||[Jan. 11th, 2009|10:49 pm]
The science of complexity and related research
This article which describe how the herbicide Atrazine and phosphate runoff harm frogs in the US, paints a picture of a bewildering mesh of effects, which required detailed experiments to uncover.|
Atrazine is known to kill off pickerel frogs directly, but for the declining northern leopard frog of Minnesota, the story turned out to be more complex. Researchers quantified more than 240 separate environmental factors, finding a strong correlation between atrazine and parasite infections in the frogs. But a correlation isn't the same as cause and effect, so experiments were needed.
What the researches found, were that atrazine weakened the immune system of frogs, as had also been shown earlier. But both atrazine and phosphate runoff caused more algae to grow, which became food for snails, boosting their numbers. The snails are for a short time a host for the trematode parasite, which later tries to infect frogs and their tadpoles. Indirectly, atrazine therefore boosted the number of parasites in the water. So did phosphate, but it was only together with atrazine's immunity-weaking effect that it could deliver a double-whammy to the frog population. With a weak immune system, the frogs died from infections or had deformed limbs.
From a complexity science viewpoint, the finding is a reminder that datamining can't reveal everything, the dots were only connected after old-fashioned experiments were performed, with controlled variables. But note that the article describe cause and effect without invoking any of the causal loops familiar to many in complexity science, especially those familiar with system dynamics. Most notably the lifecycle of the trematode parasite. After leaving the snail and having infected the frog, the trematode must wait for a bird or other predator to eat the frog. The predator then excretes the trematode, which is ready to once again infect snails.
The loop is what unlocks the questions needed to be asked in managing this problem. Would reducing atrazine and phosphate every second year be enough to keep the trematode population in check? Is atrazine ok if there are other runoffs that kill snails? Or what if there's some additional runoff that kill off whatever is competing with the snail for algae? Where are the birds and fish that prey on snails?
The complex mesh of effects seen in nature means it's harder to spot if and how what we do harm the environment. But when these networks start getting mapped, it's my opinion that we get a much larger toolbox for fixing the problems. When "everything is connected to everything else" there's so many more knobs we could tweak to improve the odds for these frogs.
Trematode larva being ejected from a snail