DOI: 10.5061/dryad.5mkkwh776
title: Data from: Individual and interactive effects of chronic anthropogenic disturbance and rainfall on taxonomic, functional and phylogenetic composition and diversity of extrafloral nectary-bearing plants in Brazilian Caatinga

description: Chronic anthropogenic disturbance (CAD) and climate change represent two
 of the major threats to biodiversity globally, but their combined effects
 are not well understood. Here we investigate the individual and
 interactive effects of increasing CAD and decreasing rainfall on the
 composition and taxonomic (TD), functional (FD) and phylogenetic diversity
 (PD) of plants possessing extrafloral nectaries (EFNs) in semi-arid
 Brazilian Caatinga. EFNs attract ants that protect plants against insect
 herbivore attack and are extremely prevalent in the Caatinga flora.
 EFN-bearing plants were censused along gradients of disturbance and
 rainfall in Catimbau National Park in north-eastern Brazil. We recorded a
 total of 2,243 individuals belonging to 21 species. Taxonomic and
 functional composition varied along the rainfall gradient, but not along
 the disturbance gradient. There was a significant interaction between
 increasing disturbance and decreasing rainfall, with CAD leading to
 decreased TD, FD and PD in the most arid areas, and to increased TD, FD
 and PD in the wettest areas. We found a strong phylogenetic signal in the
 EFN traits we analysed, which explains the strong matching between
 patterns of FD and PD along the environmental gradients. The interactive
 effects of disturbance and rainfall revealed by our study indicate that
 the decreased rainfall forecast for Caatinga under climate change will
 increase the sensitivity of EFN-bearing plants to anthropogenic
 disturbance. This has important implications for the availability of a key
 food resource, which would likely have cascading effects on higher trophic
 levels.
description: We characterised CAD using
 a global multi-metric disturbance index previously established for the
 study plots (Arnan et al. 2018b). The index combines three types of source
 information: (i) indirect landscape measures using satellite imagery in
 ArcGIS 10.1 software: proximity to the nearest house, and proximity to the
 nearest road; (ii) socio-ecological information obtained by interviewing
 local households: number of people, number of goats, number of cattle and
 firewood use; and (iii) direct field measures of the length of goat
 trails, the density of goat and cattle dung, extents of live-wood
 extraction and fire-wood collection.  We obtained data on mean annual
 rainfall for each plot from the WorldClim global climate data repository
 for 1970-2000 (Hijmans et al. 2005) with 1 km resolution using the
 “maptools” package for R 3.1.2 (R Core Team 2014). We used woody plant inventory
 data that have previously been published for the 20 0.1-ha plots (Rito et
 al. 2017a). Species were assessed as bearing extra floral nectaries (EFNs)
 on the basis of published literature (e.g. Elias 1983; Rico-Gray and
 Oliveira 2007; Melo et al. 2010) and information available on the World
 List of Plants with Extrafloral Nectaries (Weber et al. 2015). When the
 information was unclear or contradictory (such as for some species of the
 euphorb genera <i>Cnidosculus</i>, <i>Croton</i>
 and <i>Jatropha</i>), we performed our own field collections
 and samples were sent to Estadual University of Bahia herbarium (HUNEB
 Herbarium) and Vale do São Francisco herbarium (HVASF Herbarium), where
 they were examined under a stereomicroscope for extra floral
 nectaries. For
 each species we used information from Weber et al. (2015), Queiroz (2009)
 and Melo et al. (2010) to document three traits related to nectar
 secretion and attraction/access to ant attendants: EFN morphological type,
 location and arrangement. Eight of the EFN morphological types recognized
 by Weber et al. (2015) occurred in our study species: (i) elevated; (ii)
 flat-elevated; (iii) digitiform-elevated; (iv) concave-elevated; (v)
 stipitate; (vi) globose; (vii) impregnated in slot and (viii) glandular
 trichomes. We recognized eight EFN locations in our study species: (i)
 base of petiole; (ii) petiole (other than the base); (iii) interpetiolar;
 (iv) rachis; (v) base of leaflet; (vi) leaf tip; (vii) leaf margin and
 (viii) floral pedicel. EFNs can occur either in isolation or arranged in
 groups (Díaz-Castelazo et al. 2005), categorised as: (i) isolated; (ii)
 variably isolated/paired; (iii) paired and (iv) grouped (&gt; 2 EFNs),
 with multiple EFNs providing greater total nectar resources (Apple and
 Fenner 2001; Lange et al. 2017).