The final word on why biodiversity loss is bad

by Luigi Guarino on June 8, 2012

There’s a pile of papers on my desk. In a corner of my desk, actually, where I don’t have to look at them too often. Here are their titles:

I just added one yesterday: “Meta-analysis at the intersection of evolutionary ecology and conservation.” You’ve spotted the trend, right? I was planning to write about the whole bunch of them together, a mega-post on the latest thinking on the relationship between biodiversity on the one hand and ecosystem health on the other. They’ve been there for months. I just haven’t been able to get round to them, what with one thing and another. Like work, mainly. And maybe a bit of laziness.

But there’s an upside to prevarication. You wait long enough to do something, if the thing is really important, you’ll find someone does it for you. And so it has proved on this occasion, because “Biodiversity loss and its impact on humanity” has just come out in Nature, and it provides a comprehensive review of the sort of papers that have been sitting in that corner of my desk, lots of them, going back years.

Which means all I need to do here is further summarize the already admirably succinct synthesis that the authors provide.1 And that I think I can do in a few bullet-points:

  • Loss of biodiversity (really loss of diversity in functional traits) decreases the efficiency and stability of ecosystems.
  • The impacts of biodiversity loss on ecosystem functioning are big, accelerating and predictable.
  • Biodiversity is predictably positively correlated with the provisioning of some ecosystem services, but the data in the case of other services is either mixed, insufficient or runs counter to expectation.

And yes, the dataset included crops, and here’s the snippet of the summary table that deals with agrobiodiversity and ecosystem services:2

No doubt about the importance of genetic diversity to yield, though surprisingly mixed results for species diversity. But look at the numbers of data points involved (N): 575 data syntheses (DS) for genetic diversity and 100 for species diversity. Makes that pile of papers I’ve been avoiding look rather puny. And me not just a bit lazy.

Footnotes:
  1. Apart from maybe also sending you to Mongabay.com for their take. []
  2. “Data presented here are summarized as follows: green, actual data relationships agree with predictions; yellow, Data show mixed results; red, data conflict with predictions. Exp, experimental; N, number of data points; Obs, observed; SPU, service providing unit (where natural enemies include predators, parasitoids and pathogens).” []

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Dave Wood June 8, 2012 at 6:22 pm

Luigi: I think these people (often the same sets) are looking in the wrong place. For example, the claim that “High plant diversity is needed to maintain ecosystem services” is not so in the real world. For example, plant and animal diversity collapses towards the poles yet the efficiency (what does that mean?) and stability of the ecosystems cannot be questioned compared to the fragility of tropical forests and coral reefs (and look at the fisheries productivity of cold seas). And look at the interface between land and water. Here monospecific stands bear the brunt of ecosystem services – mangroves, Pacific kelp; Spartina, marram grass and lots more in marine conditions, and reed beds in freshwater, filtering sediment, land-building, and purifying water. And then there are the fire climaxes: gorse, Imperata, Eucalyptus, and then invasive species – Eichhornia, Bromus tectorum, Leucaena and lots more; and plantation forestry, where introduced trees mimic the natural monodominant stands in the regions or origin – Caribbean pine in Australia, Eucalyptus in South America; and then all the monodominant palms – Euterpe, sago, Bactris.

These provide ecosystem services without benefit of diversity and sometimes food and/or timber. Why should the emphasis always be of trying to show some very small benefits of diverse ecosystems when there are very many ecosystems – often `marginal’ that work well on a biological shoestring.

The proponents of “It has to be biodiverse to get ecosystem services” are looking (always and deliberately) in the wrong place. Further, some of these attempts are linked to thrusting species-diverse `agroecology’ down the throats of farmers in developing countries (don’t get me started on that).

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