Human activities have been responsible for huge impacts on natural ecosystems (Oliver et al. 2016). Fragmentation, habitat loss and habitat degradation are the main sources of biodiversity loss and ecosystem function hampering (Fahrig 2013; Oliver et al. 2016) in high human-modified landscapes (Tscharntke et al. 2012). Considering the difficulty of assessing the biodiversity response to different types of human impacts, the use of bioindicators has been proposed (McGeoch 1998). Bioindicators are groups of organisms which diversity patterns and ecological functions clearly and predictably respond to anthropogenic impacts (McGeoch 1998; Del Toro et al. 2012).
Ants are excellent bioindicators because they have a large biomass in almost all terrestrial habitats, participate in several ecosystem functions (predation, seed dispersal, pollination, and others) (Leal et al. 2015), have mutualistic associations with other organisms (Del Toro et al. 2012; Parker 2022; Hojo 2022), are relatively easy to sample and identify (Agosti et al. 2000), and predictably respond to human impacts (Underwood and Fisher 2006; Philpott et al. 2010). However, among diversity patterns, species richness and diversity indexes have presented a coarse response to human impacts (Ribas et al. 2012). Thus, several studies have highlighted that ant species composition clearest and most expected answer to several natural and human-induced impacts (Gollan et al. 2011; Ribas et al. 2012; Schmidt et al. 2013).
Ant species differ regarding their habitat preference, which allows for classifying them into habitat-use guilds, such as: forest or open habitats specialists or habitat generalists (Leal et al. 2017; Vasconcelos et al. 2018; Andersen 2019). These ant guilds respond distinctly to human-induced impacts (Martins et al. 2022). For example, forest specialists are very sensitive to disturbance, which generally presents a low number of species richness, abundance, and biomass. On the other hand, open habitat and generalist ants have elevated values in highly disturbed environments, such as in low forest cover landscapes (Paolucci et al. 2017; Martins et al. 2022). This distinct response of habitat use by ant guilds can be understood as a winner-loser approach (McKinney and Lockwood 1999; Filgueiras et al. 2021), where there are many specialist ant losers and few generalist and open-habitat specialist ants winners in response to anthropogenic disturbances (Paolucci et al. 2017; Martins et al. 2022). Although the response of habitat use guilds to ecological and environmental changes has been accessed (Paolucci et al. 2017; Vasconcelos et al. 2018, Martins et al. 2022), a standard way to assign ants in these guilds is lacking, which hampers the reproducibility and broad using of habitat use ant guilds in ant diversity studies and monitoring programs.
Forest-pasture shifting is a major land use change in Brazil (Mapbiomas 2021), leading to negative impacts on biodiversity and ecosystem services (Fearnside 2005; Imazon 2021). In this sense, the state of Acre in the southwestern Brazilian Amazon has experienced expressive changes in landscape dynamics over the last four decades, mainly by forest-pasture shifting (Acre 2010; INPE 2020; Mapbiomas 2021). Human-modified landscapes represent 13% of Acre territory (Azevedo 2021), with 80% represented by pastures. Thus, these land-use shifting in Acre could be seen as a model of human impacts on Amazonian ecosystems and biodiversity mainly in the region called as “Arc of Deforestation” (Nogueira et al. 2007, 2008).
Most studies on ant assemblages as bioindicators in Amazon biome have approached the effects of forest-pasture shifting on ant diversity (e.g., Oliveira and Schmidt 2019; Menezes and Schmidt 2020). The addition of habitat use ant guilds can give a clearer understanding of ant assemblages response to forest shifting, which can be applied to all kinds of land use changes that promote deforestation (Andersen 2019).
In this study, we propose a standard protocol to classify the ant fauna in habitat-use guilds (forest specialists, open-habitat specialists, and generalists). Besides the use of standard assemblage parameters (i.e., species richness and species composition), we verified habitat-use ant guilds as a complementary predictable parameter on the use of ant assemblages as bioindicators. Specifically, we hypothesized that forest specialists, open-habitat specialists, and generalist ants would present distinct responses to forest-pasture shifting. We expected that the forest-pasture shifting promotes a decrease in the species richness of forest specialists and an increase in open-habitat specialists, while the generalists would have few changes in species richness because they can live in both habitats (Paolucci et al. 2017; Martins et al. 2022).