“A breath of fresh air in the foraging theory: the importance of wind for food size selection in a central place forager”

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Andrea Marina Alma, Alejandro G. Farji-Brener, and Luciana Elizalde

Ants adjust their load size to wind speed optimizing the rate of food intake

An Acromyrmex lobicornis worker carrying a leaf fragment in Patagonia, Argentina.
(Credit: Andrea Marina Alma)

The load size selected by organisms depends on the costs of transportation, manipulation and discovery, and biotic constraints such as predation and competition. However, studies about the effect of abiotic factors on loading prey selection are few and limited to evaluation of how these factors affect animal movement. In regions characterized by strong and constant wind, leaf-cutting ants spend more time bringing resources to their nests. Wind negatively affects ant movement, decreasing their speed and blowing the ants off foraging trails. Considering this, Andrea Marina Alma and colleagues at the Laboratorio Ecotono has developed a mathematical model unifying theory, individual ant behavior, the effect of wind, and the underground tasks that determine load size. In addition, they have tested whether the model predictions agree with ant behavior, sampling the load size transported by workers in windy regions of Patagonia, Argentina.

They found that as wind speed at ground level increased from 0 to 2 km/h, load size decreased from 91 to 30 mm², a prediction that agreed with empirical data from windy zones, highlighting abiotic factors’ relevance to predicting foraging behavior. Furthermore, wind reduced the range of load sizes that workers should select to maintain a similar rate of food intake and decreased the foraging rate by ~70% when wind speed increased 1 km/h.

The results suggest that wind could negatively reduce the fitness of colonies and limit the geographic distribution of leaf-cutting ants. The model developed offers a complementary explanation of why load size in central-place foragers (i.e., animals that forage in a patch at some distance and then return resources to a central place) may not fit theoretical predictions. Although it would be necessary to adjust some parameter values, the model could also serve as a basis in studying the effects of other factors—environmental (e.g., temperature, rain, light), biotic (e.g., parasitoid attack, competitors) or anthropic (e.g., pesticides)—that influence central-place foragers. Read the Article