Abstract
Climate warming has been linked with changes in the spatiotemporal distribution of species and the body size structure of ecological communities. Body size is a master trait underlying a host of physiological, ecological and evolutionary processes. However, the relative importance of environmental drivers and life history strategies on community body size structure across large spatial and temporal scales is poorly understood. We used detailed data of 83 copepod species, monitored over a 57‐year period across the North Atlantic, to test how sea surface temperature, thermal and day length seasonality relate to observed latitudinal‐size clines of the zooplankton community. The genus Calanus includes dominant taxa in the North Atlantic that overwinter at ocean depth. Thus we compared the copepod community size structure with and without Calanus species, to partition the influence of this life history strategy. The mean community body size of copepods was positively associated with latitude and negatively associated with temperature, suggesting that these communities follow Bergmann's rule. Including Calanus species strengthens these relationships due to their larger than average body sizes and high seasonal abundances, indicating that the latitudinal‐size cline may be adaptive. We suggest that seasonal food availability prevents high abundance of smaller‐sized copepods at higher latitudes, and that active vertical migration of dominant pelagic species can increase their survival rate over the resource‐poor seasons. These findings improve our understanding of the impacts that climate warming has on ecological communities, with potential consequences for trophic interactions and biogeochemical processes that are well known to be size dependent.
Highlights
Body size relates to the fitness, ecology and physiology of organisms, and is considered a master trait (Brown et al 2004, Barton et al 2013)
Distribution of copepod community body size (CCS) across the North Atlantic differed among the seasons (ANOVA, p < 0.05, F = 528.36, n = 684, Fig. 2)
We demonstrate that copepods in the North Atlantic follow Bergmann’s rule, with larger species being more common at higher latitudes
Summary
Body size relates to the fitness, ecology and physiology of organisms, and is considered a master trait (Brown et al 2004, Barton et al 2013). Laboratory experiments and meta-analyses have revealed that within ectothermic species body size co-varies strongly with temperature (Atkinson 1994, Horne et al 2015) and can be influenced by seasonality in species with multiple generations per year (Horne et al 2015). The influence of temperature and seasonality on ectotherm community size structure across large spatial and temporal scale is still understudied. Studies over large spatiotemporal scales accounting for species redistributions and local extinction may provide important insights into how community structure responds to ongoing climate warming (Stocker et al 2014)
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