title: Host specificity in vascular epiphytes: a review of methodology, empirical evidence and potential mechanisms.
abstract: Information on the degree of host specificity is fundamental for an understanding of the ecology of structurally dependent plants such as vascular epiphytes. Starting with the seminal paper of A.F.W. Schimper on epiphyte ecology in the late 19th century over 200 publications have dealt with the issue of host specificity in vascular epiphytes. We review and critically discuss this extensive literature. The available evidence indicates that host ranges of vascular epiphytes are largely unrestricted while a certain host bias is ubiquitous. However, tree size and age and spatial autocorrelation of tree and epiphyte species have not been adequately considered in most statistical analyses. More refined null expectations and adequate replication are needed to allow more rigorous conclusions. Host specificity could be caused by a large number of tree traits (e.g. bark characteristics and architectural traits), which influence epiphyte performance. After reviewing the empirical evidence for their relevance, we conclude that future research should use a more comprehensive approach by determining the relative importance of various potential mechanisms acting locally and by testing several proposed hypotheses regarding the relative strength of host specificity in different habitats and among different groups of structurally dependent flora.
authors.affiliation: Universität Oldenburg, Institut für Biologie und Umweltwissenschaften, AG Funktionelle Ökologie, Carl-von-Ossietzky-Straße 9-11, D-26111 Oldenburg, Germany ka.wagner@uni-oldenburg.de.
authors.forename: Katrin
authors.initials: K
authors.lastname: Wagner
authors.affiliation: Universität Oldenburg, Institut für Biologie und Umweltwissenschaften, AG Funktionelle Ökologie, Carl-von-Ossietzky-Straße 9-11, D-26111 Oldenburg, Germany.
authors.forename: Glenda
authors.initials: G
authors.lastname: Mendieta-Leiva
authors.affiliation: Universität Oldenburg, Institut für Biologie und Umweltwissenschaften, AG Funktionelle Ökologie, Carl-von-Ossietzky-Straße 9-11, D-26111 Oldenburg, Germany Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Balboa, Ancón, Panamá, República de Panamá
authors.forename: Gerhard
authors.initials: G
authors.lastname: Zotz
keywords: Biodiversity; host bias; host preference; host specificity; specialization; structurally dependent plants; vascular epiphytes