Hindawi Publishing Corporation Psyche Volume 2012, Article ID 896473, 8 pages doi:10.1155/2012/896473 Research Article Undecomposed Twigs in the Leaf Litter as Nest-Building Resources for Ants (Hymenoptera: Formicidae) in Areas of the Atlantic Forest in the Southeastern Region of Brazil Tae Tanaami Fernandes,1 Rogerio´ Rosa da Silva,2 Debora´ Rodrigues de Souza,1 Natalia´ Araujo,´ 1 and Maria Santina de Castro Morini1 1 Laboratorio´ de Mirmecologia, Universidade de Mogi das Cruzes, 08701-970 Mogi das Cruzes, SP, Brazil 2 Museu de Zoologia da Universidade de Sao˜ Paulo, Avenida Nazar´e 481, Ipiranga, 04263-000 Sao˜ Paulo, SP, Brazil Correspondence should be addressed to Maria Santina de Castro Morini, [email protected] Received 12 June 2012; Revised 15 September 2012; Accepted 17 September 2012 Academic Editor: Diana E. Wheeler Copyright © 2012 Tae Tanaami Fernandes et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In tropical forests, the leaf-litter stratum exhibits one of the greatest abundances of ant species. This diversity is associated with the variety of available locations for nest building. Ant nests can be found in various microhabitats, including tree trunks and fallen twigs in different stages of decomposition. In this study, we aimed to investigate undecomposed twigs as nest-building resources in the leaf litter of dense ombrophilous forest areas in the southeastern region of Brazil. Demographic data concerning the ant colonies, the physical characteristics of the nests, and the population and structural of the forest were observed. Collections were performed manually over four months in closed canopy locations that did not have trails or flooded areas. A total of 294 nests were collected, and 34 ant species were recorded. Pheidole, Camponotus,andHypoponera were the richest genera observed; these genera were also among the most populous and exhibited the greatest abundance of nests. We found no association between population size and nest diameter. Only tree cover influenced the nest abundance and species richness. Our data indicate that undecomposed twigs may be part of the life cycle of many species and are important for maintaining ant diversity in the leaf litter. 1. Introduction rich in terms of taxonomy, morphology, and function [13– 15], and its high diversity [5, 14, 16] has been associated with Ants represent only 2% of the described insect fauna; how- vegetation structure and the biotic and abiotic characteristics ever, they constitute more than 50% of the animal biomass of the habitat [17, 18]. of tropical forests, savannas, fields, and other important In the leaf litter, ants have access to food resources, habitats [1, 2]. The majority of ant species inhabit the locations for nest building, and a favorable microclimate soil and/or leaf litter [3]. In tropical forests, approximately [17, 19–23]. The variation in nest-building locations among 50% of the ant fauna may be associated with the leaf litter species is a prerequisite for the maintenance of leaf-litter [4], but the factors that structure these communities are ant species diversity [24]. Despite a reasonable amount of poorly understood [5, 6], especially for communities that ecological knowledge, the biology of the majority of leaf- live in the leaf litter of the Brazilian Atlantic Rainforest. One litter species is still largely unknown [25]. fundamental goal of ecology is to understand the structure Litter-nesting ants are a particularly useful group for and maintenance of diverse tropical assemblages [7]. community-level comparisons because litter can be exhaus- Studies of the diversity of leaf-litter ants are relatively tively searched to provide accurate data on nest density and abundant [8, 9], and several studies have been conducted species richness, regardless of weather [6]. Ant nests in the in the Atlantic Rainforest sites selected for the present study leaf litter are located among interstices, in the interior of (see [10–12]). The ant fauna that inhabits the leaf litter is fruits, between leaves, or in branches and trunks at various 2 Psyche Table 1: Locations of sampling sites in southeastern Sao˜ Paulo state, Brazil. Municipality Sampling sites (acronym) Geographical coordinates Altitude (m) Size∗ (ha) Ribeirao˜ do Campo Dam (RC) S 23◦3810;W45◦4957 780 200 Ponte Nova Dam (PN) S 23◦3419;W45◦4410 783 200 Salesopolis´ Reserva do Incra (RI) S 23◦3639;W45◦4947 750 130 Estac¸ao˜ Biologica´ de Boraceia´ (EBB) S 23◦3156;W45◦5047 780 96 Museum of Energy Dam (ME) S 23◦3347;W45◦5010 790 100 Municipal Natural Park Francisco Affonso de Mello (PNMFAM) S 23◦3122;W46◦1116 810 350 Itapeti Ecological Station (EEI) S 23◦3033;W46◦1414 820 89 Mogi das Cruzes Legal Reserve (RL) S 23◦3035;W46◦1422 830 104 Agro-Environmental Nucleus (NA) S 23◦2947;W46◦1227 810 20 Fazenda Santo Alberto (SA) S 23◦2621;W46◦0950 690 130 ∗ Approximate size of the sampling areas. stages of decomposition [26]. Among the resources provided All of the undecomposed twigs with lengths of 10 to by the leaf litter, twigs/trunks are essential for ant nests to 30 cm and containing ants were manually collected and occur [27]. individually placed in plastic bags for later identification. Small ants and those with little dispersal ability, such This twig size was selected because smaller twigs were as species of Myrmicinae and the tribe Dacetini or species generally decomposing in the sampling areas. Furthermore, of Ponerinae, can be found by breaking pieces of branches the selected size was the approximate size of most of the and twigs that have fallen in the leaf litter or by looking ant-colonized twigs [27]. Only the twigs that were found on in rotten trunks [28]. However, fallen trunks are colonized the surface were collected because they are the most recent by few species [29]; twigs are important for the nesting of resources in the leaf litter. a higher number of species, especially twigs in stages of The number of twigs with nests was recorded (=the decomposition [27]. This preference may be related to the density of the nests), and the ants were identified to the ants’ access to the inside, as digging is easier [27], or to genus level using identification keys. The species were moisture, which is the limiting factor for leaf-litter ants [5]. identified by comparison with the examples deposited in In the present study, we investigated in detail the ant the reference collection of the Zoological Museum of the species that use twigs that are still undecomposed, a subset University of Sao˜ Paulo (Museu Zoologia da Universidade of twigs that is less exploited by ants [27]. Furthermore, de Sao˜ Paulo) (MZSP). The taxonomic scheme proposed by to investigate the determinants of community organization, [33] was used. Vouchers are deposited in the collection of we collected measurements related to twig characteristics, the Myrmecology Laboratory of the University of Mogi das colony structure (workers, alates, and immature ants), can- Cruzes (Universidade de Mogi das Cruzes) and the MZSP. opy cover, and litter depth. 2. Methods 2.2. Characterization of the Nests, Demographic Data, Canopy Cover, and Litter Depth. Using a digital pachymeter, the total 2.1. Study Area and Sampling. Thecolonieswerecollected diameter of the twigs that contained colonies was measured; in 10 dense ombrophilous forest fragments [30]located fivemeasurementswereconductedoneachtwig.Thecounts in the Upper Tieteˆ Hydrographic Basin in the state of of immature ants (eggs, larvae, and pupae) and workers were Sao˜ Paulo, Brazil (Table 1). The sampling expeditions were performed using a manual counter. only conducted once during the experimental period. The The canopy cover was recorded at the center and at the samples were collected between September and December vertices of each of the 16 m2 plots using a Nikon D80 digital of 2010 (approximately one sampling per week), spanning camera with a fish-eye objective. The Gap Light Analyzer the region’s rainy season [31]. Each sampling expedition was (GLA) application version 2.0 was used to analyze the images conducted one day after rain in locations without trails, [34]. without flooded areas and under a closed canopy. The The litter depth was measured using calipers at the vegetation of the collection areas was similar and composed corners and in the center of each 1 m2 parcel. These small oftreesthatwere2to20minheightwithtrunksthathad parcelswererandomlymarkedwithineach16m2 parcel. The a diameter at chest height that was equal to or greater than average of five values was used to define the stratum depth. 20 cm. Six 16 m2 parcels were delimited in each area along a linear transect. The plots were separated by 50 m to ensure 2.3. Data Analysis. Comparisons among the collection sites the independence of the samples [16, 32]. were made using the number of occurrences of the species The sampling effort for each plot was constant (collection (presence and absence data). The ant richness was compared time = 30 minutes, and number of collectors = 3perplot). using accumulation curves based on the number of species Psyche 3 45 40 Estimated richness 35 30 Observed richness 25 20 Species richness 15 10 5 0 3.37 30.3 50.5 70.7 90.9 10.1 16.83 23.57 43.77 77.43 84.17 151.5 131.3 171.7 191.9 37.03 57.23 63.97 97.63 111.1 144.77 158.23 104.37 117.83 124.57 138.03 164.97 178.43 185.17 198.63 Occurrence Figure 1: Accumulation and estimated species richness curves in undecomposed twigs in the leaf litter of dense ombrophilous forest. that occurred. The expected number of species was deter- of nests.