Can you guess what this is a photograph of?

It’s an algal bloom on the surface of a lake, seen from above. The algae are growing so well because of eutrophication due to shallow depths, low flow, and high nutrient inputs. The pattern is beautiful, but the lake itself is a mess. When I say lake, I should say river – in this case, the River Glyme, flowing through the grounds of Blenheim Palace in Oxfordshire. In the 1760s, it was dammed by “Capability” Brown as part of the park landscape.

The result is elegant (at least if you ignore the algae), but leaves much to be desired from the standpoint of ecological functionality. The lake is a pale imitation of a natural one, and the gardens require far more maintenance than the forests and pastures they replaced.

These engineered landscapes make me think of one particularly controversial area of ecology: the relationship between biodiversity and ecosystem functioning. A basic premise of much conservation biology is that more species result in better functioning, more robust ecosystems – this is one of the key reasons to fight species loss. Yet here is an example of a site with far more species than the woodland it replaced, yet demonstrably lower levels of functionality, and far more fragility. The palace is thus a counterexample. Is this phenomenon common? And if it is, does this undermine this key assumption? In support of this, Vellend et al. showed that over the past century there has actually been no systematic loss in biodiversity in local study areas. Their conclusion held regardless of what happened over that century – climate change, pollution, species invasions, introduction of grazing, fire, and so on. The one exception (unsurprisingly) was the conversion of natural ecosystems to monoculture agriculture. As ecosystems degrade, they don’t necessarily lose species. Rather it seems to be the case that species from across regions spread out, equalizing the composition of different local sites.

So what should we take away from this story? That conserving biodiversity is not useful? I wasn’t sure until I walked through the grounds of that palace. A better interpretation – the one taken by Vellend et al., is that the number of species in a site is itself not a useful indicator of functioning. The performance of these species, and their response to unforeseen changes, matters more. The high diversity of garden plants and algae at Blenheim Palace should not be our measure of functionality. Conservation to keep up species numbers will not succeed, but conservation to keep up functionality may. It is a more nuanced message, but one that more ought to hear.

(Properly defining functionality, of course, becomes the next major issue – and that will have to wait for another post.)