Question

Two different ant species, Pseudomyrmex and Myrmica, are sometimes found together on the branches of acacia trees. Researchers remove all Pseudomyrmex from one acacia tree. They observe that after removal, the population of Myrmica begins to increase.

From another acacia tree, they remove all Myrmica, and notice that this has apparently no effect on the population of Pseudomyrmex.

Several weeks later, the researchers observe that the tree with no Pseudomyrmex has been grazed to a stump by local tapirs. The tree with no Myrmica and all the acacias with both ant species, remain un-grazed.

In order to test whether there is a mutualistic relationship between acacia trees and Pseudomyrmex, what additional experiment needs to be done?

A

None, the evidence from this observation is enough.

B

A removal experiment in which Pseudomyrmex is placed on a different species of tree

C

A removal experiment in which both species of ant are placed on a different species of tree

D

A laboratory analysis of the chemicals produced by the tree

E

A removal experiment in which tapirs are kept away from the tree

What type of effect might Pseudomyrmex be having on the tapirs?

A

direct positive

B

direct negative

C

indirect positive

D

neutral

Answer 1

mutualism or symbiosis means that both the participating/interacting organisms have benefited from the relationship. From the experiment, by removing Pseudomyrmex, we have observed that the presence of Pseudomyrmex on the acacia trees protects the trees from grazing by tapirs. However, since Pseudomyrmex populations did not show any increase when the Myrmica ants were removed, how they benefit from the tree is not clear. Therefore, another experiment in which Pseudomyrmex ants are placed on an entirely different tree species (option B) needs to be done.  If in this experiment, we observe a decrease in the Pseudomyrmex population, then it would be clear that Pseudomyrmex has some benefits from acacia trees and that the relationship is mutualistic.

Pseudomyrmex is having a direct negative effect on tapirs by preventing them from grazing on acacia trees. If it were a direct positive one, tapirs would have been able to graze on acacia trees when Pseudomyrmex are present on the tree. in an indirect positive effect, presence of Pseudomyrmex on the trees would have resulted in some product which would benefit the tapirs.