Andrés Canavero

Diet of the South American frog Leptodactylus ocellatus (Anura, Leptodactylidae) in Uruguay

The diet of Leptodactylus ocellatus (L., 1758) was studied in specimens collected at Maldonado Department (Uruguay), where monthly surveys were made between August 1998 and March 2000. A total of 143 frogs were collected, measured, sexed, and dissected, to assess stomach contents. The anurans were grouped into three age classes and four categories (considering sex and capture date). The trophic amplitude for each age class and sex-season category was quantified using Shannon-Weaver Index, and the trophic niche overlap between ages and categories by using the Pianka Index. Comparisons among treatments were made by G-tests. The most important prey items were coleopterans (IRI = 2547), and significant correlations were found between predator and prey sizes. The major differences on diet composition were found between extreme age classes (froglets and adults). Significant differences were also detected between sexes in the cold season but not in the warm season. Any of these changes in diet may be related with the availability of prey.

Bullfrog (Lithobates catesbeianus) invasion in Uruguay

This is the first report of North American bullfrogs, Lithobates catesbeianus (=Rana catesbeiana), invasion in Uruguay. This Anura was introduced for farming proposes in 1987, but at present most of the farms are closed. At one of these closed farms, located at Rincón de Pando, Canelones, we report the occurrence of a feral population of L. catesbeianus. This invasion point is at an early stage and restricted to one or two ponds. We also report the effects of L. catesbeianus invasion in the community structure. This includes species composition and species size structure. In this system bullfrog tadpoles constitute a very important proportion of the present biomass. Bullfrog tadpoles appear to be displacing native amphibians and having some type of positive interaction with fishes. At the invaded system we found more fish species and larger sizes of the shared fish species. We analyze the involved risks of this invasion, the ecological impact by predation, the competition and habitat modification, and the potential of bullfrog to act as pathogens vector. We also recommend taking measures in order to avoid the expansion of this population. There is also the need of studies to search for new invasion points in Uruguay, especially where bullfrog farms were located.

Conservation status assessment of the amphibians and reptiles of Uruguay

The native species of amphibians and reptiles of Uruguay were categorized according to the IUCN Red List criteria. Out of 47 amphibian species, seven are listed as Critically Endangered (CR), five as Endangered (EN), one as Vulnerable (VU), three as Near Threatened (NT), and two as Data Deficient (DD); the remaining species are considered to be Least Concern (LC). Among the 64 species of reptiles evaluated, one is listed as Critically Endangered (CR), seven as Endangered (EN), two as Vulnerable (VU), one as Near Threatened (NT) and seven as Data Deficient (DD); the rest are considered to be Least Concern (LC). The use of these results as an additional criterion in the definition of protected areas in Uruguay will contribute towards the conservation of the aforementioned threatened species and their associated ecosystems.

Composition and vegetation structure in a system of coastal dunes of the “de la Plata” river, Uruguay: a comparison with Legrand’s descriptions (1959)

Abstract Forestation in dune systems blocks the transport of sand, making possible the extension of agriculture or urban development into coastal areas. This process, which has been taking place for a century on the Uruguayan shore, has affected the landscape and the composition and structure of plant communities. In this study, we describe the composition and structure of vegetation stands of a dune system at the seaside resort “El Pinar,” Canelones, Uruguay. In addition, we compare it with a previous survey published by Legrand in Anales del Museo de Historia Natural 6:73, 1959. We recorded 76 species; with Asteraceae, Poaceae, Cyperaceae, and Apiaceae the most represented families. A cluster analysis was used to identify main groups of plant associations. This analysis defined seven groups. The group associated with the foredunes environment exhibits the lowest richness, with indicative species typical of extreme psammophilic environments. Five groups occur in interdune depressions associated with humid sites. The last group was defined in the fixed dunes environment. The species composition similarity was low in comparison with Legrand′s (1959) survey; furthermore we found a greater presence of non-native species. We associate this change with the presence of Acacia longifolia, a species with an extremely high invasive potential, considered an ecosystem transformer. Our proposal is the development of an investigation program to assess the effectiveness and challenges of potential management practices. We also suggest applying the tactic of eradication of A. longifolia on the fixed dunes, through different practices of management (e.g., manual control operations, biologic control agents, and the use of fire).

Temporal and Spatial Activity Patterns of Three Species in the Leptodactylus fuscus Group (Amphibia, Leptodactylidae)

Abstract. Space and time are two of the main dimensions of the ecological niche. Because of their high dependence upon aquatic environments during breeding activity, anuran assemblages are interesting models for studying inter-populational relationships. The overlap in habitat use could be particularly high, especially for seasonal species and among taxa that share a common phylogenetic history. Three species of the Leptodactylus fuscus group occur in a semi-permanent pond at Cerro Verde (Rocha, Uruguay): L. latinasus, L. mystacinus and L. gracilis. The aim of this work was to describe the spatial and temporal calling patterns of the three species and the effects of environmental conditions upon them on a daily scale. Their relative abundance was quantified over four weeks (December 2004–January 2005) during the first half of the night along a transect using acoustic surveys. Nestedness, segregation, Jaccards index and association analysis were calculated, revealing a nested pattern with low overlap between species in the occupation of microhabitats. On the temporal axis, the calling behavior of the species seems to be better described by the time of night than by temperature, humidity, or atmospheric pressure. These analyses also showed a non-linear association of activity with time of night, indicating that higher activity occurs at different hours for each species.

Coastal Dunes changes from 1966 to 2001 in the de La Plata River, Uruguay

Hereby we present a historical reconstruction of the coastal landscape for an area of the dune system of Rio de la Plata in Uruguay. In order to achieve our purpose, we performed an analysis of photographs taken of the area in the years 1966, 1976, 1982, 1987, 1994 and 2001, which were loaded to a geographic data system. For a long period of time we detected an increment and advancement of the vegetation coverage towards the coast. Based on a logistic regression, we inferred a transmission pattern predicting that the system would achieve a maximum of 85% coverage via a model of cyrtoid phenomenon. These results make sense once we consider management plans for the restoration of degraded areas, which have been afforested in the past century with the purpose of disrupting the sand dune dynamics and facilitating urban development. Currently, those areas are densely populated with increasing reports of housing and infrastructure destruction due to beach loss and the invasion of exotic species. Our approach incorporates the historical vision of the landscape as a tool for the restoration of degraded ecosystems, and at the same time proposes certain strategies for the management and control of Acacia longifolia, which constitutes the main exotic species that has invaded and modified the dune system of coastal Rio de la Plata.