Abstract
BackgroundDespite enormous environmental variability linked to glacial/interglacial climates of the Pleistocene, we have recently shown that marine diatom communities evolved slowly through gradual changes over the past 1.5 million years. Identifying the causes of this ecological stability is key for understanding the mechanisms that control the tempo and mode of community evolution.Methodology/Principal FindingsIf community assembly were controlled by local environmental selection rather than dispersal, environmental perturbations would change community composition, yet, this could revert once environmental conditions returned to previous-like states. We analyzed phytoplankton community composition across >104 km latitudinal transects in the Atlantic Ocean and show that local environmental selection of broadly dispersed species primarily controls community structure. Consistent with these results, three independent fossil records of marine diatoms over the past 250,000 years show cycles of community departure and recovery tightly synchronized with the temporal variations in Earth's climate.Conclusions/SignificanceChanges in habitat conditions dramatically alter community structure, yet, we conclude that the high dispersal of marine planktonic microbes erases the legacy of past environmental conditions, thereby decreasing the tempo of community evolution.
Highlights
Environmental variability and historical contingencies shape ecosystems by controlling the spatial distribution of species, promoting biological innovation and extinction and, driving the evolution of communities [1,2,3]
Ecological theory has yielded two main classes of mechanisms to account for patterns of biodiversity and community assembly: 1) limited dispersal of species combined with unrestricted entry into communities [4], and 2) species’ dispersal combined with environmental filtering [5,6]
Analysis of modern phytoplankton communities Data of extant phytoplankton communities were extracted from the Atlantic Meridional Transect (AMT) database
Summary
Environmental variability and historical contingencies shape ecosystems by controlling the spatial distribution of species, promoting biological innovation and extinction and, driving the evolution of communities [1,2,3]. Niche-assembly models are expected to have more predictable community composition among sites and/or time periods characterized by similar environmental conditions [6] In between these two extreme scenarios, high dispersal rates characteristic of organisms such as marine microbial plankton may potentially overwhelm the effect of spatial constraints and environmental determinants, giving rise to random species’ distributions (‘everything is everywhere’) [7]. The ‘everything is everywhere’ hypothesis implies a lack of biogeographic patterns, and, over the last decade, has been a subject of intense debate among aquatic microbial ecologists [7,8,9] Overall, these ecological theories may help to explain the patterns of biodiversity and community structure observed in the fossil record [2]. Identifying the causes of this ecological stability is key for understanding the mechanisms that control the tempo and mode of community evolution
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