The current loss of species is orders of magnitude faster than the previously fossilised five major waves of species extinction. These species losses are largely caused by the human utilisation of natural ecosystems. The goal of the Convention on Biological Diversity (CBD) to reduce the rate of species loss has not been achieved, mainly due to the increasing stress on ecosystems. In this context, research into the relationship between biodiversity and the functioning of ecosystems (BEF) has become a dominant field of research in ecology and evolutionary research. Various fundamental questions in this field of research have not yet found a general answer. Which processes lead to the natural patterns of biodiversity? How will biodiversity react to global change and human influence at local, regional and global levels? What influence do changes in biodiversity have on functional aspects of ecosystems?

The current state of research therefore does not fully meet society's need to predict short- and long-term changes in biodiversity, the resulting consequences for ecosystem functions and scenarios for how societies can react to them. Although human land use influences the bio-geochemical dynamics of marine and terrestrial ecosystems, the mutual interaction of these dynamics across ecosystem boundaries has hardly been investigated to date. Functional biodiversity research, on the other hand, is mainly limited to a few model organisms or communities. As a result, BEF research has mainly excluded the in situ consequences of interactions, adaptations, extinctions and evolution of small organisms (bacteria to meiofauna), although these organisms contribute disproportionately to biodiversity, biomass and bio-geochemical dynamics. Similarly, relationships in ecosystems of poor accessibility such as tropical forests, soil systems and open oceans have also been ignored. Furthermore, BEF research has been limited to simple concepts of biodiversity (species number) and functionality (primary production), excluding the importance of other functional groups of species and other levels of biodiversity integration such as genetic diversity. Likewise, effects across trophic levels of the complex food webs of natural ecosystems and the interactions between multiple functional processes were not considered.

Over the last decade, BEF experiments have shown that there are positive, negative and idiosyncratic BEF relationships that vary across ecosystems and species communities. Although these experiments have documented detailed relationships for specific ecosystems, they have not been able to document general principles as to why relationships vary between ecosystems and communities. Thus, there is an urgent need to bring BEF research together with ecological theory in order to generalise the patterns. Theoretical ecology has in recent decades generated novel generalising models to understand the importance of stoichiometry (nutrient compositions), allometry (body mass distributions), food web structure and spatial distributions of species. These unbiased models enable novel mechanistic concepts of how species vary with respect to general traits and, consequently, how differences in species diversity and composition of communities translate into functional properties of ecosystems.

BEFmate will extend research through five central objectives:

• Objective 1: Understand the relationships between biodiversity and ecosystem functions across the boundaries between marine and terrestrial ecosystems
• Aim 2: To characterise the functional consequences of biodiversity loss across the tree of life and from genes to ecosystems;
• Aim 3: Fuse ecological and evolutionary aspects of functional biodiversity research;
• Aim 4: Synthesise BEF research with ecological theory on stoichiometry, allometry and food web structure;
• Aim 5: Understanding how neutral and dispersal processes influence BEF relationships in space and time.