Influence of forest type and tree species on canopy ants (Hymenoptera: Formicidae) in Budongo Forest, Uganda

Abstract

The arboreal ant fauna was investigated in Budongo Forest, a seasonal rain forest in Uganda, using the insecticidal fogging technique. Ants were collected from 61 trees, between 7 and 33 m in height, belonging to four tree species. Trees were growing in adjacent plots of forests characterized by different use and structure: an old primary forest, a primary swamp forest along a small river, and a secondary forest where selective logging was carried out for 30 years. A total number of 37,065 ants, belonging to 161 species in 30 genera were collected. Considering the high number of species found only once, the completeness of the canopy ant fauna was relatively high and of relatively similar magnitude as samples from the Neotropics or the Oriental region. Up to 37 ant species on a single tree, with an average of 18.2 species per tree, were found. Forty-four ant species (28.1%) were found only once, less than ten individuals were found for each of 88 species (54.7%), but 64.0% of all individuals belonged to one of five species. Considering the high numerical dominance of a few ant species like a Pheidole sp., Tetramorium aculeatum (Mayr) and a Crematogaster sp., there is some evidence for an ant mosaic in the lower canopy of the Budongo Forest. Individual numbers of ants were strongly correlated with nests in the fogged tree, though the ants were not homogeneously distributed in the tree crowns. Diversity measures that strongly depend on individual numbers such as the Morisita-Horn index or rarefaction methods were calculated, but results were not concordant with those of incidence-based estimates such as jack-knife calculations. Differences in ant species richness and faunal composition between tree species were low, but more significant between forest types. The ant fauna in the secondary forest was less diverse with 12.6% fewer species compared to the primary forest sites. The average number of ant species per tree was significantly lower in the secondary forest (<20% of the species; F=8.03, df=59, P<0.01) than in the undisturbed forest types. Cataulacus, Leptothorax, Tetraponera, and Polyrhachis, which are typical canopy-dwelling ant genera, had a significantly higher diversity and frequency in the two primary forest types (F=4.17, df=53, P<0.05). Secondary forest trees are often younger, lacking dead branches and epiphytes which are important requisites for ant colonization on trees.

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

“…Yet, one might wonder how this can occur despite the fact that the expansion of the TDAAs' territories obligatorily passes through the occupancy of neighboring trees whose taxa are distributed more or less haphazardly. In fact, this host-tree selection is also influenced by the age of the trees, the presence of extrafloral nectaries, and the taxa of the associated hemipterans (Bigger 1993;Majer 1993;Blüthgen et al 2000Blüthgen et al , 2004Dejean et al 2000Dejean et al , 2007Dejean et al , 2015Schulz and Wagner 2002;Blüthgen and Stork 2007). All these parameters likely play a role in the expansion of the territories, favoring those ant species which can meet their requirements during competition for a given tree.…”

“…Indeed, ant mosaics have been observed in the upper canopies of African, Asian, and Neotropical rainforests (Blüthgen and Stork 2007;Davidson et al 2007;Dejean et al 2007;Ribeiro et al 2013). Second, selective plant attractiveness has been shown experimentally (Djiéto-Lordon and Dejean 1999) or deduced through the distribution of TDAAs (Dejean et al 2007), and an ontogenetic succession of ant species follows the sequence of stages in tree development (Bigger 1993;Schulz and Wagner 2002;Watt et al 2002;Dejean et al 2008Dejean et al , 2015Souza da Conceição et al 2015). Third, when the canopy is irregular with tree crowns at different heights, the continuity of the territories is broken.…”

Impacts of major predators on tropical agroforest arthropods: comparisons within and across taxa

“…Ants and birds are taxonomically important predators of arthropods in natural and agricultural settings (Way and Khoo 1992;Marquis and Whelan 1994;Perfecto and Castiñeiras 1998;Greenberg et al 2000;Schmitz et al 2000;Sanz 2001;Mols and Visser 2002;Van Bael et al 2003), and likely differentially affect prey based on differences in their mobility, size, and life history. Ants are numerous in tropical forests (>10,000 ha −1 ) (Schulz and Wagner 2002;Watt et al 2002), patrol smaller areas than birds, cooperatively forage (using recruitment or tandem running) using chemical signals to alert other ants (Hölldobler and Wilson 1990), and generally cannot easily attack large or highly mobile prey (Koptur 1984). Relative to ants, birds are scarce (10-50 individuals ha −1 of forest or agroforest, R. Greenberg, personal observation).…”

Inventário estruturado de formigas (Hymenoptera, Formicidae) em floresta ombrófila de encosta na ilha da Marambaia, RJ

“…Apenas um pequeno número de armadilhas conseguiu capturar formigas. Quando comparados com outros estudos de formicifauna de dossel (SCHONBERG et al, 2004;SCHULZ & WAGNER, 2002), o número de espécies registrado na copa das árvores na ilha da Marambaia foi pequeno. Isto ocorreu porque a instalação das armadilhas não ocorreu adequadamente devido às lianas, epífitas e do próprio sub-bosque.…”