembola: Onychiuridae) on West Spitsbergen

The feeding biology of the arctic collembolan Onychiurus arcticus (Tullberg) is described from West Spitsbergen, based on a combination of gut content analyses for field collected and microcosm-living animals, together with laboratory feeding trials. There was wide variation in the food items consumed by individual animals, reflecting the wide choice available in the environment. Most animals fed predominantly on living and dead bryophytes, detritus and to a lesser extent algal cells. Laboratory trials showed that O. arcticus feeds as a herbivore on a range of bryophyte species. The presence of dense aggregations below bird cliffs and elsewhere may reflect the distribution of particularly favourable microenvironments

Extreme adaptive life-cycle in a high arctic aphid, Acyrthosiphon svalbardicum

1 The year-round biology of a high arctic aphid is described for the first time. 2 The life-cycle is shown to be genetically determined, and thus markedly different to temperate species where the observed polymorphism is governed primarily by external environmental cues. 3 The fundatrix, which emerges from the overwintering egg, gives birth directly to sexual morphs, a phenomenon previously undescribed in the Aphidinae. This process is essentially prevented in temperate aphids by an endogenous mechanism, the interval timer. 4 In addition to the sexual morphs, the fundatrix produces a small number of parthenogenetic individuals (viviparae) that give rise to a third generation. This last generation consists exclusively of oviparae and males that would increase the number of overwintering eggs provided there is sufficient thermal budget for them to mature and oviposit before conditions become adverse. 5 The position of particular morphs in the birth sequences of the second and third generations maximize the chances of survival in harsh conditions, whilst enhancing the likelihood that individuals from the third generation will add to the number of overwintering eggs. 6 Guaranteed egg production combined with an in-built flexibility to produce an extra generation in particularly favourable seasons, confer adaptations to the high arctic environment, and ideally suit this aphid to exploit elevated temperatures in an era of climate change

Global change and Arctic ecosystems: conclusions and predictions from experiments with terrestrial invertebrates on Spitsbergen

Extensive studies on invertebrates from Ny-Ålesund, Spitsbergen, Svalbard and more limited data on aphids from Abisko, Sweden, produced the following main conclusions: (1) The population response to raised summer temperatures differed between the above and the below ground species, both in terms of speed and magnitude. (2) Similar animal communities responded differently to similar temperature manipulations on sites with different vegetation cover and composition. (3) For soil animals the between-year and between-site variations in population densities, were greater than the differences produced by the temperature manipulation experiments at any one site in any year. (4) Infrequent extreme climatic events strongly influence long-term trends in population density and community composition. (5) The population response of invertebrates to climate warming is greatest and most rapid at the coldest sites. (6) The spatial distribution of the above ground insect herbivores on their host plant is temperature limited. (7) The numerical abundance of flying predators/parasitoids of the above-ground herbivores is low. (8) The spatial distribution of some predators may be thermally restricted and less extensive than that of their prey. (9) Habitat temperature is the driving variable determining the flight activity patterns of insects. (10) Increased summer temperatures may alter or disrupt the seasonal patterns of insect emergence, particularly in species where the life cycle is cued into the seasonal rhythm. (11) The common species of arctic soil mites and Collembola are well adapted to survive enhanced summer temperatures, providing that moisture is not limited. (12) Water availability during the summer growing period is probably of greater significance than temperature in determining the survival and success of many arctic soil invertebrate groups. (13) Arctic soil microarthropod species are well adapted to survive and operate at subzero and low positive summer temperatures. (14) Freeze-thaw events represent critical points in the life history of the microarthropods. (15) Supercooling points are sometimes poor indicators of the capacity of arctic soil microarthopods to survive low temperatures. From these findings predictions are made as to how high arctic communities will respond to predicted changes in climate

Thermal Environments of Arctic Soil Organisms during Winter

This paper compares winter soil temperatures at five high arctic sites (Ny Alesund, West Spitsbergen) and one subarctic site (Slattatjakka, Abisko) during 1992/93 and 1993/94. At the high arctic sites snow cover afforded slight insulation where minimum air temperatures were as low as -32 degrees C (March 1993). However, snow did not accumulate significantly until late winter, by which time the ground had cooled to approximately -20 degrees C. The polar night aided soil cooling by minimizing solar heat gain. Soil temperatures at 3 cm depth during the autumn freeze were initially higher than surface temperatures, but once frozen, the zone inhabited by soil microarthropods (approximately 10 cm depth) remained isothermal and closely tracked air temperature. By contrast, throughout the spring thaw, the soil at 3 cm depth was cooler than the surface. Hence, snow cover reduced absolute minimum temperatures in late winter but prolonged the effective winter period. Hence soil organisms may be inactive for up to 79% (289 d) of the year, owing to the extended period that the ground is frozen. The incidence of daily ground freeze/thaw events was reduced at high arctic sites compared with a subarctic location. Similarly, there were differences in temperature means and minima at the adjacent high arctic sites dependent on location and topography; for example, on opposite coasts of the Broggerhaloya, West Spitsbergen the minimum temperatures in 1993/94 were -15.7 degrees C (Stuphallet) and -8.2 degrees C (Kjaerstranda). Terrestrial microarthropods inhabiting sites with late snow accumulation and cold air temperatures experience extreme low soil temperatures and hence require effective cold-hardiness strategies