DOI: 10.5061/dryad.r2280gbc7
title: Spatial relationships between spiders and their host vascular epiphytes within shade trees in a Mexican coffee plantation

description: Within tree canopies, vascular epiphytes create habitats for other taxa,
 and their heterogeneous spatial distribution could affect the distribution
 of organisms associated with them, such as spiders. This study was
 performed in shade trees of a rustic coffee plantation located within a
 Tropical Cloud Forest region of Mexico. We used a spatially explicit
 approach to examine (1) if the richness and abundance of epiphyte-dwelling
 spiders have a positive association with epiphyte abundance within trees
 and (2) if spiders (richness and abundance) show the same patterns of
 spatial distribution as the epiphytic habitat. We found that spiders were
 distributed on gradients of the same type as their host epiphytes. These
 gradients were: a decrease from the center toward the edges of the tree
 and a decrease from the base of the trunk toward the canopy. Spiders also
 had aggregation patches with similar dimensions to those exhibited by
 their host epiphytes. Those spiders' patches were fully explained
 when their epiphytic habitat was also aggregated within trees. Spatial
 models suggested that epiphytes and spiders were also spatially structured
 at scales larger than a tree and smaller than an epiphyte mat. Our
 findings demonstrate that the spatial distribution of epiphyte-dwelling
 spider communities, may partly be explained by the distribution patterns
 of their host plants. However, other environmental and biotic factors, not
 associated with epiphyte communities, are likely to be responsible for the
 remaining spatial patterns of spider distribution.
description: <b>Data
 collection</b> We used traditional single
 rope-climbing to manually extract the majority of vascular epiphytes
 present in the trees (i.e., bromeliads, orchids, cacti, Piperaceae, ferns,
 aroids, and others [hemiepiphytes]). Only the epiphytes present at the
 very ends of the branches were not collected, due to the unsafe climbing
 conditions. The removal of the epiphytes was carried out in a period of
 approximately six weeks per tree, between October 2013 and March 2014.
 Prior to extraction, the position of each epiphyte on its host tree was
 mapped in three dimensions. Mapping was done by establishing a Cartesian
 coordinate plane (<i>X</i>, <i>Y</i>) on each tree
 using measuring tapes attached to the main trunk. The center of the tree
 (i.e., the trunk) was considered as the origin and the axes had a
 South-North (<i>Y</i>) and a West-East (<i>X</i>)
 direction. The <i>X-Y</i> position was measured perpendicular
 to the trunk and parallel to the ground, independently from the origin of
 the branch. The third axis (<i>Z</i>) corresponded to the
 height and was measured drawing the measuring tape from each epiphyte,
 perpendicularly to the ground. Once removed, epiphytes were
 placed in properly labelled plastic bags and subsequently dismantled in
 the laboratory to collect all spiders present on each individual plant.
 The spiders were collected manually while alive and preserved in 80%
 ethanol. The adult individuals were sorted into morphospecies according to
 their morphological traits (somatic or sexual). When possible, individuals
 were assigned to species using taxonomic keys. <strong>Variables</strong> For each observation unit, we quantified the richness of the vascular epiphyte groups (bromeliads, orchids, cacti, Piperaceae, ferns, aroids, and others [hemiepiphytes]), biomass (measured as dry weight) and abundance (number of individuals per mat). An epiphyte with an independent root system or several epiphytes of the same taxonomic group sharing the same rhizosphere were considered as one individual. For spiders, we recorded species richness (number of species per mat) and abundance (number of individuals per mat). <b>Data analysis</b> <strong>Spatial modeling</strong> To model the spatial distribution of epiphytes and their hosted spider, we performed a two-stage analysis for each plane. In the first stage, we modeled gradients (i.e., monotonic changes in some direction) using simple linear models. In the second stage, we modeled aggregation patches (i.e., aggregation zones where the values of a variable are more similar to each other than expected by chance) using variography, as a way to estimate the degree of spatial dependence. <strong>Average and spatial relationship</strong> Once we analyzed the spatial distribution of spiders and epiphytes, spatialized linear models (Generalized Least Square- GLS) were used to determine the explanatory power of epiphyte abundance on the variation in spider richness and abundance and their spatial distribution in the trees.