SCENIC – Scaling the effects of niche and ecological interactions on species coexistence

Niche and coexistence are two overarching concepts in Ecology and Evolution. As such, they are part of a wide variety of phenomena, and have also been defined in multiple ways. Virtually each ecological and evolutionary subdiscipline uses a different running definition of these two terms, with larger differences as the focus of these disciplines changes in biological, spatial and temporal scale. This implies that understanding the intricate relationship between niche and coexistence requires working at multiple scales of work, seeking for commonalities between definitions, and identifying which elements can be transferred (or translated from one scale to another), and how. Previous work from project UNITED allowed reaching a preliminary understanding of how niche-driven responses to gradients acting at different scales interact with each other and influence the outcome of local interactions, thereby influencing the outcome of natural selection in local communities. SCENIC seeks to extend this initial body of theory from the succession-like dune plant communities and the simple experimental moss communities studied in UNITED, to other systems and biological, temporal and spatial scales. The main objective of SCENIC is to assess how niche-mediated species responses to environmental gradients acting at different scales and biotic interactions determine the ecological and evolutionary consequences of coexistence. We will (a) explore the implications of coexistence at different levels and for a diverse array of study systems; and (b) improve the experimental approaches used by UNITED to evaluate some of the hypotheses derived from the project, and obtain a deeper understanding of the influence of species and individual niches on community processes. To do this, we will study the effects on coexistence on two key ecological features, niche and interactions across different levels of organisation (local communities, metacommunities and entire regions) and from ecological, evolutionary and biogeographical perspectives, using two complementary approaches: top-down (Subproject 1) and bottom-up (Subproject 2).

Subproject 1: Finding generalities from the pleiad of contingent evidences coming out from bottom-up ecological research has been elusive. This Subproject will use a top-down perspective (i.e. from regional to local communities, species and finally individual responses) to explore the effects of co-existence and interactions on niche-driven responses of species and individuals and the outcome of natural selection at multiple scales, from macroecological and macroevolutionary patterns to metacommunity dynamics and (micro)evolutionary processes. We will use existing data (complemented with additional surveys and/or experiments when necessary) and develop specific experiments to understand how coexistence may modify realized niches (i.e. niche-driven responses) and ultimately trigger niche evolution. That is, how ecological interactions can affect the fundamental niche. SCENIC aims to advance further the theoretical framework developed by UNITED, through four overarching objectives: (1) Determine the effects of co-occurrence on niche evolution and species distributions at large spatial and temporal scales; (2) Assess the effects of spatial and temporal (meta)population dynamics on niche-mediated responses; (3) Understand the role of local interactions on the selection and evolution of niche characteristics; and finally (4) advance the theory on the role of niche and interactions on species coexistence and evolution under realistic scenarios of natural selection. These objectives will be achieved through a diverse array fo analyses, experiments and models. First, we will conduct studies on macroecological and (macro)evolutionary patterns on insects, island plants, Iberian mosses and ostracod symbionts, focusing on effects happening at the level of species distributions, dispersal processes, and occupancy patterns. We will also study early successional stages of coastal Mediterranean shrubs and the influence of local and regional environmental gradients on the coexistence of holm and cork oaks along large geographical areas. In the search for understanding how natural selection operates under the influence of interactions, we will perform experiments with spider mites and rice varieties and their weeds, mimicking local evolutionary processes along environmental gradients under coexistence between relatives. Finally, we will merge theoretical models coming from UNITED with models of niche evolution based on quantitative genetics and metacommunity models. The empirical and experimental results of the both SCENIC subprojects will be used to recreate credible scenarios of natural selection, with the end objective of providing realistic models of the evolution of responses to large- and small-scale gradients when two or more relatives (species, isolines) coexist.