Browsing through the site stats recently, I came across a string that someone had used to find our site: that string was “how many plants and animals do we need”. And I realised that the question embodied in that string is a fundamental part of all the discussion about biodiversity in the public sphere. There’s a perception that insistence on the importance of biodiversity is a lot of tree-hugging nonsense, perhaps because the broader public don’t really understand why it’s important.
So how many plants and animals do we need? Well, for starters, we need the ones we eat, and the ones they eat. We also need a certain amount of plant life to maintain a decent balance of oxygen in the atmosphere, to anchor the soil and prevent wind or water from blowing or washing away all the soil needed by our crops, and we need the small organisms in the soil to aerate it and turn waste into nutrients (otherwise we’d be hip deep in cow dung and veggie scraps).
The question behind the question is, do we need all the rest? Do we really need lots of different varieties of trees and grasses? Do we need all those fish and sharks and cephalopods? Do we need all the ugly animals as well as the big impressive ones and the small cute ones?
You can probably tell that I’m going to say yes, we do need them. But it’s not only because I’m a soft-hearted tree-hugger – we really do need them. Why?
Well, an ecosystem is something like a house of cards: once it’s established, pulling the wrong card can collapse the whole thing. A previous post about sharks contains several examples of this, where plunging shark numbers had devastating effects on mollusc or fishing industries, and could even affect the amount of oxygen available for breathing.
Biodiversity can even benefit the food industry. Monoculture (large expanses of a single crop) makes the crops vulnerable to pests and diseases, as there is an infinite (from an insect’s point of view) amount of food available, so they will just feed and breed until the food runs out. In order to prevent this, huge amounts of pesticides are sprayed, which inevitably make their way into the water table and the ocean. As an alternative, polyculture, by reducing the amount of any given food for a pest within a certain range, prevents these plagues, and thereby reduces or avoids the need for pesticides.
So we definitely need some biodiversity. But how much? That’s very much a ‘piece of string’ question: we have no way of knowing which parts are vital until that part is lost and things go badly wrong. The precautionary principle would definitely suggest that we try to maintain as much biodiversity as we can, since while the effects of localised pest plagues or fisheries die-offs are bad, each catastrophe makes the larger ecosystem more vulnerable.
Biodiversity: it’s not just a good idea, it should be the law.