title: The Surales, Self-Organized Earth-Mound Landscapes Made by Earthworms in a Seasonal Tropical Wetland.
abstract: The formation, functioning and emergent properties of patterned landscapes have recently drawn increased attention, notably in semi-arid ecosystems. We describe and analyze a set of similarly spectacular landforms in seasonal tropical wetlands. Surales landscapes, comprised of densely packed, regularly spaced mounds, cover large areas of the Orinoco Llanos. Although descriptions of surales date back to the 1940's, their ecology is virtually unknown. From data on soil physical and chemical properties, soil macrofauna, vegetation and aerial imagery, we provide evidence of the spatial extent of surales and how they form and develop. Mounds are largely comprised of earthworm casts. Recognizable, recently produced casts account for up to one-half of total soil mass. Locally, mounds are relatively constant in size, but vary greatly across sites in diameter (0.5-5 m) and height (from 0.3 m to over 2 m). This variation appears to reflect a chronosequence of surales formation and growth. Mound shape (round to labyrinth) varies across elevational gradients. Mounds are initiated when large earthworms feed in shallowly flooded soils, depositing casts that form 'towers' above water level. Using permanent galleries, each earthworm returns repeatedly to the same spot to deposit casts and to respire. Over time, the tower becomes a mound. Because each earthworm has a restricted foraging radius, there is net movement of soil to the mound from the surrounding area. As the mound grows, its basin thus becomes deeper, making initiation of a new mound nearby more difficult. When mounds already initiated are situated close together, the basin between them is filled and mounds coalesce to form larger composite mounds. Over time, this process produces mounds up to 5 m in diameter and 2 m tall. Our results suggest that one earthworm species drives self-organizing processes that produce keystone structures determining ecosystem functioning and development.
authors.affiliation: Technische Universität Braunschweig (TUB), Institut für Geoökologie, Langer Kamp 19c, D-38106, Braunschweig, Germany.|CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul Valéry Montpellier - EPHE, 1919 route de Mende, 34293 Montpellier Cedex 5, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Zangerlé
authors.affiliation: Department of Geography and Natural Resource Sciences, McGill University, Montreal, QC, H3A 2T5, Canada.
authors.forename: Delphine
authors.initials: D
authors.lastname: Renard
authors.affiliation: Department of Archaeology, College of Humanities, University of Exeter, Exeter, EX4 4QE, United Kingdom.
authors.forename: José
authors.initials: J
authors.lastname: Iriarte
authors.affiliation: Fundacion Universitaria Internacional del Tropico Americano (Unitropico), Cra. 19, Yopal, Colombia.
authors.forename: Luz Elena
authors.initials: LE
authors.lastname: Suarez Jimenez
authors.affiliation: Fundacion Universitaria Internacional del Tropico Americano (Unitropico), Cra. 19, Yopal, Colombia.|Laboratorio de Perifíton, CEP: 87020-900 - Maringá - PR Universidade Estadual de Maringá (UEM), Av. Colombo, 5.790 - Bloco G-90, Sala 8, Maringá, Brazil.
authors.forename: Kisay Lorena
authors.initials: KL
authors.lastname: Adame Montoya
authors.affiliation: Luxembourg Institute of Science and Technology, Environmental Research and Innovation Department, 41 rue du Brill, L-4422, Belvaux, Luxembourg.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Juilleret
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul Valéry Montpellier - EPHE, 1919 route de Mende, 34293 Montpellier Cedex 5, France.|Institut Universitaire de France, Paris, France.
authors.forename: Doyle
authors.initials: D
authors.lastname: McKey
mesh_terms: D000818:Animals; D003105:Colombia; D009835:Oligochaeta / Q000502:physiology*; D010781:Photography; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D014687:Venezuela; D053833:Wetlands
chemical_list: D012987:Soil