Some thoughts on ecology, evolution and economics

Consequences of biodiversity

Biodiversity is a great value for humans (see Sources of biodiversity).  Many would argue that it is even more important than that – that it is a key aspect of how ecosystems work. The logic for this is straightforward.  Species with similar body plans and lifestyles form a set of “spare parts” (often rather dramatically compared to the rivets holding an airplane together).  If you lose too many of these parts, the ecosystem stops working. The evidence for this idea has been, until recently, rather weak.  In fact, the opposite logic – that too many species would make an ecosystem unstable – held sway for a time as a result of Robert May‘s modelling results.

Two aspects of ecological science have made the importance of biodiversity difficult to study: measurement and replication.

How do you measure diversity?


Biodiversity itself is difficult to measure with a single number and so are its reputed benefits, namely stability  and efficiency. The most common measure of diversity, the number of species in an ecosystem, can be misleading.  Let’s consider a fruit bowl:

The number of species in this bowl is three.  That remains true whether there are 10 apples , 1 banana and 1 orange or a more equal representation, as seen in the photo.  An ecosystem dominated by  one species presents a different experience to the observer and likely a different set of interactions among the species than would be expected with an equal abundance of species. Fortunately, ecologists have come up with some neat mathematical ways to express the degree of dominance by one or a few species.

One ecosystem, two ecosystem, red ecosystem, blue ecosystem


The problem with replication in ecology comes from the fact that we like to study large ecosystems with a wide range of body sizes in them.  These ecosystems require much work and tend to be quite different from each other.  Many factors could explain the differences in their performance apart from the number of species in them.  The approach that ecologists have been drawn towards is studying many small field or greenhouse plots.  This allows them to make conclusions about how important the number of species is in determining how ecosystems work.

Last week, a panel of experts published a definitive review of over 600 experiments using these small ecosystems.  The publication in the journal Nature was timed to coincide with the Rio +20 meeting on managing our biosphere.  They concluded that:

1. Ecosystems with more species are more stable – at least as measured by how reliable the weight of living matter produced by the ecosystem is concerned. They conceded that it is unlikely that diversity could predict all the various ways in which stability can be measured.

2. Ecosystems with more species are more efficient – they consistently captured more of the available nutrients,water, light or prey and converted them into living matter.  This ability was not absolute, however. They noted that 65% of the time, a pure stand of the most productive species could produce more living matter than a highly diverse stand.  It is thought, however,that the diverse ecosystems will produce more over a period of decades.

3. Ecosystem services are more reliably produced by diverse ecosystems – these services; including providing food and fibre and regulating pests, climate and soil formation; are the ways that we depend on natural systems for our survival.  In 13 of 22 services examined, humans receive better yields and  less disruptions from ecosystems with more species .

Shall we conserve?


Biodiversity is clearly more than an aesthetic experience- it is literally a way of life.  As we learn our role as gardeners and herdsmen on this planet, we must not reach for the easy solution of encouraging just a handful of species and varieties to cover the land. Diverse natural groupings of species are hardy and productive.  Though we may yet find out how many rivets of life we can pry out of the biosphere’s hull before it stops working, I am confident that we will start valuing each of these as part of the whole.



Leave a Reply

Your email address will not be published.

You may use these HTML tags and attributes:
<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>