KNO9: Herbivory in the Arctic – understanding large-scale patterns and processes of a key ecological interaction

Date: Tuesday October 9, 2018

Location: Kero, Lappia Hall

Time: 15:00-16:30

Ongoing changes in the composition of plant and herbivore communities in northern regions are likely to have a large impact on the dynamics of arctic ecosystems, their ability to respond to changes, and the livelihoods of northern people who hunt or herd herbivorous animals. Even though plant-herbivore interactions have long been studied in the Arctic, the general finding is that the role of herbivory depends on where and when it takes place. Given the importance of herbivory and the context-dependency of the outcomes of this interaction, there is a need of pan-arctic efforts in data collection and development of data layers that are comparable at a biome-wide scale. Since its establishment in 2014, the Herbivory Network has worked towards addressing the role of herbivory in Arctic and alpine ecosystems, and developing new approaches to harmonise research efforts. This session will include presentations illustrating central achievements of the Herbivory Network and recent developments in the field of Arctic herbivory. The presentations will emphasize and discuss possible ways to consolidate collaborative research on herbivory to understand the relevance of this ecological interaction at a biome-wide scale.

Chairs: Isabel C. Barrio, Agricultural University of Iceland; Eeva Soininen, UiT – The Arctic University of Norway

Format: Series of presentations followed by discussion

  • Biome-wide patterns and drivers of Arctic herbivores functional and phylogenetic diversity: Eeva Soininen, UiT – The Arctic University of Norway pdf
  • Establishing baselines for future monitoring of invertebrate herbivory in the Arctic: Isabel C Barrio, Agricultural University of Iceland pdf
  • PanArctic variation in anti-browsing defense in tundra dwarf birches: Elin Lindén, Department of Ecology and Environmental Science, Umeå University pdf
  • Drivers of vegetation change in the high Arctic: Virve Ravolainen, Norwegian Polar Institute 
  • It takes two to make plants produce defences: Tundra herbivores create heterogeneous landscapes in palatability: Katarina Inga, Arctic University of Norway in Tromsø  



Biome-wide patterns and drivers of Arctic herbivores functional and phylogenetic diversity

James Speed, NTNU; Eeva Soininen, UiT

Understanding the forces shaping biodiversity patterns, particularly for groups of organisms with key functional roles, will help predict the responses of ecosystems to environmental changes. Recent efforts of the Herbivory Network have evaluated the relative role of different drivers in shaping the diversity patterns of vertebrate herbivores, a group of organisms exerting a strong trophic influence in terrestrial Arctic ecosystems. In order to better relate biome-wide patterns Arctic herbivore biodiversity to ecological and evolutionary processes, we have assessed functional and phylogenetic diversity in addition to species diversity. Ecological processes, in terms of trophic interactions with plants and predators had a central role in determining biogeographic patterns of the herbivore guild. Hence, rapid ongoing environmental changes in the Arctic are likely to affect herbivore diversity through impacts on both primary productivity and changes in predator communities via range expansion of predators from lower latitudes.


Establishing baselines for future monitoring of invertebrate herbivory in the Arctic

Isabel C Barrio, Agricultural University of Iceland

Invertebrate herbivores depend on external temperatures for their growth and metabolism, and as temperatures in tundra ecosystems increase, the rates of invertebrate herbivory are expected to increase. However, little is known about the current levels of invertebrate herbivory in tundra, and we are missing critical information to evaluate future changes. Recent efforts to describe the baseline level of invertebrate herbivory have assessed leaf damage for a single plant species across the Arctic, and at the plant community level. Data were collected using standardized protocols at a large number of sites across the tundra biome. Results suggest that invertebrate herbivory is prevalent across the tundra biome but occurs at low intensity. Local drivers, rather than large scale climate patters determine the intensity of invertebrate herbivory at the community level, but large-scale relationships with temperature and precipitation are evident when looking at a single host plant. Establishing baselines will help monitoring efforts and our ability to detect changes in a main biotic interaction in tundra ecosystems. In addition, parallel efforts are needed to determine the status and trends of invertebrate herbivore species, a main knowledge gap identified in the upcoming State of the Arctic report by the Circumpolar Biodiversity Monitoring Programme (CBMP).


PanArctic variation in anti-browsing defense in tundra dwarf birches

Elin Lindén, Department of Ecology and Environmental Science, Umeå University; Mariska te Beest, Copernicus institute, Utrecht University; Maja Sundqvist, Umeå University; Johan Olofsson, Umeå University; et. al.

Shrubs are currently increasing in the Arctic. A warmer climate is probable the main driver of these vegetation changes, but there is regional variation in shrub increase not solely explained by climate. Herbivory is also a key factor regulating the density and extent of tundra shrubs. Additionally, regional variation in anti-browsing defense, i.e. various deterrent and/or toxic compounds, is hypothesized to control the herbivory pressure and thereby affect shrubification patterns. Dwarf birches are found throughout the tundra biome, and are often the dominant shrub. They can be divided into two functional groups based on their anti-browsing defense: Resinous (better defended) and non-resinous (lesser defended) birches. By biome-wide sampling, this study investigated the panArctic variation in anti-browsing defense within and among the different dwarf birch types and taxa. Resinous birches had indeed in average higher concentrations of toxic terpenes than non-resinous shrubs. However, the ranges in chemical composition were overlapping and neither functional groups nor taxa are sufficient to understand the variation in defense compounds within dwarf birches. This gives a more nuanced description of how the anti-browsing defense of arctic dwarf birches varies and can increase our understanding of how plant-herbivore interactions will affect the greening of the Arctic.


Drivers of vegetation change in the high Arctic

Virve Ravolainen (Norwegian Polar Institute), Ingibjörg Svala Jónsdóttir (University of Iceland), Eeva Soininen (UiT – The Arctic University of Norway), Mads Forchhammer (University Centre on Svalbard), René van der Wal (University of Aberdeen), Åshild Ø. Pedersen (Norwegian Polar Institute)

Current knowledge on vegetation change in the high-Arctic suggests short- and long-term climatic forcing is linked with herbivores. Using Svalbard as a case study we outline conceptual models that can guide future ecosystem-based, adaptive monitoring and ecological studies. In the High-Arctic, moist habitats dominated by either mosses or herbaceous plants are those expected to change most strongly and rapidly. Typically, these habitats function as hot spots of primary production and plant and herbivore diversity. The current warming of the Arctic may drive these habitats towards a dominance of herbaceous plants facilitated by herbivore foraging. Specifically, combined with the disturbance from herbivores, the climate impact can increase soil temperature and permafrost thaw depth and change hydrology. In extreme cases of disturbance, open patches with degraded vegetation cover develop. The likely additive effects of herbivores and warming climate may drive the whole ecosystem from a moss-dominated, cool soil, shallow permafrost, slow nutrient cycling system towards a herbaceous-dominated ecosystem with warmer soil, deeper permafrost and faster nutrient cycling system. This turns the tundra from being a carbon sink to a carbon source. We also discuss how to improve spatial organization of monitoring such that herbivore and vegetation characteristics are taken into account.


It takes two to make plants produce defences: Tundra herbivores create heterogeneous landscapes in palatability

Katarina Inga (Arctic University of Norway in Tromsø), Matteo Petit Bon (UiT The Arctic University of Norway & UNIS The University Centre in Svalbard), Freja Fagerholm (UiT), Tove Aagnes Utsi (UiT), Kari Anne Bråthen (UiT)

The research addresses the effect of herbivores' capacity to modify nutrient concentrations in plants. In turn the composition of the nutrient concentration in the plant can affect other plants abundance. The study is conducted in the reindeer migratory- and summer grazing range and is therefore a part of the Sámi cultural heritage. The combination of different sized herbivores in the area gives insight of the effect of both the long- and short-time effects of the herbivores' population dynamics. The plant’s nutrient concentration responses are dependent on which herbivore is present in both space and time. Hence, it includes biodiversity in managed areas (reindeer herding) and the resilience and adaptations to fluctuations in different mammalian populations and the cumulative effects of land-use. Our findings are important to better understand the variation in the landscape and that the effect of disturbance in one area do not only have one direction. Silica-rich grasses have low palatability and are often abundant in pastures. Herbivory can trigger silica accumulation in these grasses, decreasing their palatability. However, in the tundra herbivory does not induce silica accumulation in grasses, indicating herbivory may rather keep silica-rich grasses in younger stages, preventing their silica accumulation. Here we address these opposing ideas in tundra grasslands, where both small rodents and reindeer are common herbivores. Applying a methodology that enabled us to assess temporal and spatial dynamics in both leaf silica and nutrient concentrations, we found herbivory to both increase and decrease the palatability of silica-rich grasses, embracing both ideas. Either herbivore alone caused increased palatability of the silica-rich grasses. Reindeer summer activity caused silica concentrations to be lower, whereas nutrient concentrations rose in response to small rodent winter disturbance. However, the combined grazing by both herbivores caused silica accumulation and nutrient concentrations to decrease, reducing palatability of the silica-rich grasses. Our results show that, rather than driving the palatability in one direction or having no effect, herbivores and silica-rich grasses are interacting in ways that create a fine-scaled mosaic of palatable states in tundra grasslands.

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