Patches of Earth with no plants are eye-catching. They stand out because the default, lucky for us, is that plants are everywhere, and if they’re absent it’s typically because of something obvious and dramatic. Perhaps a bolder, a concrete parking lot, a sand dune, or a riverbed. But if it’s not something like that, and you’re even somewhat intrigued with natural history and ecology, you will wonder what causes these plantless patches. Questions come to mind: is the soil different? Is there more or less water there? Some pollutant perhaps? Or maybe a busy animal of some sort is the cause?
So called Devil’s Gardens in the Amazon sparked these types of questions. These are patches in dense rainforest that lack large trees and other vegetation, except for one species of shrub. A monoculture in a place where you can sometimes find more tree species in one hectare (2.5 acres) than in all of North America. Supposedly the indigenous people in these region said these monocultures were caused by evil spirits, which is where the name comes from. Maybe that is a story they told, but I think it’s very unlikely that they didn’t have a sense of what was going on.
Devil’s Gardens are the work of ants. But not just ants, also a specialized plant (the single species of shrub) that gives food and shelter to the ants. The ants kill any other plants that come into contact with their favorite bed and breakfast. It works out great for the ants and the shrub and this partnership excludes all the other plants. Fairly recent research isolated the specific mechanisms (including that the ants use an herbicidal acid!) and eliminated alternative explanations with clever experiments. But I highly doubt that the indigenous naturalist didn’t know that ants were partially responsible. For the vast majority of human history humans were all great naturalists because careful observation and understanding of nature were necessary for survival. Humans that are not excellent naturalist are a modern phenomena.
I recently found a patch of plant-free ground near Prescott, Arizona (see the photo above). I initially did suspect ants but when I first looked around I didn’t see any. And I didn’t see any holes where they might gain access to underground lairs either. What else could it be? Maybe it’s a rocky outcropping caused by some bizarre geologic process? Or humans dumped a pile of gravel here, kind of the contemporary equivalent of a geologic mechanism? Or maybe I just wasn’t looking hard enough? Maybe what felt like a warm morning to me (an endotherm warmed by burning up all the chips and salsa I’d been eating recently) might actually be pretty chilly for ants adapted to the hot summer Arizona sun?
With that line of thought I found my answer. There were holes in the patch of gravel, they were just smaller than expected. And there were ants, but only a few just peeking out of their holes, and moving very slowly. Lucky for me, slow-moving ants are much easier to photograph.
These are a species of seed-eating harvester ant, Pogonomyrmex occidentalis to be specific (thanks to Alex Wild for the ID). Apparently it’s the upturned tooth at the base of the mandible that is the distinguishing characteristic for this species, and luckily enough I got a photo showing that specific detail. They are known to build giant mounds of gravel where they chew down all plants to the ground. Read more about them here.
There’s nothing more fundamental to human existence and survival than natural history. Thomas Fleischner describes natural history as “the oldest continuous human tradition“. But now because most of us as individuals don’t live and die based on our understanding of the non-human world around us, our skills at recognizing and explaining anomalies have atrophied. But they are not lost, and they must not be lost.
Collectively our ability to recognize patterns and oddities among organisms and landscapes, and then the motivation to devote the attention to detail and scientific rigor to explain those patterns in nature, is still fundamental to our survival. Climate change and a litany of other issues caused by overpopulation and growing resource demands make our collective well-being and survival increasingly tied to our understanding of biological phenomena and how they respond new environmental conditions. This is not so different from pre-industrial humans, except that we have the handicap that many of our natural history skills have diminished. This is why maintaining our curiosity and attentiveness to the non-human world is critical. Every time you step outside you can practice those skills. Look for anomalies and ask questions about why they exist. Then conjure up your innate naturalist to carefully observe and accurately explain what you see. We still need these skills to solve many of the most pressing issues threatening our survival. Practice them, teach them.