Authors Tobias Merkle and Rudiger Wehner
In this article, the authors investigate the behavior of desert ants, Cataglyphis fortis, as they try to search their nests after their navigation system has failed. Through the experiment, the authors tried to ascertain if there are factors other than the distance traveled which affects the search pattern of the ants. The authors hypothesized that the distance traveled is not the only factor that determines the ants uncertainty but there are also other factors that affect the ants confidence in their path integrator.
Desert ants do not leave a chemical train but rather make use of a strategy known as path integration wherein the ants remember the distances and directions traveled and use them to return safely and quickly back to their nests. However, these path integrators are error prone and previous studies have shown that if the ants do not find the nest where it should be according to the path integrator, they begin a systematic search pattern to quickly find the nest entrance. This systematic search follows a predetermined shape but the width of the search depends on the length of the foraging excursion. If the ant had traveled a small distance in its foraging excursion, its systematic search loop would be much smaller than if it had traveled a longer distance away from the nest. Thus, the more confident the ant is in its path integrator, the shorter distance it will travel during its systematic search. The present study attempts to find if spatial distance covered by the ants during the systematic search is exclusively determined by the distance traveled or if they also depend on other cues and how robust these other cues are.
The experiment was performed on wild desert ants in southern Tunisia and all tested ants belonged to the same colony. There were no visible landmarks around the nest and the foraging area. Before beginning the test, the ants were trained by using a feeder placed about 20 meters south of the nest and the ants that encountered the feeder were marked with a color code. These ants were allowed to forage for one full day before they were tested.
During the test, the ants were captured after they had picked up a food crumb and transferred to a test area. The ants were captured at three places after having traveled a distance of 50 from the feeder to the nest (50-in), after having a traveled a distance of 75 from the feeder (25-in) and at the entrance of the nest (0- in). Fifty ants were captured at each of these distances. The 0-in ants were used as a control. Once transferred to the control area, they were allowed to run their home vector and then their systematic search pattern was recorded.
Once the ants started their systematic search, the center of their search was identified and the width of the search distribution was calculated. To check if the differences in this width of distribution vanished after searching for a long time, the width was calculated three times when the overall search lengths had reached 20, 40 and 50 m. The comparisons between the three groups of ants were carried out using the Kruskal-Wallis one way analysis.
The results showed that the 0-in ants searched in a much narrower area when compared to the 50-in and 25-in ants. These results were also presented in the form of three diagrams showing the paths traveled by the ants in the three groups. In the discussion section, the authors compared the data of the present study with that of an earlier study in which the search loop of 100-in ants was studied. It was found that ants that had been captured at the feeder and transferred to the test area had a much wider search loop than even the 50-in and 25-in ants. Based on this, the authors suggest that when the ants are allowed to reel even a part of their home runs in familiar area, they display much more confidence in their path integrator. The results were also compared to another study in which ants were captured immediately after they left their nest. In this study, when released on the test area, the ants did not start foraging but instead immediately started searching for the nest and their search extensions were extremely small. This experiment suggested that the path integrators were set to zero only after entering the nest and even being in the vicinity of the nest does not reset it.
Based on these results the authors concluded that the 0-in ants had much more confidence in their path integrators, suggesting that factors other than the distance traveled were also involved in their confidence of their path integrators. These other cues could be a variety of things including soil conditions, horizon landmarks or the presence of nest-mates. The authors also discussed an alternative explanation for their results and dismissed it because it was not adequately supported by the observations made. Thus the experiment upheld their initial hypothesis that factors other than distance traveled influences the confidence that desert ants have in their path integrators. For future studies, the authors suggest trying the find if such additional factors do indeed exist, what they are and how they interact with the path integrator. Thus the authors recognize the limitations of the findings of their experiment and realize that the experiment only suggest at the existence of factors others than distance in determining the ants confidence in its path integrator. They leave it to future researchers to confirm the suggestions made by their experiment.
Desert ants do not leave a chemical train but rather make use of a strategy known as path integration wherein the ants remember the distances and directions traveled and use them to return safely and quickly back to their nests. However, these path integrators are error prone and previous studies have shown that if the ants do not find the nest where it should be according to the path integrator, they begin a systematic search pattern to quickly find the nest entrance. This systematic search follows a predetermined shape but the width of the search depends on the length of the foraging excursion. If the ant had traveled a small distance in its foraging excursion, its systematic search loop would be much smaller than if it had traveled a longer distance away from the nest. Thus, the more confident the ant is in its path integrator, the shorter distance it will travel during its systematic search. The present study attempts to find if spatial distance covered by the ants during the systematic search is exclusively determined by the distance traveled or if they also depend on other cues and how robust these other cues are.
The experiment was performed on wild desert ants in southern Tunisia and all tested ants belonged to the same colony. There were no visible landmarks around the nest and the foraging area. Before beginning the test, the ants were trained by using a feeder placed about 20 meters south of the nest and the ants that encountered the feeder were marked with a color code. These ants were allowed to forage for one full day before they were tested.
During the test, the ants were captured after they had picked up a food crumb and transferred to a test area. The ants were captured at three places after having traveled a distance of 50 from the feeder to the nest (50-in), after having a traveled a distance of 75 from the feeder (25-in) and at the entrance of the nest (0- in). Fifty ants were captured at each of these distances. The 0-in ants were used as a control. Once transferred to the control area, they were allowed to run their home vector and then their systematic search pattern was recorded.
Once the ants started their systematic search, the center of their search was identified and the width of the search distribution was calculated. To check if the differences in this width of distribution vanished after searching for a long time, the width was calculated three times when the overall search lengths had reached 20, 40 and 50 m. The comparisons between the three groups of ants were carried out using the Kruskal-Wallis one way analysis.
The results showed that the 0-in ants searched in a much narrower area when compared to the 50-in and 25-in ants. These results were also presented in the form of three diagrams showing the paths traveled by the ants in the three groups. In the discussion section, the authors compared the data of the present study with that of an earlier study in which the search loop of 100-in ants was studied. It was found that ants that had been captured at the feeder and transferred to the test area had a much wider search loop than even the 50-in and 25-in ants. Based on this, the authors suggest that when the ants are allowed to reel even a part of their home runs in familiar area, they display much more confidence in their path integrator. The results were also compared to another study in which ants were captured immediately after they left their nest. In this study, when released on the test area, the ants did not start foraging but instead immediately started searching for the nest and their search extensions were extremely small. This experiment suggested that the path integrators were set to zero only after entering the nest and even being in the vicinity of the nest does not reset it.
Based on these results the authors concluded that the 0-in ants had much more confidence in their path integrators, suggesting that factors other than the distance traveled were also involved in their confidence of their path integrators. These other cues could be a variety of things including soil conditions, horizon landmarks or the presence of nest-mates. The authors also discussed an alternative explanation for their results and dismissed it because it was not adequately supported by the observations made. Thus the experiment upheld their initial hypothesis that factors other than distance traveled influences the confidence that desert ants have in their path integrators. For future studies, the authors suggest trying the find if such additional factors do indeed exist, what they are and how they interact with the path integrator. Thus the authors recognize the limitations of the findings of their experiment and realize that the experiment only suggest at the existence of factors others than distance in determining the ants confidence in its path integrator. They leave it to future researchers to confirm the suggestions made by their experiment.
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