Author: isabel

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Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems

This paper summarizes the need for herbivory studies and presents the protocols designed by the Herbivory Network.

Plant-herbivore interactions are central to the functioning of tundra ecosystems, but their outcomes vary over space and time. Accurate forecasting of ecosystem responses to ongoing environmental changes requires a better understanding of the processes responsible for this heterogeneity. To effectively address this complexity at a global scale, coordinated research efforts, including multi-site comparisons within and across disciplines, are needed. The Herbivory Network was established as a forum for researchers from Arctic and alpine regions to collaboratively investigate the multifunctional role of herbivores in these changing ecosystems. One of the priorities is to integrate sites, methodologies, and metrics used in previous work, to develop a set of common protocols and design long-term geographically-balanced, coordinated experiments. The implementation of these collaborative research efforts will also improve our understanding of traditional human-managed systems that encompass significant portions of the sub-Arctic and alpine areas worldwide. A deeper understanding of the role of herbivory in these systems under ongoing environmental changes will guide appropriate adaptive strategies to preserve their natural values and related ecosystem services.

Reference: Barrio, I.C., Hik, D.S., Jónsdóttir, I.S., Bueno, C.G., Mörsdorf, M.A., Ravolainen, V.T. (2016) Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems. Polar Science 10: 297-302.

Link to publication / request a copy

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Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia

frozen reindeer

According to oral histories collected among fully nomadic tundra Nenets on Yamal Peninsula in West Siberia, extreme weather (rain-on-snow) events resulting in significant mortality within tundra herds have occurred roughly once per decade during the past century.

The extreme weather events of November 2006 and 2013 caused mass reindeer starvation that we were able to track in detail using state-of-the-art satellite sensors. The most recent rain-on-snow event of November 2013 resulted in ca. 61,000 reindeer deaths, about 22% out of 275,000 reindeer on the Yamal Peninsula at the time. Empirical data and modelling efforts for the events in 2006 and 2013 found that the likely trigger was brief periods of significant Barents and Kara sea ice retreat during early November. Relatively warm, open water and fragmented ice allowed high levels of atmospheric humidity to develop, while onshore winds combined with anomalously high November air temperatures led to eventual rainfall over extensive continental areas in the Nenets and Yamal-Nenets Autonomous Okrugs.

Socio-economic and ecological implications of the 2013-14 event will play out for years to come. The herders who lost their reindeer through starvation have resorted to full-time fishing in situ, while also borrowing breeding stock to rebuild their herds. In the meantime, northern Yamal pastures that are normally subject to intense grazing pressure in summer will likely experience less grazing and trampling.

Reference: Forbes, B.C., Kumpula, T., Meschtyb, N., Laptander, R., Macias-Fauria, M., Zetterberg, P., Verdonen, M., Skarin, A., Kim, K.Y., Boisvert, L.N. and Stroeve, J.C. (2016) Sea ice, rain-on-snow and tundra reindeer nomadism in Arctic Russia. Biology Letters 12(11):20160466.

Link to publication

Picture: Reindeer frozen into the snowpack in Spring 2014 (photo: Roma Serotetto)

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Herbivores affect the distribution of rare plants in alpine and Arctic tundra

Domestic sheep in Norway

Herbivores influence many aspects of ecosystems in Arctic and alpine tundra, from plant population dynamics and community composition to soil carbon storage and nutrient cycling. Herbivory is a multi-scale process, herbivores select their food at small spatial scales, but also at large spatial scales in terms of their ranges and distributions.

We have a good understanding of how herbivores affect site level dynamics, but not larger scale dynamics. Indeed, while climatic variables have been successfully used to model species distributions, biotic interactions including herbivory have been notably absent from such approaches. However, a recent study seeks to change this.

Herbivory Network members James Speed and Gunnar Austrheim from the NTNU University Museum at the Norwegian University of Science and Technology have published a paper in the journal Biological Conservation where they use a national-level data set mapping densities of all large herbivores to predict the distribution of rare plant species within Norway. The study focussed on seven arctic and alpine tundra plant species on the Norwegian Red List for species, and the main herbivores grazing in these ecosystems – domestic sheep along with both wild and semi-domestic reindeer.

Although climatic variables were the most important factor in controlling the distribution of all seven species, there was a clear signal of herbivore densities influencing the distributions. This was most notable for Primula scandinavica (Scandinavian primrose). Low densities of herbivores were associated with low habitat suitability for this species. Speed and Austrheim mapped the regions of Norway where herbivore density was the factor most limiting the distribution of each rare plant species. There was little overlap in these areas between the seven plant species. This suggests that the management of herbivore populations for the conservation of rare plant species needs to be specific for each location and plant species.

Reference: Speed, J.D.M. & Austrheim, G. (2017) The importance of herbivore density and management as determinants of the distribution of rare plant species. Biological Conservation, 205:77-84. http://dx.doi.org/10.1016/j.biocon.2016.11.030

Picture: Domestic sheep in Norway (photo: Atle Mysterud)

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HN meeting – Iceland, 2016

We had a successful meeting in Reykjavik, Iceland in September, 2016. A total of 34 HN members joined us from Scandinavia, England, Russia, Canada, and the U.S. The agenda of the meeting was to launch new collaborative projects, to strengthen the ongoing ones, and to form strategies for steering and research collaboration within the network.

During the meeting, we discussed the following projects:

  • An assessment of the functional diversity of herbivore assemblages across the Arctic led by James Speed. This work follows from the Barrio et al. (2016) data material and aims to summarize the functional groups and phylogenetic diversity of arctic herbivores.
  • A systematic review on the effects of herbivores on tundra soils led by the soil working group (Maria Väisänen, Guillermo Bueno, Maria Tuomi and Francis Brearley). This work will revise the current knowledge on the impacts of herbivores on tundra soils through literature search. A report of this workshop will be soon uploaded to the HN website.
  • Identification of data gaps in tundra herbivory research led by Eeva Soininen, James Speed and Jennifer Forbey. Eeva and James are developing a systematic protocol that aims to create a systematic map of the conducted herbivory research. Jennifer will lead a review on what kind of paradigms have been prominent in herbivory research for the last decades.
  • The assessment on the effects of historical grazing within tundra sites led by Martin Mörsdorf. In the workshop discussion on the methods in defining historical grazing effects within tundra study sites was initiated, which could be developed into a protocol during the next meetings.

At the end of the meeting we concluded that the Herbivory Network should continue to be an open, active network, where members are encouraged to take active roles in developing new initiatives and networking opportunities.

You can find the workshop report here.

Funding for this workshop was provided by:

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Experimental warming increases herbivory by leaf‐chewing insects in an alpine plant community

caterpillar

Tone Birkemoe and collaborators have recently published a paper on the effects of experimental warming on insect herbivory. Here’s Tone’s summary of their paper:

Climate warming is predicted to affect species and trophic interactions worldwide, and alpine ecosystems are expected to be especially sensitive to changes. In this study, we used two ongoing climate warming (open-top chambers) experiments at Finse, southern Norway, to examine whether warming had an effect on herbivory by leaf-chewing insects in an alpine Dryas heath community.

We recorded feeding marks on the most common vascular plant species in warmed and control plots at two experimental sites at different elevations and carried out a brief inventory of insect herbivores. Experimental warming increased herbivory on Dryas octopetala and Bistorta vivipara. Dryas octopetala also experienced increased herbivory at the lower and warmer site, indicating an overall positive effect of warming, whereas B. vivipara experienced an increased herbivory at the colder and higher site indicating a mixed effect of warming.

The Lepidoptera Zygaena exulans and Sympistis nigrita were the two most common leaf-chewing insects in the Dryas heath. Based on the observed patterns of herbivory, the insects life cycles and feeding preferences, we argue that Z. exulans is the most important herbivore on B. vivipara, and S. nigrita the most important herbivore on D. octopetala. We conclude that if the degree of insect herbivory increases in a warmer world, as suggested by this study and others, complex interactions between plants, insects, and site-specific conditions make it hard to predict overall effects on plant communities.

A popular version of the paper is available in Norwegian from this web-page: http://blogg.nmbu.no/insektokologene/2016/09/spiser-insekter-mer-planter-i-en-varmere-verden/

Reference: Birkemoe T, Bergmann S, Hasle TE, Klanderud K. (2016) Experimental warming increases herbivory by leaf‐chewing insects in an alpine plant community. Ecology and Evolution 6(19):6955-6962

Link to the publication

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Biotic interactions mediate patterns of herbivore diversity in the Arctic

herbivore diversity map

Understanding the forces that shape biodiversity is essential for improving our ability to predict the responses of ecosystems to rapid, ongoing environmental change.  In the Arctic, herbivores often play a key role in the functioning of terrestrial ecosystems.  The diversity of herbivores varies across the Arctic, and until now, no one knew whether this was shaped by physical environmental factors, like temperature, or biotic factors, such as plant productivity.

We collected information on the distribution of all 73 species of vertebrate herbivores that occur in the Arctic.  Vertebrate herbivores are particularly important as they affect the structure and dynamics of plant communities and provide food for higher trophic-level predators.  The results of this study showed that herbivore diversity in the Arctic is higher in areas with greater plant productivity and with higher diversity of predators.  The interactions between plants, herbivores and predators, occurred over large spatial scales across the Arctic, in ecosystems where patterns of biodiversity were supposed to be affected mainly by temperature variation.

Reference: Barrio, I.C., Bueno, C.G., Gartzia, M., Soininen, E.M., Christie, K.S., Speed, J.D., Ravolainen, V.T., Forbes, B.C., Gauthier, G., Horstkotte, T., Hoset, K.S., Høye, T.T., Jónsdóttir, I.S., Lévesque, E., Mörsdorf, M.A., Olofsson, J., Wookey, P.A. and Hik, D.S. (2016) Biotic interactions mediate patterns of herbivore diversity in the Arctic. Global Ecology and Biogeography 
25(9):1108-1118

Link to publication

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Quantifying muskox plant biomass removal and spatial relocation of nitrogen in a high arctic tundra ecosystem

The muskox (Ovibos moschatus), a key species in the arctic tundra, is the only large-bodied herbivore in Northeast Greenland. At Zackenberg, muskoxen can be found in some of the highest densities in the world. Consequently, a significant grazing pressure of muskoxen is expected there.

In addition, the impact on the nutrient budgets may be even larger, as herbivores tend to feed on plant parts that are rich in nutrients, and they may also redistribute nitrogen and other nutrients through defecation and urina­tion across the landscape.

This study quantify the biomass removal and nitrogen relocation by muskoxen during the snow-free period in the years 1996 to 2013 in the high arctic tundra ecosystem at Zackenberg, Northeast Greenland. By doing this, we aim at not only quantifying the muskox as a key herbivore, but also its role as redis­tributor of nutrients.

Muskoxen removed almost negligible amounts of the available forage, with under 1% during the summer. However, the muskoxen redistributed large amounts of nitrogen between vegetation types. Muskoxen at Zackenberg forage mainly in the graminoid-dominated areas, but defecate primarily in Salix snowbeds, resulting in net nitrogen transfers from the nitrogen-rich wet habitats to the nitrogen-poor, drier habitats in the same magnitude as the dissolved inorganic nitrogen pool in similar arctic soils. Hence, while the quantitative impact of muskox biomass removal seems negligible, its role as a nitrogen carrier in a nitrogen limited ecosystem is likely to have a significant impact on tundra communities. The results thus stress the central role of muskoxen in the tundra ecosystem.

Reference: Mosbacher JB, Kristensen DK, Michelsen A, Stelvig M, Schmidt NM.  (2016) Quantifying muskox plant biomass removal and spatial relocation of nitrogen in a high arctic tundra ecosystem. Arctic, Antarctic, and Alpine Research 48:229-240

Link to publication

Picture: Muskox grazing (photo: Jesper Mosbacher)

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HN workshop – ITEX 2015

Open Top chamber from the ITEX site in Auðkúluheiði

We organised a workshop on herbivory during the 21st ITEX meeting in Uppsala. The aim of the workshop was to discuss the impacts of herbivory, both by vertebrate and invertebrate herbivores, within experimental warming manipulations. Discussions were guided by an outline that was made available to participants before the workshop. As a result of the workshop we are now working on a draft on current knowledge and future challenges in understanding the role of herbivory in modulating the responses of tundra plants to warming, with a special focus on integrating herbivores into warming experiments. The workshop was organized by Johan Olofsson, Isabel C Barrio and Ingibjörg Svala Jónsdóttir.

Workshop agenda – Friday Sept 18, 2015 (10:00 – 12:20)

10:00 Herbivory in the Arctic, the past, the present and the future? Johan Olofsson
10:20 Herbivory in ITEX: standardized protocols and progress since last ITEX meeting. Isabel C Barrio
10:25 Presentation of the workshop: plan and expected outcomes
10:30 Coffee break
10:40 Discussion groups
12:00 Wrap-up and conclusions
12:20 Reporting to participants in other workshops
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Arctic Biodiversity Congress 2014

ABC 2014 meeting and conference session

The Herbivory Network organized a side meeting and chaired a scientific session during the Arctic Biodiversity Congress in Trondheim, in December 2014.  The aim of these activities was to advance the development of a general, standardized protocol for measuring herbivory in tundra ecosystems in arctic and alpine environments, and to strengthen communication with the Circumpolar Biodiversity Monitoring Program (CBMP).

Side meeting

The side meeting identified the main challenges in the development of a general protocol to measure herbivory and established the next steps for achieving this goal. Overall, there was a broad agreement among the side meeting participants on the need of collaborative efforts to address herbivory questions across different sites and at different spatial scales, and thus the necessity of implementing common protocols to monitor herbivory and its impacts on tundra ecosystems.  Two main overarching research questions will guide the development of the protocol:

  • QUESTION 1. How do herbivores affect tundra vegetation? What causes temporal and spatial variation in the outcomes of plant-herbivore interactions?
  • QUESTION 2. How do herbivores modulate the responses of tundra vegetation to environmental change?

Scientific session: “How to approach collaborative research on herbivory: an ecological interaction of key importance”

The scientific session included expert talks focusing on main groups of herbivores in these systems (i.e. mammals, birds, insects), long-term ongoing monitoring efforts and comprehensive monitoring programs, and a final round table discussion.

  • The Hudson Bay Project – 20 years of collaboration to characterize the effects of goose herbivory in Hudson Bay (Ken Abraham)
  • Registering mammalian herbivory in plant communities (Kari Anne Bråthen)
  • Arctic insect herbivory: current knowledge and future directions (Toke Høye)
  • Herbivory and the Circumpolar Biodiversity Monitoring Program (Jason Taylor)

You can find the meeting report here.

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