Nora C. Doerder, Charles F. Brush High School, Lyndhurst, Ohio

Pam Prince, The New Horizons School, Colorado Springs, Colorado

Tom Sisneros, Belen Middle School, Belen, NM

Derek Wiberg, Framingham High School, Framingham, Massachusetts

The presence of concrete trails throughout La Selva Biological Research Station may offer advantages to foraging Leaf Cutting ants (Atta cephalotes). This study attempts to measure the effect of the concrete trails on the distance ants forage, the number of foraging ants, the speed at which they travel and the biomass they are able to transport. Comparisons were made between trails that utilize the cement and those exclusively in the forest. A comparison of the speed and traffic on the respective segments of trail was also done. Our data suggests that use of concrete trails gives Leaf Cutting ants a foraging advantage.

Leaf cutting ants (Atta cephalotes) are widely distributed throughout Costa Rica in forests below 2000 m in elevation. While these ants can be somewhat destructive they also play an important role in the cycling of nutrients. The ants cut small sections of leaves from different sources and carry them to their nests to be used as a medium for growing fungus (Holldolbler 1990). The fungus is used primarily as a food source for the larvae but also as a secondary source of carbon for the adults. Typically, the ants will travel between 50-100m to find and harvest leaves. Leaf cutting ants tend to be resourceful and extremely productive (Wetterer). They will form well-groomed trails 6-12cm wide between the nest and a Leaf source. These trails resemble a heavily traveled highway. The ants also take advantage of fallen logs as a corridor and readily incorporate them into their transportation system.

Rows of leaf carrying ants are a common appearance on cement trails suggesting that the ants may be using the trails to their advantage for leaf foraging. Our issue of concern was impacts of humans on ecosystems. Do concrete surfaces provide a smooth even surface with fewer obstacles compared to the surrounding forest? We chose to investigate the influence that these cement trails have on the ants and their harvesting tendencies. We attempted to answer the following questions in order to more accurately describe the Leaf Cutting-concrete trail relationship: Does leaf traffic increase on ant trails that include concrete trails? Do the ants carry larger loads on trails that include concrete trails? Does the concrete enable the ants to go longer distances to harvest leaves? And finally, do the ants travel faster with a load on trails that include concrete trails? We expected that trails that include concrete would provide Leaf Cutting ants with a foraging advantage.

Nest and trail selection was based on four criteria. First, an active foraging trail - defined as a trail with >10 Leaf carrying ants/minute past a given point - was found on a concrete trail. Second, the leaf source and the nest could be found. Third, a second active trail was found from the nest that did not use the concrete. Finally, the leaf source of the second trail could be located. With these criteria met, the nest and trails could be used in our study. They were labeled nest (N#), TIC (trails incorporating concrete) and Natural Trails (NT) for trails totally off the concrete.

Click on a thumbnail to see the enlarged Graph
Figure 1	Figure 2	Figure 3


Figure 4		Figure 5

The data in Figure 1 show that Leaf-cutting ant trails that incorporated concrete trails - even minimally - were longer than natural trails. In contrast, Figure 2 shows that natural trails had a greater number of ants using the trail than did those using concrete. However, leaf mass, leaf area and ant speed (Figures 3, 4, 5 respectively) generally support our hypothesis that the concrete trails offer Leaf-Cutting ants foraging advantages over natural trails. The exception found in Figure 1 for Nest one natural trail’s leaf mass may be explained by the fact that the ants were carrying heavier veins and stems, rather that leaf pieces. The surface area measurements in Figure 3 show a smaller surface area for these pieces.

Limitations to this study include that the data came from only three nests. We attempted to randomize the collection of leaf samples to be measured by placing an obstacle in the path of the ants and collecting from the “log jam” that resulted. There may have been some bias in picking leaves because of the necessity of removing ants from their leaves before the soldiers arrived. In addition, the size of the leaf carried is directly related to the size of the ant. (Janzen, 1983) We did not consider the source species of the leaves as a possible variable.

Further studies could include additional nest data and possibly locating nests adjacent to the cement trail as a comparative measure. Nests that are next to a cement trail may maximize use of that cement trail.

The ATTAtudes would like to thank all the other members of team two for their assistance in locating Leaf-cutting ant nests. The support and encouragement of our Woodrow Wilson Foundation leaders, Tom Langen, Melanie Phelps, Jim Cole and John Cozza to finish in a timely fashion was appreciated. We also would like to thank the researchers at La Selva for the use of their laboratory equipment.

THE EFFECT OF CONCRETE TRAILS

**ON LEAF-CUTTING ANT (Atta cephalotes) FORAGING**




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Pic 4: Finding the nest	Pic 5 Survey the trail