Inventory of Ant Fauna in the Influence Area of a Small Hydropower Plant in the State of Paraná, Brazil

The present study provides additional information on the occurrence of ant species in the southwestern region of the state of Paraná. The most frequent species found in the samples are characteristic of anthropized environments and are commonly reported in studies evaluating ant fauna in southern Brazil [43,44,45,46]. Compared to the others, the slightly higher richness and diversity recorded at Site 3 can be explained by the more advanced stage of forest regeneration in this area. The similarity in ecological descriptors across sites suggests that the ant fauna in the more recently regenerating areas (Sites 1 and 2) is beginning to reflect patterns of structural complexity similar to those found in more preserved environments, such as Site 3. The time required for community reestablishment in regenerating areas can vary from five years [47,48] to more than two decades for full recovery [49]. Lutinski et al. [8], in a study conducted in the municipality of Marmeleiro (southwestern Paraná), identified 55 ant species, a lower richness than found in the present study (72 species). The genera Acromyrmex, Brachymyrmex, Camponotus, Linepithema, and Pheidole were also the most frequent in that study. The environments sampled in Marmeleiro consisted of small forest fragments and agricultural areas, showing similarities in species composition and richness with the sites sampled in the indirect influence area (AII) of the SHPP in Mangueirinha. Ants of the subfamily Dolichoderinae are typical of anthropized environments in southern Brazil [46]. The genera Dorymyrmex and Linepithema include species frequently encountered in a wide range of habitats in the region [45,50]. According to Fernández [32] and Baccaro et al. [51], some species within these genera, such as L. humile, have pest potential. The omnivorous habits and presence of six such species in this study indicate environmental degradation at the sampled sites. Camponotus was the most species-rich genus in the samples. Ants in this genus are widely distributed throughout the Neotropical region and are known for their pronounced polymorphism and omnivorous behavior [52]. They forage from the ground to the canopy and are often involved in mutualistic relationships and chemical defense interactions with other organisms [18,51]. Camponotus mus, C. rufipes, and C. sericeiventris are widely distributed in the state of Santa Catarina [45] and are commonly found in anthropized environments [50]. The genera Brachymyrmex, Crematogaster, Nylanderia, and Wasmannia are characterized by omnivorous and generalist behavior [18,53]. The presence of these ants may indicate environmental pressure due to adjacent agricultural activity or habitat fragmentation [54]. Their small body size and mass recruitment behavior [18,51] may favor efficient nesting, dominance over food sources, and frequent detection in samples. The high Neotropical diversity of Pheidole and Solenopsis is supported by the recording of dozens of species in localized studies [16]. Their broad distribution and dispersal ability make some species locally abundant. According to Silvestre et al. [18], these genera nest in the ground and form large colonies. They are aggressive generalists frequently recorded in disturbed environments [55]. The environmental conditions of the AII, particularly at Sites 1 and 2, may be conducive to the presence of these ants. The occurrence of ants belonging to the genera Cephalotes, Myrmelachista, Procryptocerus, and Pseudomyrmex in the AII highlights the role of forest fragments in supporting their populations. These ants require vegetation structures for shelter and nesting. Cephalotes ants, in particular, are strongly associated with vegetation, using it as a food source and nesting substrate [32,52]. Pseudomyrmecinae ants are diurnal, visually oriented, agile patrollers that depend on myrmecophilous plants, often visiting nectaries and preferring closed, humid forests, although some species can occur in more open areas [56]. Myrmelachista ants are tiny and frequently found inside seeds. Although restricted to the Neotropics, they exhibit a broad geographic distribution [32]. The presence of these genera underscores the importance of conserving forest remnants as refuges for these insects. Five species of leaf-cutting ants were recorded, all from the genus Acromyrmex. These ants are known for their potential economic impact, as they harvest green plant material to cultivate the fungi they consume [57]. Endemic to the Neotropical region and polymorphic, Acromyrmex play an important role in soil dynamics. Their underground galleries improve soil aeration, while their waste and feces enrich the soil [18,51]. The occurrence of species from the genera Cyphomyrmex, Gnamptogenys, Hypoponera, Mycocepurus, Neoponera, and Pachycondyla also reinforces the need for conserving forest fragments and maintaining the leaf litter layer, which provides shelter and food for these ants [18,51]. Gnamptogenys, Hypoponera, Neoponera, and Pachycondyla are specialized predators that forage in soil litter. According to Lattke [58], these genera are commonly associated with shaded, humid environments and prey on small invertebrates, usually without specificity. Mycocepurus ants, in contrast, use decomposing organic matter to cultivate symbiotic fungi used as food [18]. The Chao1 estimator indicated that the true ant richness in the AII is likely higher than the observed richness. This outcome is expected when sites are assessed individually [59]. However, when the AII is considered as a whole, the seven sampling events reduced the gap between observed and estimated richness to less than 10%. The implementation of the SHPP did not result in a reduction in ant species richness in the AII. Certain ant species are more sensitive to environmental changes [60] and may decline or disappear in altered habitats. In such cases, ecological niches left vacant may be filled by more generalist species, which tend to dominate in anthropized environments. The diversity recorded in the present study (72 species) reinforces the bioindicator potential of ant assemblages in areas influenced by hydropower developments. Although this richness is considerable, it is lower than that reported in other surveys conducted in the State of Paraná. For example, Franco and Feitosa [61] recorded 163 ant species in the natural grasslands of Campos Gerais using multiple sampling techniques. This difference may be attributed to the type of environment sampled, open and preserved landscapes versus forest fragments under anthropogenic pressure, as well as the broader methodological approach employed in their study. Nevertheless, the species composition observed in Mangueirinha, characterized by generalist species and the presence of forest-associated taxa, demonstrates that even indirectly affected areas can sustain expressive ant communities. Another relevant study conducted in São Camilo State Park [62] reported 108 ant species, including new records for both Paraná and southern Brazil, in fragments of seasonal semideciduous forest. Although species richness was lower in the present inventory, the results are comparable when considering this study’s standardized pitfall method and smaller spatial scale. Moreover, the number of site-exclusive species and the richness estimate (Chao1) suggest that actual diversity in the study area may be underestimated. Together, these findings indicate that preserved grassland environments and secondary forest fragments play complementary roles in regional ant conservation, highlighting the importance of including varied vegetation types and disturbance levels in environmental impact assessments. Despite the valuable data obtained, a notable limitation of the present study is the exclusive use of the pitfall trapping method, which may lead to an underestimation of the true species richness and diversity. Recent studies emphasize the importance of combining multiple sampling techniques, such as pitfall traps, Winkler extractors, Malaise traps, and manual collection, to better capture the functional and taxonomic diversity of ant communities, especially in heterogeneous environments [61,63]. For example, Franco and Feitosa et al. [61] conducted a detailed inventory in the natural grasslands of Paraná using pitfall, Winkler, and manual sampling methods, resulting in higher recorded richness and diversity, particularly of species less detectable by single methods. Similarly, Lutinski et al. [63] demonstrated that combining different collection methods allowed for a more comprehensive assessment of ant communities in forest fragments of southwestern Brazil, revealing species that would not have been detected using only pitfall traps. The construction and operation of hydropower dams profoundly alter environmental drivers, with cascading effects on ant assemblages. Flooding and habitat fragmentation eliminate nesting sites and microhabitats, facilitating the replacement of specialist ant species by generalists and opportunists, thereby altering community composition, diversity, and functional structure [8]. Additionally, changes in microclimate (e.g., temperature, soil moisture, light regime), resource availability, and soil connectivity affect abundance and trophic interactions [18]. These responses can be asynchronous, immediate losses of sensitive taxa followed by community reassembly over years or decades, making ant communities sensitive indicators for environmental monitoring and the effectiveness of mitigation strategies [64]. Hydropower development exerts persistent long-term impacts on soil and vegetation, frequently impairing ecosystem recovery. Reservoir-induced inundation alters soil physico-chemical properties, including reduced oxygenation, organic-matter loss, and nutrient alteration, while construction activities accelerate compaction and erosion, reducing infiltration and increasing sedimentation risk [65]. Vegetation is affected through outright removal, shifts in species composition, loss of arboreal strata, and reduced structural heterogeneity, undermining ecosystem services such as carbon sequestration, slope stability, and habitat provisioning. These effects may endure for decades, especially under continuing anthropogenic pressures (e.g., land-use change, fires, invasive species), underscoring the need for long-term restoration planning and sustained ecological monitoring to restore functional resilience [64].