Some thoughts on ecology, evolution and economics

Wearing out the fabric

The fourth of five fundamental theories in ecology that I outlined in my last post states that landscapes – and the services they offer us -will wear out if too much natural habitat is removed.  The actual percentage of the landscape that qualifies as “too much” is up for debate. The original “percolation theory” simulations suggested a very precise 40.72% of natural habitat can be lost without making it difficult for species to cross the landscape.  The actual point at which we have worn out the fabric of the land so that it starts to have economic costs is harder to estimate.

imagesThe answer comes in two parts:
1) How do  native species  perceive the landscape as they try to move across it and allow their  population to survive? and
2) How do the species combine to offer ecosystem services that we ultimately depend on for fluids, fresh air, food, fuel and fibre?

We will not deal with the second part of the answer in this post any more than to say that ecosystem services are more valuable when they are closer to large groups of people and that, as we have discussed before, a greater diversity of species is better at providing these services.

As for the first part of the answer, each species perceives the landscape differently. In particular, they differ in their:

specificity – some species need a very special combination of circumstances to survive.  These species will always view the landscape as fragmented and will likely be rare.
mobility – even large gaps in the landscape can be overcome with rapid and safe movement (e.g. flight)
wariness – some species give human activity a wide berth – for example, they may be sensitive to noise. This inevitably makes the landscape more fragmented for them.
reproduction – species that can reproduce quickly (short generation times and large families) can make the most of the relatively few opportunities to move across a fragmented landscape.

It is the distribution of these properties among the native species of an area that determines how much fragmentation the landscape can withstand.  A recent international meeting called for the protection of 17%  of natural land (leaving 83% for some development) in all countries by 2020 (and 10% of the water). Reed Noss and his colleagues argue that politicians and their staff consistently underestimate the  proportion of land needed to maintain nature.  They suggest that 50% would be much more sustainable. They forget that the international agreement also calls for these reserves to be “well connected”.  If taken seriously, such a measure would easily protect 25% or more of the landscape, taking in all the connecting bits.  Ecologists should strive to give those politicians the information to make a sustainable fabric from the cloth that we have been given.

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