The role of biodiversity in ecosystem functioning is well understood on the small scale of experimental studies, but has proved challenging to quantify on the scale of natural systems. Working with a paucity of locations that are sufficiently pristine to host investigations does not help. One such natural laboratory is the Chagos Archipelago in the Indian Ocean. Writing in Nature Ecology & Evolution, Cassandra Benkwitt and co-authors set out to study how biodiversity and ecosystem functioning co-vary among the coral reefs of these remote islands (https://www.nature.com/articles/s41559-020-1203-9).
Specifically, they measured two metrics for ecosystem functioning – biomass and productivity – in fish populations, and compared this to species diversity. Biodiversity was strongly correlated with both measures of ecosystem functioning.
Importantly, these close links were maintained, even when the reefs came under stress from two distinct instances of human-induced change: coral bleaching from an extreme heatwave and the effects of non-native rats, which have infested some islands but not others. The bleaching directly reduced fish biodiversity in the reefs. The rats, on the other hand, diminished seabird populations by eating eggs and preying on chicks, which in turn reduced the deposition of guano and hence the transport of nutrients to the waters and the reefs. In both cases, although ecosystem function was still reduced either directly or indirectly by anthropogenic stresses, the pattern remained that greater biodiversity was coupled to greater ecosystem function.
If we hope to mitigate our impact on the natural systems of this planet, maintaining biodiversity should be a key priority, alongside a reduction in the sources of human-induced environmental change.