Species DO Matter: New analyses confirm biodiversity and ecosystem function are linked

Biodiversity is literally the biotic richness present within species, among species and across ecosystems on this planet.  Biodiversity is declining rapidly.  When I wrote Chapter 7 of Our Dying Planet, on biodiversity loss and the Holocene Mass Extinction, I delved into the scientific evidence for the presumed link between biodiversity and the effective functioning of ecosystems.  Ecological theory holds that the level of biodiversity contributes to ecosystem resilience in the face of environmental disturbance and change, and therefore biodiversity contributes to the capacity of ecosystems to continue to provide the goods and services upon which we and other life depend.  Loss of biodiversity leads to loss of resilience and a reduced capacity to continue to produce environmental goods and services.  I concluded that while there were a number of studies supporting this theory, the available science was still too limited to make definitive statements about its correctness.  Logically, it will be quite unlikely that ecosystems will continue to operate normally if the anticipated losses of biodiversity take place over the remainder of this century, but the science could not yet say this definitively.  Despite this, I still argued that economic self-interest alone should be enough to cause humanity to seek ways of stemming the alarming rate of biodiversity loss.

Science has advanced in the couple of years since I wrote that.  Or, more precisely, substantial analyses of experimental results obtained over the past 20 years have appeared just recently.  These permit a more definitive statement than I was prepared to provide two years ago.

In particular, two important papers by a group of biodiversity researchers appeared in the journal, Nature, on 7^th June 2012.  The first of these, led by Bradley Cardinale of University of Michigan, with colleagues from 12 other institutions scattered across the USA, Canada, UK, France and Sweden, is a review assessing the impacts of biodiversity loss on humanity.  It provides a series of six  ‘consensus statements’ concerning the effects of biodiversity on ecosystem function.  The first and most important states:

“There is now unequivocal evidence that biodiversity loss reduces the efficiency by which ecological communities capture biologically essential resources, produce biomass, decompose and recycle biologically essential nutrients”.

The second is almost as important:

“There is mounting evidence that biodiversity increases the stability of ecosystem functions through time”.

The remaining four get into specific details, of which number three:

“The impact of biodiversity on any single ecosystem process is nonlinear and saturating, such that change accelerates as biodiversity loss increases”.

What this one means, in plain English, is that as biodiversity falls there will initially be little measurable effect on ecosystem function, however as the extent of loss increases the effects will mount, more and more rapidly, possibly even with the dreaded thresholds and tipping points that ecologists keep talking about with respect to climate change and other aspects of our environmental  crisis.  All the concerns I expressed a couple of years ago are fully vindicated by these statements.

And look at the wording.  These scientists have put it on the line:  there is now unequivocal evidence.  No wiggle room there.

The accompanying paper is led by David Hooper of Western Washington University with colleagues from nine other institutions in USA, Canada and Sweden (four authors, including Hooper and Cardinale, were on both papers).  These authors provide some of the key analyses supporting the Cardinale review, and focus their attention on the relative strength of biodiversity loss, versus other stressors, in affecting ecosystem function.  Their Figure 1 is complex but informative:

In this figure the thing to focus on is the thick red line backed by a gray band which shows the progressive loss in primary productivity (= photosynthesis to produce organic matter) as species are lost from the ecosystem.  The effect starts out slow when only a few species are lost, but increases rapidly as losses of species mount (supporting the third consensus statement in the other paper).  Various other data in the figure show that the effect of biodiversity loss is just as large as are effects of other known environmental stressors.

The overwhelming message provided by these two articles in a prestigious, peer-reviewed journal is that biodiversity loss definitely does matter; it matters for ecosystem function, and it matters for our well-being and quality of life.  Think about this the next time you hear that another species has been placed on the endangered species list, or the next time you realize that you have not heard a particular bird or frog species since your childhood.  Biodiversity loss is insidious in that it is all around us, but its effects creep up upon us.