Biotic interactions may be more important than climate for shaping animal niches

<title>Abstract</title> <p>The response of ecosystems to ongoing rapid climate change is dependent on individualistic species response and biotic interactions 1,2. It is therefore critical to know how realised niches shift with changing climate and changing biotic interactions among species 3,4. At present, empirical niche investigations rarely include biotic niche dimensions and are limited to short time spans 5. Sedimentary ancient DNA (sedaDNA) is revolutionising our ability to study the development and dynamics of ecosystems by enabling the simultaneous identification of plants and animals from their past living environments 6,7. Here, we develop this method by combining sedaDNA from ten lakes in northern Fennoscandia with a novel compilation of regional rock-art and bone records, as well as palaeo-topography, to reconstruct animal arrival times, changes in plant–herbivore-carnivore networks, and estimate shifts in the biotic and climatic niches for key animal species over the last 16 ka. Marine fauna and tundra plants appeared soon after deglaciation, and birds and freshwater species arrived at approximately 13 ka. However, reindeer did not appear until 5 millennia later at 11 ka, and most terrestrial mammals arrived only in the last 8 ka after vegetation had stabilised. Realised climatic and biotic niches shifted with increased herbivore niche-filling, and niche-overlap increased with ecosystem complexity build-up, implying increasing herbivore interactions. Our study provides the first long-term empirical evidence that shifts in biotic interactions may be more important than climate for shaping ecosystems, and must be considered when attempting to mitigating effect of climate change.</p>