Network properties of arboreal plants: Are epiphytes, mistletoes and lianas structured similarly?

Network analyses provide a unified framework to evaluate different types of species interactions. We used a network approach to comparatively evaluate three types of arboreal plant metacommunities. Interactions between mistletoes, lianas and epiphytes and their host trees were quantified in two New Zealand forests and individual-based null models were used to test for non-random patterns in network degree, nestedness and negative co-occurrence patterns. Arboreal plants were simulated to randomly occur on individual host trees to derive 'null' interaction matrices, which were then compared to the observed matrix. Results showed that mistletoes, lianas and epiphytes had very different network properties. Mistletoe and liana degree distributions exhibited fewer links than expected under the null model, indicating strong host preferences. Conversely, degree distributions for epiphytes were consistent with randomised expectations. Mistletoes and lianas were less nested than null model expectations and instead showed support for negative co-occurrence patterns, meaning mistletoe and liana species tended to have mutually exclusive host preferences. Conversely, epiphytes were more nested than expected by chance and showed positive co-occurrence patterns. Overall results indicate that plant-plant interactions exhibited by different types of arboreal plants have very different network properties. We hypothesize that these differences result from (1) differences in coevolutionary dynamics between arboreal plants and their hosts, which range from parasitic (mistletoes) to commensal (epiphytes), and (2) biotic interactions among arboreal plant species for access to host trees. (C) 2008 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved.