What are the effects of herbivore diversity on tundra ecosystems? A systematic review protocol

Abstract

Background: Changes in the diversity of herbivore communities can strongly infuence the functioning of northern ecosystems. Diferent herbivores have diferent impacts on ecosystems because of diferences in their diets, behaviour and energy requirements. The combined efects of diferent herbivores can in some cases compensate each other but lead to stronger directional changes elsewhere. However, the diversity of herbivore assemblages has until recently been a largely overlooked dimension of plant–herbivore interactions. Given the ongoing environmental changes in tundra ecosystems, with increased infux of boreal species and changes in the distribution and abundance of arc‑ tic herbivores, a better understanding of the consequences of changes in the diversity of herbivore assemblages is needed. This protocol presents the methodology that will be used in a systematic review on the efects of herbivore diversity on diferent processes, functions and properties of tundra ecosystems.<p> <p>Methods: This systematic review builds on an earlier systematic map on herbivory studies in the Arctic that identi‑ fed a relatively large number of studies assessing the efects of multiple herbivores. The systematic review will include primary feld studies retrieved from databases, search engines and specialist websites, that compare responses of tun‑ dra ecosystems to diferent levels of herbivore diversity, including both vertebrate and invertebrate herbivores. We will use species richness of herbivores or the richness of functional groups of herbivores as a measure of the diversity of the herbivore assemblages. Studies will be screened in three stages: title, abstract and full text, and inclusion will fol‑ low clearly identifed eligibility criteria, based on their target population, exposure, comparator and study design. The review will cover terrestrial Arctic ecosystems including the forest-tundra ecotone. Potential outcomes will include multiple processes, functions and properties of tundra ecosystems related to primary productivity, nutrient cycling, accumulation and dynamics of nutrient pools, as well as the impacts of herbivores on other organisms. Studies will be critically appraised for validity, and where studies report similar outcomes, meta-analysis will be performed.