Author: isabel

Diet composition in herbivores differs greatly from season to season because they eat many types of grasses, shrubs, and forbs. This flexibility allows arctic-alpine species like mountain hares (Lepus timidus) to cope with changing environmental conditions over the seasons and the corresponding changes in food quantity and quality. Understanding how, when, and why animals use certain areas is critical to their conservation and management.  

Rehnus and Bollmann investigated the distribution of pellets and of individual core activity areas of mountain hares in the Swiss Alps and compared differences between spring and autumn. Pellets were collected from 2014 to 2019; individuals were determined using an established, non-invasive genetic technique.

Their study presents details about altitudinal shifts in the feeding sites and activity areas of mountain hares in the Alps. They conclude that the annual “wave” of greening from lower to higher elevations, which correlates with forage availability and quality, explains this shift. However, further research is needed on how these shifts are affected by climate change and how they interact with nutritional needs and thermoregulatory mechanisms.

Reference: Rehnus, M., Bollmann, K. (2020) Mountain hares Lepus timidus follow the green-up wave in the pursuit of high-quality food. Wildlife Biology, 2020, 3: 00720. doi: 10.2981/wlb.00720

You can find the full paper here.

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Picture: Mountain hare during grooming in early-summer (photo © Rolf Giger).

Herbivory can modify vegetation responses to climatic changes, but climate and herbivory also affect each other and rarely work in isolation from other ecological factors. Thus, it is challenging to predict how herbivory counteracts, amplifies and interacts with climate impacts. We used experimental exclosures in Norway and Canada to investigate how moose browsing can modify climatic responses of boreal trees. By modeling complex causal pathways including several climatic factors, multiple tree species, competition, tree height, time, food availability, and herbivore presence, density and browsing intensity, we found that moose can indeed counteract positive temperature responses of trees. However, this effect varied between tree species depending on moose foraging preferences. Furthermore, we found that moose can contribute positively to the growth of some trees by constraining growth of competing trees. This “cooling power” of herbivory appears to be highly context-dependent, so in order to understand its potential to prevent changes induced by warming climate, ecological complexity needs to be acknowledged.

Reference: Vuorinen, Katariina E. M., Anders L. Kolstad, Laurent De Vriendt, Gunnar Austrheim, Jean‐Pierre Tremblay, Erling J. Solberg, and James D. M. Speed (2020) Cool as a moose: How can browsing counteract climate warming effects across boreal forest ecosystems? Ecology: e03159.

You can find the full paper here.

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Picture: A field site in Gaspesie (Photo by Katariina E. M. Vuorinen).

In the long-term, herbivores can alter nutrient dynamics in tundra ecosystems by changing the functional composition of the vegetation. Yet, herbivores may also alter nutrient dynamics by modifying plant-community nutrient levels, and these changes are likely to happen much faster than structural changes. Here, by using novel Near Infrared-Reflectance Spectroscopy (NIRS) methodology, we quantified the effects of small rodents and reindeer on tundra-grassland plant-community nitrogen and phosphorus levels throughout a single growing season. Herbivores were immediate, positive modifiers of plant-community nutrient levels. Plant-community nutrient contents in herbivore-affected tundra were still much higher in senescent leaves at the end of the summer, suggesting that herbivory is accelerating short-term tundra-grassland nutrient dynamics. Overall, our findings from tundra-grasslands align with theoretical expectations of positive herbivore effects on nutri­ent cycling in relatively productive ecosystems, when domi­nant, nutrient-rich growth forms benefit from herbivory.

Reference: Petit Bon, M., Inga, K. G., Jónsdóttir, I. S., Utsi, T. A., Soininen, E. M., & Bråthen, K. A. (2020). Interactions between winter and summer herbivory affect spatial and temporal plant nutrient dynamics in tundra grassland communities. Oikos. https://doi.org/10.1111/oik.07074

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Picture: experimental sites at Ifjordfellet, Finnmark, northern Norway (photo: Matteo Petit Bon)

Arctic ecosystems are especially sensitive to climate change. As the Arctic warms, shrubs have been observed to expand. Such changes in vegetation could have major implications on how Arctic ecosystems respond to and feedback on climate change. However, it remains unclear why such shrub expansion remains spatially uneven across the Arctic, with herbivory suggested as a key regulating factor. This study mapped the changes in shrub cover in Yamal Peninsula over three decades using satellite imagery and related these changes to summer temperature and reindeer population size. Surprisingly, we found no evidence that shrubs had expanded, despite the increasing temperatures. At the same time, local reindeer population size grew by over 75%. The results indicate that herbivory pressures could counteract the climate-induced shrub expansion in the region. This suggests that the strategic management of semi-domesticated reindeer husbandry could be a promising tool to maintain tundra landscapes in a warming Arctic. 

Reference: Verma, M., to Bühne, H.S., Lopes, M., Ehrich, D., Sokovnina, S., Hofhuis, S.P. and Pettorelli, N., 2020. Can reindeer husbandry management slow down the shrubification of the Arctic?. Journal of Environmental Management, 267:110636
https://doi.org/10.1016/j.jenvman.2020.110636

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Image credit: @Photo by Steve Morgan/GreenPeace

During the last century, moose have taken advantage of increasing shrubs in the tundra and expanded their northern range into Arctic Alaska. As the Arctic warms up, shrub patches along rivers are aggregating and coalescing to form larger and more connected patches, creating more moose habitat. Models predict that moose habitat will likely more than double by 2099 in Arctic Alaska. Current research focuses on how this expected increase in moose habitat will affect future opportunities for moose hunting in remote communities of the region.

Reference: Zhou, J., Tape, K.D., Prugh, L., Kofinas, G., Carroll, G., Kielland, K. (2020) Enhanced shrub growth in the Arctic increases habitat connectivity for browsing herbivores. Global Change Biology
https://doi.org/10.1111/gcb.15104

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Picture: Shrub expansion enhances habitat connectivity for browsing herbivores like moose, Alces alces (Photo: Ken Tape, University of Alaska Fairbanks)