Ana Inés Borthagaray

Scale-dependent patterns of macrofaunal distribution in soft-sediment intertidal habitats along a large-scale estuarine gradient

We investigated the pattern of distribution of intertidal soft-bottom fauna in streams and lagoons of the Uruguayan coast at three spatial scales. The Río de la Plata and the Atlantic Ocean produce on this coast a large-scale gradient in salinity, defining a freshwater (west), an estuarine (central) and a marine (east) region. Within each region, there are several streams and coastal lagoons (sites) that define a second scale of variability. A third scale is given by intertidal gradients within each site. Species richness and total abundance was low in the freshwater west region and high in the central and east regions. The community in the west region was characterized by the clam Curbicula fluminea; in the other regions, it was dominated mainly by the polychaete Heteromastus similis. The polychaete Nephtys fluviatilis was more abundant in the east region, while another polychaete, Laeonereis acuta, characterized the central region. Sediment fractions did not vary significantly at this scale. At the scale of the sites, species richness and total macrofaunal abundance were higher in coastal lagoons than in streams. Coarse sands were more common in coastal lagoons, while medium and fine sand characterized the sediment in streams. Within each site, species richness and total abundance increased towards the lower intertidal level; the macrofauna of the upper levels were a subsample of the fauna occurring at the lower levels. There was also a significantly lower proportion of fine sand at the upper level. At regional scales, the observed patterns may be indirectly or directly related to the gradient in salinity, through differential physiological tolerance to osmotic stress. At the scale of the sites, variability may be explained mainly by geomorphological and sedimentological differences between lagoons and streams. Variation among levels may be related to gradients in desiccation, colonization and predation.

Vegetation pattern formation in a fog-dependent ecosystem

Vegetation pattern formation is a striking characteristic of several water-limited ecosystems around the world. Typically, they have been described on runoff-based ecosystems emphasizing local interactions between water, biomass interception, growth and dispersal. Here, we show that this situation is by no means general, as banded patterns in vegetation can emerge in areas without rainfall and in plants without functional root (the Bromeliad Tillandsia landbeckii) and where fog is the principal source of moisture. We show that a simple model based on the advection of fog-water by wind and its interception by the vegetation can reproduce banded patterns which agree with empirical patterns observed in the Coastal Atacama Desert. Our model predicts how the parameters may affect the conditions to form the banded pattern, showing a transition from a uniform vegetated state, at high water input or terrain slope to a desert state throughout intermediate banded states. Moreover, the model predicts that the pattern wavelength is a decreasing non-linear function of fog-water input and slope, and an increasing function of plant loss and fog-water flow speed. Finally, we show that the vegetation density is increased by the formation of the regular pattern compared to the density expected by the spatially homogeneous model emphasizing the importance of self-organization in arid ecosystems.

Inferring species roles in metacommunity structure from species co-occurrence networks

A long-standing question in community ecology is what determines the identity of species that coexist across local communities or metacommunity assembly. To shed light upon this question, we used a network approach to analyse the drivers of species co-occurrence patterns. In particular, we focus on the potential roles of body size and trophic status as determinants of metacommunity cohesion because of their link to resource use and dispersal ability. Small-sized individuals at low-trophic levels, and with limited dispersal potential, are expected to form highly linked subgroups, whereas large-size individuals at higher trophic positions, and with good dispersal potential, will foster the spatial coupling of subgroups and the cohesion of the whole metacommunity. By using modularity analysis, we identified six modules of species with similar responses to ecological conditions and high co-occurrence across local communities. Most species either co-occur with species from a single module or are connectors of the whole network. Among the latter are carnivorous species of intermediate body size, which by virtue of their high incidence provide connectivity to otherwise isolated communities playing the role of spatial couplers. Our study also demonstrates that the incorporation of network tools to the analysis of metacommunity ecology can help unveil the mechanisms underlying patterns and processes in metacommunity assembly.

Ophiuroidea (Echinodermata) from La Coronilla-Cerro Verde (Uruguay): a new record for the Uruguayan coast

Carranza, A., Borges, M., Rodriguez, M. & Borthagaray, A.I. Ophiuroidea (Echinodermata) from La Coronilla-Cerro Verde (Uruguay): a new record for the Uruguayan coast. Biota Neotrop. Sep/Dez 2007 vol. 7, no. 3 http://www.biotaneotropica.org.br/v7n3/pt/abstract?article+bn01607032007. ISSN 1676-0603. La Coronilla-Cerro verde has been proposed as the first marine protected area in Uruguay. As part of a detailed benthic biodiversity assessment at the reserve, we analyzed the ophiuroid fauna collected in the intertidal and shallow subtidal during 2005 and 2006. Three species of ophiuroids were identified: Amphioplus lucyae, Amphipholis squamata and Amphiodia sp. Only two species belonging to the genus Amphiodia (A. pulchella and A. planispina) have been previously mentioned for Uruguayan waters, indicating that the unidentified species found in this study constitutes a previously unreported species.

The brown mussel Perna perna in the native mussel beds of Cerro Verde (Uruguay)

*Investigacion & Desarrollo, Facultad de Ciencias, Igua 4225, C.P.11.400, Montevideo, Uruguay. †UNDECIMAR, Facultad de Ciencias, Igua 4225, C.P.11.400. ‡Departamento de Ecologia and Centro de Estudios Avanzados en Ecologia y Biodiversidad (CASEB), Pontificia Universidad Catolica de Chile, Casilla 114-D, Santiago, Chile. ∫Instituto de Ecologia y Biodiversidad (IEB), Casilla 653, Santiago, Chile. *Equal authorship. §Corresponding author: e-mail: alvardoc@fcien.edu.uy

Effects of Metacommunity Networks on Local Community Structures: From Theoretical Predictions to Empirical Evaluations

Abstract Although empirical support for it is at an early stage of development, metacommunity theory has become a mainstream component in ecological thinking. Four paradigms encapsulate proposed metacommunity mechanisms: (1) colonization–competition trade-off in “patch dynamics,” (2) community-dependent species–environment fitting in “species sorting,” (3) increase in local persistence through immigration from more successful populations in the “mass effect,” and (4) trait-independent assemblages of “neutral processes.” Using metapopulation models, we highlight the wide range of patterns predicted by different mechanisms. Neutral and mass effects should be enhanced by dispersal, thereby constraining the conditions for species sorting. The relative effects of dispersal on dominant and subordinate species determine the weakening or strengthening of patch dynamics. Potential methodological approaches to field-data evaluation of metacommunity theoretical predictions are considered here. The key difference among paradigms lies in the putative role of traits on species performance in different communities. We argue for the use of functional biodiversity analyses by maximum entropy (MaxEnt) procedures as powerful tools for distinguishing metacommunity mechanisms. The effect of dispersal on metacommunity mechanisms also requires realistic field-testing. The centrality–isolation gradient may directly determine dispersal, while graph theory provides measures of isolation and network structure; nevertheless, estimation of metacommunity networks is not straightforward. Percolation distances, minimum spanning trees, and physical connections between patches are excellent approaches toward this problem of estimation, but the configurations they describe may differ from the functional metacommunity network. We propose an estimation method based on maximization of network–local pattern coherence, and we consider further alternatives. The combined use of MaxEnt and graph theories will likely contribute significantly to advances in metacommunity concepts through rigorous validations based on field-collected data.

A modularity-based approach for identifying biodiversity management units

BackgroundTaxon- and/or ecosystem-based definitions of management units typically focus on conspicuous species and physical habitat limits; these definitions implicitly assume that these classification systems are related to the mechanisms that determine biodiversity persistence. However, ecological theory shows that this assumption may not be supported. Herein, we introduce the use of modularity analysis for objectively identifying management units and topological roles that land cover type plays on species movement through the landscape.MethodsAs a case study, we used a coastal system in Uruguay, with 28 land cover types and five taxa (from plants to mammals). A modularity-based approach was used to identify subsets of habitats with biotic affinity, termed modules, across the different taxonomic groups. Modularity detects the tendency of some land cover types to have a higher probability of the mutual interchange of individuals than other land cover types. Based on this approach, pairs of habitats that co-occur in the same module across taxa were considered in the same biodiversity management units (BMU). In addition, the topological role of each habitat was determined based on the occurrence of species through the landscape.ResultsOur approach determined three management units that combine land cover types usually considered independent, but instead are interrelated by an occurrence-based ecological network as proxies of the potential flow of individual and land use. For each selected taxon, the specific topological role of each habitat was determined.ConclusionsThis approach provides an objective way of delineating spatial units for conservation assessment. We showed that land cover types within these spatial units could be identified as refuges for specific types of biodiversity, sources of propagules for neighboring or overall landscapes, or stepping-stones connecting sub-regions. The preservation of these topological roles might help maintain the mechanisms that drive biodiversity in the system. Interestingly, the role of land cover type was strongly contingent on the taxa being considered. The method is comprehensible, applicable to policy and decision-makers, and well-connected with ecological theory. Moreover, this approach complements existing methods, introduces novel quantitative uses of available information, determines criteria for land cover classification and identifies management units that are not evident through other approaches.