BIODIVERSITY: DO ECOSYSTEMS “FUNCTION”

As so frequently happens, new debates resembles old ones.  In the early part of the 19^th century biologists pondered the question of function, mainly regarding anatomical parts.  While it would seem obvious that the function of a fin is to swim and the function of a wing is to fly, what of the appendix?  And could there be negative function of normal characteristics?  Is the function of the hand to grasp or to make a fist to defend oneself?  It seemed patently obvious that philosophically all one had to do was eliminate the structure and see what happens.  But deeper thinking philosophers correctly pointed out the folly of such experimentation (cutting off the hand, would we conclud the function of the hand was to keep the blood from spilling out the arm?). 

            The problem was, it seems, a failure to articulate the question properly.  To the question “what is the function of x” one must always qualify, “with respect to the desired condition y. “  And it seems rather arbitrary what might be the condition y.   The debate was largely rendered moot with the paradigmatic shift in favor of the Darwinian revolution.  Rarely does anyone seriously ask what is the function of x any longer, but the question “what is the adaptive significance of x” is the question that biologists, probably intuitively, sought to ask in the fist place.

            We are currently witnessing a growth in the idea of ecosystem function.  Yet serious questions about what that might mean are only rarely brought up.  On the one hand there are obvious functions, pollination of crops, control of pests, provisioning of nitrogen to tree plantations.  However, in all such cases the implied normative content of function is obvious, and the conundrum that is parallel with the original anatomical use of the word function is scarcely recognizable.  Yet it is there.  The implied “with respect to y” makes the original question,” what is the function of biodiversity?”, have meaning.

            There is a philosophical problem here.  Words not only have specific meaning, they also carry a halo of context, baggage so to speak, from previous usage.  In their passion to promote the conservation of biodiversity, advocates tacitly sought to leverage this context to their advantage.  If something has a function that implies that the predicate in which it is functioning is normative.  That is, we wish it to “function well” and if it is “unfunctional” or characterized as “with negative function,” we seek to “repair” it.  Using this normative aspect of function is sensible under many situations.   The switch on the wall functions to turn on the light, the light on my computer screen functions to allow me to read the text I type.  And with biodiversity, biodiversity functions to make pollination of crops more efficient, or to control pests, or to control decomposition so as to provide nutrients in a timed fashion to the trees in the plantation, or to increase the yield of the fishery.  In all such cases the predicate is clearly implied and the conundrum faced by early anatomists is resolved by admitting a normative goal.

            However, the problem returns  when talking about non-managed systems, so-called natural ecosystems -- the normative content associated with the word function again rears its head.  In evaluating the function of biodiversity  (or one of its surrogates, e .g., species richness, evenness, connectivity, etc…) in natural systems, the phrase “the function of biodiversity” becomes as curious as the phrase “the function of the appendix” originally was.  Attempts to divest function of its normative content is a fools errand.  The problem is that natural ecosystems are just there and they do not function in the same way as an automobile, or a washing machine or a farm do.  They exist.  The notion that greater biodiversity leads to faster nutrient cycling, for example, leads to the obvious question why would one want to cycle nutrients faster?  Or higher productivity (remember one of the most “productive” ecosystems in the world is a cane sugar plantation)?  In the end, claims that biodiversity contributes to this or that “function” in natural ecosystems boil down to the fact that when biodiversity changes, something about the ecosystem changes too, not exactly a revolutionary idea.