Maren Johnson writes — We got up at varying times this morning; it all depended on what your project was. The way Dr. E graded us in this section of the course was by having us do 2 research projects, one in the rainforest and the other in the reef. That night we presented our findings in videos that we had spent the day putting together. Here are the projects:
Leaf Cutter Ants: Day and Night
Lydia Cook, Ashley Malpica, Rebecca Gorodetzky
As part of the Field Studies in Belize class, lead by Dr. Evans, our group conducted a study on the daily habits of leaf cutter ants, specifically trends shown around the clock. We hiked in different parts of the rainforest where we observed many behavioral trends in leaf cutter ants. On one of our night hikes we saw that the ants tended to be more active during night than during the day and were carrying more leaves at this time. Additionally, we noticed that not all of the ants returning to the colony were carrying leaves and that there was a net movement towards the tree at dusk and a net movement away from the tree at dawn. We decided to study these behaviors in the ants during different times of the day. To do this we picked 4 different trails and observed them for 5 minutes each at different hours of the day. We hypothesized that the productivity (the number of leaves) and the efficiency (the percentage of colony-bound ants carrying leaves) would increase at dusk and will reach its peak at night and decrease at dawn. Also, we hypothesized that more ants were traveling to the tree at dusk than were traveling away from the tree and vise versa at dawn. Our results supported this hypothesis, yet there was some outlying evidence that suggests that these trends are not universal. For example, at the Bunkhouse trail, the leaf harvest was highest at night and lowest during the day. The efficiency was also highest at night, but we could not get data for the daytime efficiency because there were no ants on the trail. Finally, there was a net movement of ants towards the tree at dusk, which supported our hypothesis, but there was also a net movement of ants towards the tree at dawn, which did not support our hypothesis. In conclusion, our hypotheses were mostly supported by the evidence found from our four ant trails. However, there were a few exceptions which suggest that the trends are not universal for all leaf cutter ant colonies at BFREE.
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Cohune Palms in the BFREE Forest: Jaina Gandhi and David Pride
Rainforests are most noted for their diversity of both plant and animal species. At the BRFREE forest, however, we were surprised to see the presence of a dominant tree species that covered most of the landscape. The Cohune palm, a structurally dominant species, was seen in all size classes in the BFREE forest. A hypothesis made famous by two biologists Janzen and Connell, assumes that tropical rainforests maintain high diversity because pressures caused by herbivory and pathogens make it impossible for one species to become dominant. The Janzen-Connell model suggests that trees are established at a specific distance from their ‘parent’ tree. This distance is far enough away to avoid competition and herbivores specific to the parent tree yet it is close enough in order to be successfully dispersed. Thus, the tree species is recruited in this ‘sweet spot’ distance and other tree species fill in the spaces in between.
In our project we decided to measure the abundance and size-class distribution of Cohune palms in two sites containing only one parent tree. We found that the Cohune palm did not display a specific distance where recruitment was successful. Seeds and seedlings were abundant closer towards the parent tree while small and large juvenile trees were evenly, yet sparsely distributed around the parent tree. Cohune palms did not seem to be limited by herbivores or pathogens specific to their parent and did not seem to be limited by competition with the parent as well.
We speculate that the Cohune palm does not adhere to the Janzen-Connell hypothesis because of factors such as seed morphology, hurricane resistance and shade tolerance. Like most big-seeded plants, the palm has a nutrient and carbon rich package that can sustain it for long periods. Because of this the seeds have a buffer period and are less susceptible to competition as they have large embryonic stores. The Cohune palm is also quite hurricane resistant. The palm is able to take advantage of hurricanes. When other species are uprooted, the palm is able to colonize light gaps. However, unlike gap dependent species, the Cohune palm is shade tolerant and can continue to grow and develop. Because of these traits, the Cohune palm is a dominant tree in the BFREE forest and functions as a foundation species.