Gabriel Laufer

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.

Mamíferos invasores en Uruguay, historia, perspectivas y consecuencias

Relevar la presencia de especies exoticas y conocer sus atributos ecologicos es un importante insumo para la conservacion de la biodiversidad. A traves de una revision bibliografica y de colecciones cientificas, se recabaron datos de dieta, tamano corporal, historia y estatus de invasion de los mamiferos exoticos reportados en Uruguay. Se realizaron modelaciones de nicho para cada especie en base a modelos de Maxima Entropia. Tambien se estimo el cambio generado en la estructura trofica de la biota de mamiferos del Uruguay causado por los procesos de introduccion y perdida de especies. El cambio en los tamanos corporales se evaluo en relacion a los datos de distribucion de tamanos estimados para los principales grupos troficos de mamiferos. Este analisis se realizo a nivel de riqueza de especies y biomasa total por grupo trofico, estimada a partir de alometrias conocidas. Los resultados sugieren que el cambio en biomasa es estimable solo conociendo el exponente de las alometrias entre densidad y tamano corporal, no requiriendose conocer la constante de normalizacion. Las especies recientemente extintas son de mayores tamanos corporales y frecuentemente de dietas carnivoras en comparacion a las actuales. Contrariamente, las especies introducidas son omnivoras (Mus musculus, Rattus norvegicus, Rattus rattus, Sus scrofa) y herbivoras (Lepus europaeus, Bubalus bubalis, Capra hircus, Axis axis, Dama dama). Estos cambios en la composicion de especies se ven exacerbados cuando los consideramos desde el punto de vista de la biomasa. Asimismo evaluamos la idoneidad climatica del territorio uruguayo para el establecimiento de dos especies potencialmente invasoras, la ardilla de vientre rojo (Callosciurus erythraeus) que estaria expandiendo su rango de distribucion en Argentina y el vison americano (Neovison vison) que ha sido recientemente introducido con fines de cria comercial. No obstante la relativa homogeneidad geografica y climatica del paisaje de Uruguay, las estimaciones de idoneidad ambiental para el potencial de establecimiento de especies exoticas indican importantes variaciones a lo largo del territorio y entre especies. Nuestro estudio remarca la fortaleza de la teoria ecologica para adelantarse en el estado basico de las especies y su impacto, incluso cuando la informacion disponible sobre estas y los sitios de invasion es limitada.

The use of ephemeral reproductive sites by the explosive breeding toad Melanophryniscus rubriventris (Anura: Bufonidae): is it a predator cue mediated behavior?

Amphibians detect quality signals when selecting reproduction sites. We hypothesize that Melanophryniscus rubriventris, an explosive breeding toad that reproduces in small, ephemeral water bodies, is able to select sites without predators. We performed a field experiment simulating oviposition sites, two with predators (tadpoles and bugs) and one control. Contrary to our expectations, we obtained no differences in the number of eggs deposited. We also performed an experiment to test the capability of M. rubriventris tadpoles to detect potential predators. Tadpoles could not detect predators, as other species did. Melanophryniscus rubriventris is selecting spawning sites following other signals, not predation risk. Identifying selection cues is crucial to protect species that depend on threatened habitats.

Experimental Test of Intraspecific Competition Mechanisms Among Tadpoles of Leptodactylus ocellatus (Anura: Leptodactylidae)

Abstract Intraspecific competition is predicted to strongly influence species abundance and dynamics through two main mechanisms: consumption and interference of resources. Tadpoles were used in experiments in which we tried to elucidate the relative importance of each mechanism. Our goal was to apply this experimental procedure to Leptodactylus ocellatus, a common South American anuran, a species whose larvae exhibit aggregative behavior and receive parental care. Previous work suggests that tadpole schools should present lower levels of intraspecific competition. Tadpoles from a single nest were reared in the laboratory in three densities (1, 2, and 4 individuals/container) and three food levels (1, 2, and 4 ration multiples) in a randomized three-block design for a factorial analysis of variance, up to day eight. Contrary to previous work with other species, our results show both the absence of interference competition effects, and that larval growth depends only on per capita food availability. The differences between species in intraspecific competition mechanisms are probably related to strong differences in ecology and life history. Leptodactylus ocellatus tadpoles could be directing interference competition away from their kin, reducing schooling costs. Further studies (including kinship as a factor) would give more information about these larvae, allowing a better understanding of the evolutionary and ecological mechanisms behind the biological patterns observed in Leptodactylus species.

Current status of American bullfrog, Lithobates catesbeianus, invasion in Uruguay and exploration of chytrid infection

The American bullfrog Lithobates catesbeianus is an invasive species that can strongly affect native amphibian communities through competition, predation, or introduction of diseases. This frog has invaded multiple areas in South America, for which niche models predict suitable environments across much of the continent. This paper reveals the state of the invasion of this species in Uruguay and its possible relationship with the chytrid pathogenic fungus, Batrachochytrium dendrobatidis. Surveys at invaded sites were conducted from 2007 to 2015, identified two populations undergoing recent range expansion (one of them exponential), two populations that failed to establish, and a new record in an urban area of the capital city, Montevideo. In all the analysed feral populations, chytridiomycosis was found. Our data suggest that the invasion of L. catesbeianus in Uruguay is at an early stage, with very localized populations, which might allow for the implementation of cost-effective management plans, with eradication constituting a plausible option.

Figure 1 In A New Species Of Elachistocleis (Anura: Microhylidae) From North-Western Argentina

FIGURE 1. Elachistocleis haroi sp. nov., holotype (FML 24900), dorsal and ventral views of body, and head profile. White bar 1 cm.