Ecology is the unit many students enjoy. Nature documentaries really help to sell the content. Who doesn’t love watching cute otters as they munch away on pesky sea urchins? But even the most avid nature lover still can get a few nature facts wrong. We all make mistakes, so no big deal. Let’s NOT keep these misconceptions going. Below are some of the most frequent ecology misconceptions I have seen in the high school biology classroom.
This misconception is pervasive. I have seen it in professionally published food web diagrams. This means that students may have seen this in a textbook or other online resource or in the worst-case scenario been taught by a teacher they had before you *cringe*. While it is true that plants do get their energy from the sun, the sun is abiotic and therefore has no place in a food web. Food webs are only composed of biotic factors. Any abiotic factor should be excluded. So sorry Sun, you don’t belong here.
Removing this misconception is important for a complete understanding of the rule of 10. The rule of 10 describes that approximately 10% of the energy from one trophic level moves on to the trophic level above it. The rule of 10 will not work if the Sun is a part of the food web. Less than 1% of the sun’s energy hits the Earth. That is a lot less than 10%. It can also confuse students when they are trying to count the number of trophic levels. If they count the sun as a trophic level, all other trophic levels will be off. To avoid confusion be sure to explain that food webs and energy pyramids only concern themselves with how energy flows through the biotic factors of an ecosystems. Show an example of a correct food web and ask students, “why is there no sun?” can help address this misconception
Predators provide vital checks and balances to every ecosystem. If herbivores are allowed to reproduce and live they will eat all of the vegetation resulting in decreased biodiversity and a destabilized ecosystem. This was first observed by Aldo Leopold when he saw wild vegetation greatly diminish after humans killed all of the wolves in Yellowstone. Predators help protect plants and thus encourage an increase in biodiversity. Predators are another important piece of a healthy ecosystem, not a burden upon it. Students see predators and think “how awful, they are killing that poor herbivore!” but if predators do not eat, then there are no plants to feed the herbivores. A grim look at wildlife, but that is why we call it wild. You can watch “How Wolves Change Rivers” to help address this misconception.
Plants employ all manner of defenses. From thorns to toxins plants are constantly defending their turf. This misconception is probably the easiest on this list to dispel. Once students think about the purpose of thorns they instantly realize that just because a plant does not move, does not mean it is defenseless. This does not mean every plant never wants to be eaten. Fruit is designed to distribute seeds and some types of grass benefit from being grazed upon. If we slow down and look closely, plants become a lot more interesting. If you have a lot of GT kids in your class you might have your students imagine they are a plant and describe what they might do to prevent a herbivore from munching on them.
I suppose the analogy is fine, but many students actually think that if one person is mean to another that they are by definition a parasite. In ecology however, two organisms have to be different species in order to qualify as symbionts. If they are the same species, they are in competition. This is important when we describe ecosystems. Birds that fly together and help each other are not considered symbionts because they are the same species. Nor are wolves who hunt together, nor the trees that share resources, nor the vampire bat that takes but does not share. It is true that symbiotic relationships act as a great analogy for intraspecies relationships, but if we are being rigorous, they do not qualify. This misconception will not really impact their understanding of ecology, but it could change how they understand evolution. Species that help each other, or act altruistically toward each other are helping their own genes survive. The same can be said for organisms that are in mutualistic relationships but it is not true for parasitism. Whenever an organism acts like a parasite, they are helping their genes survive at the detriment of another species’ genes. When organisms of the same species compete in this way the strongest genes survive, so intraspecies competition has an overall beneficial effect on the species while parasitism may not. Parasitism could lead to beneficial genes, but it does not do so by necessity. This misconception is not one I would pick on too much, but it can be useful to make the distinction between intraspecies competition and parasitism.
It is true we have no natural predators, but we are far from the top of the food chain. Most humans are somewhere between trophic level 2 and 3. Trophic level 1 are producers. Trophic level 2 are vegans. Most humans are not vegans. Instead we eat an omnivorous diet. Making us trophic level 3. The longest food chains have about five links, five trophic levels. This is because of the rule of 10. There simply is not enough energy to support higher trophic levels. Humans are far from trophic level 5. Meaning we are not the top of the food chain. We might be at the end of a chain, but it is not the longest. Some might argue that saying we are at the top of the food chain just means that nothing eats us, but that is not true either. Plenty of things decompose us when we die, and many more try to kill us when we are alive (I’m looking at you microbes). So unless we are cremated, we are not the end of the chain. We are not at the end or the top. We are about the middle. And that is okay. We are a part of this world. Like every other organism we have our role to play. To address this misconception, have students draw their own food chain. Have them write down what they eat, and what they eat eats. Then have them compare the food chain they made to one from another ecosystem.
Many people have strong political opinions about the ecosystem and our claim to the world. Many people are unaware of the impact that they are having on the ecosystem. They are unaware of how their actions are shaping the world around them. Out of sight, out of mind. I believe one of our jobs as biology teachers is to show students how their actions impact the ecosystems around them and help them think of ways to reduce their negative impacts. This does not mean we all need to become granola-eating tree huggers (although that would be fine with me if it happened). But I do think we should recognize that plastic in the ocean is bad, and take our sand shovels, buckets, and trash with us when we leave the beach. If everyone did this we would have a richer world. The small changes we make, in aggregate, can have a huge effect on the world. We are all a part of this world and we are not getting another one. Let us take care of what we have so it will last long into the future. To address this misconception, have students imagine what their room would look like if they never cleaned it (for some of them this will be easy because it will be just how it currently is) and then relate that to polluted ecosystems.
You can address these misconceptions with your students directly or as they come up in class. If you need some help teaching ecology, check out the Create An Ecosystem Project. Students will design their very own ecosystem and use it to show the major topics of ecology.