Latitudinal gradient of nestedness and its potential drivers in stream detritivores

Understanding what mechanisms shape the diversity and composition of biological assemblages across broad-scale gradients is central to ecology. Litter-consuming detritivorous invertebrates in streams show an unusual diversity gradient, with a-diversity increasing towards high latitudes but no trend in g-diversity. We hypothesized this pattern to be related to shifts in nestedness and several ecological processes shaping their assemblages (dispersal, environmental filtering and competition). We tested this hypothesis, using a global dataset, by examining latitudinal trends in nestedness and several indicators of the above processes along the latitudinal gradient. Our results suggest that strong environmental filtering and low dispersal in the tropics lead to often species-poor local detritivore assemblages, nested in richer regional assemblages. At higher latitudes, dispersal becomes stronger, disrupting the nested assemblage structure and resulting in local assemblages that are generally more species-rich and non-nested subsets of the regional species pools. Our results provide evidence that mechanisms underlying assemblage composition and diversity of stream litter-consuming detritivores shift across latitudes, and provide an explanation for their unusual pattern of increasing a-diversity with latitude. When we repeated these analyses for whole invertebrate assemblages of leaf litter and for abundant taxa showing reverse or no diversity gradients we found no latitudinal patterns, suggesting that function-based rather than taxon-based analyses of assemblages may help elucidate the mechanisms behind diversity gradients. Fil: Boyero, Luz. Universidad del Pais Vasco; España. Basque Foundation for Science; España. Doñana Biological Station; España Fil: Pearson, Richard G.. James Cook University; Australia Fil: Swan, Christopher M.. University of Maryland; Estados Unidos Fil: Hui, Cang. University of Stellenbosch; Sudáfrica. African Inst.itute for Mathematical Sciences; Sudáfrica Fil: Albariño, Ricardo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue; Argentina Fil: Arunachalam, Muthukumarasamy. Manonmainam Sundaranar University; India Fil: Callisto, Marcos. Universidade Federal do Minas Gerais; Brasil Fil: Chará, Julián. Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria; Colombia Fil: Chará Serna, Ana M.. Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria; Colombia Fil: Chauvet, Eric. Universite de Toulose - Le Mirail; Francia Fil: Cornejo, Aydeé. Instituto Conmemorativo Gorgas de Estudios de la Salud; Panamá Fil: Dudgeon, David. University of Hong Kong; China Fil: Encalada, Andrea C.. Universidad San Francisco de Quito; Ecuador Fil: Ferreira, Verónica. Universidad de Coimbra; Portugal Fil: Gessner, Mark O.. Leibniz - Institute Of Freshwater Ecology And Inland Fisheries; Alemania. Berlin Institute of Technology; Alemania Fil: Gonçalves Jr. , José F.. Universidade Do Brasilia; Brasil Fil: Graça, Manuel A. S.. Universidad de Coimbra; Portugal Fil: Helson, Julie E.. University Of Toronto; Canadá Fil: Mathooko, Jude M.. Egerton University; Canadá Fil: McKie, Brendan G.. Swedish University of Agricultural Sciences; Suecia Fil: Moretti, Marcelo S.. University of Vila Velha; Brasil Fil: Yule, Catherine M.. Monash University; Australia