Feeling Stressed? Biodiversity Can Help

If you’re an ecosystem, that is.

Having more species makes ecosystems better able to withstand stressful environmental conditions, according to a new study published recently in the journal Ecology Letters.

Researchers Bastian Steudel and colleagues conducted a downsized biodiversity experiment using microcosms and communities of microalgae (single celled algae that are commonly used to feed aquaculture shellfish and health conscious Californians). This is the stuff of science caricature: people in lab coats and glasses, shaking beakers growing with green goo. Cool.

When the environment in the beakers was made stressful either by making it hot or salty (not conditions that most cells like), the stressful conditions had a stronger negative effect on the miniature ecosystems with fewer species. How well the ecosystems in the beakers were functioning was determined essentially by how much the algae community as a whole was growing.

You can see the same effect in landscapes that don’t require a microscope to study:  When conditions are good the yield from crops of one species like corn or wheat can be enormous but when the going gets tough—like during hot, dry summers—these crops suffer more than biodiverse natural systems in the same places.

There is a good chance you’re wondering how relevant algae in a bunch of beakers are for studying ecosystems. Fair question. What ‘lab’ studies like this are really good for is testing a theory. In this case, the theory is that biodiversity has an effect on how ecosystems deal with stressful conditions. To help demonstrate a theory you need to rule out other potential explanations by controlling as many sources of variation as possible except those that you are testing—in this case environmental stress—something you simply cannot do robustly in the field.

Imagine trying to find somewhere to look at algal communities where every aspect of the environment was the same except the temperature…impossible. What lab tests are not good for is parameter estimation. In other words, knowing how big the effect of biodiversity on ecosystem function is. This can only be measured in the field because all those other variables that we control in the lab do in reality interact with biodiversity and the overall effect is the combination of biodiversity and all the other environmental differences experiences by ecosystems.

So why does having more species help ecosystems function better in stressful environments? More species increases the likelihood of having some species that are more tolerant of these harsh conditions, some species might even benefit from the decreased performance of other species and be able to increase faster, and some species might even modify the environment making it less harsh for other species. Probably all of these happen.

Could Steudel and colleague’s results simply be explained by one or two salt and heat tolerant species that end up in the beakers with more species? Well, their experimental design, involving nearly 3,500 beakers, controlled for this well—hence the value of a lab experiment.

Although the beaker is quite literally a different world than what The Nature Conservancy and other conservation organisations work in, these results are still relevant for conservation. Environments are becoming more stressful. Much of the effort of the Conservancy and many other conservation groups and agencies has been dedicated to retaining biodiversity in landscapes. The justification for this has rested as much on value judgements as it has on science (which is fine), but studies like this are like a concrete foundation—they greatly strengthen the structure above it.

(Image: drought-stressed corn. Source: Flickr user _-0-_ via a Creative Commons license.)

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