Trichome Removal by Hitchhikers in Two Leaf-cutting Ant Species (Hymenoptera: Formicidae)

Despite the known evidence that hitchhiker ants protect workers against attack by phorid parasitoids, several alternative hypotheses are suggested for the occurrence of hitchhikers on leaf-cutting ants. One hypothesis suggests that hitchhikers clean leaf fragments and remove pathogens. We hypothesized that hitchhikers can act in the removal of leaf trichomes. Activities of hitchhikers (HH) are reported based on three laboratory and eight field colonies of leaf-cutting ants (Atta spp.). We evaluated whether the presence of trichomes increases the frequency of HH in leaf fragments transported to the colony. Furthermore, we evaluated if fragment size and the time that the fragment remains in the foraging arena could influence HH frequency. The removal of trichomes by HH of laboratory colonies was recorded on video. Hitchhikers were more frequent in fragments with trichomes in both laboratory and field colonies. In the field, the distance from the foraging site did not influence the amount of HH. The proportion of HH in laboratory, however, was most frequent only during the first hour of foraging. The presence of HH is correlated to the size of fragments. We also observed removal of trichomes as an additional role of hitchhikers

Spatial Distribution of Acromyrmex balzani (Emery) (Hymenoptera: Formicidae: Attini) Nests Using Two Sampling Methods

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 grassland 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 aggregation 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

Composition and Richness of Arboreal ants in Fragments of Brazilian Caatinga: Effects of Secondary Succession

Ecological succession is a complex processes involving changes in the structure of plant community and it is an important factor determining the structure of arboreal ants assemblages, but little is known about the effects of succession on ant assemblages in regions of Tropical Dry Forests (TDFs), such as the Brazilian Caatinga. The aim of this study was to investigate the effects of ecological succession on the richness and species composition of arboreal ants in fragments of Caatinga, testing the following hypothesis: i) the richness of arboreal ants increases along a gradient of forest succession, in response to tree richness and/or density; ii) species composition of arboreal ants differs among stages of forest succession due to differences in vegetation structure in theses stages. This study was conducted in 15 plots distributed in three areas with different stages of secondary succession (early, intermediate and late). Tree density and richness were used as surrogate of vegetation structure. Ants were sampled using the technique of beating the foliage and baited pitfall traps, where five trees were sampled per plot, totaling 75 individual trees sampled. We sampled 37 species of ants, distributed in 16 genera and five subfamilies. Ant richness differed among stages of succession and seasons, with higher number of species in the late succession and rainy period, also increasing with tree richness and density. Besides, there was a distinct composition of ant species among stages of succession and seasons. Results obtained in this study reinforce the importance of using ants as environmental bioindicators, since the sensitivity to environmental variations of this group enables us to differentiate early and late successional stages of forest succession in Caatinga environment

Age Polyethism in Atta sexdens (Linnaeus) (Hymenoptera: Formicidae)

This study aimed to verify age polyethism occurrence in medium-sized (cephalic capsule = 2.3 ± 0.21 mm) and small-sized (cc = 1.4 ± 0.10 mm) workers from Atta sexdens (Linnaeus) colonies. Four laboratory colonies were used, and they were maintained at 25 ± 2 °C, with 75 ± 3% relative humidity and a 12-hour photoperiod. Workers from these colonies were marked after their emergence and observed throughout their lifetime to determine which tasks they performed. The number of ants performing each activity was analyzed using linear mixed-effect models (LME), considering the temporal effect and the block design (colonies). We found that fungal garden maintenance tasks were frequent for both sizes, but their occurrence decreased significantly from the ninth week. The foraging activity occurred gradually in both sizes, with stabilization in the number of workers from the fourth week onwards and declined in the last three weeks of lifespan. Waste management tasks occurred throughout life but were more frequent during the first two weeks of life, in both medium and small workers. Therefore, age polyethism may be related to all activities; however, foraging tasks presented a distinct pattern compared to tasks in the fungus garden and refuse dump, where younger ants were more frequently observed

Ant assemblages (Hymenoptera: Formicidae) in three different stages of forest regeneration in a fragment of Atlantic Forest in Sergipe, Brazil

This study aimed to compare the soil ant communities in the Atlantic Forest, in two areas in the restoration process; an area reforested for seven years and another for five years, and a native forest fragment, located near Laranjeiras city in Sergipe State, Brazil, in February (dry season) and June (wet season) 2012. We estimated whether the richness and composition of ants significantly differed between areas. In each sampling area, five plots (20 × 50m) were delineated, spaced 150 m apart, in which five pitfall traps without bait were installed, located 10 m apart, totaling 25 traps/sample area. We sampled 82 morphospecies distributed among 31 genera and seven subfamilies. The richness of ants did not differ between the three study areas (F = 1.71, p = 0.19). The species composition of ants did not differ between forested areas, but differences were observed in the native forest fragment. The species with the highest frequency of occurrence that can serve as indicators in reforested areas were: Pheidole (group Fallax) sp7, Camponotus (Myrmaphaenus) and Crematogaster abstinens. In remnant forests, the species Camponotus renggeri, Pheidole sp.4 and Pseudomyrmex tenuis can indicate environments unless they are disturbed. The results show that ants are sensitive to changes in vegetation and can be used as bioindicators of disturbed areas and/or native forests, and also highlight the importance of conserving remaining forests

FATORES AMBIENTAIS AFETAM A ABUNDÂNCIA DE BROMÉLIAS EPÍFITAS EM FLORESTA TROPICAL SAZONAL SECA

Epiphytes can have both your richness and abundance altered by environmental conditions. In this study, we tested whether host plant characteristics (phorophyte) and other environmental factors contribute to the increased abundance of vascular epiphytes. Seventy-five fixed 20 × 20 m plots were sampled, distributed among three fragments of Dry Seasonal Tropical Forest (Caatinga) in three municipalities of Sergipe, Brazil: Poço Redondo (area 1), Porto da Folha (area 2) and Poço Verde (area 3). The hypotheses tested were: I. the greater the structural complexity of the phorophyte, greater the abundance of epiphytes in response to a greater diversity of fixing sites; II. Epiphyte abundance will be positively related to environmental factors that favor photosynthetic activity and nutrient absorption. Thus, a positive relationship between abundance and light, air relative humidity and altitude is expected, as well as a negative relationship between abundance, air temperature (possible water stress) and canopy cover (greater shading). 2,728 epiphytes were observed belonging to six species of Bromeliaceae, registered in 514 phorophytes of 29 species and 15 families. The abundance of epiphytes responded to some characteristics of the phorophytes and some of the abiotic factors. Thus, trunks with larger diameter and number of branches, smooth rhytidome and higher temperatures positively influenced the abundance of epiphytes, while increases in altitude and humidity affected the abundance negatively. It is concluded that the abundance of epiphytes in Caatinga fragments is directly associated with factors such as phorophyte structure and microclimatic conditions.Keywords: Caatinga, Interaction epiphyte-phorophyte, Microclimate.As epífitas podem ter tanto a riqueza quanto a abundância alteradas pelas condições ambientais. Nesse estudo, testou-se se características da planta hospedeira (forófito) e outros fatores ambientais contribuem com o aumento da abundância de epífitas vasculares. Foram amostradas 75 parcelas fixas de 20 × 20 m, distribuídas por três fragmentos de Floresta Tropical Sazonal Seca (Caatinga) em três municípios de Sergipe, Brasil: Poço Redondo, Porto da Folha e Poço Verde. As hipóteses testadas foram: I. quanto maior a complexidade estrutural do forófito, maior será a abundância das epífitas, em resposta a uma maior diversidade de sítios de fixação; II. a abundância de epífitas será positivamente relacionada com os fatores ambientais que favorecem a atividade fotossintética e a absorção de nutrientes. Assim, espera-se uma relação positiva entre a abundância e a luminosidade, a umidade relativa do ar e a altitude, bem como uma relação negativa entre a abundância, a temperatura do ar (possível estresse hídrico) e a cobertura de dossel (maior sombreamento). Foram observadas 2.728 epífitas pertencentes a seis espécies de Bromeliaceae, registradas em 514 forófitos de 29 espécies e 15 famílias. A abundância de epífitas respondeu a algumas características dos forófitos e alguns dos fatores abióticos. Assim, troncos com maior diâmetro e número de ramificações, ritidoma liso e temperaturas elevadas influenciaram positivamente a abundância de epífitas, enquanto incrementos na altitude e na umidade afetaram a abundância negativamente. Conclui-se que, a abundância de epífitas em fragmentos de Caatinga está, diretamente, associada a fatores como a estrutura do forófito e as condições microclimáticas.Palavras-chave: Caatinga, Interação epífita-forófito, Microclima