What are the prospects for global biodiversity?

I've talked about how threatened freshwater biodiversity is and what threatens it now. In this post I want to consider the outlook for global biodiversity in the future. I don't think we are yet in a state of 'biodiversity crisis' (a term frequently used on blogs and forums) as there are still hotspots of amazing diversity on the planet. Are we heading for crisis however? If so, how quickly? 

I'll look at Jenkins' (2003) paper Prospects for Biodiversity, which has been cited 103 times. This theoretical study tackles the above questions for global biodiversity by looking at what to expect by 2050. Jenkins presents an overview of other research in the area, focusing on extinction risk and population reduction in birds, terrestrial and marine mammals and freshwater fishes, habitat losses to agriculture, forest cover and wilderness. Assumptions include around 9 billion people by 2050, that IPCC predictions on climate change hold true and that humans don't behave very differently.

A key theme is huge biodiversity losses in developing countries in tropical regions as they develop. These areas - South America, sub-Saharan Africa, Indonesia and the Philippines - have suitable forested land available for conversion to agriculture, which will be needed to feed and clothe an increasing global population. Deforestation here will take a heavy toll on global biodiversity, as many of these areas are highly biodiverse with high endemism. Developed countries on the other hand, are predicted changes in distribution of species with climate change, but a fairly stable biodiversity overall. Temperature forest cover should rise and species loss in developed farmland areas slow - but these are dependent on the current green movement retaining momentum and working long term.

A recurring element is the scarcity of large animal species, in the remaining tropical forest and in the oceans, due to resource overexploitation. Freshwater biodiversity is predicted to particularly suffer. Jenkins cites WWF Living Planet Index data from 1970 - 2000 that shows freshwater biodiversity falling far faster than marine or forest, and states that human pressures on freshwater habitats will only increase. The greatest freshwater biodiversity losses will take place in urban tropical and arid areas, mainly from pollution, overfishing and water abstraction, and even in developed countries aquatic biodiversity is still predicted to worsen, this time due to invasive species.

All in all, a rather bleak picture for global biodiversity; monumental reductions in species diversity, particularly for certain types of ecosystem or taxa. Jenkins of course points out the difficulties in prediction; extinction rates are a simple concept, but deciding what they are likely to be in future is stymied by lack of knowledge. We are ignorant of the actual species diversity out there, unable to comprehensively monitor extinction in discovered species and uncertain of how many species we may save in the future.

Perhaps the most interesting point Jenkin's makes is that the predicted shift to "biotically impoverished" habitats is not expected to cause problems for humanity. This is quite contrary to much of the wider literature which cites biodiversity as hugely important for humanity as a provider of natural services (such as nutrient recycling, flood control or carbon sequestration), having important aesthetic and cultural value and as a provider of food, building and trade resources. Have a look at this and this website, which give the classic breakdown of 'why save biodiversity'.

However, "biotically impoverished" doesn't mean no biota, just a less diverse range of species. Jenkins' point does make sense; you don't really need a wide range of tree species to soak up CO², intercept rainwater or provide timber. He suggests that ecologists have yet to find compelling evidence that wild systems are better at the above mentioned functions/values than human modified ones. A person's concept of an aesthetically pleasing environment is often not a natural one - mine is the Somerset countryside, for example, a man-made landscape with far lower biodiversity than the pre-agricultral ecosystem. If conservationists fail to show that high biodiversity is highly important for human prosperity, I imagine the prospects for global biodiversity to become even more bleak.

One aspect of biodiversity Jenkins fails to mention: it's inherent value as a 'database' of genetic information and chemical products. This must be considered as having value like an insurance policy; a high biodiversity is worth maintaining just in case humans need to use it for new medicines or genetic code in the future. Finally, is this the reason we 'need' to save natural ecosystems? A key unknown in Jenkins predictions is us - he has assumed our attitude and behavior will not change "radically". Are humans prepared to make big changes to save biodiversity 'just in case' we need it later on?

References:

Jenkins, M. (2003) 'Prospects for Biodiversity', Science, 302, 1175-7.