Diet and Spatial Pattern of Foraging in Ectatomma opaciventre ...

614 Sociobiology Vol. 58, No. 3, 2011
and roots) in the diet of E. brunneum (=quadridens). A preference for ants
was also observed in E. permagnum, which showed a diet consisting almost
exclusively of workers and winged individuals of Pheidole and Camponotus
(Paiva & Brandão 1989), and in Pachycondyla striata, which includes in its
diet foragers of Odontomachus, Camponotus, Pheidole, Solenopsis, Atta, and
even other Pachycondyla (Medeiros & Oliveira 2009).
The proportion of ants preyed on by E. ruidum was observed to be similar
both in the dry (18.8%) and in the rainy (17.2%) season. Although its diet
consisted of 19 items, almost 30% of them corresponded to liquids rich in
carbohydrates, such as extrafloral nectar, honeydew, and fruit pulp (Lachaud
1990). Similarly, in E. tuberculatum, liquid foods represented more than 35%
of its diet (Valenzuela-González et al. 1995). Collecting resources of animal
origin requires longer foraging distances; capturing and transporting them
is more time consuming compared with liquid foods (Harkness & Harkness
1976; Fourcassié & Oliveira 2002). This “preference” for other ants is not
likely to be due to selectivity by the foragers, but to the low diversity of food
items available in the environment. This can be proved in the laboratory, since
workers of E. opaciventre easily accept other food items, such as mealworms,
which are not found in their natural environment.
The predatory behavior observed in E. opaciventre was very similar to that
found by Pie (2004) in the Brazilian savanna and by Tofolo and Giannotti
(2009) in the laboratory: prey aggressiveness determined the type of approach
used by the workers. As a consequence of the absence of recruitment previously
described for this species, the size of the food item collected was dependent
on the capacity of the worker to carry it without help, one at a time. This
behavior is characterized as social facilitation, that is, the return of a forager
to the nest that may increase activity inside the nest, leading other collectors
to leave and search for food sources even in the absence of a chemical trail or
any other directional information, as observed in Pachycondyla goeldii (Orivel
2000) and E. ruidum (Lachaud 1985).
In the degraded area studied, the foragers of E. opaciventre did not stay
more than 5.14 m away from the nest. A similar behavior was observed by
Medeiros and Oliveira (2009) in numerous colonies of Pachycondyla striata.
Fourcassié and Oliveira (2002) reported that, in Dinoponera quadriceps,
this distance was more than twice as long, reaching 13 m. Pie (2004) also