For our
final project of the semester, my partner and I investigated the extent of the
relationship between ants and the plant Pentaclethra
macroloba in varying degrees of light intensity. Here at La Selva, we participated
in independent, as opposed to faculty-led, projects. This means that my partner
and I came up with the idea for our experiment and designed the methods
ourselves. We were curious to learn more
about how environmental factors may affect ant-plant associations. Some ant-plant relationships are strict
mutualisms; in other words, the plant produces nutritious food bodies to
attract a specific species of ant, which in turn protects the plant from
herbivory by attacking insects and removing larvae from the leaves. However, the relationship between ants and P. macroloba is known as a diffuse
mutualism because while both the plant and the ants benefit from the
interaction, it is an indirect benefit and not required for their
survival. The plant still produces food
(within extrafloral nectaries) to attract the ants, but it is a smaller reward
in terms of nutritious value. The ants that come are typically generalists (not
necessarily a specific species) and they still provide some protection against
herbivory by patrolling the leaves and occasionally removing a potential
herbivore.
We thought that plants with access
to more sunlight would have more resources and energy available to allocate
towards producing higher quality extrafloral nectaries that would in turn
attract more ants. We tested this hypothesis by placing small pieces of tuna on
the leaves of P. macroloba plants and
measuring how long it took for the ants to appear on the leaf and how long it
took for them to actually make contact with the tuna. Other variables we
recorded included the height of the plant, the number of extrafloral nectaries,
percent herbivory, and canopy cover. Counting
the extrafloral nectaries proved much more difficult than I anticipated, as
they are so small that I had to use a magnifying glass and a light in order to
be able to see them at all. The weather was also an obstacle at times; we
couldn’t set up the tuna baits when it was raining because the ants are not
active during rain and it would have just washed off the leaves anyway.
At the end of the project, we were
able to share our results not only with the class but also at a poster session
in which we presented in Spanish to the local community. Though at times it was challenging to
communicate exactly what I wanted to say, I’m really grateful to have had the
opportunity to practice my Spanish, especially since I had to utilize a more
scientific vocabulary than I am accustomed to. I think the combination of the independent
project and poster presentation was the perfect way to culminate the semester by
bringing together everything I have learned and sharing it both with my peers
and with the local community.