Coastal fog deserts in the Americas: Functional convergence in plant communities?
Functional convergence is a central issue to study community assembly. It can be studied by the distribution of functional traits and by effects of environmental factors. Thus, it is relevant to understand the effects of climate change. Communities like arid lands with a strong abiotic filtering can be prime subjects for the study of functional convergence. There is little information on the variation of plant functional traits in arid environments, and even less in the narrowly restricted and extremely fragile coastal fog deserts. In America, coastal fog deserts are distributed in the Atacama Desert (AD) of South America, and the Sonoran Desert of Baja California (BC) in North America. Facing the Pacific Ocean, both deserts occur at roughly the same latitude. Small changes in environmental conditions, especially those related to water availability strongly affect the distribution and abundance of plants. Here, we explore community similarity by the comparison of the distribution of convergent plant functional traits between the two deserts. We studied five localities: two in BC and three in AD. To characterize species abundance, and trait distribution we used 90 Gentry plots and 43 Braun-Blanquet relevés. We also analyzed historical temperature and precipitation data from its meteorological stations.
We recorded 7938 individuals in 89 and 84 species for AD and BC, respectively. No species were shared among deserts. Seven genera were common. Preliminary results indicate convergence in traits like plant height, photosynthetic pathway, life and growth forms, succulence and leaf lifespan with less than 5 % difference on trait proportion between areas. Traits like spinescense, wax and hairs had larger differences (6-18%). As expected, the climatic variables were not normality distributed. A Mann-Whitney U Test showed not statistically significant differences in the median temperature between areas (P = 0.071). However, the precipitation is significantly different with almost no rainfall in AD (P<0.001). Nevertheless, fog is more prevalent and intense in AD than BC, probably acting like a compensatory factor. There is partial trait convergence between areas probably related with environmental filtering process. To confirm this we are quantifying fog influence and analyzing the potential phylogenetic constraints.