Question

A scientist records the population of two interacting species. From his initial observations, the scientist claims the two species live in a parasitic relationship. A graph of the data is shown below.

Population of 2 interacting species Number of organisms - Species 1 Species 2 10 20 30 40 50 60 70 80 90 100 Time

Based on the data, use supporting evidence to agree or disagree with the claim of the scientist. If you refute the claim, describe a better explanation for the observations.

Answer 1

In this case, I disagree with the statement for several reasons. First of all, if you observe the graph lines, you will notice that both species are tightly related. Species 1 and Species 2 increase the number of organism at the same. When one of them increase the number of organism, the other one increases as well. If this were a parasitic relationship, one of the species would be more affected than other but this is not the case. However, it seems peculiar that species 2 have a lower number of organisms in comparison with specie 1. This does not mean that species 1 influence negatively over species 2.

This is probably a commensalism relationship. I will use as an example the relationship between sharks and remoras. The remoras instead of looking for their own food, prefer to adhere to sharks, and feed on the remains of food that escape from their mouths, in this way they do not invest energy hunting and are always well fed. At the same time, the remora can eliminate the ectoparasites from the shark and also cleaning the epidermal tissue. As we can observe, both animals get a benefit.

In this case, a shark is mostly accompanied by two or more remoras. So, we are observing a relationship ratio of 1:4 or 1:2. Four remoras per shark.

This is what we can observe in this graph, both species are growing together and getting a benefit but species 1 are naturally more numerous than species 1 and that is the reason why the difference between the two lines of the graph.

In conclusion, both species are in a commensalism situation. When one species proliferate, the other does as well. But species 1 are more numerous than species 1. So more than one specie 1 is getting benefits from just one individual of the species 2.