Diet and Spatial Pattern of Foraging in Ectatomma opaciventre ...
Diet and Spatial Pattern of Foraging in Ectatomma opaciventre ...
Diet and Spatial Pattern of Foraging in Ectatomma opaciventre ...
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614 Sociobiology Vol. 58, No. 3, 2011<br />
<strong>and</strong> roots) <strong>in</strong> the diet <strong>of</strong> E. brunneum (=quadridens). A preference for ants<br />
was also observed <strong>in</strong> E. permagnum, which showed a diet consist<strong>in</strong>g almost<br />
exclusively <strong>of</strong> workers <strong>and</strong> w<strong>in</strong>ged <strong>in</strong>dividuals <strong>of</strong> Pheidole <strong>and</strong> Camponotus<br />
(Paiva & Br<strong>and</strong>ão 1989), <strong>and</strong> <strong>in</strong> Pachycondyla striata, which <strong>in</strong>cludes <strong>in</strong> its<br />
diet foragers <strong>of</strong> Odontomachus, Camponotus, Pheidole, Solenopsis, Atta, <strong>and</strong><br />
even other Pachycondyla (Medeiros & Oliveira 2009).<br />
The proportion <strong>of</strong> ants preyed on by E. ruidum was observed to be similar<br />
both <strong>in</strong> the dry (18.8%) <strong>and</strong> <strong>in</strong> the ra<strong>in</strong>y (17.2%) season. Although its diet<br />
consisted <strong>of</strong> 19 items, almost 30% <strong>of</strong> them corresponded to liquids rich <strong>in</strong><br />
carbohydrates, such as extrafloral nectar, honeydew, <strong>and</strong> fruit pulp (Lachaud<br />
1990). Similarly, <strong>in</strong> E. tuberculatum, liquid foods represented more than 35%<br />
<strong>of</strong> its diet (Valenzuela-González et al. 1995). Collect<strong>in</strong>g resources <strong>of</strong> animal<br />
orig<strong>in</strong> requires longer forag<strong>in</strong>g distances; captur<strong>in</strong>g <strong>and</strong> transport<strong>in</strong>g them<br />
is more time consum<strong>in</strong>g compared with liquid foods (Harkness & Harkness<br />
1976; Fourcassié & Oliveira 2002). This “preference” for other ants is not<br />
likely to be due to selectivity by the foragers, but to the low diversity <strong>of</strong> food<br />
items available <strong>in</strong> the environment. This can be proved <strong>in</strong> the laboratory, s<strong>in</strong>ce<br />
workers <strong>of</strong> E. <strong>opaciventre</strong> easily accept other food items, such as mealworms,<br />
which are not found <strong>in</strong> their natural environment.<br />
The predatory behavior observed <strong>in</strong> E. <strong>opaciventre</strong> was very similar to that<br />
found by Pie (2004) <strong>in</strong> the Brazilian savanna <strong>and</strong> by T<strong>of</strong>olo <strong>and</strong> Giannotti<br />
(2009) <strong>in</strong> the laboratory: prey aggressiveness determ<strong>in</strong>ed the type <strong>of</strong> approach<br />
used by the workers. As a consequence <strong>of</strong> the absence <strong>of</strong> recruitment previously<br />
described for this species, the size <strong>of</strong> the food item collected was dependent<br />
on the capacity <strong>of</strong> the worker to carry it without help, one at a time. This<br />
behavior is characterized as social facilitation, that is, the return <strong>of</strong> a forager<br />
to the nest that may <strong>in</strong>crease activity <strong>in</strong>side the nest, lead<strong>in</strong>g other collectors<br />
to leave <strong>and</strong> search for food sources even <strong>in</strong> the absence <strong>of</strong> a chemical trail or<br />
any other directional <strong>in</strong>formation, as observed <strong>in</strong> Pachycondyla goeldii (Orivel<br />
2000) <strong>and</strong> E. ruidum (Lachaud 1985).<br />
In the degraded area studied, the foragers <strong>of</strong> E. <strong>opaciventre</strong> did not stay<br />
more than 5.14 m away from the nest. A similar behavior was observed by<br />
Medeiros <strong>and</strong> Oliveira (2009) <strong>in</strong> numerous colonies <strong>of</strong> Pachycondyla striata.<br />
Fourcassié <strong>and</strong> Oliveira (2002) reported that, <strong>in</strong> D<strong>in</strong>oponera quadriceps,<br />
this distance was more than twice as long, reach<strong>in</strong>g 13 m. Pie (2004) also