DOI: 10.5061/dryad.0rxwdbs38
title: Data supporting: Drivers of individual-based, antagonistic interaction networks during plant range expansion

description: 1. Range expansion in plant populations, especially at the colonization
 front, can be either limited by disproportionately large effects of
 antagonistic interactions or facilitated by their release. How the
 strength of antagonistic interactions changes along successional gradients
 during range expansion is still poorly documented, especially when diverse
 assemblages of plant antagonists (rodents, invertebrates, and birds)
 combine within interaction networks. 2. We study the changes in
 individual-based, predispersal seed-pulp predator networks along a
 colonization gradient in a rapidly-expanding Juniperus phoenicea
 population in Doñana National Park (SW Spain). Additionally, we analysed
 the role of individual plant traits and neighbourhood attributes in
 network configuration by using Exponential Random Graph Models. 3. Seven
 seed-pulp consumer animal species varied significantly in their frequency
 of interaction and prevalence. While invertebrate species were well
 established in old and intermediately mature stands, greenfinch (Chloris
 chloris) was dominant at the colonization front. Variable species roles
 and spread of interactions among individual plants generated changes in
 the configuration of interactions during plant expansion. 4. Individual
 plant traits strongly determined the topology of these networks, although
 with differences between stands. Increasing individual crop size and seeds
 per cone increased the interaction odds of individual plants, while seed
 viability showed the opposite effect. The network topology at the
 colonization front appeared less driven by individual traits, possibly
 because of the short interaction history of this recently established
 area. The disproportionately large effect of C. chloris in these
 recently established stands, potentially resulted in large seed losses
 during range expansion. 5. Synthesis.  Turnover of
 antagonistic interactions, characterized the colonization front, resulting
 in more heterogeneous interaction strengths among individual plants. We
 found no evidence for a complete or sizeable antagonistic release
 of J. phoenicea at the colonization front promoting this rapid
 expansion. It becomes necessary to explore interactions with seed
 dispersers to understand how antagonistic and mutualistic plant-animal
 interactions balance during range expansion. Our study highlights the
 importance of an individual-based approach in understanding how
 interactions are structured and driven in natural changing landscapes.
description: Sampling
 interactions We monitored each of the 105 focal plants
 during the two consecutive study seasons, using different methods (see
 Online Suppl. Mat. of published paper for details). To collect data on
 rodent interactions, we combined two sampling methods: camera-trap survey
 and live-trapping. We conducted 8 direct night-time trapping campaigns and
 the photo-trapping sampling effort involved a total of 201,600 hours of
 recording, both methods evenly distributed among focal plants. For both
 methods we consider the presence of a species under a focal plant as a
 potential interaction. We quantified invertebrate interactions by
 dissecting 50 mature cones from each focal plant per season (number of
 analysed cones = 7,906 cones). We identified antagonistic species and
 their markings based on Roques et al., (1984). When a parasitoid was
 recorded, we assigned the event as a detection of the host species, and
 indicative of one interaction of the plant with the corresponding host
 pulp-seed predator species. Finally, <em>C.
 chloris</em> interactions were quantified by seed traps placed under
 focal plants to collect the remnants of cones falling during their visits.
 Based on video records of foraging finches during full visits to the
 plants (mean [±1SD] of 4,5 ± 2,6 cones consumed per visit), we estimated
 that every four damaged cones found in the seed traps conservatively
 indicate one visit event by <em>C. chloris</em> in an
 individual plant. We carried out 35 checks of the seed-trap during the
 entire sampling, in which we counted the number of cones attacked, and
 emptied the trap. To handle the same interaction units for all data, we
 calculated the frequency of occurrence of each animal interaction for its
 survey. For example, how frequently an insect species was present in a
 cone relative to all the analysed cones, or how frequently we detected at
 least one <em>C. chloris</em> visit during weekly seed-traps
 checks. Plant
 characteristics  We thoroughly sampled a set of intrinsic and
 extrinsic plant traits known to influence animal preferences across the
 105 focal plants. We considered plant traits that could drive interactions
 with pre-dispersal seed-pulp predators hierarchically (Sallabanks, 1993):
 first, the individual neighbourhood context, then general plant traits,
 and finally at a higher scale of detail, cone quality traits. To
 characterize the juniper neighbourhood density and productivity of each
 plant we used the georeferenced location of all the individuals in each
 stand and estimated by direct count the cone production in all the juniper
 individuals growing in a buffer area of 100
 m<sup>2</sup> surrounding each focal individual. For each
 focal individual, we recorded its height, the two maximum diameters of its
 canopy projection, canopy area, and total cone crop size. Direct counts of
 cones were carried out by scanning the whole plant canopy area and
 counting the cones with a hand-counter. We used the harvested cones (50
 cones per plant) to measure cone traits. For each plant, we measured the
 average values of maximum length and diameter of the cones, total fresh
 mass, pulp mass, seed mass, one-seed mass, number of seeds per cone and
 seed viability was estimated by flotation
 procedure.
description: Specific code for this research is available in our gitHub
 Repository: https://github.com/PJordano-Lab/Juniperus_antagonists_2022