Effect of Bamboo Dominance on Leaf-Litter Ant Assemblages in the Southwestern Amazon Forest.

In the Southwestern Brazilian Amazon, the Brazil nut tree Bertholletia excelsa is the most conspicuous remnant element of original forest ecosystems in human-modified landscapes. They often exist in pastures that have very different environmental characteristics than forests. In our study, we surveyed the ant fauna of Brazil nut trees in forest and pasture habitats in the Southwestern Brazilian Amazon. Specifically, we addressed the following questions: (i) How do arboreal ant assemblages of Brazil nut tree crowns change based on habitat type? (ii) What is the contribution of forest ant species from Brazil nut tree crowns to ant assemblages in pasture Brazil nut tree crowns? (iii) What features of pasture Brazil nut trees lead to a greater number of arboreal ant species? We selected 20 trees in each habitat type (forest and pasture) and collected ant samples both at the soil surface and at tree crowns, sampling a total of 184 ant species. Species composition was primarily determined by sampling layer. We found that the number of ant species was 63% lower in pasture than in forest tree crowns. The dissimilarity between the ant assemblages of tree crown and soil surface remained almost the same in both habitats. There was relatively little overlap in species composition in the forest tree crowns versus the pasture tree crowns, with species replacement component highly contributing to the differences. We conclude that scattered Brazil nut trees plays limited role on the conservation of its associated biodiversity in human-modified landscapes such as pastures.

The species richness and composition of ant assemblages at the extrafloral nectaries of four Costus spp. (Zingiberaceae) in Panama were quantified to determine (1) the relative specificity of these ant—plant mutualisms, and (2) the ecological factors that influence ant assemblages. Although inflorescences of Costus spp. commonly produce extrafloral nectar for several months (species means 1—2 mo, range to 4 mo), there was little turnover in ant—species composition on individual inflorescences. A total of 34 ant species in five subfamilies were observed, but plant species varied significantly in ant species richness. The number of ant species expected from equal sampling (40 inflorescences per Costus sp.) was 9 for C. pulverulentus, 13 for C. scaber, 15 for C. allenii, and 20 for C. laevis. Among—species differences in ant species richness were not a function of plant distribution, the volume or composition of extrafloral nectar, or the duration of nectar flow. The number of ant species was positively correlated with inflorescence height, which varied from 0.6 to 2.0 m. The differences in ant species richness with inflorescence height were due primarily to the addition of arboreal ants, which increased from 3 species representing 3% of all ant species observations on the shortest plant, C. pulverulentus, to 12 species representing 62% of all ant observations on the tallest plant, C. laevis. The number of terrestrial ant species varied only from six to eight. Cumulative ant—species curves as a function of number of inflorescences sampled (N = 41—80) did not plateau for any Costus sp., indicating that a large number of ant species can utilize extrafloral nectar in this system. The high ant species richness and the similarity in nectar characteristics among Costus spp. suggest these are relatively generalized mutualisms with limited coevolution between the plants and their attendant ants. The brief period of extrafloral nectar production (° = 36—55 d), coupled with spatial variation in ant species distributions, probably limit the degree of specialization among mutualists. This is in contrast to more specialized ant—plant mutualisms where plants are relatively predictable sources of food and/or nest sites for ants.

Productivity is a key driver of ecosystem structure and function, so long-term studies are critical to understanding ecosystems with high temporal variation in productivity. In some deserts, productivity, driven by moisture availability, varies immensely over time (rainfall) and space (landscape factors). At high productivity, species richness is expected to be driven in opposing directions by abundance (More Individuals Hypothesis - MIH) and competition. While studies investigating the impacts of spatial variation in productivity on community structure are common, the impacts of temporal variability on productivity are poorly understood. We tested how well rainfall predicted the activity, species numbers and assemblage composition of ants and if responses were moderated by landscape position. We also asked whether the number of species (richness per sampling unit and estimated species richness) responded directly to rainfall or was moderated by ant activity or competition from dominant ants. Over a 22-year period, when annual rainfall fluctuated between 79mm and 570mm, we sampled ants using pitfall traps in paired dune and swale habitats in the Simpson Desert, Australia. We used climate records over this period to model changes in ant assemblages. Activity of dominant ants responded primarily to long-term rainfall, increasing exponentially, while subordinate ants responded to short-term weather and time. Consistent with the MIH, the number of ant species was best predicted by activity, particularly that of subordinate ants. Activity of dominant ants had a declining positive effect on numbers of species. Landscape position strongly predicted species composition, while long-term rainfall determined composition at genus level but not species level. Over time, species composition fluctuated, but several genera consistently increased in activity. Productivity moderators such as long-term rainfall and landscape position are key drivers of ant activity and composition in the study ecosystem, acting indirectly on numbers of species. Numbers of species were explained largely by ant activity, making a strong case for the MIH, but not competition. Longer periods of low rainfall may indirectly reduce species richness in desert ecosystems. However, a trend to increasing richness over time may indicate that conservation management can ameliorate this impact.

Impacts of forestry on ant species richness and composition in warm-temperate forests of Japan

Ants are key indicators of ecological change, but few studies have investigated how ant assemblages respond to dramatic changes in vegetation structure in temperate forests. Pests and pathogens are causing widespread loss of dominant canopy tree species; ant species composition and abundance may be very sensitive to such losses. Before the experimental removal of red oak trees to simulate effects of sudden oak death and examine the long-term impact of oak loss at the Black Rock Forest (Cornwall, NY), we carried out a rapid assessment of the ant assemblage in a 10-ha experimental area. We also determined the efficacy in a northern temperate forest of five different collecting methods--pitfall traps, litter samples, tuna fish and cookie baits, and hand collection--routinely used to sample ants in tropical systems. A total of 33 species in 14 genera were collected and identified; the myrmecines, Aphaenogaster rudis and Myrmica punctiventris, and the formicine Formica neogagates were the most common and abundant species encountered. Ninety-four percent (31 of 33) of the species were collected by litter sampling and structured hand sampling together, and we conclude that, in combination, these two methods are sufficient to assess species richness and composition of ant assemblages in northern temperate forests. Using new, unbiased estimators, we project that 38-58 ant species are likely to occur at Black Rock Forest. Loss of oak from these forests may favor Camponotus species that nest in decomposing wood and open habitat specialists in the genus Lasius.

Soil compaction, a process that decreases the free space among soil particles and hinders the underground movement of soil organisms, is one of the increasing impacts of mankind on the world’s ecosystems. We investigated the responses of subterranean ants to soil compaction by testing the following predictions: (i) soil from a trail is more compressed, leading to (ii) a decrease in species richness and a selective shift in ant assemblage composition, which is made up by (iii) species with a smaller body size that can apply a greater relative strength to move through soil particles. We carried out this study in and outside of a recreational ecology trail in a forest fragment in Vicosa, MG, Southeastern Brazil. The compaction was higher in the soil from the trail than outside of it. No change was observed in species richness, but soil compaction promoted a shift in ant assemblage composition, with ant size decreasing with an increase in soil compaction. However, ants did not appear to apply a greater strength to soil particles for moving in habitats with a high soil compaction. Overall, organisms at superficial soil layers appeared to be sensitive to even moderate human impacts that promote a filtering of the ant assemblage species composition, with small body size being a required trait.

Several studies have evaluated the impacts of intensified human activities on biodiversity, but far less effort has been directed toward evaluating the maintenance of ecosystem functions in human-modified landscapes. We investigated the impacts of habitat shifts from forest to pasture on assemblages of seed-removing ants in the southwestern Brazilian Amazon. We specifically addressed the following hypotheses regarding assemblages of seed-removing ants: (i) pasture ant assemblages have fewer species than do forest ant assemblages and are composed of a markedly different set of species; (ii) pasture ant assemblages remove less seeds than do forest ant assemblages; and (iii) forest and pasture ant assemblages contain different sets of key species for seed removal. We collected ants that were baited with artificial seeds in 10 forest areas and 10 adjacent pastures and found that shifting from forest to pasture reduced the number of species of seed-removing ants and altered species composition. We also found that, although seed removal percentage of was higher in pasture, these species were low quality seed dispersers, which was supported by our identification of key species for seed removal. We conclude that when considering the removal of seeds by ants as a proxy to assess the role of biodiversity in ecosystems, it is necessary to consider the importance of each species for removal according to habitat type affinity. Our findings highlight the importance of forest habitat for the effective conservation of ant diversity and their ecological functions in human-modified ladscapes.

Edge effects on epigeic ant assemblages in a grassland–forest mosaic in southern Brazil

In this study, we investigated the mechanisms behind species coexistence and the relationships between functional diversity and species richness in ant assemblages in both forest and pasture habitats in the southwestern Brazilian Amazon. We addressed the specific question: What is the primary mechanism for species coexistence in forest and pasture habitats? According to the identified mechanism in each habitat, we had the following alternative expectations: (i) niche partitioning – we expected to observe a linear positive relationship between functional diversity and species richness, indicating a complementary relationship; or (ii) niche filtering – a positive constant asymptotic relation between functional diversity and species richness, indicating a functional redundancy relationship. In total, we sampled 91 ant species, 82 species in a forest habitat and 16, in a pasture habitat. In the forest habitat we identified niche filtering as the structuring mechanism of the ant assemblage, but we were unable to identify a clear mechanism in the pasture habitat. Although the relationship between functional diversity and species richness was positive in both habitats, the relationship was weaker in the forest habitat, indicating a greater functional redundancy among the ant species in this habitat. Our results reinforce the divergence of species coexistence mechanisms and ant assemblage structures in both natural and human-modified habitats in the Southwestern Brazilian Amazon.

Ant assemblages on littered food waste and food removal rates in urban–suburban parks of Tokyo

Ants account for 30% of terrestrial biomass and are highly sensitive to environmental variables. Present study investigated the effect of altitude (400-900 m) and vegetation type (mixed woodland and pine plantations in Hanthana forest) on litter ants. Two transects were laid at each of the five 100 m elevation levels. For hand-picking and litter extraction of ants, 1 m2 plots were laid at every 20 m intervals along the two sides of each transect. A total of 8689 ants in 9 subfamilies 32 genera and 56 morpho-species were collected. Subfamily Myrmicinae had the highest number of genera (15) and species (26 spp.). Genus Pheidole was represented by the highest number of species (5 spp.) while Solenopsis sp. 1 was the most widely distributed and abundant (6420 individuals) species. The mixed woodlands, regardless of elevation, were richer in ant species than pine plantations. Permutation test (ρ=0.30, P=3%) revealed a weak relationship between ant assemblages and environmental variables. Findings indicated that the difference in litter ant species assemblages and diversity in Hanthana Forest is possibly due to differences in vegetation types rather than altitude.

One important strategy to conciliate forest conservation and economic development is the use of reduced-impact logging techniques. Here we evaluated the effects of low-intensity forest management on ant assemblages and vegetation structure in a managed area in the southeast of Acre State, Brazil. Ground-dwelling and arboreal ants, and several forest-structure descriptors were sampled in nine paired areas located in control (unlogged) and logged areas in 2005, 2007 and 2009. None of the forest structure predictors were related with either the treatment or the time since logging. However, some ant assemblage’ descriptors were related with logging activities. Arboreal and ground-dwelling ant species richness was similar between unlogged and logged areas, but more ground-dwelling ant species were found in areas logged in 2005 compared with areas logged in 2009. Ground-dwelling ant assemblage composition differed between treatments (logged and unlogged) and year of logging, but species composition heterogeneity was similar between areas. Arboreal ant assemblage composition was not related with treatment and year of logging, but assemblage composition was more heterogeneous in managed areas, suggesting that species that forage on the understory vegetation may be more resilient than ground-dwelling species. The general results of functional group approach suggest that changes of species composition between control and managed areas are more related with differences in ant species occurrence than ant species richness. Selective logging had limited effect on both vegetation descriptors and ant assemblage structure, suggesting that the conciliation of impact reduction techniques with low intensity extraction seems a promising alternative for sustainable logging activity in tropical forests.

The partitioning of gamma diversity into its alpha and beta components has been used to quantify the effects of natural habitat reduction on species diversity and distribution. Ant assemblages respond to anthropogenic changes, allowing their use as an indicator of biodiversity conservation in human‐modified landscapes. We investigated the responses of gamma, alpha, and beta diversity of ant assemblages to a forest cover gradient in southwestern Brazilian Amazon. Our prediction was that increasing forest cover would increase gamma diversity, which in turn is driven more by increasing beta diversity than alpha diversity along the forest cover gradient. Additionally, we expected that increasing beta diversity would be mainly driven by species replacement. We sampled ants within 12 circular areas (radius: 500 m) with different forest cover percentages in Chico Mendes Extractive Reserve, state of Acre, southwestern Brazilian Amazon. Gamma and beta diversity, but not alpha diversity, responded positively to the forest cover gradient. Additionally, species replacement was the main driver of beta diversity along the forest cover gradient. Areas with low levels of forest cover probably offer limited variation in habitats, resources, and conditions and, thus, harbor a low number of ant species that can easily disperse spatially and leading to species composition simplification. We recommend the use of diversity partitioning for indicator groups as an efficient way to monitor biodiversity and control the process of biota simplification at the human‐modified landscapes, showing the response of species diversity and distribution to human impacts.Abstract in Portuguese is available with online material.

This study identified the main biological mechanisms governing the diversity of ants on different ecological time scales. Ants were sampled in 15 plots distributed in early, intermediate and late stages of succession (five plots per stage) at the Parque Estadual da Mata Seca, Brazil. At each sample point, unbaited pitfall traps were installed in hypogaeic, epigaeic and arboreal strata. We collected 95 ant species from 26 genera and nine subfamilies. Our results indicated that there was an increase in species richness in advanced stages of succession. We also observed that ant assemblages were different among successional stages. For the arboreal and epigaeic strata, species richness did not change with succession progression, but species composition of these two strata differed among successional stages. Unlike to arboreal and epigaeic ants, hypogaiec ant species richness was higher in the intermediate and late stages of succession and the composition of hypogaeic ants differed among successional stages. Similarity between ant species foraging in arboreal and epigaeic strata decreases with succession progression and β-diversity was higher in advanced successional stages. Additionally, species richness was higher in the dry season, whereas the composition of ant assemblages did not change between seasons. A considerable fraction of the ant assemblage was found only in advanced stages of succession, demonstrating the importance of secondary habitats in maintaining biodiversity in dry forests.

Habitat edges are regarded as important components of heterogeneous landscapes. Diverse theories exist about the diversity and functional role of edges, and no generalisation have been possible so far, thus case studies are important for better understanding the landscape scale processes. Forest management highly modified the structure and tree species composition of the European forests. The sylvicultural intensification resulted in the rise of the proportion of non-native, intensively managed forest stands. In the present study we explore the response of spider and ant assemblages to forest stand type and the edge effect between native poplar and nonnative conifer plantations in Hungary. We applied pitfall traps to sample the ground-dwelling spiders and ants. Four plots consisting of the two forest types and the transition zones between them were selected. Five transects for each replicated plot were sampled. We identified the significant indicator species of the different habitat types. We found significant differences in the species richness (i.e. number of species) of ants and spiders of the different habitat types. We detected intermediate spider species richness at the edge indicating that edges separate a higher quality habitat from one that has lower resource quality; however, the species richness of ants was the highest at the edge and did not differ between the two forest types. The positive impacts of edge was found due to presence of generalist and grassland species at the edge and presumably edges separate patches that provide complementary resources also increasing the number of ant species.Our results indicate that forest type affects the species compositions of ground-dwelling spiders and ants. Our study also shows that habitat type had a major effect on the species richness and composition of spider and ant assemblages, suggesting that local forestry management plays a crucial role in preserving the native invertebrate fauna of forests.