title: Global distribution of a key trophic guild contrasts with common latitudinal diversity patterns.
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.
authors.affiliation: Wetland Ecology Department, Doñana Biological Station-CSIC, Avda Americo Vespucio sn/n, E-41092 Sevilla, Spain. luz.boyero@ebd.csic.es
authors.forename: Luz
authors.initials: L
authors.lastname: Boyero
authors.forename: Richard G
authors.initials: RG
authors.lastname: Pearson
authors.forename: David
authors.initials: D
authors.lastname: Dudgeon
authors.forename: Manuel A S
authors.initials: MA
authors.lastname: Graça
authors.forename: Mark O
authors.initials: MO
authors.lastname: Gessner
authors.forename: Ricardo J
authors.initials: RJ
authors.lastname: Albariño
authors.forename: Verónica
authors.initials: V
authors.lastname: Ferreira
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Yule
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Boulton
authors.forename: Muthukumarasamy
authors.initials: M
authors.lastname: Arunachalam
authors.forename: Marcos
authors.initials: M
authors.lastname: Callisto
authors.forename: Eric
authors.initials: E
authors.lastname: Chauvet
authors.forename: Alonso
authors.initials: A
authors.lastname: Ramírez
authors.forename: Julián
authors.initials: J
authors.lastname: Chará
authors.forename: Marcelo S
authors.initials: MS
authors.lastname: Moretti
authors.forename: José F
authors.initials: JF
authors.lastname: Gonçalves
authors.forename: Julie E
authors.initials: JE
authors.lastname: Helson
authors.forename: Ana M
authors.initials: AM
authors.lastname: Chará-Serna
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Encalada
authors.forename: Judy N
authors.initials: JN
authors.lastname: Davies
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lamothe
authors.forename: Aydeè
authors.initials: A
authors.lastname: Cornejo
authors.forename: Aggie O Y
authors.initials: AO
authors.lastname: Li
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Buria
authors.forename: Verónica D
authors.initials: VD
authors.lastname: Villanueva
authors.forename: María C
authors.initials: MC
authors.lastname: Zúñiga
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Pringle
mesh_terms: D000818:Animals; D044822:Biodiversity; D003710:Demography; D005247:Feeding Behavior; D020387:Food Chain; D007448:Invertebrates / Q000502:physiology*