Trait variance leads to the spurious higher temperature sensitivity of heterotrophs than autotrophs

Bingzhang Chen, University of Strathclyde, Department of Mathematics and Statistics, Glasgow, United Kingdom, David Montagnes, University of Liverpool, School of Biological Sciences, Liverpool, United Kingdom, Qing Wang, Jinan University, Department of Ecology, Guangzhou, China and Susanne Menden-Deuer, University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States
The relative temperature sensitivity of autotrophs and heterotrophs have important ramifications for the global scale processes, including oceanic production. We investigated three hypotheses that might lead to the lower temperature sensitivity of phytoplankton than : 1) phytoplankton has a lower interspecific temperature sensitivity than microzooplankton. 2) the sample size of phytoplankton is greater than that of microzooplankton. 3) the trait variances of phytoplankton are greater than those of microzooplankton. We fit the unimodal temperature performance curve to each taxon of both phytoplankton and microzooplankton, obtained their thermal traits and calculated the interspecific temperature sensitivity. We also did a permutation test to test the second hypothesis. Our analyses rejected the first two hypotheses and suggested that the greater variances of phytoplankton thermal traits are the key to the lower apparent temperature sensitivity of phytoplankton than microzooplankton. Our results implicate that further efforts should be invested into identifying species trait distributions and scaling up the traits of individual species to the community response.