DOI: 10.5061/dryad.4j0zpc89d
title: Host spatial structure and disperser activity determine mistletoe infection patterns

description: What processes and factors are responsible for species distribution are
 long-standing questions in ecology and a key element for conservation and
 management. Mistletoes provide the opportunity to study a forest species
 whose occurrence is expected to be constrained by multiple factors as a
 consequence of their life form. We studied the mistletoe Tristerix
 corymbosus (Loranthaceae) on its most common hosts species in northwest
 Patagonia. The seeds of this mistletoe are almost exclusively dispersed by
 the small arboreal and endemic marsupial Dromiciops gliroides
 (Microbiotheridae). We assessed the underlying causes of plant spatial
 patterns through point pattern analysis and we used different variables
 that characterize the neighborhood around each host to analyze the
 relative effect of host availability, potential for disperser movement,
 and canopy light conditions. We found that potential hosts were strongly
 aggregated and that the three most common host species were distributed
 independent of each other. Considering all host species together, infected
 and non-infected host were individually aggregated but segregated from
 each other. The aggregated pattern of infected hosts could be explained in
 part by the template of potential hosts distribution, but was subsequently
 modulated by the activity of the mistletoe disperser. Potential for
 disperser movement,  the proximity to reproductive mistletoes and
 habitat complexity, increased mistletoe infection probability. However,
 neighboring host availability decreased mistletoe infection probability,
 and tree DBH (used as surrogate for light conditions) had no detectable
 effect. Our results suggested that the distribution of mistletoe infection
 was determined by the structure of potential host populations and by the
 marsupial disperser activity. Compared to bird dispersed mistletoes, the
 scale of the infection was smaller and the proximity to reproductive
 mistletoes and habitat complexity were important for seed arrival and
 infection. The interplay between landscape structure and disperser
 activity determine the spatial structure of mistletoe future generations.
description: Data were collected on a plot of 0.9 ha (80 x 100 m) where we
 mapped all potential hosts, trees, and habitat
 complexity in X-Y coordinates. We recorded all potential hosts in species
 and status as infected with mistletoe or non-infected. For each mistletoe,
 we recorded the reproductive status (juvenile or reproductive) by the
 presence of flowers or fruits. Habitat complexity was measure as
 understory vertical structure within the plot, we defined interceptions
 points separated by 2 m (total of 2104 points). At each point, we recorded
 the number of branches (minimum diameter 1 mm) that intercept a 3 m
 vertical pole. Branches with diameter greater than 1 mm allow the
 marsupial to move through the understory. To derive a proxy for light
 conditions, we recorded X-Y coordinates for canopy trees species with
 diameter at breast height (DBH) greater than 5 cm. We define this minimum
 DBH because canopy trees species of this size or larger affect light
 conditions in the understory. We estimate the characteristics of
 neighborhoods around focal hosts within a fixed radius of 5 m from the
 focal host. All spatial point-pattern analyses were performed using the
 Programita software and with R software version 3.6.1 (R Development Core
 Team 2015).