Latitudinal phytoplankton distribution and the neutral theory of biodiversity
KAUST DepartmentRed Sea Research Center (RSRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Marine Science Program
Plankton ecology Research Group
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AbstractRecent studies have suggested that global diatom distributions are not limited by dispersal, in the case of both extant species and fossil species, but rather that environmental filtering explains their spatial patterns. Hubbell's neutral theory of biodiversity provides a framework in which to test these alternatives. Our aim is to test whether the structure of marine phytoplankton (diatoms, dinoflagellates and coccolithophores) assemblages across the Atlantic agrees with neutral theory predictions. We asked: (1) whether intersite variance in phytoplankton diversity is explained predominantly by dispersal limitation or by environmental conditions; and (2) whether species abundance distributions are consistent with those expected by the neutral model. Location: Meridional transect of the Atlantic (50° N-50° S). Methods: We estimated the relative contributions of environmental factors and geographic distance to phytoplankton composition using similarity matrices, Mantel tests and variation partitioning of the species composition based upon canonical ordination methods. We compared the species abundance distribution of phytoplankton with the neutral model using Etienne's maximum-likelihood inference method. Results: Phytoplankton communities are slightly more determined by niche segregation (24%), than by dispersal limitation and ecological drift (17%). In 60% of communities, the assumption of neutrality in species' abundance distributions could not be rejected. In tropical zones, where oceanic gyres enclose large stable water masses, most communities showed low species immigration rates; in contrast, we infer that communities in temperate areas, out of oligotrophic gyres, have higher rates of species immigration. Conclusions: Phytoplankton community structure is consistent with partial niche assembly and partial dispersal and drift assembly (neutral processes). The role of dispersal limitation is almost as important as habitat filtering, a fact that has been largely overlooked in previous studies. Furthermore, the polewards increase in immigration rates of species that we have discovered is probably caused by water mixing conditions and productivity. © 2012 Blackwell Publishing Ltd.
SponsorsWe thank all who contributed to collecting the samples on the different cruises. This study was supported by the UK Natural Environment Research Council through the Atlantic Meridional Transect consortium (this is contribution number 215 of the AMT programme). Special thanks go to D. Harbour, who counted most of the samples to the species level. We acknowledge the contribution of S. Hubbell (Department of Ecology and Evolutionary Biology, University of California) for reviewing carefully this paper and providing useful comments. This research was funded by the project Malaspina (Consolider-Ingenio 2010, CSD2008-00077) and from the European Commission (contract no. 264933, EURO-BASIN: European Union Basin-scale Analysis, Synthesis and Integration). This is contribution 590 from AZTI-Tecnalia Marine Research Division.
JournalGlobal Ecology and Biogeography