Temperature effects on body size of freshwater crustacean zooplankton from Greenland to the tropics
The body size of zooplankton has many substantive effects on the function of aquatic food webs. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, calanoids, and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74o latitude and encompassing a temperature range of 2–30°C. Cladoceran body size declined with temperature, in a marginally significant manner (P = 0.10). For cyclopoids, the decline was more significant (P = 0.05). In both cases, there was considerably more variation around the regression lines than previously observed; suggesting that other variables such as fish predation played a role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclopoids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation.
KeywordsZooplankton size Latitudinal patterns Global comparison
The authors are grateful to the many field and laboratory support staff who collected and analyzed zooplankton in the study regions. Without their support this paper would not have been possible. The data collection in Florida was supported financially by the South Florida Water Management District. The groups from Aarhus University and METU were supported by the MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu). The data collection in Turkey was supported by TUBİTAK-ÇAYDAG (Projects 105Y332 and 110Y12) The Greenland studies was supported by the Research Council for Nature and Universe, Greenland Climate Research Centre and the Danish Agency of the Environment. The data collection in Ethiopia was supported by the National Science Foundation (NWO) project R83-206 and by the Schure-Beijerinck-Popping Fund of the Royal Netherlands Academy of Arts and Sciences (KNAW) project SBP/JK/2004-14. The Canadian studies were supported by the National Science and Engineering Research Council and the Ontario Ministry of Natural Resources. Data collection in Brazil was supported by CNPq (Proc. 521.513/93-6) and FAPEMIG (CBS 1897/96) grants. The work in Florida was done under CRIS Project FLA-FRE-005152 and was supported by the National Sea Grant College Program of the United States Department of Commerce, National Oceanic and Administration, under NOAA Grant NA06OAR-4170014. The authors thank Roger Bachmann for pre-reviewing this paper and providing many valuable comments.
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