High resistance towards herbivore-induced habitat change in a high Arctic arthropod community

Mammal herbivores may exert strong impacts on plant communities, and are often key drivers of vegetation composition and diversity. We tested whether such mammal-induced changes to a high Arctic plant community are reflected in the structure of other trophic levels. Specifically, we tested whether substantial vegetation changes following the experimental exclusion of muskoxen (Ovibos moschatus) altered the composition of the arthropod community and the predator-prey interactions therein. Overall, we found no impact of muskox exclusion on the arthropod community: the diversity and abundance of both arthropod predators (spiders) and of their prey were unaffected by muskox presence, and so was the qualitative and quantitative structure of predator-prey interactions. Hence, high Arctic arthropod communities seem highly resistant towards even large biotic changes in their habitat, which we attribute to the high connectance in the food web

Limited dietary overlap amongst resident Arctic herbivores in winter: complementary insights from complementary methods

Snow may prevent Arctic herbivores from accessing their forage in winter, forcing them to aggregate in the few patches with limited snow. In High Arctic Greenland, Arctic hare and rock ptarmigan often forage in muskox feeding craters. We therefore hypothesized that due to limited availability of forage, the dietary niches of these resident herbivores overlap considerably, and that the overlap increases as winter progresses. To test this, we analyzed fecal samples collected in early and late winter. We used molecular analysis to identify the plant taxa consumed, and stable isotope ratios of carbon and nitrogen to quantify the dietary niche breadth and dietary overlap. The plant taxa found indicated only limited dietary differentiation between the herbivores. As expected, dietary niches exhibited a strong contraction from early to late winter, especially for rock ptarmigan. This may indicate increasing reliance on particular plant resources as winter progresses. In early winter, the diet of rock ptarmigan overlapped slightly with that of muskox and Arctic hare. Contrary to our expectations, no inter-specific dietary niche overlap was observed in late winter. This overall pattern was specifically revealed by combined analysis of molecular data and stable isotope contents. Hence, despite foraging in the same areas and generally feeding on the same plant taxa, the quantitative dietary overlap between the three herbivores was limited. This may be attributable to species-specific consumption rates of plant taxa. Yet, Arctic hare and rock ptarmigan may benefit from muskox opening up the snow pack, thereby allowing them to access the plants.</p

On the interplay between hypothermia and reproduction in a high arctic ungulate

For free-ranging animals living in seasonal environments, hypometabolism (lowered metabolic rate) and hypothermia (lowered body temperature) can be effective physiological strategies to conserve energy when forage resources are low. To what extent such strategies are adopted by large mammals living under extreme conditions, as those encountered in the high Arctic, is largely unknown, especially for species where the gestation period overlaps with the period of lowest resource availability (i.e. winter). Here we investigated for the first time the level to which high arctic muskoxen (Ovibos moschatus) adopt hypothermia and tested the hypothesis that individual plasticity in the use of hypothermia depends on reproductive status. We measured core body temperature over most of the gestation period in both free-ranging muskox females in Greenland and captive female muskoxen in Alaska. We found divergent overwintering strategies according to reproductive status, where pregnant females maintained stable body temperatures during winter, while non-pregnant females exhibited a temporary decrease in their winter body temperature. These results show that muskox females use hypothermia during periods of resource scarcity, but also that the use of this strategy may be limited to non-reproducing females. Our findings suggest a trade-of between metabolically driven energy conservation during winter and sustaining foetal growth, which may also apply to other large herbivores living in highly seasonal environments elsewhere.publishedVersio

Interaction webs in arctic ecosystem : Determinants of arctic change?

Peer reviewe

Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map

Herbivores modify the structure and function of tundra ecosystems. Understanding their impacts is necessary to assess the responses of these ecosystems to ongoing environmental changes. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic. Strong spatial variation in herbivore effects implies that the results of individual studies on herbivory depend on local conditions, i.e., their ecological context. An important first step in assessing whether generalizable conclusions can be produced is to identify the existing studies and assess how well they cover the underlying environmental conditions across the Arctic. This systematic map aims to identify the ecological contexts in which herbivore impacts on vegetation have been studied in the Arctic. Specifically, the primary question of the systematic map was: “What evidence exists on the effects of herbivores on Arctic vegetation?”

ZOTUs

Denoised, chimera-filtered, and clustered ZOTUs from the sequence data

ZOTUtabs

ZOTUtab linking ZOTUs to samples (and replicates)

Data from: High resistance towards herbivore-induced habitat change in a high arctic arthropod community

Mammal herbivores may exert strong impacts on plant communities, and are often key drivers of vegetation composition and diversity. We tested whether such mammal-induced changes to a high Arctic plant community are reflected in the structure of other trophic levels. Specifically, we tested whether substantial vegetation changes following the experimental exclusion of muskoxen (Ovibos moschatus) altered the composition of the arthropod community and the predator-prey interactions therein. Overall, we found no impact of muskox-exclusion on the arthropod community: the diversity and abundance of both arthropod predators (spiders) and of their prey were unaffected by muskox presence, and so was the qualitative and quantitative structure of predator-prey interactions. Hence, high Arctic arthropod communities seem highly resistant towards even large biotic changes in their habitat, which we attribute to the high connectance in the food web