DOI: 10.13102/sociobiology.v60i2.162-168Sociobiology 60(2): 162-168 (2013) Spatial Distribution of Acromyrmex balzani (Emery) (Hymenoptera: Formicidae: Attini) Nests Using Two Sampling Methods L Sousa-Souto, AB Viana-Junior, ES Nascimento Introduction The spatial distribution of organisms in an environ- ment is a key parameter in studies of population ecology (Krebs, 1989; Begon et al., 1996). It allows the inference of ecological aspects of great importance such as the dispersal pattern of individuals, possible existence of competition or other agonistic interactions, the density of individuals in the study area and species dominance at the community level (Brower et al., 1997). These inferences, in turn, enable the development of pest management programs (Ferguson et al., 2003), to cope with invasive species (Zhu et al., 2007) and to plan conservation strategies in the case of rare and endan- gered species (Beissinger & Westphal, 1998). Although it is a good tool in population studies, spatial distribution is dependent of several variables that determine the suitability of sites for the establishment of individuals in the environment, such as sun exposure, soil or air humidity, altitude, availability of food and shelter, and sites for nest- ing and breeding (Soares & Schoereder, 2001; Van Gils & Vanderwoude, 2012). Abstract The spatial distribution (SD) of organisms is a key parameter in studies of population ecology. Among the methods to describe the SD of sessile organisms, sampling by way of plots and transects are widely used. The measurement of the distance between individuals (“nearest neighbor”) is a simple method that has not been employed in population studies with ants. This study aimed to evaluate the SD of ant mounds of Acromyrmex balzani (Emery, 1890), using both plot sampling and nearest neighbor methods in order to evaluate which method is more appropriate for determining SD of this species. In January 2013 we established 359 plots of 10 m2 on a fragment of grass- land in Sergipe, Brazil. In the same study area 25 colonies were randomly selected and the distance of the closest neighbor colony was determined. In total, 153 ant mounds were sampled (plots) and the density was estimated in 975 × colonies ha-1. Colonies were clumped in the environment either by plot sampling (χ2 = 453.93; p < 0.05) as well as by the method of nearest neighbor (Ax = 0.67, t = -1.72, p < 0.05). The aggrega- tion of A. balzani colonies found in this study may be due to habitat heterogeneity or relate to the strategy of colony foundation. We conclude that the use of the nearest neighbor method was as accurate as the plot sampling method, providing the same results with much lower sampling effort. Sociobiology An international journal on social insects 1 - Universidade Federal de Sergipe, São Cristóvão, SE, Brasil rESEArCH ArTICLE - ANTS Article History Edited by Gilberto M M Santos, UEFS, Brazil received 10 April 2013 Initial acceptance 17 May 2013 Final acceptance 22 May 2013 Key words Population ecology, leaf-cutting ants, nest density, nearest neighbor Corresponding author: Leandro Sousa-Souto Universidade Federal de Sergipe Programa de Pós-Grad. em Ecologia e Conservação, São Cristóvão-SE, Brazil 49100-000 E-Mail: leandroufv@gmail.com In general, the distribution (dispersal) of organisms in the environment can be differentiated in three spatial ar- rangements: (1) random, (2) aggregate or contagious, when the organisms tend to be distributed in groups, and (3) regular or uniform, when the individuals are uniformly distributed in a population (Taylor, 1984; Krebs, 1989; Begon et al., 1996). In nature, organisms are rarely distributed in an arrangement as uniform as plants in agroecosystems; instead, they are usu- ally aggregative (Gao, 2013). For ants, clumped distributions may reflect the spatial heterogeneity of the habitat in relation to resource availability (Belchior et al., 2012; Van Gils & Vanderwoude, 2012), reflect the outcome of the reproductive strategy (Rissing et al., 1986; Nicholas & Vilela, 1996; De- bout et al., 2007) or are related to the social behavior of some species (Soares & Schoereder, 2001; Schatz & Lachaud, 2008). A completely random distribution (in which the posi- tion of an organism is completely independent of any other position in the same population) may reflect an environment with homogeneous provision of resources, where intraspe- cific competition is negligible (Soares & Schoereder, 2001). On the other hand, uniform distribution may also indicate the Sociobiology 60(2): 162-168 (2013) 163 existence of strong intraspecific competition between indi- viduals in the population, such as when animals defend sites for mating or foraging (Bernstein & Gobbel, 1979; Schatz & Lachaud, 2008). Two main methodological approaches are used to de- scribe the spatial distribution of organisms (Brower et al., 1997). One involves sampling through plots (frequently re- ferred to as plot sampling or quadrat sampling) where the sampling is done by marking plots in different locations in the community and counting the number of organisms (ant nests) in each plot, followed by data comparisons using in- dices and probability models (i.e. Poisson distribution and Morisita’s index) (Soares & Schoereder, 2001; Schatz & Lachaud, 2008; Silva Junior et al., 2013). Another method involves sampling the distance between individuals (usually plants and sessile organisms) or between the individual and a random point previously established, known as “nearest neighbor” method (Brower et al., 1997; Gao, 2013). Dis- tance methods can help us to determine whether ant mounds are growing or having foraging territories in discernible (and often ecologically important) patterns or are randomly dis- persed. Many intra-specific relationships among ant mounds are difficult to observe without using distance based sampling techniques. Moreover, the effectiveness of plot sampling de- pends on plot size and shape and this method fails in giving the relative positions of individuals within plots (Gao, 2013). However, due to the influence of several environmental fac- tors involved, more than one index should be estimated be- fore concluding about the spatial arrangement of a particular species (Brower et al., 1997; Mollet et al., 1984). Leaf-cutting ants of the genera Atta and Acromyrmex are considered important modifiers in their environments, promoting the turnover and aeration of soil in areas adjacent to the mounds, incorporating organic matter to the system (Moutinho et al., 2003; Sousa-Souto et al., 2008), acting in carbon and nutrient cycling (Stenberg et al., 2009; Sousa- Souto et al., 2012a) and directly affecting the plant commu- nity structure (Garrettson et al., 1998; Leal & Oliveira, 1998; Corrêia et al., 2010). However, species of these two genera are also considered major pests in Brazilian agroecosystems by causing considerable damage due to intense and constant attacks on plants at all stages of development (Della Lucia 2011; Nickele et al., 2013). For this reason, the majority of studies examining the spatial distribution of leaf-cutting ant mounds were made in reforestation areas, with the goal of developing pest management plans to control these ants (Caldeira et al., 2005; Cantareli et al., 2006; Nickele et al., 2009). This study evaluates the spatial distribution of mounds of Acromyrmex balzani using the methods of plot sampling and nearest neighbor distance. If different sampling methods produce similarly robust results, the simplest method would thus be more appropriate for determining the spatial distribu- tion of this ant species in the future. Material and Methods Study area The study was performed on a fragment of grassland, located in the municipality of São Cristovão, Sergipe, Bra- zil (11 º 00’54 “S, 37 º 12’21” W). The dominant vegeta- tion consists of grasses and herbs, mainly Paspalum notat- um Flügge (Poaceae), Cynodon dactylon L. (Poaceae) and Richardia brasiliensis Gomes (Rubiaceae) (Poderoso et al., 2009). The average annual temperature is 29 ºC with average annual rainfall of about 2000 mm. The soil type is Spodo- zol, mainly sandy clay, deep, with low fertility, high poros- ity (draining rainfall), high acidity and salinity (Sousa-Souto et al., 2012b). The leaf-cutting ant A. balzani is commonly found and is clearly the most abundant leaf-cutting ant spe- cies in the study area. Nests of A. balzani are small (0.2 to 1m2 of area) compared with other leaf-cutting ant species but with population densities that may reach beyond 100 nests per hectare (Poderoso et al., 2009; Sousa-Souto et al., 2012b; Silva Junior et al., 2013). Each nest has a single entrance (Fig. 1 A-B) with a depth varying from 12 to 150 cm. This ant species relies mainly on leaves from monocotyledons (Fowl- er et al., 1986) which are deposited within the nest chamber (Poderoso et al., 2009). The waste material is delivered out- side the colony, forming small piles of refuse (Mendes et al., 1992; Sousa-Souto et al., 2012b). Fig. 1 – Acromyrmex balzani (Emeri) in the study area. A – Workers in the nest entrance. B – Detail of a nest entrance formed by two tubes of straw and other vegetable waste. C - General view of the area with nest mounds (blank spots). L Sousa-Souto, AB Viana-Júnior, ES Nascimento - Spatial Distribution of Acromyrmex balzani nests164 Ant sampling In a fragment of approximately 0.5 ha, during Janu- ary 2013 (dry season), we established 360 plots of 2 x 5 m (10 m2), with a total sampled area of 3,600 m2 (72% of the total area of fragment). In each plot, the number of colonies of A. balzani was obtained and the data were subjected to analyses of dispersion in order to determinate the type of spatial distribution. We used three index of dispersion: The Poisson probability model of distribution, Morisita’s index of dispersion and the nearest neighbor method (Brower et al., 1997). For Poisson model, the observed frequency is com- pared with the expected frequency, calculated by the formula: P(x) = (µx e-µ)/x!, where: P(x) = probability of finding x ant nests within plot; µ = average number of nests; a positive real number (1, 2, 3...) and e = is the base of the natural logarithm (= 2.71828...). The distribution pattern obtained can be com- pared by Chi-square statistic (Brower et al., 1997). In addition to the adjustment of the Poisson distribu- tion, data were submitted to the Morisita’s index of disper- sion: Id = n (∑X2-N)/(N(N-1)) where n is the number of plots, ∑X2 is the squares of the number of ant mounds per plot, summed over all plots and N is the total number of mounds counted on all n plots (Brower et al., 1997). For the nearest neighbor method, random points (ant mounds) were located in the 5,000 m2 stand and the distance from each sampling point to the nearest ant nest was mea- sured (n = 25 mounds). Only one measurement was made from each random nest, and all distances for all mounds were summed and divided to yield one average distance. We then determined whether mounds were distributed random- ly, regularly, or were clumped using an aggregation index A1 = (D/μ)2 (Clark & Evans, 1954), where D is the mean distance between these pairs of ant mounds; that is the mean nearest neighbor distance. The statistical significance of A1 is determined by μ=1/(2√(n/A)), where SE = 0.26136/√(n2/A) and the critical value of t is that for infinite (∞) degrees of freedom. Polydomy for A. balzani has been described (Caldato, 2010), meaning, two or more ant mounds in the same plot could be subnests associated with a single colony. However, for the purpose of this study, any ant mound was considered a sampling unit, considering that the physical presence of an ant mound can affect the plant community as well as the es- tablishment of another colony, regardless of being a subnest or the main colony. Results We sampled 351 mounds of A. balzani in the 360 plots, with values ranging from 0 to 6 mounds per plot (Figs. 1C and 2). The nest density of 0.04 nests/m2 and an average number of 0.98 ant mounds/plot found in this study is high (975 × colonies ha-1), since the densities for this species can vary from 80-210 colonies × ha-1 in similar environments of Fig. 2 – Schematic representation of the 359 plots distributed in the study area (3,600 m2 of a total of 5,000 m2) and the frequency of A. balzani colonies per plot. Table 1 – The observed data from figure 01 and the probabilities expected from the Poisson Distribution with a mean (μ) of 0.98 ant mounds per plot. Number of ant mounds in plot (X) Observed frequency ƒ(X) Observed Probability p(X) Poisson Probability P(X) 0 154 0.43 0.38 1 110 0.31 0.37 2 54 0.15 0.18 3 33 0.09 0.06 4 6 0.02 0.01 5 0 0.0 0.0 6 2 <0.01 0.0 Sociobiology 60(2): 162-168 (2013) 165 the study region (Poderoso et al., 2009; Sousa-Souto et al., 2012b). For another leaf-cutting ant species (Ac. landolti) nest density can reach values of 2,000 colonies per hectare (Fowler et al., 1986). The values obtained in the plot sampling method (χ2 = 37.22; p < 0.05 and Iδ = 1.35) indicate that the colonies are clumped in the environment (Table 1). The same results were obtained using the nearest neighbor method (t = -1.72; p < 0.01). The mean distance between the pairs of ant mounds was 4.05 m and most of them (70%) were in a range of 2 to 6 m (Fig 3). Discussion The present study evaluated the spatial distribution of A. balzani through sampling plots and nearest neighbor methods. Both methods indicated the ant mounds were ag- gregately distributed, corroborating our hypothesis that dif- ferent sampling methods give similar results for nest spatial distribution. These results contrast with previous studies of leaf-cutting ant species in Eucalyptus spp. forests, where the distribution of nests was random (Caldeira et al., 2005; Nick- ele et al., 2009). However, the aggregate spatial arrangement of ant nests has also been observed in pasture (Silva Junior et al., 2013) as well as in environments with native vegeta- tion (Rissing et al., 1986; Soares & Schoereder 2001). Other ant species also show an aggregate distribution pattern, such as Solenopsis invicta (Buren) (Almeida et al., 2007), Myc- etophylax simplex (Emery) (Albuquerque et al., 2005) and several litter ant species (Soares & Schoereder, 2001). For social insects, aggregate distribution of nests may occur in response to physical (habitat heterogeneity) and biological factors (low rate of dispersion, nest budding or chance of survival increased when the organisms are grouped) (Nicholas & Vilela, 1996; Elisei et al., 2012; Leal et al., 2012). Termites, for example, have aggregated distribu- tion when favorable soil conditions to the nest establishment are distributed in patches (Dias et al., 2012) or when foraging sites are sparsely distributed (Filho et al., 2012). The uniform pattern of distribution is common in some ant species and occurs when there is high nest density (Nicholas & Vilela, 1996). Such a distribution may be due to high intraspecific competition for resources, involving territory defense by colonies (Bernstein & Gobbel, 1979; Soares & Schoereder, 2001). The usual limiting resources for ants are food and nesting sites (Fowler et al., 1983; Leal et al., 2012). It is pos- sible, however, that these resources are not limited for leaf- cutting ants in pasture and cultivated fields or Eucalyptus for- ests, so that intra and interspecific competition might not be strong because these habitats have a constant abundance of food resources. The high density of aggregately distributed ant mounds found in this study indicate that A. balzani do not show aggressive defense behavior for their foraging sites. In fact, it is common to find workers of different colonies in the same foraging site without any incidents of aggressive behavior (personal obs.). Besides, the occurrence of subnests around the main nest (polydomy) was found for A. balzani (Caldato, 2010). One could say that polydomy can mask the real dispersion pattern of this ant species, because a propor- tion of ant mounds could be subnests from a same main col- ony, leading to a clumped pattern in the landscape. Since the confirmation of polydomy is only possible through experi- ments of aggression (Caldato, 2010), and considering that the impact of an ant mound on herbivory is similar, regardless of the origin of the mound (subnests or the main nest), we can assume that the aggregate pattern of ant colonies is prevalent, even with a high rate of polydomy. Fig 3. – Frequency of ant mounds of A. balzani according to the distance between pairs of mounds. The high density of ant mounds found in the pres- ent study can be explained by the preference of these ants for open and human perturbed areas. Previous studies have found that other leaf-cutting ant species such as Acromyrmex lobicornis (Emery), Ac. landolti Forel and Atta laevigata (F. Smith) are abundant in areas with greater sun exposure, mostly open places (grasslands and pastures) or sites with trees or shrubs with reduced canopy cover (Bucher & Monte- negro, 1974; Clark & Evans, 1954; Nickele et al., 2009; Silva Junior et al., 2013). It is possible that interspecific competition also act in determining the aggregate pattern of colonies of leaf-cutting ants. Colonies of species with large numbers of workers and aggressive behavior, such as Atta sexdens or At. laevigata may be present in foraging areas coexisting with Acromyrmex spp., confining the latter to restricted sites within the frag- ment or forcing these colonies to emigrate (Fowler, 1977; L Sousa-Souto, AB Viana-Júnior, ES Nascimento - Spatial Distribution of Acromyrmex balzani nests166 1983). In his study about distribution of leaf-cutting ants in Paraguay, Fowler (1983) proposed that the most important factor determining the local abundance of leaf-cutting ant species was interspecific competition. In other words, in sites where Acromyrmex species were locally abundant, Atta spe- cies were rare or absent, and vice versa. Indeed, in our study area we found two colonies of At. opaciceps with an average area of 5 m2 which were located on plots which also hadcolo- nies of Ac. balzani. It is possible that competition is mini- mized by differentiation of the time of foraging (Ac. balzani is diurnal whereas At. opaciceps is nocturnal) and the type of resources collected (leaves of grasses versus shrubs and trees). In a previous study, Wetterer (1991) investigated the overlap of foraging areas between colonies of At. cephalotes and Ac. octospinosus, noting that there was only a single case of simultaneous exploitation of of the same resource (flowers). Several other differences in foraging strategies (e.g., type of substrate harvested, foraging time, size range of foragers) were also concluded to contribute to the sustained coexistence of these species (Wetterer, 1991). Future stud- ies focusing on the interaction of these two genera will help clarify whether the dispersion of colonies is determined by the presence of interspecific competitors. The use of plots is a well-established method for studying the dispersion pattern of colonies in leaf-cutting ants. This method is appropriate in reforestation areas (Pinus and Eucalyptus spp.), where planting areas are divided into quadrats according to the age of trees. However, the use of the nearest neighbor method, as seen in this study, proved to be just as effective as plot sampling for determining distribution patterns of colonies in environments under native vegetation and fragments with irregular shape, making it a preferred method since we can provide the same results with lower sampling effort, com- pared with plot sampling method. Acknowledgments The authors are grateful to Hans Kelstrup for the revi- sion of the English and to Bianca Ambrogi for her comments in a previous version. We thank two anonymous reviewers for helpful comments on the manuscript. This study was sup- ported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). References Albuquerque, E. Z., Diehl-Fleig, E. & Diehl, E. (2005). Density and distribution of nests of Mycetophylax simplex (Emery) (Hymenoptera, Formicidae) in areas with mobile dunes on the northern coast of Rio Grande do Sul, Brazil. Rev. Bras. Entomol., 49, 123-126. Almeida, F. S., Queiroz, J. M. & Mayhé-Nunez, A. J. (2007). Distribuição e abundância de ninhos de Solenopsis invicta Buren (Hymenoptera: Formicidae) em um agroecossistema diversificado sob manejo orgânico. Floresta e Ambiente, 14 (1), 33 – 43. Begon, M., J.L. Harper and C.R. Towsend. (1996). Ecology: Individuals,Populations and Communities . 3rd ed. Black- well Scientific, Oxford, 1068 pp. Beissinger, S.R. & Westphal, M.I. (1998). On the use of demographic models of population viability in endangered species management. J. Wild. Manag., 62(3): 821–841. doi:10.2307/3802534 Belchior, C., Del-Claro, K., Oliveira, P. S. (2012). Seasonal patterns in the foraging ecology of the harvester ant Pogono- myrmex naegelii (Formicidae, Myrmicinae) in a Neotropical savanna: daily rhythms, shifts in granivory and carnivory, and home range. Arthrop.-Plant Inter., 6(4): 571-582. doi: 10.1007/s11829-012-9208-1 Bernstein, R. A. & Gobbel, M. (1979). Partitioning of space in communities of ants. J. Anim. Ecol., 48: 931–942. Brower, J. E., Zar, J. H. & Von Ende, C. N. (1997). Field and Laboratory Methods for General Ecology. New York: WCB Bucher, E.H., Montenegro, R. (1974). Hábitos forrajeros de cuatro hormigas simpátridas del gênero Acromyrmex (Hy- menoptera: Formicidae). Ecología, 2: 47-53. Caldato, N. (2010). Biologia de Acromyrmex balzani Em- ery, 1890 (Hymenoptera, Formicidae). Master Degree Dis- sertation. Faculdade de Ciências Agronômicas, UNESP, Botucatu, 92 p. Caldeira M.C., Zanetti R., Morais, J.C. & Zanuncio, J.C. (2005). Distribuição espacial de sauveiros (Hymenoptera: Formicidae) em eucaliptais. Cerne, 11: 34-39. Cantarelli, E. B., Costa, E. C., Zanetti, R. & Pezzutti, R. V. (2006). Plano de amostragem de Acromyrmex spp. (Hy- menoptera: Formicidae) em áreas de pré plantio de Pinus spp. Cienc Rural, 36: 385-390. Clark, P.J. & Evans, F.C. (1954). Distance to nearest neigh- bor as a measure of spatial relationships in populations. Ecol- ogy, 35: 445-453. Corrêa, M. M., Silva, P. S. D., Wirth, R., Tabarelli, M., Leal, I. R. (2010). How leaf-cutting ants impact forests: drastic nest effects on light environment and plant assemblages. Oecologia, 162: 103-115. Debout, B., Schatz, G., Elias, M., Mckey, D. (2007). Poly- domy in ants: what we know, what we think we know, and what remains to be done. Biol. J. Linn. Soc., 90: 319–348. doi: 10.1111/j.1095-8312.2007.00728.x Della Lucia, T. M. C. (2011). Formigas cortadeiras: da bio- ecologia ao manejo. Viçosa, MG: Ed da UFV. Dias, N. P., Medeiros, L. R., Pazini, J. B. & Silva, F. F. (2012). Sociobiology 60(2): 162-168 (2013) 167 Distribuição espacial de Procornitermes sp. (Isoptera: Ter- mitidae) em função das propriedades físicas do solo em área de pastagem no município de São Borja, Rio Grande do Sul. Rev. Bras. Agroecol., 7(2): 104-111. Elisei, T.,Ribeiro Junior, C., Fernandez, A. J., NUNES, J. V., Souza, A. R., Prezoto, F. (2012). Management of social wasp colonies in eucalyptus plantations (Hymenoptera:Vespidae). Sociobiology, 59(3): 1167-1174. Ferguson, A.W., Klukowski, Z., Walczak, B., Clark, S.J., Mugglestone, M.A., Perry, J.N. & Williams, I.H. (2003). Spatial distribution of pest insects in oilseed rape: implications for integrated pest management. Agric. Ecos. Environ., 95: 509–521. Filho, O. P., Souza, J. C., Souza, M. D. & Dorval, A. (2012). Distribuição espacial de cupinzeiros de Cornitermes snyderi (Isoptera: Termitidae) e sua associação com teca. Pesq. Flor. Bras. 32(70): 59-66. Fowler, H. G. (1977). Field response of Acromyrmex cras- sispinus (Forel) to aggression by Atta sexdens (Linn.) and predation by Labidus predator (Fr. Smith) (Hymenoptera: Formicidae). Aggress. Behav., 3: 385-391. Fowler, H. G. (1983). Distribution patterns of Paraguayan leaf-cutting ants (Atta and Acromyrmex) (Formicidae: At- tini). Stud. Neotrop. Fauna Environ., 18: 121-138. Fowler, H.G., Forti, L. C., Pereira-da-Silva, V., Saes. N. B. (1986). Economics of grass-cutting ants. In: C.S. Lofgren & R.K. Vander Meer (Eds.), Fire ants and leaf-cutting ants – biology and management (p. 18-35). Boulder: Westview Press. Gao, M. (2013). Detecting spatial aggregation from distance sampling: a probability distribution model of nearest neigh- bor distance. Ecol. Res., 28: 397–405. doi: 10.1007/s11284- 013-1029-x Garrettson, M., Stetzel, J. F., Halpern, B. S., Hearn, D. J., Lu- cey, B. T. & Mckone, M. J. (1998). Diversity and abundance of understorey plants on active and abandoned nests of leaf- cutting ants (Atta cephalotes) in a Costa Rican rain forest. J. Trop. Ecol., 14(1): 17-26. Krebs, C.J. (1989). Ecological Methodology. Harper and Row, New York, 654 pp. Leal, I. R., Oliveira, P. S. (1998). Interactions between fun- gus-growing ants (Attini), fruits and seeds in cerrado vegeta- tion in Southeast Brazil. Biotropica, 30: 170-178. Leal, I. R., Filgueiras, B. K. C., Gomes, J. P., Iannuzzi, L., Andersen, A. N. (2012) Effects of habitat fragmentation on ant richness and functional composition in Brazilian Atlantic forest. Biodiv. Conserv., 21: 1687–1701. Mendes, W. B. A., Freire, J. A. H., Loureiro, M. C., Nogueira, S. B., Vilela, E. F. & Della Lucia, T. M. C. (1992). Aspectos ecológicos de Acromyrmex (Moellerius) balzani (EMERY, 1890) (Formicidae: Attini) no município de São Geraldo, Minas Gerais. An. Soc. Entomol. Bras. 21, 155–168. Mollet, N., Trumble, J. T. & Sevacherian, V. (1984). Com- parison of dispersion and regression indices for Tetranychus cinnabarinus (Boisduval) (Acari: Tetranychidae) populations in cotton. Environ. Entomol., 13: 1511-1514. Moutinho, P., Nepstad, D. C., Davidson, E. A. (2003). Influ- ence of leaf-cutting ant nests on secondary forest growth and soil properties in Amazônia. Ecology, 84: 1265-1276. Nicholas, J. T. & Vilela, E. F. (1996). Territorial mechanisms in postnuptial flight gynes of the leaf-cutting ant Atta laevi- gata (F.Smith). An. Soc. Entomol. Bras., 24: 389-400. Nickele, M. A., Pie, M. R., Filho, W. R. & Penteado, S. R. C. (2013). Formigas cultivadoras de fungos: estado da arte e direcionamento para pesquisas futuras. Braz. J. For. Res., 33 (73): 53-72. Nickele, M.A., Reis, W.F., Oliveira, E.B. & Iede, E.T. (2009) Densidade e tamanho de formigueiros de Acromyrmex cras- sispinus em plantios de Pinus taeda. Pesq. Agropec. Bras., 44(4): 347-353. Poderoso, J.C.M., Ribeiro, G.T., Gonçalves, G.B., Men- donça, P.D., Polanczyk, R.A., Zanetti, R., Serrão, J.E. & Zanuncio, J.C. (2009). Nest and foraging characteristics of Acromyrmex landolti balzani (Hymenoptera: Formicidae) in Northeast Brazil. Sociobiology, 54: 361-372. Rissing, S. W., Johnson, R. A. & Pollock, G. B. (1986). Natal nest distribution and pleometrosis in the desert leaf-cutter ant Acromyrmex versicolor (Pergande) (Hymenoptera: Formici- dae). Psyche, 93: 177-186. Schatz, B. & Lachaud, J-P. (2008). Effect of high nest density on spatial relationships in two dominant Ectatommine ants (Hymenoptera: Formicidae). Sociobiology, 58: 623-643. Silva Júnior, M.R., Castellani, M.A., Moreira, A.A., D’esquivel, M.S., Forti, L.C. & Lacau, S. (2013). Spatial Distribution and architecture of Acromyrmex landolti Forel (Hymenoptera, Formicidae) nests in pastures of southwest- ern Bahia, Brazil. Sociobiology, 60: 20-29. doi: 10.13102/ sociobiology.v60i1.20-29 Soares, S. M. & Schoereder, J. H. (2001) Ant-nest distribu- tion in a remnant of tropical rainforest in southeastern Brazil. Insectes Soc., 48: 280-286. Sousa-Souto, L., Guerra, M. B. B., Ambrogi, B. G. & Perei- ra-Filho, E.R. (2012a). Nest refuse of leaf-cutting ants mineralize faster than leaf fragments: Results from a field experiment in Northeast Brazil. Appl. Soil Ecol., 61: 131- 136. Sousa-Souto, L., Santos, D. C. J., Ambrogi, B. G., Santos, M. J. C., Guerra, M. B. B. & Pereira-Filho, E. R. (2012b). L Sousa-Souto, AB Viana-Júnior, ES Nascimento - Spatial Distribution of Acromyrmex balzani nests168 Increased CO2 emission and organic matter decomposi- tion by leaf-cutting ant nests in a coastal environment. Soil Biol. Biochem., 44: 21–25. Sousa-Souto, L., Schoereder, J. H., Schaefer, C. E. G. R. & Silva, W. L. (2008) Ant nests and soil nutrient availability: the negative impact of fire. J. Trop. Ecol., 24: 639-646. Taylor, L. R. (1984). Assessing and interpreting the spatial distributions of insect populations. Annu. Rev. Entomol., 29: 321-357. Van Gils, H. A. J. A. & Vanderwoude, C. (2012). Leafcutter ant (Atta sexdens) (Hymenoptera: Formicidae) nest distri- bution responds to canopy removal and changes in micro- climate in the southern colombian Amazon. Fla. Entomol., 95: 914-921. Wetterer, J. K. (1991). Foraging ecology of the leaf-cutting ant Acromyrmex octospinosus in a Costa Rican rain forest. Psyche, 98: 361-372. Zanuncio, J. C., Lopes, E. T., Zanetti, R., Pratissoli, D. & Couto, L. (2002). Spatial distribuition of nests of the leaf- cutting ant Atta sexdens rubropilosa (Hymenoptera: Formici- dae) in plantations of Eucalyptus urophylla in Brasil. Socio- biology, 39: 231-242. Zhu, L., Sun, O. J., Sang, W., Li, Z., Ma, K. (2007). Pre- dicting the spatial distribution of an invasive plant species (Eupatorium adenophorum) in China. Landsc. Ecol., 22(8): 1143-1154. doi: 10.1007/s10980-007-9096-4