The Tangled Web of Life

by Amanda K. Martin, M.S. in Biological Sciences

Figure 1: American toad (Anaxyrus americanus) using a large log as shelter. Photo by Amanda K. Martin.

Ecologists study how organisms interact with their environment; however this can be quite difficult as a result of how messy life really is. Organisms interact in multiple ways, not only within their own species (two male deer fighting), but with other species (a snake squeezing a mouse) and their environment (a turtle basking on a log) which includes abiotic factors such as sunlight, wind, and water. What specific ways do animals interact with one another? Well they can compete, avoid predation, forage for food, seek shelter, disperse to other areas and it can be even more complicated when animals interact with humans! Humans are a major force that influences where organisms are located and what resources are available to them.

Figure 2: A monarch butterfly (Danaus plexippus) foraging on swamp milkweed (Asclepias incarnate). Photo by Amanda K. Martin.

Looking at foraging, there are two main types of organisms: producers and consumers. Producers are able to make their own food, these are plants. Through a process called photosynthesis, plants are able to convert sunlight into energy (ATP). By creating their own food, plants do not need to disperse or travel to other areas to eat. However, consumers are unable to make their own food, they must forage or travel to locate their food and eat it in order to obtain energy. There are different types of consumers: herbivores, omnivores, and carnivores. Herbivores consume plant material in order to survive. Herbivores such as monarch butterflies, deer, and muskrats forage for plants and consume either pieces or all of the available plant. Omnivores are animals that consume both plants and animals (meat) such as turtles, humans, and raccoons. Finally, carnivores consume only meat, they do not eat plants. These animals are at the top of the food chain such as hawks, snakes, and lions.

Figure 3: Without regulation from a predator, deer populations can explode and have negative impacts. Photo by Amanda K. Martin.

The available food resources are based on a pyramid, where the most abundant food resources are plants, fewer herbivores, less omnivores, and finally a small amount of carnivores. If the abundances of any category increase above carrying capacity, then the ecosystem will fall apart. For an example, when wolves were removed (extirpated) from Yellowstone, elk populations skyrocketed. This in turn reduced available plants, the elks overgrazed and other herbivores were unable to forage for food because there were too many elks. With the reintroduction of wolves, the elk population decreased and the system was once again balanced. A positive side effect of the reintroduction of the wolves was the increased grizzly bear population because there were available elk carcasses to consume.

Figure 4: A Northern water snake (Nerodia sipedon) resting in a leaf pile. Photo by Amanda K. Martin.

The food web is composed of many food chains (a linear flow of energy from one organism to the next). For an example, sunlight provides energy for vegetation, the muskrat eats the vegetation, while the snapping turtle can eat small muskrats, and finally the great blue heron eats the snapping turtle. This is a food chain for which each organism is one link in a chain. Food webs are created when multiple food chains are put together for which more organisms interact with one another. Not only does the great blue heron eat snapping turtles, but it can eat muskrats or water snakes, whereas the water snake could eat the muskrat. Each organism is linked together and when humans impact their environment, it can alter the food web. Some organisms can replace other lost species; however we do not know the true impact of our actions typically until it’s too late. By preserving or protecting habitat, we can reduce negative effects on multiple species!

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