Why do we need biodiversity?

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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.

[Featured image: Blue Starfish (Linckia laevigata) resting on hard Acropora coral. Lighthouse, Ribbon Reefs, Great Barrier Reef. Image by Richard Ling, licensed under Creative Commons v. 3.0]


  1. Good job! It also helps professionals involved in the study of biodiversity to understand the extend of gap between them and those who does not know much about ecology.

    1. Many thanks, Igor. It would be nice if the importance of maintaining diversity was more widely recognised, but since it’s not, we have to do what we can. And as you say, any means that help to bridge that gap will help.

  2. Part of me suspects that some of the more vicious critics of “tree-huggers” are motivated by the same sort of religious fanaticism that motivated the arsonists who destroyed the Library of Alexandria and the Wahhabists who recently destroyed libraries in Mali. If the finches of the Galapagos Islands had been exterminated, would Darwin have had his insight (yeah, yeah, Wallace… I know).

    The “God of the Gaps” is easier to maintain when there are more gaps. And yes, I am a cynic… why do you ask?

    1. There’s certainly something in what you say, B^4. If your whole world view depends on biodiversity being unimportant, then you may get very vehement about saying so.

      Cynic? Sadly, more of a realist, I think. Sometimes I find it hard to sustain the sunny and hopeful demeanour that’s required in order to keep trying to get the word out.

      But I take heart that, as with other societal and economic issues, years and decades of patient work is bringing these issues into the public consciousness, and getting acceptance in more minds. Biodiversity and climate change are at least now well-known and talked about, whereas in the past they were the preserve of a self-selecting few.

      And this one particular issue tends to make itself known: fisheries, for instance, are becoming aware of what happens when you knock one species out, and our state (South Australia) has been re-invigorating previously concreted creeks and rivers by planting local reed species and saltbush etc., to rebalance the native wetland habitat (there are some major issues with our main water source, as it flows through several states, but that’s a whole other kettle of fish).

    1. Hi Wanxin, and thanks for your comment – it’s very flattering that you like my work. I’ll answer your points one at a time, I think.

      Firstly, I used the expression “not just a good idea, it should be the law” mainly because it echoes a common English usage that comes from a humorous poster that said “Gravity – it’s not just a good idea, it’s the law”. This was a joke based on the different usage of the word ‘law’: we use the word to refer to physical laws that govern the universe and to legal laws that govern our societies.

      Secondly, when I said that “we have no way of knowing which parts are vital until that part is lost and something goes badly wrong”, I wasn’t quite accurate. We *do* have some ideas about what’s vital, but we don’t really know how much destruction is too much, at least until after it’s happened and there’s a crisis. But the next sentence strongly recommends that we try to avoid destroying anything, if possible: the precautionary principle basically means we should do nothing that *might* cause harm. So it’s up to those who think it’s harmless to prove that’s the case, not the other way around.

      Biodiversity is a very complex issue: there are about 8 1/2 million species on Earth, and they have complex relationships. Think of the ecosystem as a web – each animal or plant has a relationship to lots of other animals and plants, and they in turn have relationships, and so on. Plants need water, sunlight, and particular temperatures and soil conditions to grow, as well as wind or birds or fire to distribute their seeds and worms and other soil creatures to compost and aerate the soil. Animals eat plants or other animals, and need particular temperatures or air pressure to live and breed. Ocean creatures need a particular concentration of salt in the water, as well as different levels of water pressure.

      In short, everything depends on everything else, and, like the house of cards I mentioned, taking one small species out of the system can have a large effect. You might want to read this post (https://biodiversityrevolution.wordpress.com/2013/04/19/henry-fords-biggest-mistake/), about how Henry Ford’s rubber plantation failed because he didn’t take account of biodiversity, or this one about what happened when shark numbers were reduced: https://biodiversityrevolution.wordpress.com/2012/11/20/sharks-who-needs-them/

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