Ants Project

As part of the general project, aimed at analyzing the reciprocal effects of seeds and their consumers and the possible consequences of those effects on plant population dynamics, our research is focused on the relationships between granivorous ants and seeds. We want to evaluate the potential impact of ants on seed reserves, but at the same time we are interested in studying the effects of seed availability on the ecology of these ants. Both types of studies are usually carried out independently. Investigations on the role of ants as granivores (the top-down approach) and those centered on the ants' responses to variations in their resources (the bottom-up approach) are common. However, research programs do not frequently include both approaches jointly.

Ants are one of the main granivorous groups in arid ecosystems. Their importance has been thoroughly evaluated in the Northern Hemisphere where foraging and seed consumption may have important effects on seed reserves and on vegetation. In contrast, little is known about the biology of granivorous ants in South American deserts. Almost no basic information on these species was available before our studies. For example, species of the genus Pogonomyrmex have been extensively studied in North America where they make up the bulk of ant assemblages and play a prevailing role in desert ecology. In South America the importance of these ants as seed consumers is unknown.

A few years ago we began to study the granivorous ants-seeds system in the Biosphere Reserve of Ñacuñán located in the central region of the Monte desert of Argentina. It has long been assumed that assemblages of granivorous ants are less diverse and that their seed consumption is also much depressed in South America than in similar habitats in the world. However, recent studies have shown that diversity and seed consumption aren't less important than in other warm deserts. In Ñacuñán, there are about 15-17 ant species capable of removing seeds (especially the ones belonging to the specialized genera Pogonomyrmex, Pheidole and Solenopsis). This number is larger than the one reported at a local scale in North American and Australian deserts.

In the central Monte desert, ants are the most important granivores in spring and autumn but their consumption is depressed during autumn–winter. Daily and seasonal foraging patterns of these species are variable as well as their preference for specific microhabitats, principally as a response to microclimatic conditions. More precisely, the effects of these ants on plant community are mediated through spatial and temporal foraging patterns and seed selection within foraging patches. Knowledge of these aspects leads us to a realistic evaluation on the role of these animals as seed consumers. Our previous studies and the ones which we are currently carrying out address the following questions: what is the temporal activity pattern of these species?; which microhabitats do they take the seeds from?; which seeds do they consume? Together with this we are analyzing how the variation in the seed availability levels affects the ecology of some of these species: do they change their behaviour and foraging strategies when there are changes in seed availability?; do they change the microhabitats where they take the seeds from? ; how is their diet affected?