Carmen G. Montaña

CAN STABLE ISOTOPE RATIOS PROVIDE FOR COMMUNITY‐WIDE MEASURES OF TROPHIC STRUCTURE?

Stable isotope ratios (typically of carbon and nitrogen) provide one representation of an organisms trophic niche and are widely used to examine aspects of food web structure. Yet stable isotopes have not been applied to quantitatively characterize community-wide aspects of trophic structure (i.e., at the level of an entire food web). We propose quantitative metrics that can be used to this end, drawing on similar approaches from ecomorphology research. For example, the convex hull area occupied by species in δ13C–δ15N niche space is a representation of the total extent of trophic diversity within a food web, whereas mean nearest neighbor distance among all species pairs is a measure of species packing within trophic niche space. To facilitate discussion of opportunities and limitations of the metrics, we provide empirical and conceptual examples drawn from Bahamian tidal creek food webs. These examples illustrate how this methodology can be used to quantify trophic diversity and trophic redundancy in food webs, as well as to link individual species to characteristics of the food web in which they are embedded. Building from extensive applications of stable isotope ratios by ecologists, the community-wide metrics may provide a new perspective on food web structure, function, and dynamics.

Diet-Morphology Correlations in the Radiation of South American Geophagine Cichlids (Perciformes: Cichlidae: Cichlinae)

Genera within the South American cichlid tribe Geophagini display specialized feeding and reproductive strategies, with some taxa specialized for both substrate-sifting and mouth brooding. Several lineages within the clade also possess an epibranchial lobe (EBL), a unique pharyngeal structure that has been proposed to have a function in feeding and/or mouth brooding. A recently published genus-level phylogeny of Neotropical cichlids was used as the evolutionary framework for investigating the evolution of morphological features presumably correlated with diet and mouth brooding in the tribe Geophagini. We tested for possible associations between the geophagine epibranchial lobe and benthic feeding and mouth brooding. We also addressed whether the EBL may be associated with unique patterns of diversification in certain geophagine clades. Tests of binary character correlations revealed the EBL was significantly associated with mouth brooding. We also tested for a relationship between diet and morphology. We analyzed stomach contents and morphometric variation among 21 species, with data for two additional species obtained from the literature. Principal Components Analysis revealed axes of morphological variation significantly correlated with piscivory and benthivory, and both morphology and diet were significantly associated with phylogeny. These results suggest that the EBL could be an adaptation for either feeding or mouth brooding. The EBL, however, was not associated with species richness or accelerated rates of phyletic diversification.

The Casiquiare river acts as a corridor between the Amazonas and Orinoco river basins: biogeographic analysis of the genus Cichla

The Casiquiare River is a unique biogeographic corridor between the Orinoco and Amazonas basins. We investigated the importance of this connection for Neotropical fishes using peacock cichlids (Cichla spp.) as a model system. We tested whether the Casiquiare provides a conduit for gene flow between contemporary populations, and investigated the origin of biogeographic distributions that span the Casiquiare. Using sequences from the mitochondrial control region of three focal species (C. temensis, C. monoculus, and C. orinocensis) whose distributions include the Amazonas, Orinoco, and Casiquiare, we constructed maximum likelihood phylograms of haplotypes and analyzed the populations under an isolation‐with‐migration coalescent model. Our analyses suggest that populations of all three species have experienced some degree of gene flow via the Casiquiare. We also generated a mitochondrial genealogy of all Cichla species using >2000 bp and performed a dispersal‐vicariance analysis (DIVA) to reconstruct the historical biogeography of the genus. This analysis, when combined with the intraspecific results, supports two instances of dispersal from the Amazonas to the Orinoco. Thus, our results support the idea that the Casiquiare connection is important across temporal scales, facilitating both gene flow and the dispersal and range expansion of species.

Comparative feeding ecology and habitats use of Crenicichla species (Perciformes: Cichlidae) in a Venezuelan floodplain river

Feeding behavior and habitat use of two species of pike cichlids, or mataguaros, (Crenicichla lugubris and C. aff. wallacii) were studied in the rio Cinaruco, a floodplain river in the Venezuelan llanos. We examined 309 individuals of C. lugubris and 270 individuals of C. aff. wallacii from both the main channel and lagoons throughout the falling-water phase of the annual hydrological cycle. Crenicichla lugubris was common within habitats that contained rocks or woody debris, whereas C. aff. wallacii was more abundant in lagoons than the main channel, especially within shallow areas containing leaf litter. Although we did not capture C. aff. wallacii in rocky shoals, they sometimes were observed in these habitats. Crenicichla lugubris was larger than C. aff. wallacii (198.4 mm and 44.6 mm, respectively). Analysis of stomach contents showed that larger specimens (> 100 mm SL) C. lugubris fed mostly on small fishes (e.g. characids, cichlids), but juveniles ( 100 mm CP) se alimentaram principalmente de peixes pequenos (e.g. caracideos e ciclideos), e os menores (< 100 mm CP) consumiram principalmente larvas aquaticas de insetos, escamas de peixes e camaroes. Crenicichla aff. wallacii se alimentou de insetos aquaticos e outros invertebrados associados ao folhico.

Intercontinental comparison of fish ecomorphology: null model tests of community assembly at the patch scale in rivers

Community assembly is affected by environmental filtering that restricts viable phenotypes and by species interactions that impose limits on interspecific trait similarity. Relative influences of these processes should vary according to habitat features and dispersal. Species dispersion within assemblage trait space also should vary in relation to species richness, strength of competition, and the spatiotemporal scale of analysis. We examined ecomorphological diversity of two freshwater fish families (Neotropical Cichlidae, Nearctic Centrarchidae) to test theories of local assembly from regional species pools and theories of species packing within mesohabitat patches. Cichlid and centrarchid assemblages were surveyed in four floodplain rivers (two in South America and two in North America) during low-water periods when fish densities are highest. Surveys were conducted in four mesohabitat types (submerged wood, leaf litter, rocks, sand bank) within river channels and floodplain lakes. We measured 23 morph...

Gape size influences seasonal patterns of piscivore diets in three Neotropical rivers

We examined diets of four piscivores, two in the order Perciformes (Cichla temensis and C. orinocensis) and two in the order Characiformes (Boulengerella cuvieri and B. lucius), from the Cinaruco, La Guardia, and Ventuari rivers in Venezuela throughout the wet-dry seasonal cycle. The four piscivores consumed a phylogenetically and morphologically diverse group of fishes, reflecting the overall diversity of fish species in these rivers. At the start of the falling-water period, Cichla consumed large prey, especially the abundant, migratory, fish of the genus Semaprochilodus. As these relatively large prey became depleted during the dry season, Cichla tended to consume smaller prey. For Boulengerella, gape limitation precluded consumption of larger, seasonally abundant, fishes, and so prey sizes were more consistent throughout the seasonal cycle. Our findings show how prey abundance and gape limitations interact to influence seasonal patterns of predator-prey interactions.

Pulsing hydrology determines top‐down control of basal resources in a tropical river–floodplain ecosystem

Variable hydrology of rivers strongly affects biophysical factors that influence primary production and population densities, thereby affecting the relative influence of bottom-up and top-down processes in trophic networks. Many tropical floodplain rivers have sustained seasonal flood pulses driven by precipitation patterns of the Intertropical Convergence Zone. These changes in flow alter concentrations of dissolved nutrients, aquatic primary productivity, and per-unit-area densities of aquatic organisms. Therefore, one would predict that the strength of top-down effects of animals on basal resources should shift as the annual flood pulse progresses. We conducted a series of field experiments in a Neotropical lowland river to test for effects of hydrologic phase, habitat (in-channel vs. floodplain aquatic habitat), and benthic-feeding fish and meiofauna on particulate organic matter, chlorophyll, and benthic microalgae. Net ecosystem productivity of this oligotrophic river is higher during the low phase ...

On the Diet of the Frogs of the Ceratophryidae: Synopsis and New Contributions

Abstract. The frogs of the family Ceratophryidae (comprised of three genera containing 12 species) are well known for their voracious feeding behavior and unique morphologies in both larval and post-metamorphic life stages. Nevertheless, relatively little is known about the diet of these species, especially in nature. We summarized the current knowledge of the diet of larval and post-metamorphic ceratophryids in both natural and experimental settings by conducting a literature review, specimen dissections, and field observations. Prior to this study, diet information did not exist for one fourth of the species in the family: Ceratophrys calcarata, Ceratophrys joazeirensis Ceratophrys stolzmanni, and Ceratophrys testudo. We add, for the first time, information on the diet of Ceratophrys calcarata. In addition, our survey revealed that relatively few detailed studies with large sample sizes have been conducted on the diet of these frogs. Frequently, knowledge of the diet of a species is derived from palatability experiments using captive individuals (often a single individual). From those diet studies that were conducted under natural conditions, ceratophryids can be classified as generalist, opportunistic predators, often preying on a wide variety of invertebrate and vertebrate prey. All species of ceratophryids for which we obtained information on diet were found to consume vertebrates, with anuran prey occurring in nearly all species. Even less is known about the diet of the tadpoles of these species; while cannibalism is assumed to be widespread, we found evidence for cannibalism at the larval stage in only three species. Future studies should attempt to understand the trophic ecology of these species under natural scenarios at both life stages, and an ontogenetic approach using individuals across multiple size classes could elucidate the niche shifts associated with these species from larva to adult.

Linking fish colonization rates and water level change in littoral habitats of a Venezuelan floodplain river

Change in water level during the annual hydrologic cycle of tropical floodplain rivers results in continuous disassembly and reassembly of faunal communities in littoral habitat patches. As such, the rate of water level change should influence colonization rates of vagile organisms among habitat patches. We experimentally tested this hypothesis in a Venezuela floodplain river using artificial rocky patches as sampling units, water level change as the independent variable, and total number of individual fish that colonized a patch as the response variable. Water level significantly affected the total number of individuals that colonized patch habitats, i.e., rapidly receding waters were associated with higher colonization rates. Results suggest that water-level recession directly affects community assembly by influencing the rate at which individuals abandon and colonize local habitat patches.

Species-level phylogeny of ‘Satan’s perches’ based on discordant gene trees (Teleostei: Cichlidae: Satanoperca Günther 1862)

Neotropical rivers are home to the largest assemblage of freshwater fishes, but little is known about the phylogeny of these fishes at the species level using multi-locus molecular markers. Here, we present a phylogeny for all known species of the genus Satanoperca, a widespread group of Neotropical cichlid fishes, based on analysis of six unlinked genetic loci. To test nominal and proposed species limits for this group, we surveyed mtDNA sequence variation among 320 individuals representing all know species. Most nominal species were supported by this approach but we determined that populations in the Xingu, Tapajós, and Araguaia+Paraná Rivers are likely undescribed species, while S. jurupari and S. mapiritensis did not show clear genetic distinction. To infer a phylogeny of these putative species, we conducted maximum likelihood and Bayesian non-clock and relaxed clock analyses of concatenated data from three genes (one mitochondrial, two nuclear). We also used a multi-species coalescent model to estimate a species tree from six unlinked loci (one mitochondrial, five nuclear). The topologies obtained were congruent with other results, but showed only minimal to moderate support for some nodes, suggesting that more loci will be needed to satisfactorily estimate the distribution of coalescent histories within Satanoperca. We determined that this variation results from topological discordance among separate gene trees, likely due to differential sorting of ancestral polymorphisms.