A Comparison of Ground and Canopy Leaf Litter Ants (Hymenoptera: Formicidae) in a Neotropical Montane Forest

The most conspicuous habitat discontinuity in forests is that between ground and canopy. These two microhabitats support strikingly distinct biotic communities. Among ants, species that nest in the ground or in leaf litter are typically in different genera from arboreal species, which nest in or on plants, the two groups exhibiting divergent morphologies which reflect their respective nesting habits (Wheeler 1910, Wilson 1959). The arboreal microhabitat is clearly three-dimensional (Richards 1983) and has inspired investigations of vertical stratification among arboreal taxa, including birds (Pearson 1971, Terborgh |980), mammals (Harrison 1962), and flying insects (Bates 1944, Sutton et al. 1983). Arboreal ants exhibit vertical stratification, some species being restricted to high canopy, others to forest understory (Wilson 1959). The ground microhabitat is generally considered to be a twodimensional layer of soil and leaf litter, home to an ant community very distinct from the arboreal community. In many tropical forests, however, large amounts of leaf litter and other organic material accumulate in the canopy, imparting a three-dimensional structure to dead organic matter. The "crown humus" (Jenik 1973) consists of litter intercepted from overstory tree branches and from abscissed epiphyte tissues. Accumulations of crown humus are particularly pronounced in montane forests (Nadkarni 1984; P6cs 1976, 1980).