Sometimes scientists work in a lab, under carefully coordinated conditions finely tuned to elicit certain reactions from whatever they’re studying. Sometimes, they work in the field, under whatever circumstances nature serves up when they happen to be outside, observing, measuring, recording, and sweating or shivering, depending on the day.
Ecologists are interested in how the natural world works – lab experiments can fill in the details, but they (by definition) don’t include all of the variables that are actually at play in the real world. Field observations can flesh out the big picture, but without control over environmental dynamics, researchers often can’t be sure which factors are responsible for observed changes.
One way to balance the strengths and weaknesses of these two approaches is to move the lab outside – which is just what two researchers from the Netherlands Institute of Ecology did when they wanted to investigate the way nutrients and plant-eating ducks affect aquatic vegetation, as reported recently in the journal Oecologia.
The scientists combined the benefits of a controlled setting – they used 20 man-made ponds in their experiment, all the same size, shape, and depth – with the advantages of working in a natural system: they filled the ponds with lake water and exposed them to the daily rhythms of weather and sunlight by working outside.
The researchers fertilized half of the experimental ponds with extra nutrients, and introduced ducks – which eat mainly plants, though they also consume insects – to half of each type of pond (fertilized and unfertilized). By the end of the experiment, the fertilized ponds with ducks had 50% less plant material than the fertilized ponds without ducks, but in the unfertilized ponds, the ducks didn’t appear to have eaten any of the aquatic plants. The scientists suspect that this may have been due to plant nutrient levels – the plants in the fertilized ponds contained more nutrients than the ones in the unfertilized ponds, which could have made them more appetizing to the ducks. The fertilized ponds also developed a different plant community than the unfertilized ponds – perhaps the most prevalent plant in the fertilized ponds simply tasted better, from the ducks’ perspective, than the plant that came to dominate the unfertilized ponds.
“In our study,” the scientists write, “the effect of plant species and pond nutrient status cannot by fully separated and the relative importance of plant species and plant nutrient concentrations in determining grazing pressure thus remains to be investigated in more detail.” Therein lies the challenge of experiments conducted in natural settings – when all factors cannot be controlled, it’s difficult to tease apart which ones are most important.
Field and lab studies both have advantages and drawbacks, but, luckily for science, not the same ones – fieldwork and lab work are two sides of the same coin, complementary tools that scientists can use to puzzle out the mysteries of the natural world.