Plant Selection and Foraging Patterns in Two Species of Leaf‐Cutting Ants (Atta)

Abstract

Three colonies each of two species of leaf-cutting ants (A tta colombica Guer. and A Ita cephafotes L.) were studied for 1 yr in the Guanacaste Province of Costa Rica to determine the following: (I) Do colonies of Atta cut leaves from a limited number of species (i.e., are they selective)? (2) What determines which plant species are attacked? (3) Do leaf-cutters optimize foraging in terms of energy expended by attacking palatable plants closest to the nest or do they distribute their efforts more or less evenly throughout their foraging territory? Several lines of evidence support the hypothesis that A. ccphalotes and A. colombica are selective in terms of plant material attacked. The ants sampled a large majority of the plant species present, but concentrated their foraging on a restricted subset of species. The mature leaves of only 31.4% and 22.0% of the species present were readily acceptable to A. colombica and A. ci'phalotes, respectively. The new leaves of another 12-16 plant species were acceptable. Different colonies of the same A tta species consistently attacked the same plant species if they were available, cut leaves from the same species at similar rates, and even attacked the same species of plants at the same time of year. The amount of material cut from host plant species was not correlated with host plant abundance in four of the six colonies studied, and was even slightly negatively correlated in two of these four. An analysis of plant distance from the nest versus amount harvested shows that palatable plant species close to the nest have a greater probability of being visited by the ants, but do not necessarily suffer more defoliation than other such plants within 50-60 m of the nest. Amount harvested decreases greatly for plants farther than 60-80 m from the nest. Thus colonies of A tta do not normally concentrate their efforts on plants closest to the nest, but foraging cannot be described as evenly distributed either.The factor responsible for selectivity in colonies of A tta is probably the internal chemistry of the material selected. An A tta colony must provide the fungus garden with a proper balance of nutrients and moisture without overloading it with secondary compounds from the plants selected. The ants' attempt to solve this problem may explain some of the complexities of leaf-cutter foraging behavior.

Field colonies of leaf‐cutting ants select plant materials containing low abundances of endophytic fungi

“…Furthermore, we collected leaves from a variety of tree species growing near the trees that the ants were collecting leaves from. Ants are known to collect leaves from a large number of species and one study found that A. colombica sampled leaves from 77% of plant species present and preferably cut leaves from over half of the species present when new leaves were being flushed, as they were during our study period (Rockwood 1976). Therefore, we are confident that using a variety of species in comparing the ant-selected leaves to ambient leaves provided little bias to our results given that the ants preferentially defoliate the majority of species with new leaves.…”

Recursos vegetais usados por Acromyrmex striatus (Roger) (Hymenoptera, Formicidae) em restinga da Praia da Joaquina, Florianópolis, Santa Catarina, Brasil

“…Acromyrmex octospinosus (Reich, 1793) (THERRIEN et al 1986) e em algumas espécies de Atta, a saber: Atta cephalotes (ROCKWOOD 1976, 1977, BERISH 1986, VASCONCELOS 1990b, Atta colombica (ROCKWOOD 1976(ROCKWOOD , 1977, Atta insularis (PINTERA 1983), Atta laevigata (VASCONCELOS 1997) e Atta sexdens (Linnaeus, 1758) (VASCONCELOS 1990b). Geralmente os estudos dão mais destaque às espécies de plantas muito utilizadas, mas FOWLER et al (1991) recomendam que se deve também relacionar esse grande número de espécies pouco usadas com os requerimentos nutricionais do fungo simbionte.…”

“…Apesar das dificuldades de comparação, há mais citações para Leguminosae em regiões de mata tropical (Atta cephalotes, CHERRETT 1968, ROCKWOOD 1976, HUBBELL et al 1984 e Atta colombica, ROCKWOOD 1976), enquanto que, em ambientes não florestais, sejam pastagens ou áreas em processos de sucessão secundária, pode haver predomínio de Gramineae ou um equilíbrio no uso de espécies destas três famílias botânicas (Acromyrmex landolti Forel, 1884, WEBER 1947 apud WEBER 1982; Acromyrmex lundi pubescens Emery, 1905, FOWLER & CABELLO 1978; Atta cephalotes, BLANTON & EWEL 1985;Atta vollenweideri Forel, 1893, CARVALHO & TARRAGÓ 1982. Leguminosae também foi a família de planta com maior taxa de visitas por diversas espécies de formigas, em um estudo que quantificou o uso de recursos líquidos provenientes de plantas e acessíveis a uma comunidade de formigas em região costeira, no México (RICO-GRAY 1993).…”

Foraging behavior of leaf cutting ants: How do workers search for their food?

“…For this purpose, workers need to select and forage a large number of plant species (Rockwood, 1976). Foraging depends on the size, density of quality of the available food source (Traniello, 1989).…”