Gamma, alpha, and beta diversity of ant assemblages response to a gradient of forest cover in human‐modified landscape in Brazilian Amazon

Abstract

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.

Land‐use change in the Amazon decreases ant diversity but increases ant‐mediated predation

“…According to the environmental filter hypothesis, local changes associated by different habitats promote a filter that selects species able to establish and survive in those sites (Clavel et al, 2011; Martins et al, 2022; McKinney & Lockwood, 1999; Olden, 2006; Olden et al, 2016). More heterogeneous and complex habitats, such as the Amazon Forest, tend to harbour a greater species diversity (Costa & Schmidt, 2022; Tews et al, 2004). However, the conversion from Amazon Forest to shifting cultivation (limited to some crops) and pasture (grassland monoculture) was associated with habitat homogenisation, due to the decrease of plant species and more homogenous environmental conditions in these anthropogenic land uses.…”

“…Species turnover has been reported as the main component of βsør‐diversity (Soininen et al, 2018). This species replacement may be due to greater heterogeneity in forest environments, which is positively related to taxonomic diversity (Ribas et al, 2003; Stein et al, 2014), in addition to anthropogenic disturbances favouring generalist and more resistant species (Costa & Schmidt, 2022; Solar et al, 2015). In the same context, as taxonomic diversity is directly related to functional diversity (Bihn et al, 2010), this conversion from forest to shifting cultivation and pasture, with replacement by generalist species, might alter ecosystem functions in these sites.…”

“…The climate in the region is humid tropical, with a mean annual temperature of approximately 27°C. The mean annual rainfall is between 1800 and 2200 mm, with the rainy season occurring between November and April and the dry season occurring during the months of June, July, and August (Costa & Schmidt, 2022). Ants were sampled in August 2019 during the dry season, since it is not possible to reach the sampled sites in the rainy season.…”

“…Substantial conversion from semi‐natural habitats to anthropogenic land uses (such as from forest to agriculture) and intensive management (such as mechanised agriculture or pasture), tends to decrease ant α‐diversity (species richness of a site) and β‐diversity (difference in species or community composition between sites), causing the homogenisation of biotic communities (Ahuatzin et al, 2019; Costa & Schmidt, 2022; Escobar‐Ramírez et al, 2020; Queiroz et al, 2020; Solar et al, 2015, 2016). These changes in species composition can be caused by species replacement in human‐modified habitats (Costa & Schmidt, 2022; Solar et al, 2015), which, in addition to changes in species diversity, can also impact fundamental ecosystem functions (Bihn et al, 2010; Martins et al, 2022). In addition, conversion from semi‐natural habitats to anthropogenic land uses decreases the diversity of specialist ant species while increasing the diversity of generalist ant species (Escobar‐Ramírez et al, 2020; Martins et al, 2022; Solar et al, 2015).…”