Macroevolution structure of functional tradeoffs that determine long-term species coexistence in a desert winter annual plant system

Background/Question/Methods  

Fundamental tradeoffs create differentiated demographic response to environmental variation, thus mechanically promote species coexistence. However, studies of macroevolutionary patterns and structures of functional traits are limited. Lack of long-term dynamics across different scales makes it difficult to place phylogenetic relatedness among species and phylogenetic independent local community processes in the framework of species coexistence. Functional tradeoffs can offer us this unique sally port to disentangle underlying mechanisms of species coexistence. We have identified and measured a set of functional traits that reliably showed functional tradeoffs among different species, Water-Use-Efficiency (WUE) and Relative-Growth-Rate (RGR) in our desert winter annual plant system located at desert laboratory in Southern Arizona. Using phylogenetically independent contrasts we investigated the macroevolutionary structure of functional tradeoffs by assessing phylogenetic niche conservatism in our winter annual plant community.

Results/Conclusions  

We found evidence of phylogenetic signals of WUE-RGR trade-off in our community such that evolutionarily more closely related species tend to resemble each other in their functional tradeoffs. Moreover, the abundance of species played a role in the stregthen of the functional trade-off. Collectively this indicates that community assembly among our winter annual plants maybe driven largely by competitive exclusion. Furthermore, our results are consistent with the pattern found at larger spatial scale studies in tropical tree communities and shed light on community assembly patterns in arid regions.