| Summary: | Mosses form important ecosystems for many organisms and these systems can be referred to as the bryosphere. Invertebrates form a food web within the bryosphere and facilitate the break down of detritus and therefore play a significant role in ecosystem nutrient cycling. Trophic cascades and top-down control are important elements in community dynamics and the effects of environmental changes on trophic cascades in food webs depend on which trophic level is most greatly affected. Global warming is a present danger and could have a drastic impact on current and future ecosystems. The objective of this experiment was to determine the effects of temperature on the meso- and microfauna associated with the moss Racomitrium lanuginosum and to analyse the structure and composition of the communities within the bryosphere. The experiment was carried out in the spring of 2019 but the samples were collected in November 2018 at Þingvellir, Iceland and stored at 4°C. Seven samples were collected and split in two, one half went into an 8°C chamber and the other into a 20°C chamber. After two months the samples were taken out of the chambers and divided into two segments, the green, photosynthetically active upper segment and the brown, decaying lower segment, to study the differences between them. The experiment demonstrated that increasing temperature does have an effect on some taxa but the effects were different and not equally strong on all of them. Protists and nematodes were significantly affected by temperature and both favour 20°C over 8°C while mites and collembolas (springtails) were negatively affected by increasing temperature. Increased temperature was negatively affecting the abundance of the top predators (mites, collembolas and tardigrades), and positively increasing the abundance of first-level predators (nematodes and rotifers), while the top predators were shown to have a direct negative impact on the abundance of the first-level predators, fungi and cyanobacteria. Increased abundance in the first-level ...
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