DOI: 10.5061/dryad.kprr4xh1t
title: Spatial variability of hosts, parasitoids and their interactions across a homogeneous landscape

description: Species assemblages and their interactions vary through space, generating
 diversity patterns at different spatial scales. Here, we study the
 local-scale spatial variation of a cavity-nesting bee and wasp community
 (hosts), their nest associates (parasitoids), and the resulting
 antagonistic network over a continuous and homogeneous habitat. To obtain
 bee/wasp nests we placed trap-nests at 25 sites over a 32 km2 area. We
 obtained 1541 nests (4954 cells) belonging to 40 host species and
 containing 27 parasitoid species. The most abundant host species tended to
 have higher parasitism rate. Community composition dissimilarity was
 relatively high for both hosts and parasitoids, and the main component of
 this variability was species turnover, with a very minor contribution of
 ordered species loss (nestedness). That is, local species richness tended
 to be similar across the study area and community composition tended to
 differ between sites. Interestingly, the spatial matching between host and
 parasitoid composition was low. Host b-diversity was weakly (positively)
 but significantly related to geographic distance. On the other hand,
 parasitoid and host-parasitoid interaction b-diversities were not
 significantly related to geographic distance. Interaction β-diversity was
 even higher than host and parasitoid b-diversity, and mostly due to
 species turnover. Interaction rewiring between plots and between local
 webs and the regional metaweb was very low. In sum, species composition
 was rather idiosyncratic to each site causing a relevant mismatch between
 hosts and parasitoid composition. However, pairs of host and parasitoid
 species tended to interact similarly wherever they co-occurred. Our
 results additionally show that interaction β-diversity is better explained
 by parasitoid than by host β-diversity. We discuss the importance of
 identifying the sources of variation to understand the drivers of the
 observed heterogeneity.
description: Data were collected in 25 plots distributed across the Garraf
 Natural Park (Barcelona, NE Spain). In each plot we placed a trap-nesting
 station facing SE. Each station contained seven drilled wood blocks with
 inserted paper tubes. Each wood block accommodated 25 tubes of one of the
 following diameters (2, 3, 4, 5, 6, 7 and 8 mm), resulting in 175 nesting
 cavities per station. Paper tube length was 5 cm for the 2 and 3 mm
 diameters and 15 cm for the rest. Nesting stations were checked every 2
 weeks and tubes containing occupied nests were pulled out, taken to the
 laboratory and replaced with empty ones, so that there were nesting
 cavities of all diameters available at all times. Nesting stations
 remained in the field from February to October, in 2011 and 2013. Data of
 the two years are pooled together. Nests were kept in a
 temperature chamber simulating monthly ambient temperatures of the study
 site. Upon one year from collection, nests were dissected. The nests of
 solitary bees and wasps contain a variable number of cells, some of which
 may be parasitized. We recorded the contents of each cell (identity of the
 host or the parasitoid).