Networks of epiphytic orchids and host trees in Brazilian gallery forests

Abstract

Abstract:Species interactions have been recently depicted as networks, in which each species is connected to one or more other species in binary interaction matrices. Forty networks of epiphytic orchid and host tree species were assessed in Brazilian gallery forests. The nestedness of the networks was estimated with the NODF index and the significance was tested with null models. The phylogenetic structure of the network was also assessed, by searching for phylogenetic signals in the number of interactions and in the similarity of interacting species. In total, 105 orchid species and 132 host tree species were sampled. A nested pattern in all orchid–host tree networks was found. However, phylogenetic signals were not observed. The results support that the host specificity of orchids is small and most of the interactions occur among generalist orchids and generalist host trees. While the concept of species-specificity can thus be rejected, the extreme alternative – that interacting orchids and host trees are not a random subset of the regional species pool – can be dismissed as well. However, factors other than phylogenetic history may structure interaction networks of epiphytic orchids and host trees.

Evaluating factors that predict the structure of a commensalistic epiphyte–phorophyte network

“…A phylogenetic signal is not uncommon in mutualistic and antagonistic interactions [13,14,59]. Similar to our findings, the commensalistic networks between orchid epiphytes and their host trees do not show a phylogenetic signal [26]. The lack of phylogenetic signal could be related to the small size of the phylogenies [55].…”

“…Epiphytes represent 10 per cent of the diversity of living vascular plants [23] attaining their highest diversity in the Neotropics [24]. Studies of networks have found high values of nestedness [3,5,25]; no phylogenetic signal in species interaction patterns [26]; and the generalization of species partly or fully explained by species abundance [5,25]. However, no attempt has been made to incorporate other explanatory variables that might determine the structure of epiphyte -phorophyte networks.…”

Low modularity and specialization in a commensalistic epiphyte–phorophyte network in a tropical cloud forest

“…A nested pattern in epiphyte–phorophyte networks can result from several processes, including succession of vascular epiphytes, species abundances, phorophyte characteristics (e.g., phorophyte size, such as height or trunk diameter), and network size (Burns, ; Ceballos et al., ; Francisco et al., ; Zotarelli et al., ). For instance, sequential colonization by generalist pioneer epiphyte species may facilitate the colonization of other epiphyte species (Burns, ; Silva, Ferreira, Lima, & Soares ; Taylor et al., ). Alternatively, Zhao et al.…”

“…Therefore, large trees can play an important role in network structure and promote diverse epiphyte communities. The nested pattern indicates that specialization is low (e.g., Silva et al., ), and most of the interactions occur among generalist epiphytes and generalist phorophytes. In fact, specificity is expected to be weaker in structurally dependent plants such as epiphytes (Ceballos et al., ; Wagner et al., ).…”

“…Given the importance of vascular epiphytes, recent efforts have been made to understand the occurrence of general patterns in epiphyte–phorophyte networks (Burns, ; Ceballos et al., ). However, many of these studies investigate subsets of relatively poor species communities (Burns, ; Ceballos et al., ), or they focus on specific groups such as bromeliads (Sáyago et al., ) and orchids (Silva et al., ; Zotarelli et al., ). Moreover, these studies were conducted to understand interactions along the horizontal organization (Burns, ; Zhao et al., ).…”