Limits of diversity
Biodiversity has generally positive effects on valued ecosystem functions. Grasslands with more plant species, for example, tend to be better at recycling nitrogen and resisting invasion. Given this relationship, conservationists often use the loss of biodiversity to assess functional responses to environmental change, such as habitat loss. Depending on the function, however, different species and their numbers matter more or less. For example, nitrogen-fixing plants provide unique functions, and many mangroves are needed to protect a shoreline. How can environmental change affect an ecosystem’s function without altering the number of species there?
Jurg Spaak, from the University of Namur, Belgium, and colleagues took a two-pronged approach, using simple mathematical models and data from existing experimental studies of freshwater systems species. In both approaches, a changing environment affected ecosystem function independent of changes in species number. In theory, small environmental changes could even lead to functional collapse. The composition of species mattered, including how mutually competitive they were. To sustain critical ecosystem functions, then, conserving biodiversity is just the beginning.
photo: dolvita108, CCO