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Montevideo, Uruguay

California sea lion (Zalophus californianus) rookeries in the Gulf of California are structured genetically in distinct groups. Despite this evidence for regional differentiation, the sea lion population of the Gulf of California is managed as a single unit. To prioritize the allocation of limited resources for conservation and to improve the effectiveness of management actions, ecological differences among rookeries should also be considered. This is important to be able to further define and subsequently manage the rookeries on a regional level. The aim of the present study was to identify patterns of similarity among California sea lion rookeries in the Gulf of California, using nine demographic, biological, ecological, and biogeochemical databases: population censuses, trace metal content in bone, diet diversity, presence of Leptospira serovarieties, stable isotopes, incidence of osteoarthritis, sea surface temperature, and chlorophyll a concentration. A second objective was to characterize each region on the basis of these variables in order to focus management efforts. To examine the overall structure of the sea lion rookeries in the Gulf of California, we analyzed data for different combinations of variables and rookeries using multivariate analysis. The scenario with the highest explanatory power resulted in the separation of the rookeries into four groups: Northern Gulf, Ángel de la Guarda, Central Gulf, and Southern Gulf. Diet and sea surface temperature were the variables that contributed most strongly to the definition of the groups. Groupings showed geographic coherence and were consistent with previously proposed genetic units and oceanographic regions of the Gulf of California. The resulting multivariate pattern should facilitate the management of California sea lion rookeries, provide better tools to protect against environmental contingencies, and help to guide future management plans. Source

Burress E.D.,Appalachian State University | Duarte A.,Seccion Zoologia Vertebrados | Gangloff M.M.,Appalachian State University | Siefferman L.,Appalachian State University
Ecology of Freshwater Fish | Year: 2013

Characterization of food web structure may provide key insights into ecological function, community or population dynamics and evolutionary forces in aquatic ecosystems. We measured stable isotope ratios of 23 fish species from the Rio Cuareim, a fifth-order tributary of the Rio Uruguay basin, a major drainage of subtropical South America. Our goals were to (i) describe the food web structure, (ii) compare trophic segregation at trophic guild and taxonomic scales and (iii) estimate the relative importance of basal resources supporting fish biomass. Although community-level isotopic overlap was high, trophic guilds and taxonomic groups can be clearly differentiated using stable isotope ratios. Omnivore and herbivore guilds display a broader δ13C range than insectivore or piscivore guilds. The food chain consists of approximately three trophic levels, and most fishes are supported by algal carbon. Understanding food web structure may be important for future conservation programs in subtropical river systems by identifying top predators, taxa that may occupy unique trophic roles and taxa that directly engage basal resources. © 2012 John Wiley & Sons A/S. Source

Carranza A.,UNDECIMAR | Defeo O.,UNDECIMAR | Arim M.,Seccion Zoologia Vertebrados
Diversity and Distributions | Year: 2011

Aim Phylogenetically related species share attributes that lead to common responses to environmental conditions, but which could also produce the exclusion of species by its relatives. These processes could generate the patterns of phylogenetic attraction or repulsion in local communities, where related species would tend to coexist more or less than expected by chance. This paper aims to (1) analyse the phylogenetic structure of a benthic gastropod assemblage in the south-western Atlantic Ocean (SAO); (2) explore the linkages between phylogenetic structure and spatial distribution patterns; (3) compare outcomes driven by the analysis of presence-only data and predictive species distribution models; and (4) explore which aspects of the gained knowledge can be useful to the design of sound conservation and/or management actions.Location Uruguayan shelf and slope in the SAO.Methods Spatial patterns in taxonomical relatedness were assessed using (1) raw presence/absence data (i.e. realized niche approach) and (2) reconstruction of the potential composition of the assemblage from niche modelling (i.e. fundamental niche approach). Null models were used to test hypotheses on assemblage structure.Results Significant departures from the null hypothesis that all species were drawn from the same assemblage were observed irrespectively of the approach, indicating the existence of non-random structures. However, a high proportion of local communities can be thought as random subsets of the regional species pool. This lack of a strong signal of a taxonomic effect could be related to the absence of a linkage between taxonomic distances and ecological similarities.Main conclusions Our results suggest a random assembly of local communities from the regional species pool and/or niche filtering independent of phylogeny as main determinants of local community composition. We also suggest that local assemblages displaying significantly higher (or lower) than expected taxonomic relatedness should be taken into consideration for designing spatially explicit conservation measures. © 2010 Blackwell Publishing Ltd. Source

Carranza A.,UNDECIMAR | Arim M.,Seccion Zoologia Vertebrados | Scarabino F.,Museo Nacional de Historia Natural CC. 399 | Defeo O.,UNDECIMAR
Oikos | Year: 2010

Community assembly rules theory attempt to understand the processes that determine the composition of local communities from a regional species pool. Nestedness and negative co-occurrence are two of the most commonly reported meta-community patterns, but almost exclusively from terrestrial and freshwater ecosystems. Here we analyzed the structure of species coexistence in six datasets containing presence/absence data for 120 marine benthic gastropod species in 249 sampling units on the Uruguayan continental shelf and Río de la Plata estuary. The ecological features of this system, such as the idiosyncratic nature of the biogeographic and oceanographic realms, are clearly different from those observed in other systems previously targeted by studies on coexistence structure. Community patterns were evaluated using null models and four structure indices. The existence of patterns in community assembly, and in particular segregated co-occurrence, was verified only when analyzing the number of checkerboard units (CH index). This indicates more mutually exclusive species pairs than expected by chance. Nestedness, on the other hand, was not detected in any dataset. Storage and rescue effects related to overall high immigration and low local extinction rates are plausible mechanisms to account for the general pattern of random species coexistence, while the segregated co-occurrence pattern depicted by the CH index may be related to differential habitat requirements within species pairs. Our study highlights the importance of analyzing metacommunity structures in alternative biological, environmental, and historical contexts in order to advance on the construction of a general ecological theory, relating patterns with the processes dominating in particular ecosystems. © 2009 The Authors. Source

Burress E.D.,Appalachian State University | Burress E.D.,Auburn University | Duarte A.,Seccion Zoologia Vertebrados | Serra W.S.,Seccion Zoologia Vertebrados | And 3 more authors.
PLoS ONE | Year: 2013

Ecological speciation is well-known from adaptive radiations in cichlid fishes inhabiting lentic ecosystems throughout the African rift valley and Central America. Here, we investigate the ecological and morphological diversification of a recently discovered lotic predatory Neotropical cichlid species flock in subtropical South America. We document morphological and functional diversification using geometric morphometrics, stable C and N isotopes, stomach contents and character evolution. This species flock displays species-specific diets and skull and pharyngeal jaw morphology. Moreover, this lineage appears to have independently evolved away from piscivory multiple times and derived forms are highly specialized morphologically and functionally relative to ancestral states. Ecological speciation played a fundamental role in this radiation and our data reveal novel conditions of ecological speciation including a species flock that evolved: 1) in a piscivorous lineage, 2) under lotic conditions and 3) with pronounced morphological novelties, including hypertrophied lips that appear to have evolved rapidly. © 2013 Burress et al. Source

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