Influence of temporal fluctuations in seed abundance on the foraging behaviour of harvester ants (Pogonomyrmex spp.) in the central Monte desert, Argentina

Abstract

The simultaneous study of the temporal dynamics of foraging behaviour, diet and seed abundance is essential to assess the way in which resources affect the behaviour and ecology of harvester ants. Here, we evaluate how fluctuations in grass seed abundance during three consecutive growing seasons influenced the foraging behaviour and diet of the harvester ants Pogonomyrmex rastratus, P. mendozanus and P. inermis in the central Monte desert, Argentina. Seed abundance of the most consumed grasses varied greatly through ant activity season, and ants altered their foraging behaviour in response to those changes. Foragers spent more time travelling and searching for food, and their foraging trips took longer during the low seed availability season. Foraging distance was very similar among species and, contrary to our expectations, did not vary between seasons. Foraging success of P. rastratus and P. inermis increased during the high availability season. This matched the seasonal pattern of foraging activity, suggesting that colonies may detect seed abundance and regulate their foraging effort with the rate of forager success. Although grass seeds were the main item in the diet of the three species, P. mendozanus, and to a lesser extent P. rastratus, turned more generalist when grass seeds were scarce. In contrast, P. inermis showed a very narrow diet breadth, only harvesting grass seeds in both seasons. Our results indicate the relevance of seed availability on foraging behaviour of harvester ants, which should be taken into account when predicting and evaluating the effect of ants on seed resources as well as numerical responses of harvester ant populations to the temporal and spatial variations in grass seed abundance.

Seasonal activity of Dinoponera quadriceps Santschi (Formicidae, Ponerinae) in the semi-arid Caatinga of northeastern Brazil

“…The increased foraging activity observed in D. quadriceps when more food is available also occurs in other ant species, in both carnivores, such as Gnamptogenys moelleri (Cogni & Oliveira 2004), Ophthalmopone berthoudi (Peeters & Crewe 1987) and Odontomachus chelifer (Raimundo et al 2009), and seed collectors, such as Pogonomyrmex rastratus, P. inermis and P. mendozanus (Pol et al 2011). These results corroborate the idea that ants adjust their activity according to food availability in the ecosystem, decreasing foraging when little food is available.…”

Foraging Activity and Trophic Spectrum of Red AntPogonomyrmex barbatusSmith, 1858, in Productivity-Contrasted Microenvironments

“…On the basis of these results, our study does not completely agree with the optimal foraging theory (OFT) that predicts wide-range diets in low productive environments, as compared to limitedrange diets in high productive environments [2]. Although that theory has been tested in different cases [14,26,27], evidence for granivory systems are limited [28], and it seems that the behavioral peculiarities of ants related to patterns of foraging for resources, make them to perform somehow away from the predictions of OFT [29].…”

poral dynamic of foraging of epigeic ants in an urban forest fragment

“…The other species that were found in the four samples had highest abundance in the months of rainy season (January and October). This results may be related to the foraging strategy of each species (PORTER;TSCHINKEL, 1987), to the physical barrier imposed by rain, to the efficiency of the pitfall trap during the rainy months, and to the variation of available resources (NUNES et al, 2011). According to Dos Santos et al, (2012), in the Cerrado biome, during the months with lowest precipitation, the availability and quality of food fall sharply, influencing populations directly, including some ant species (see COGNI;OLIVEIRA, 2004;YAMAMOTO;DEL-CLARO 2008).…”

“…The plant resource consumers, including ants, track this production in space and time, adjusting their foraging activities with food availability (e.g. CARROLL; JANZEN, 1973;POL et al, 2011;BELCHIOR et al, 2012). In the Brazilian savannah (Cerrado), precipitation is seasonally discontinuous and yields high temporal heterogeneity in food production, primarily of vegetal origins (FRANCO, 2002).…”