DOI: 10.5061/dryad.jsxksn0g0
title: From seed dispersal service to reproductive collapse: density-dependent outcome of a palm-mammal interaction

description: Interspecific ecological interactions are inherently context-dependent.
 They may vary in both magnitude and sign depending on the biotic and
 abiotic conditions, depicting a mutualism-antagonism continuum. However,
 how population abundances and the activity of interacting species modulate
 these interactions remains underexplored. Here, we chose the interaction
 between the Mediterranean palm Chamaerops humilis and the feral goat Capra
 hircus in Mallorca (Balearic Islands, Spain). We selected three study
 plots with low, intermediate and high intensities of goat activity where
 we characterized palm distribution, seed rain, seed predation, and early
 palm recruitment during two consecutive years. Since goats can cause both
 costs (e.g. florivory) and benefits (e.g. seed dispersal) to C. humilis
 performance, we investigated the following three questions: (1) Does the
 spatial distribution of adult palms vary depending on the intensity of
 goat activity? (2) Does the intensity of goat activity influence seed rain
 and its potential spatial association with adult palms? (3) To what extent
 does the intensity of goat activity determine post-dispersal events such
 as seed predation and seedling emergence? We found that adult palms showed
 a more clumped and complex distribution (double-cluster process) in plots
 with low and intermediate goat activity compared to that with high goat
 activity (simple-cluster process). In the low goat activity plot,
 dispersed seeds were spatially aggregated around adult palms, showing
 twice insect-seed predation and nearly three times lower seed germination
 success than those in the intermediate goat activity plot. Palm seed
 dispersal and recruitment were almost nil in the high goat activity plot
 due to heavy consumption of palm inflorescences and developing fruits by
 goats. Our findings demonstrate how the net outcome of plant-animal
 interactions can change from mutualism to antagonism, from reproductive
 service to reproductive collapse, depending on the abundance and the
 activity of the interacting species.
description: To evaluate the hypothesis that the outcome of the palm-goat
 interaction depends on the intensity of goat activity, we first described
 the spatial distribution of <em>C. humilis </em>by
 geo-referencing in 2019 (with a Garmin GPSMAP) all adult palms within each
 study plot. Then, we searched for dispersed seeds in two consecutive years
 (2019 and 2020) from September to December, which covered the entire seed
 dispersal seasons of <em>C. humilis</em>. Every dispersed unit
 (defined as one dispersed seed or a group of dispersed seeds) was
 geo-referenced as an independent point and covered with a wire 1-cm mesh
 cage (10 x 10 x 9 cm) to prevent seed predation, seed removal and seedling
 trampling by vertebrates. (e.g. Fedriani and Wiegand 2014). GPS
 coordinates were then imported into a geographic information system
 (Quantum GIS Team 2023). Caged dispersed seeds were checked every two
 months up to January 2022 (i.e. two years after the end of the first
 sampling season) to record seed predation by scolytine beetles, seed
 germination, seedling emergence, and seedling survival. Then, we used
 recent extensions of spatial point pattern analyses (SPPA, hereafter;
 Wiegand and Moloney 2014, Velázquez et al. 2016, Ben-Said 2021) to explore
 the data. Specifically, to characterize the spatial distribution of adult
 palms and seed rain (question 1) we fitted univariate cluster point
 process models to the data, whereas to analyze the spatial association
 between adult palms and dispersed units (question 2) we employed bivariate
 pair correlation functions together with realizations of the spatial
 independence null model. Finally, to detect spatial patterns of seed
 predation and to test the Janzen-Connell hypothesis (question 3) we used
 mark connection functions and trivariate mark correlation functions
 together with the random labeling null model.
description: All spatial point pattern analyses were carried out with the free
 software Programita (http://programita.org, Wiegand and Moloney 2014).
 Detailed descriptions of the statistical procedures are provided in
 Supporting Information.