The current rate of change in biodiversity has triggered major research efforts on biodiversity-ecosystem function (BEF) relationships. Current knowledge, however, only partially meets the societal demand for scenarios on how biodiversity will change over the short- and long-term, how these changes will affect ecosystems and their services and how society can adapt to or mitigate the changes. Although human domination of the Earth’s ecosystems affects the chemo- (the cycles and ratios of elements) and biospheres (biodiversity and composition of organisms based on their evolutionary history) of both marine and terrestrial systems, the interrelationship between these changes across ecosystems has rarely been studied simultaneously. Instead, functional biodiversity research is typically restricted to those few model organisms or communities that are easily accessible, either in the field, for experiments or for cultivation in the lab. Thus, BEF research has largely ignored the in situ consequences of the interaction, adaptation, replacement, extinction risk and evolution of small organisms (bacteria to meiofauna) despite their over-proportional contribution to global species richness, biomass and matter cycling. The same holds true for organisms in habitats of low accessibility (e.g., tropical forest canopies, soils in general or open-ocean systems). Moreover, BEF research has focused on simple concepts of both biodiversity (species richness) and function (mainly primary production), which does not reflect the importance of other organisational levels of diversity (e.g., intraspecific genetic diversity, dominance, habitat diversity, effects across trophic levels in the complex food webs characterizing natural ecosystems and of the interaction between multiple processes and functions within ecosystems.

Over the last decade BEF experiments have unraveled positive, negative or idiosyncratic patterns for different communities and species groups. While these approaches provided detailed predictions how changes in species richness may affect the functioning of specific ecosystems, a more general understanding of BEF relationships and why they differ across communities and ecosystems remained elusive. This illustrates an urgent need to synthesize BEF research with ecological theory that generalizes patterns and processes. Over the last decades, substantial theoretical progress was achieved in the understanding of the stoichiometric, allometric (i.e., body size), food-web and spatial structure of species communities. These independent bodies of theory provide an unprecedented mechanistic understanding how species differ according to these general traits, but systematic synthesizes with BEF models and experiments is still lacking.

BEFmate addresses these challenges by formulating five major goals:

• Goal 1: Understanding biodiversity-ecosystem function relationships across marine and terrestrial ecosystems.
• Goal 2: Assessing the functional consequences of biodiversity change across the tree of life and across the entire range of biological organization from genes to ecosystems.
• Goal 3: Merging ecological and evolutionary aspects of functional biodiversity research
• Goal 4: Synthesizing BEF research with ecological theory on elemental stoichiometry, species' allometry, and food-web structure.
• Goal 5: Unraveling how neutral and dispersal processes affect BEF relationships in space and time