Effects of chronic anthropogenic disturbance and rainfall on the specialization of ant–plant mutualistic networks in the Caatinga, a Brazilian dry forest. (6th April 2018)

• Record Type: Journal Article
• Authors: Câmara, Talita; Leal, Inara R.; Blüthgen, Nico; Oliveira, Fernanda M. P.; Queiroz, Rubens T.de; Arnan, Xavier
• Editors: Parr, Catherine
• Is Part Of: Journal of animal ecology. Volume 87:Number 4(2018:Jul.)
• Page Start: 1022
• Page End: 1033
• Publication Date: 2018-04-06
• Subjects: anthropogenic disturbance -- anti‐herbivore defence -- climate change -- extrafloral nectaries -- mutualistic network -- plant–animal interactions -- seasonally dry tropical forest -- specialization; Animal ecology -- Periodicals; 591.7
• DOI: 10.1111/1365-2656.12820
• Languages: English
• ISSNs: 0021-8790

Abstract

Abstract: Anthropogenic disturbance and climate change might negatively affect the ecosystem services provided by mutualistic networks. However, the effects of such forces remain poorly characterized. They may be especially important in dry forests, which (1) experience chronic anthropogenic disturbances (CADs) as human populations exploit forest resources, and (2) are predicted to face a 22% decline in rainfall under climate change. In this study, we investigated the separate and combined effects of CADs and rainfall levels on the specialization of mutualistic networks in the Caatinga, a seasonally dry tropical forest typical of north‐eastern Brazil. More specifically, we examined interactions between plants bearing extrafloral nectaries (EFNs) and ants. We analysed whether differences in network specialization could arise from environmentally mediated variation in the species composition, namely via the replacement of specialist by generalist species. We characterized these ant–plant networks in 15 plots (20 × 20 m) that varied in CAD intensity and mean annual rainfall. We quantified CAD intensity by calculating three indices related to the main sources of disturbance in the Caatinga: livestock grazing (LG), wood extraction (WE) and miscellaneous resource use (MU). We determined the degree of ant–plant network specialization using four metrics: generality, vulnerability, interaction evenness and H 2 ′ . Our results indicate that CADs differentially influenced network specialization: we observed positive, negative, and neutral responses along LG, MU and WE gradients, respectively. The pattern was most pronounced with LG. Rainfall also shaped network specialization, markedly increasing it. While LG and rainfall were associated with changes in network species composition, this trend was not related to the degree of species specialization. This result suggests that shifts in network specialization might be related to changes in species behaviour, not species composition. Our study highlights the vulnerability of such dry forest ant–plant networks to climate change. Moreover, dry forests experience highly heterogeneous anthropogenic disturbances, creating a geographic mosaic of selective forces that may shape the co‐evolution of interactions between ants and EFN‐bearing plants. Abstract : The authors show that rainfall is an important factor influencing network specialization in a facultative mutualism between ants and plants while different chronic anthropogenic disturbances differentially influenced. Remarkably, the network specialization along both gradients is driven by changes in ant species behavior rather than by specialist‐generalist replacement.