SOIL ORGANISMS - Soil Ecology - page 322

4.3.3.4 Food materials and feeding habits

In the presumed ancestral vespoid pattern of diet still retained by some ponerine ants,
larvae are fed with protein-rich animal materials while the adults are largely nectivorous.
Tobin (1994) considered that two distinct and opposing trophic shifts have occurred in
the evolution of the ants. One has involved an increasing reliance on animal matter while
the second has led to a greater degree of herbivory.
While most ant species are generalised predators and scavengers, a wide range of feed-
ing habits occurs within the family. Tobin (1994) argued that the importance of herbivory
has been greatly underestimated, in part due to the difficulties in quantitatively assessing
the origins and amounts of liquid food carried by foraging ants. Most species accept a
spectrum of food materials and only a minority have highly-specialised diets. Of 143
'New World' genera considered by Tobin (1994), only in 29 genera (20 %) were all species
considered to derive most of their nutritional requirements from animal sources. The food
resources utilised by a colony may alter qualitatively and quantitatively over time,
depending on the stage of colony development and on changing seasonal requirements
associated with such factors as reproduction (Stradling, 1987).
Many species active on the soil surface or underground depend largely on animal
food materials. Of these, specialised predators are most common in the tropics and their
incidence diminishes with increasing latitude. Lévieux (1983) reported that ca. 25 % of
the 113 species found in the savanna of Lamto in the Côte d'Ivoire were thus specialised;
some species, for example, specialise as consumers of Isopod crustacean prey, others of
termites or earthworms. Although some dietary overlaps occur, most specialised feeders
appear to rely on largely different staple food resources.
Some ants are extremely polyphagous. Cherrett (1968) reported that the leaves of
36 of 72 plant species present in his study area in Guyana were attacked by the leaf
cutter ant Atta cephalotes. Fallen flowers were also attacked. Adams (1986) and Reagan
(1986) summarised the diet of the highly-invasive introduced fire ants, mainly Solenopsis
invicta (but also S. richteri), in the southern part of the United States, These ants predate
upon a wide variety of invertebrates but also feed regularly on different tissues amongst
a range of cultivated and other plant species (Table III.16). In addition, S . invicta feeds
on honeydew excreted by sap-sucking insects (Homoptera) and enters into a mutualism
with at least some species. Further, the species predates on the tissues of some higher
animals and may effect a notable reduction of certain forms of wildlife. Adams (1986)
cites attacks on a number of nestling birds and the eggs and newborn young of reptiles
reported by a number of authors. Such invasive species may, over time, become more
harmoniously integrated into local ant communities (Hölldobler and Wilson, 1990).
Workers may forage singly or in groups within the territory of their own colony and
recruit other workers to assist in the exploitation of significant food resources. In the
absence of group transport, such ants are limited in the size of the food items they may
return to the nest by the carrying capacities of individual workers. Potential food items
may range widely in size and, in species where workers differ in size, each size class
of workers may transport separate size classes of food items. Other ants forage co-
operatively in groups and this allows them to utilise food items that would normally
be too large or too well defended to be available to individual workers.