You Can’t Kill What You Can’t Catch

Human-Created Mimics in Agriculture

Before we delve into aggressive mimicry, we’re going to take a closer look at a somewhat odd form of defensive mimicry found in plants. What makes this mimicry somewhat unique is that, unlike the other examples so far this season, it does not occur naturally. It only happens when the ecosystem has been altered in some way by people, usually in an agricultural context.

Asian rice, Oryza sativa, is a staple food source for large numbers of people throughout the world. When grouped with African rice, Oryza glaberrima, it is the third most cultivated plant in the world by weight, after only sugarcane and maize (corn). However, in rice paddies, there is a known problematic weed called early watergrass, Echinochloa oryzoides.

As anyone with a garden is aware, a large amount of labor is required in order to remove weeds for the cultivation of any plant, either commercial or ornamental. For agriculture, efficient removal of weeds can increase overall crop yields. Of course, ecologically speaking, the term weed has no inherent meaning. It is simply a label given to plants that are not wanted by people in a certain location or context.

Weed removal thus introduces a unique form of selective pressure into the environment. It is important to keep in mind that all of the mimicry examples we discuss this season are driven by natural selection. This is not a random process, but a deterministic one. If there is an undesirable weed that grows alongside a crop plant, it is less likely to be located and destroyed if it closely resembles that plant. Those individuals will pass down the mimicked traits to future generations and so the weed species can become harder to differentiate over time.

This is what happened with Oryza sativa and Echinochloa oryzoides. Both are members of the grass Family and can survive and thrive in flooded fields. Those cultivating the rice fields removed the obvious non-rice grasses, but 100% elimination of anything is difficult in such a scenario. Thus, the weed became a defensive mimic because of human actions.

Of course, this is not the first time such an event has occurred. One of the more interesting examples involves the cultivation of wheat, genus Triticum. The first evidence of wheat agriculture occurs in the floodplains of the Nile, Tigris, and Euphrates rivers (an area known as the Fertile Crescent) around 9600 BCE. Fast forward approximately 8000 years and you find the first archeological evidence of the cultivation of rye, Secale cereale, in central Europe. Wild rye is native to Turkey and most likely found its way to Europe in wheat, as it is a close relative and mimic. After thousands of years of trying to separate the rye, humans began cultivating it as a secondary crop.

Unlike our earlier mimic stories, it’s not so far-fetched to imagine yourself as the duped species because you already are! You are a farmer. Your livelihood depends on maximizing your crop yield. You can do this by removing weeds, but one of the undesirable plants closely resembles your crop species. You can’t be too zealous because then you will likely remove actual crops and not just weeds. Now imagine that you have discovered that this weed mimic is also edible (likely by accident from surviving plants mixing in with your crop yield). Now, you can save yourself aggravation and labor by taking advantage of this once problematic plant and cultivating it as well.

We’re halfway through Season 4 and we’ve been focused entirely so far on defensive mimicry. This is in part because of the way this topic was suggested by my friend, but also because it includes some of the best known examples of mimicry including the coral snake and the monarch butterfly. However, it’s now time to take a look at some other ways in which species have used mimicry to their advantage, so we’ll have our first story on aggressive mimicry next week.

If you like my stories, please like, subscribe, and share them. If you have an idea for a topic for a future season, let me know and if I use it, I’ll give you a shout out in my introductory post.