How do lianas and vines influence competitive differences and niche differences among tree species? Concepts and a case study in a tropical forest.

Lianas and other climbing plants are structural parasites of trees, generally reducing host tree survival, growth, and reproduction, yet their influences on the outcome of competition among tree species have remained largely unexplored.We propose that there are three distinct components to liana–tree interactions: prevalence, defined as the proportion of infested trees; load, defined as the mean liana cover on infested trees; and tolerance, defined as the effect of a given level of infestation on tree population growth rates. We introduce a new metric that integrates these components, the liana burden, defined as the total effect of lianas on per capita population growth rates given current prevalence, load, and tolerance. Using these metrics, we quantify variation among 33 co‐occurring tropical tree species in liana–tree interactions and its relation with shade‐tolerance.The focal tree species vary strongly in liana prevalence, load, tolerance, and burden. Interspecific variation in tolerance is the largest contributor to interspecific variation in burden. Species rankings of per capita population growth rates under current liana infestation levels differ somewhat from rankings under liana‐free conditions, and differ strongly from rankings under uniformly high liana infestation. Thus, lianas alter competitive hierarchies to benefit tree species that are relatively tolerant of and/or resistant to lianas. Among the focal tree species, shade‐tolerance is positively correlated with liana tolerance and prevalence, but largely unrelated to load and burden, meaning shade‐tolerance does not predict which species are competitively disadvantaged by lianas. We describe a variety of mechanisms by which lianas may potentially increase or decrease niche differences among tree species, including interactions with spatial and temporal environmental niche partitioning, and potential differences among tree species in relative vulnerability to different liana species.Synthesis. Lianas, like other natural enemies, can in principle alter competitive hierarchies and niche structure of co‐occurring tree species, and our analyses suggest such influences are substantial in our focal tropical tree community and likely many other tree communities as well. Quantifying these effects requires a more comprehensive approach including analyses and modelling of dynamics of liana–tree interactions and their variation with tree and liana species identities. [ABSTRACT FROM AUTHOR]