Placing phylogenetic diversity back on the evolutionary track

news and update ISSN 1948-6596 commentary Placing phylogenetic diversity back on the evolutionary track Conceptual frameworks relying on properties that are hard to measure are often challenging. A common solution is the use of proxies or sur- rogates for those properties. When molecular phylogenies became easily available and the conceptual framework by Webb et al. (2002) was published, many ecologists started to use phylogenies as proxy for ecological relationships. The study proposed straightforward hypotheses to infer community assembly processes by using phylogenetic information when trait information is not available, and rapidly became a seminal pa- per. The “phylogeny as a proxy to ecology” ap- proach assumes that closely related species should share more similar features (e.g., ecologi- cal traits, habitats, environmental tolerances) than distantly related species, a statement that can be traced back to Charles Darwin (Webb et al. 2002). Indeed, the number of studies using this approach has quickly increased in recent years (Cianciaruso 2011), even in macroecological and biogeograph- ical journals. Cianciaruso (2011) asked how macro- ecology and biogeography could benefit from phy- logenetic diversity and how we could advance the theory by using novel approaches. An article re- cently published by Gerhold et al. (2015) presents an important contribution to answer these ques- tions. Gerhold et al. (2015) is a must-read paper for anyone thinking of using the “phylogeny as a proxy to ecology” approach because it highlights that phylogenies are not good proxies to ecology, and gives ideas on how ecologists and biogeogra- phers can further connect community-level data to macroevolution. The authors challenge core assumptions that have been increasingly used in studies following the approach proposed by Webb et al. (2002). One of these assumptions is that phylogenetic clustering may be an outcome of trait clustering due to the action of environmental filters or that phylogenetic structure is mainly due to local and present-day processes. Since Webb and colleagues’ paper, several ecologists have used some of their assumptions without criticism (Gerhold et al. 2015). For instance, macroecologi- cal studies have used phylogeny as a proxy (e.g., Cardillo 2011), which should be avoided consider- ing the points made by Gerhold et al. (2015). It is important to note that other studies (e.g., May- field and Levine 2010) have raised some of the criticisms used by Gerhold et al. (2015), but the particular advantage of this new review is that it synthesizes the different criticisms to the “phylogeny as a proxy to ecology” approach. But what does Gerhold et al. (2015) have to do with biogeography? Community ecologists and biogeographers have argued that community ecol- ogy and biogeography should be further integrat- ed (Cavender-Bares et al. 2009, Cianciaruso 2011). Indeed, an attempt towards such an integration was one of the original aims of Webb et al. (2002; see their Figure 1), but it has been little explored over the years. Community ecology can benefit from biogeographic and phylogenetic approaches by putting history and evolution into the explana- tion for current patterns of biodiversity (e.g., com- munity structure) as highlighted by Gerhold et al. (2015). Biogeography in turn can benefit from community ecology elucidating how local process- es can feedback into regional processes, and help- ing explain how ecological processes shape the tree of life (i.e., phylogeny) and the current distri- bution of life on Earth (i.e., macroecological patterns) across evolutionary time via adaptation and other eco-evolutionary mechanisms. Gerhold et al. (2015) argue that ecologists would improve their researches by considering phylogeny not as a mere proxy for ecology but rather by investigating how phylogenetic pat- terns can give insight into processes that drive species coexistence or are its outcome. Ger- hold and colleagues made several points about the perils of using phylogeny as a proxy. We agree with their points. If species traits are al- ready a proxy for functionality or species’ interac- tions (with other species or the environment), would it be safe to use a proxy of a proxy? We believe that it would not. We argue that ecologists frontiers of biogeography 7.3, 2015 — © 2015 the authors; journal compilation © 2015 The International Biogeography Society