Spatial Distribution of Dominant Arboreal Ants in a Malagasy Coastal Rainforest: Gaps and Presence of an Invasive Species

Abstract

We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species—a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression.

How territoriality and host-tree taxa determine the structure of ant mosaics

“…The present study confirms the existence of an arboreal ant mosaic in the upper canopy of an African tropical rainforest, as has been shown for other tropical African, Asian, and Neotropical rainforests (Blüthgen and Stork 2007;Davidson et al 2007;Dejean et al 2007Dejean et al , 2010Ribeiro et al 2013). The characteristics of the ant mosaic noted here, in which T. aculeatum was abundant as were several carton-nesting Crematogaster species, seem intermediary between those of a secondary and those of a mature forest, both studied in Cameroon (Dejean et al 1994(Dejean et al , 2000.…”

“…Indeed, the negative impact of the presence of ground-nesting ants on the formation of the ant mosaic in plantations was demonstrated in a study conducted after insecticide treatments were stopped (Kenne et al 2003). The presence of invasive species can also play a role (Greenslade 1971;Dejean et al 2007Dejean et al , 2010Fayle et al 2013;Souza da Conceição et al 2015). Some of these species, although ground-nesting, can influence the nature of the ant mosaic in their native range where they are Bexpansive.^In the Neotropics, this is the case for Wasmannia auropunctata, which can become arboreal under certain conditions, and, to a lesser degree, for fire ants of the genus Solenopsis (Majer et al 1994;Orivel et al 2009;Dejean et al 2015;Souza da Conceição et al 2015).…”

“…Second, the canopy sledge is a 16-m 2 inflatable triangular platform carried by the dirigible and which can transport three persons from treetop to treetop. Third, the canopy bubble is a 180-m 3 helium-filled balloon 6 m in diameter which runs along a fixed line previously set in the upper canopy by the dirigible, permitting researchers to reach the tree crowns from above (Basset et al 2001;Dejean et al 2010). Fourth, we used the single rope technique (Steege 1998) to access the raft and to reach the crowns of the trees situated between the different areas covered using the previous devices, permitting us to gather samples from all 206 adjacent trees plus lianas (Appendix S1; see BElectronic Supplementary Material^).…”

Untangling complex morphological variation: taxonomic revision of the subgenus Crematogaster (Oxygyne) in Madagascar, with insight into the evolution and biogeography of this enigmatic ant clade (Hymenoptera: Formicidae)

“…Sixteen subgenera have been erected within Crematogaster by several authors (Bolton, 2011), subdividing the species diversity into groupings based upon morphological characters. In Madagascar, Crematogaster is one of the most abundant groups of ants, often a dominant element of the forest ecosystem and nesting arboreally with polydomous colonies occupying multiple trees (Blaimer, 2010; Dejean et al , 2010). Crematogaster species described from Madagascar have been assigned previously to five of the subgeneric groupings: Decacrema , Oxygyne , Orthocrema , Mesocrema and Crematogaster (sensu stricto).…”

An ant’s-eye view of an ant-plant protection mutualism

“…In highly territorial ants, pair wise confrontation tests are effective methods to determine colony membership and to deduce territory boundaries (Dejean et al 2010). We conducted confrontation tests by placing pairs of worker ants inside clean, dry plastic vials and observing their behavior for 5 min.…”