Ant Gardens

The following introduction serves as a means of beginning this webpage but there is much more that could be stated and added here. There is also an older introduction to this topic here: Holldobler and Wilson, 1990

Leal et al. (2017) - Ant gardens are formed mutualistic associations between epiphyte plants and ant species in Asian and Neotropical rainforests (Hölldobler & Wilson, 1990). Ant gardens are ant nests built on the branches of trees and on which aggregates of epiphyte species grow (Ule, 1901). The nest can hold one or, more frequently, more than one ant species and several phylogenetically distant epiphyte plant species (Orivel & Leroy, 2011). When more than one ant species occurs in the same nest, they show a parabiotic behavior, in which the ants live in close association sharing foraging trials but do not exhibit obvious parasitic or exploitative interactions (Davidson, 1988; Forel, 1898; Vantaux & Leroy, 2007; Orivel & Leroy, 2011, but see Menzel et al., 2015).

Seeds from most ant gardens epiphytes are dispersed by the associated ants, which incorporate these seeds into carton nest continuously over the lifespan of the nest (Orivel & Leroy, 2011). Although seeds from ant garden epiphytes commonly bear aril or elaiosome, seed selection by ants seem not determined by the quantity or quality of such appendages as patterns of seeds selection by ant gardens ants remains the same after the removal of such seed structures (Orivel & Dejean, 1999). In fact, it seems that ant garden ant species are attracted by a set of specific volatile compounds released by the seed coat of some of epiphyte species commonly found on ant gardens (Youngstead et al., 2008). After germination, ants of at least one species protect plants against herbivores by patrolling on leaves (Vantaux et al., 2007), while the roots and stems of epiphytes increase the stability and moisture of ant nests (Yu, 1994). Some epiphytes also provide feeding resources for ants through extrafloral nectaries (EFN), oil glands and fruits (Kleinfeldt, 1978; Hölldobler & Wilson, 1990). Although previous studies has been able to identify the general benefits for both interacting sides (see Orivel & Leroy, and references therein), it has been very hard to identify the determinants of plant and ant species composition in ant gardens, and also the roles played by different partner species in this multispecific interaction.

Weissflog, Kaufmann and Maschwitz (2017) - A large majority of vascular epiphytes in lowland forests (except for ferns and orchids) are totally dependent on ants for their establishment and proliferation (Kaufmann & Maschwitz 2006). Generally, the establishment of ant gardens follows the same behavioral patterns in all ant garden systems that have already been described by Ule (1901): Ants construct small carton nests, into which they then retrieve seeds of their epiphyte partners. However, details on ontogenetic development of ant gardens, specificity of ant and epiphyte partners, colony structure and ants’ behavior vary greatly depending on the involved species (e.g. Belin-Depoux et al. 1987, Davidson & Epstein 1989; Orivel et al. 1997, Corbara & Dejean 1996, Cedeño et al. 1999, Orivel & Leroy 2011).

As a rule, ant garden associations are beneficial for ant and epiphyte partners. Ants provide reliable short distance seed dispersal, and a highly nutritional growth substrate with good water storing capacity. They prevent water loss of the root substrate and possibly protect the plants from herbivores (e.g. Longino 1986, Davidson 1988, Kleinfeldt 1978, 1986, Schmidt-Neuerburg & Blüthgen 2007). In addition to rain water the garden is provided with honeydew from trophobionts housed within the nest (Maschwitz et al. 2010). The epiphytes stabilize the ants’ nests with their roots and might additionally sometimes offer food in form of edible fruit pulp, seed appendages or floral and/or extra-floral nectaries (e.g. Yu 1994, Davidson 1988; Kleinfeldt 1978, 1986). Again, details and degree of the mutual benefits depend on epiphyte and ant species (Weissflog et al. 1999, Kaufmann & Maschwitz 2006).