Abstract Impact of invasive species on native biota may be due to predation, competition for space or food, or indirect effects. Lionfish (Pterois volitans), invasive in the western Atlantic, is a voracious generalist predator, so it is expected to have a significant trophic overlap with native fishes of comparable size and habits. The goal of this study was to determine the diets of potential competitors of the lionfish, in particular a grouper, Cephalopholis cruentata (Graysby), and a snapper, Lutjanus apodus (Schoolmaster), and to compare them to the diet of lionfish in Xcalak, southern Mexican Caribbean. Stomach contents were analyzed and electivity and diet overlap were estimated. The trophic overlap between the lionfish and the two putative competitors, especially the grouper, was high, including prey that was consumed by the predators in higher proportion than the relative abundance of the prey in the environment, and probably at the same time of day. Lionfish and grouper shared as important diet items Stegastes sp., Halichoeres sp., Brachyura, and Palaemonidae, and most full stomachs were found during the early morning. The hypothesis of competition between them for particular prey is supported, so we advise to continue the culling programs of lionfish and also to monitor the abundance of the possible native competitors.

Resumo El impacto de las especies invasoras sobre la biota nativa puede deberse a depredación, competencia por espacio o alimento, o efectos indirectos. El pez león (Pterois volitans), invasor en el Atlántico occidental, es un voraz depredador generalista, de modo que se espera que tenga un notable sobrelape trófico con peces nativos de tamaño y hábitos comparables. El objetivo de este estudio fue determinar las dietas de competidores potenciales del pez león, en particular un mero, Cephalopholis cruentata (payaso), y un pargo, Lutjanus apodus (canchix), y compararlas con la dieta del pez león en Xcalak, sur del Caribe mexicano. Se analizaron los contenidos estomacales y se estimó la selectividad y el traslape de dietas. El traslape trófico entre el pez león y los dos posibles competidores, sobre todo el mero, fue amplio, incluidas presas consumidas por los depredadores en proporción mayor a la abundancia relativa de éstas en el ambiente, y probablemente a la misma hora del día. El león y el mero compartieron como presas importantes Stegastes sp., Halichoeres sp., Brachyura, y Palaemonidae, y la mayoría de los estómagos llenos se encontraron en horas tempranas de la mañana. Se apoya entonces la hipótesis de competencia entre ellos por presas específicas, de modo que recomendamos continuar el programa de extracción de pez león y también el monitoreo de la abundancia de los posibles competidores nativos.

Los petenes son pequeños manantiales y arroyos asociados que drenan a sistemas palustres en áreas cársticas costeras. Se estudió la composición, distribución y abundancia de la ictiofauna en dos petenes del noroeste de Campeche, en el manantial principal, el arroyo asociado, y pequeños ojos de agua secundarios (temporales), en dos épocas del año. Se registraron variables ambientales y tipos de impacto antrópico en cada petén. Se encontraron en total 27 especies de peces, con extensiones de ámbito de ‘Cichlasoma’ salvini, Rivulus tenuis, Phallichthys fairweatheri, Xiphophorus hellerii y X. maculatus. La especie dominante en ambas épocas fue Astyanax (probables híbridos A. aeneus × altior en Hampolol, A. altior en El Remate). Hubo diferencia significativa en diversidad entre ambos petenes. El análisis de conglomerados diferenció dos agrupaciones dentro de cada petén: aguas permanentes y sitios temporales. Las variables ambientales (excepto salinidad) presentaron diferencias significativas por sitio y época; un análisis de correspondencia canónica indicó que la distribución de los conjuntos de peces tuvo influencia de las variables ambientales en ambas temporadas. En términos de composición, los factores históricos juegan un papel en las diferencias ictiológicas entre ambos petenes, sobre todo por lo que concierne a la presencia de híbridos de Astyanax, así como Xiphophorus hellerii en el petén del sur (Hampolol) y de Poecilia velifera en el petén del norte (El Remate).

Ichthyofauna of karstic wetlands under anthropic impact: the "petenes" of Campeche, Mexico. "Petenes" are small springs and associated streams that drain into wetlands near the coast in karstic areas. We studied composition, distribution, and abundance of the ichthyofauna in Los Petenes region (northwest Campeche). Two petenes displaying different degrees and types of anthropic impact were selected, Hampolol and El Remate. Hampolol has a smaller area but a longer derived stream; it is located within a protected area, but has been invaded by tilapia. El Remate is a popular spa, with no tilapia; it has a larger area but a shorter derived stream. At each "petén", several sites in the main spring, the associated stream, and secondary (temporary) springs were sampled in the rainy and dry seasons. Fishing gear was variable (throw net, gill net, small and large seine nets), but effort was uniform. We recorded temperature, dissolved oxygen, salinity, and depth at each site and season; also, we noted the different types and intensities of anthropic impact (channelization, presence of exotic species, recreational use, etc.) at each petén. We compared the petenes in terms of their environmental quality and fish fauna (composition, distribution, abundance, biomass); we also tested for effects of season and site within each petén. The study found 27 species of fishes, included in 18 genera and eight families, 24 species in Hampolol and 20 in El Remate. The geographical range of ‘Cichlasoma’ salvini, Rivulus tenuis, Phallichthys fairweatheri, Xiphophorus hellerii, and X. maculatus is extended. The dominant species in both seasons was Astyanax (probable hybrids A. aeneus × altior at Hampolol, pure A. altior at El Remate), which contributed most of the abundance and biomass, together with Vieja synspila and Poecilia velifera. A significantly greater overall diversity (H’n=3.31) was recorded in Hampolol compared to El Remate (H’n=2.10). Cluster analysis of sites by species presence allowed distinction of two groupings within each petén: permanent waters (i.e., main spring, stream) vs. temporary sites (secondary springs, which dry out in winter). Environmental parameters (except salinity) presented significant differences by site and season; a canonical correspondence analysis indicated that the distribution of fish assemblages was influenced by the environmental parameters in both seasons. In terms of composition, historical factors play a role in the differences between the fish assemblages of the two petenes, especially concerning the presence of Astyanax hybrids and Xiphophorus spp. in the southern petén (Hampolol) and Poecilia velifera in the northern petén (El Remate). Rev. Biol. Trop. 57 (1-2): 141-157. Epub 2009 June 30.

Between January and September 2006, 21 crocodiles (Crocodylus acutus) were captured and six were recaptured in four lagoons located in the southern coast of Quintana Roo. Stomach contents were obtained in order to identify prey items, which were analyzed by the frequency and volume method. In decreasing order of importance, prey items were fish, crustaceans, birds, mammals and insects. Diet of crocodiles changed considerably according to their body size. Adult crocodiles added larger preys (birds and mammals) to their diet; fish and crustaceans were present in the diet at all sizes, thus showing the importance of these prey in the diet of American crocodiles.

Entre enero y septiembre de 2006 se capturaron 21 cocodrilos (Crocodylus acutus) y se recapturaron seis en cuatro sistemas lagunares de la costa sur de Quintana Roo para analizar los contenidos estomacales. Las presas encontradas en el contenido estomacal se dividieron en cinco grupos y se realizaron análisis basados en la frecuencia y en el volumen. Las presas encontradas en orden de importancia fueron peces, crustáceos, aves, mamíferos e insectos. La dieta de los cocodrilos cambió considerablemente de acuerdo con el tamaño corporal de los individuos. Los cocodrilos adultos agregaron a su dieta presas de mayor talla como aves y mamíferos. Peces y crustáceos estuvieron representados en la dieta de individuos de todas las clases de tamaño, demostrando la importancia que estas presas tienen en la dieta de C. acutus.

Thirty nine fish species are recorded in eight lagoons on the southern coast of Quintana Roo. "Cichlasoma" urophthalmus, Gambusia yucatana, Poecilia orri and Eugerres plumieri were the most widely distributed species. Cluster analysis on the lagoons, based on presence-absence of the fishes, generated a dendrogram where two lagoon complexes are identifiable, divided by the access road to Mahahual. The northern complex (Uvero, Placer, San Humberto and San Antonio) is characterized by the presence of Astyanax aeneus, "C." and Thorichthys meeki. The southern complex (Río Huach, Xcalak, Cementerio and La Aguada) is characterized by Cyprinodon artifrons, Floridichthys polyommus, Eucinostomus argenteus, E. jonesi and Gerres cinereus. Both beta and gamma diversity show an increase from north to south, a fact explained mainly by the larger number of peripheral species migrating from the adjacent reef through permanent mangrove channels to the Caribbean Sea in lagoons Río Huach and Xcalak, in the southern complex, as well as the absence of primary species in these lagoons.

Se registran 39 especies de peces en ocho lagunas de la costa sur de Quintana Roo. "Cichlasoma" urophthalmus, Gambusia yucatana, Poecilia orri y Eugerres plumieri son las especies de más amplia distribución en la zona. El análisis de clasificación jerárquica por conglomerados sobre las lagunas, basado en la composición íctica (presencia/ausencia), generó un dendrograma en donde se identifican dos complejos lagunares divididos por la carretera de acceso a Mahahual. El complejo norte (Uvero, Placer, San Humberto y San Antonio) se caracteriza por la presencia de Astyanax aeneus, "C." synspilum y Thorichthys meeki. El complejo sur (Río Huach, Xcalak, Cementerio y La Aguada) se caracteriza por Cyprinodon artifrons, Floridichthys polyommus, Eucinostomus argenteus, E. jonesi y Gerres cinereus. La tasa de recambio de especies entre las lagunas, igual que la tendencia en la diversidad gamma en la región, muestran incremento de norte a sur, lo cual responde principalmente al mayor número de especies periféricas que migran del arrecife adyacente a través de los canales de comunicación permanente con el mar Caribe que presentan Río Huach y Xcalak, en el sur, así como a la ausencia de especies primarias en dichas lagunas.

Se estudió la alimentación de siete especies de cíclidos (Archocentrus octofasciatus, A. spilurus, "Cichlasoma" robertsoni , "C." synspilum, "C." urophthalmus , Petenia splendida, Thorichthys meeki) en la laguna Caobas, sur de la península de Yucatán. Los muestreos se llevaron a cabo durante las estaciones seca y lluviosa de 1995. Los ejemplares medían menos de 41 mm LP. Se evaluó la frecuencia de aparición y la abundancia de las presas. Los ítemes alimentarios predominantes fueron los quironómidos, ácaros, copépodos, cladóceros y ostrácodos. La mayoría de las mojarras se mostraron zooplanctófagas, con la excepción parcial de P. splendida (piscívora), "C." synspilum y A. spilurus (herbívoras). A. octofasciatus tuvo el más amplio espectro alimentario y se consideró omnívoro. Thorichthys meeki mostró cambios cuantitativos en la dieta por hora del día, talla del pez y estación del año, no así por sexo.

Feeding habits of seven cichlid species (Archocentrus octofasciatus, A. spilurus, "Cichlasoma" robertsoni, "C." synspilum, "C." urophthalmus, Petenia splendida, Thorichthys meeki) in Lake Caobas, southern Yucatan Peninsula, were studied. Samples were taken with enclosure and cast nets during the dry and rainy seasons of 1995 (day and night). The environment was characterized by measuring temperature, conductivity and pH. All individuals were below 41 mm SL (N=281). Frequency of occurrence and prey abundance were analyzed. Main prey items were chironomids, mites, copepods, cladocerans, and ostracods. The cichlids fed mainly on zooplankton, with the partial exceptions of P. splendida (piscivore), "C." synspilum and A. spilurus (herbivores). A cluster analysis showed that the most similar trophic spectra were those of T. meeki, "C." robertsoni and "C." salvini, which were also the least diverse. "C." synspilum and A. spilurus had an intermediate distance between their diets and those of other species. The species with the most distinctive feeding composition were P. splendida (with the most diverse and equitable diet) and the omnivore A. octofasciatus (whose diet was the richest one). T. meeki showed quantitative diel, ontogenetic, and seasonal diet changes, but none between sexes. "C." robertsoni, "C." salvini and "C." synspilum differ in food habits in Caobas and in other localities, a fact that underscores the trophic adaptability of cichlids. Trophic overlap between cichlids in Caobas could imply absence of competition, perhaps because resources are abundant in the ecosystem.