Global distribution of a key trophic guild contrasts with common latitudinal diversity patternsReport as inadecuate

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1 Wetland ecology department Seville, Espagne 2 James Cook university AUSTRALIA 3 HKU - The University of Hong Kong 4 Marine and environmental research centre - IMAR-CMA Coimbra, Portugal 5 Department of Aquatic Ecology - Dübendorf, Suisse 6 Institute of Integrative Biology - Zurich, Suisse 7 Laboratory of limnology Bariloche, Argentina 8 Monash University Malaysia 9 Ecosystem Management, Armidale 10 Sri Paramakalyani Centre for Environmental Sciences - SPKCES Alwarkuruchi, India 11 Laboratorio de ecologia de Bentos Belo Horizonte, Brazil 12 ECOLAB - Laboratoire Ecologie Fonctionnelle et Environnement - ECOLAB 13 Institute for tropical ecosystem studies - ITES San Juan, Puerto Rico 14 Centro para la Investigacion en sistemas Sostenibles de Produccion Agropecuaria - CIPAV COLOMBIA 15 Centro de investigaciones y estudios en biodiversidad y recursos geneticos - CIEBREG COLOMBIA 16 Department of biolological sciences Toronto, Canada 17 Grupo de investigaciones de entomologicas Cali, Colombia 18 Universidad San Francisco de Quito EQUATEUR 19 Instituto conmemorativo Gorgas de esd PANAMA 20 University of Panama PANAMA 21 The University of Georgia - USA

Abstract : Most hypotheses explaining the general gradient of higher diversity toward the equator are implicit or explicit about greater species packing in the tropics. However, global patterns of diversity within guilds, including trophic guilds i.e., groups of organisms that use similar food resources, are poorly known. We explored global diversity patterns of a key trophic guild in stream ecosystems, the detritivore shredders. This was motivated by the fundamental ecological role of shredders as decomposers of leaf litter and by some records pointing to low shredder diversity and abundance in the tropics, which contrasts with diversity patterns of most major taxa for which broad-scale latitudinal patterns haven been examined. Given this evidence, we hypothesized that shredders are more abundant and diverse in temperate than in tropical streams, and that this pattern is related to the higher temperatures and lower availability of high-quality leaf litter in the tropics. Our comprehensive global survey 129 stream sites from 14 regions on six continents corroborated the expected latitudinal pattern and showed that shredder distribution abundance, diversity and assemblage composition was explained by a combination of factors, including water temperature some taxa were restricted to cool waters and biogeography some taxa were more diverse in particular biogeographic realms. In contrast to our hypothesis, shredder diversity was unrelated to leaf toughness, but it was inversely related to litter diversity. Our findings markedly contrast with global trends of diversity for most taxa, and with the general rule of higher consumer diversity at higher levels of resource diversity. Moreover, they highlight the emerging role of temperature in understanding global patterns of diversity, which is of great relevance in the face of projected global warming.

Keywords : Leaf litter quality Shredder detritivores Global distribution pattern Latitudinal diversity gradient Stream ecosystems

Author: Luz Boyero - Richard G. Pearson - David Dudgeon - Manuel A. S. Graça - Mark O. Gessner - Ricardo J. Albariño - Veronica Ferreir



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