Ants as epiphyte gardeners: comparing the nutrient quality of ant and termite canopy substrates in a Venezuelan lowland rain forest

The poor availability of suitable substrate and nutrients strongly limits the distribution and growth of vascular epiphytes in lowland rain forests (Benzing 1990, Nieder et al. 2000). In some epiphyte species nutrition may be assisted by adventitious roots that grow into animal debris in plant cavities such as domatia and bromeliad tanks (Huxley 1980). For epiphyte species lacking these modifications, animals may nevertheless play a substantial role by providing a large proportion of the limited substrate in lowland forests (Catling 1995, Longino 1986). Such associations between epiphytes and nutrient/substrate-providing animals may often be non-specific and commensalistic (Davidson & Epstein 1989, Longino 1986), while highly evolved mutualistic associations occur in the case of ant gardens which are very abundant in neotropical forests (Huxley 1980, Kleinfeldt 1986, Ule 1901). Ant gardens typically are densely inhabited by different epiphytes from various plant families whose seeds or fruits are attractive to the ants and carried into the nest (Davidson 1988). In addition, ants have been suggested to play a role in protection and nutrition of ant-garden epiphytes (Kleinfeldt 1978, 1986). Ants may benefit from epiphytes through increased nest stability (Yu 1994) or nutrition via extrafloral nectaries, fruit pulps or seed arils (Davidson 1988, Kleinfeldt 1986). In this study,we compare the nutrient quality of such ant gardens with other similar substrates rarely inhabited by epiphytes, namely nests and galleries of ants and termites.