Today in class we discussed what an ecosystem is, how they work, and how the earth is full of interconnected systems. One of those systems is a food web. A food web is a system of connected food chains, giving information essentially on “what eats what” and the different organisms existing in an environment at different trophic levels. A trophic level is simply what that animal primarily eats and where they fit in the food web (e.g., big fish eats smaller fish, who eats even smaller fish, who eats primary producers like algae or seaweed). These trophic exist in balance with one another. For example, plants exist as the primary producers within an ecosystem. Then comes the herbivores, who eat the plants, then the carnivores that eat them.
Figure illustrating how removing one trophic level would affect the rest of the food chain.
If there is a shift in population size at one trophic, however, it can cause a dramatic at a different level. Let’s look at sharks. Currently, many species of sharks are threatened or endangered due to the fishing industry. This impact on their population density trickles down to the rest of the food web. With less predators, species they typically prey on (tuna, manta rays, etc.) can thrive, and their population sizes will grow much larger than they were originally. However, they will deplete their limited resources until there is none left. Then, their population size will decrease dramatically. Not only this, but the sick or injured fish that are usually consumed by sharks could have a negative impact on schools. Apex predators like sharks also regulate more than just population sizes of their prey. They also function as the main force cycling nutrition throughout the ecosystem and removing invasive species.
This is known as a trophic cascade, a butterfly effect where if one population is affected, the rest of the food web is affected as well. Fluctuations in population occur and can drastically change the environment and the abundance of life there. It shows that our actions to the environment, no matter how small we believe them to be, have a rather large impact. This makes the need for conservation efforts even more necessary. Allowing sharks to increase their numbers through better regulation of fishing would be of instant benefit to coral reefs.
Trophic cascades are becoming increasingly common as humans continue to change these natural environments and impact the organisms living there. Currently, humans are taking sharks out of the water faster than they can reproduce. This is actively diminishing their population numbers at a significant rate, and we can already see the effects of it. Sharks are very important for maintaining healthy ocean ecosystems.
For more information on trophic cascades and shark population decline, please check out the following links:
http://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(16)00059-8
This is a wonderfully informative blog post! Not only did you explain what systems were and give a visual representation of a food web system, you also went deeper into the food web concept and how it isn’t just as simple as it looks. Many factors play into a system and you demonstrated that perfect!
Great blog post! Do you know what human activity is threatening populations of sharks?