Sergio Enrique Gómez

Bio: Sergio Enrique Gómez is an academic researcher from National Scientific and Technical Research Council. The author has contributed to research in topics: Range (biology) & Habitat. The author has an hindex of 11, co-authored 34 publications receiving 441 citations. Previous affiliations of Sergio Enrique Gómez include Facultad de Ciencias Exactas y Naturales.

Distribution of introduced and native fish in Patagonia (Argentina): patterns and changes in fish assemblages

Abstract: The interaction between native fishes and salmonids introduced in Patagonia at the beginning of the 20th Century, developed at the same time as the environmental change. The phenomenon of global warming has led to the formulation of predictions in relation to changes in the distribution of species, in the latitudinal dimension, both at intralacustrine, or small streams levels. The aim of the present work includes three main objectives: a) to compose a general and updated picture of the latitudinal distribution range of native and alien fishes, b) to analyze the historical changes in the relative abundance of Percichthys trucha, Odontesthes sp., and salmonids in lakes and reservoirs, and c) to relate the diversity and relative abundance of native and salmonid fishes to the environmental variables of lakes and reservoirs. We analysed previous records and an ensemble of data about new locations along the northern border of the Patagonian Province. We compared current data about the relative abundance of native fishes and salmonids in lakes and reservoirs, with previous databases (1984–1987). All samplings considered were performed during spring-summer surveys and include relative abundance, as proportions of salmonids, P. trucha, and Odontesthes sp. For the first time, we found changes in fish assemblages from twenty years back up to the present: a significant decline in the relative abundances of salmonids and an increase of P. trucha. We studied the association between the diversity and relative abundance of native and salmonid fishes and the environmental variables of lakes and reservoirs using Canonical Correspondence Analysis. Relative abundance showed mainly geographical cues and the diversity relied largely on morphometric characteristics. Relative abundance and diversity seem to have a common point in the lake area, included into the PAR concept. Native abundance and alien diversity were negatively related with latitude. Greater native diversity was observed in lakes with high PAR compared with salmonids. Historical changes such as southward dispersion, relative abundance changes, and geographical patterns for relative abundance and diversity are basic concepts needed not only in future research but also in management design for Patagonian fish populations.

Subtle relationships : freshwater fishes and water chemistry in southern South America

Abstract: We investigated the relationships between water chemistry and the occurrence, distribution, physiology, and morphology of fish faunas. We examined 34 species (ca. 10% of the Argentinean freshwater fish fauna) from 120 localities (5 areas) situated between 26°15′ S (Trancas, Tucuman) and 38°30′ S (Sierra de la Ventana, Buenos Aires). Fourteen chemical features are described by: conductivity, total dissolved solids, temperature, pH, CO32−, CO3H−, Cl−, SO42−Ca2+, K+, Mg2+, Na+, Mg/Ca, Mg+Ca/Na+K. Three Basic Data Matrices considering the mean, maximum and minimum values of each variable for each fish species were used in a Cluster and Principal Component Analysis. Groups of species clustered in similar ways to particular water chemistries. Similarity was the common occurrence of species in a defined area and preference for a common range of the factors considered. Groups of species so defined showed patterns of distribution related to climate, environment, trophic state and hydrographic complexity. Each cluster included some eurytopic species which appeared together at extreme chemical and geographic characteristics. Twenty four species had ranges of tolerance for the 14 variables and evidence of a grouping according to these ranges. Eighteen species which occurred at maximum or minimum absolute values for more than one factor were ordered along an eurytopy — stenotopy axis. We support the statement that species with a larger tolerance range for most factors have a higher probability of being widely distributed. Astyanax fasciatus and A. bimaculatus tolerated the highest number of maximum and minimum values, followed by Jenynsia l. lineata, A. eigenmanniorum and Trichomycterus corduvensis. Groups of species based on chemical factors showed differences in the relative number of basic morphological types.

Fishes of southern South America: a story driven by temperature

Abstract: The latitudinal extension of southern South America imposes a thermal gradient that affects the structure of marine and freshwater fish assemblages and the biology of the species through direct exposure to the temperature gradients or by means of a web of historical and ecological relationships. We have reviewed biological and ecological data of marine and freshwater fishes from the southern Neotropics, including Patagonia, and report several examples of dependence on temperature, from glacial times to today’s climate change. We were able to identify historic and present effects on the diversity of fish assemblages, isolation, southern limits for the distribution of species, and morphological variation among populations. There is a wide range of characteristics that exemplify an adaptation to low temperatures, including biochemical peculiarities, physiological adjustments, and alternative life history patterns, and these appear in both freshwater and marine, and native and exotic fishes. The consequences of stable temperature regimes in both the ocean and thermal streams deserve special mention as these shape specialists under conditions of low selective pressure. At present, habitat use and interactions among species are being subject to changes as consequences of water temperature, and some of these are already evident in the northern and southern hemispheres.

On the habitat and isolation of Gymnocharacinus bergi (Osteichthyes: Characidae)

Abstract: Gymnocharacinus bergi is a rare Paranensean fish which is the only characiform almost lacking scales in the adult. It is endemic and the only species in a peculiar spot — a tributary of the Valcheta creek — in the Somuncura plateau in northern Patagonia, Argentina, over 300 km from the nearest place with a paranensean fish fauna. Besides its geographical isolation, G. bergi occurs within an area with climatic features drastically different from those currently associated with fishes from Neotropical temperate zones. We tested the assumption that water temperature in the naked characin habitat do not agree with the northern Patagonia climate. We also considered the isolation of G. bergi within the framework of an increasing inpoverishment of the paranensean ichthyofauna along a NE-SW axis in the Buenos Aires province. For this we applied a decrement equation used in island biogeography. Our findings demonstrate that the existence of G. bergi in its isolated habitat is possible because of the thermal traits of the water at the sources of the creeks, its temperature being independent of the climate of the area. The chemical composition of water was found to be within the range of common environments in the Buenos Aires ‘pampas’ inhabited by several species of Paranensean fishes. Geographically, G. bergi lives in the last of a series of habitats which show a decreasing number of species correlated with the increasing distance from the La Plata River. Conservation status of the species is briefly discussed.

The physical–chemical habitat of the Buenos Aires pejerrey, Odontesthes bonariensis (Teleostei, Atherinopsidae), with a proposal of a water quality index

Abstract: The pejerrey, Odontesthes bonariensis (Valenciennes 1835) (Atheriniformes, Atherinopsidae) is a highly valued food and sport fish both in Argentina and abroad, and has been introduced in numerous natural and manmade environments in this country, Chile, Japan, and Italy. Considering a wide array of environments, where the pejerrey lives and somewhere it does not, we demonstrate its considerable eurytopy and define its range as water traits and chemical composition concern. Moreover, as pejerrey’s natural habitat, the pampasic lagunas (lakes of third-order) in temperate Argentina display a wider range of chemistry traits than many other environments throughout the country, we confirm its adaptability, suggested by previous introduction success. Relative influence of total conductivity and particular ions is evaluated, as well as the relationship of water traits with the fish distribution. A water quality index is provided, which allows the determination of the best conditions for pejerrey cultivation in both artificial and natural conditions. The index summarizes many traits of the realized niche of the fish.

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types

Abstract: A checklist of Recent and fossil catfishes (Order Siluriformes) is presented, summarizing taxonomic literature published through 2005. From 4624 nominal species group names and 810 genus group names, 3093 species are recognized as valid, and are distributed among 478 genera and 36 families. Distributional summaries are provided for each species, and nomenclatural synonymies, including relevant information on all name-bearing types, are included for all taxa. One new name is proposed herein: Clariallabes teugelsi, as a replacement for Clarias (Allabenchelys) dumerili longibarbis David & Poll, 1937, which is preoccupied by Clarias longibarbis Worthington, 1933, but has been treated as a valid species of Clariallabes by Teugels. Acrochordonichthys melanogaster Bleeker, 1854, is designated as type species of Acrochordonichthys Bleeker, 1857, inasmuch as no earlier valid designation has been found. A new genus Pseudobagarius , is proposed for the “ pseudobagarius group” of species formerly placed in Akysis . The status of 228 species group names remains unresolved and 31 names based on otoliths ascribed to catfishes are listed but not placed into the checklist. The current emphasis given to catfish taxonomy at present is likely to result in a dramatic increase in the total number of valid taxa as well as major changes in the membership of some of the higher level taxa recognized here.

Climate-induced changes in the distribution of freshwater fish: observed and predicted trends

Abstract: 1. Climate change could be one of the main threats faced by aquatic ecosystems and freshwater biodiversity. Improved understanding, monitoring and forecasting of its effects are thus crucial for researchers, policy makers and biodiversity managers. 2. Here, we provide a review and some meta-analyses of the literature reporting both observed and predicted climate-induced effects on the distribution of freshwater fish. After reviewing three decades of research, we summarise how methods in assessing the effects of climate change have evolved, and whether current knowledge is geographically or taxonomically biased. We conducted multispecies qualitative and quantitative analyses to find out whether the observed responses of freshwater fish to recent changes in climate are consistent with those predicted under future climate scenarios. 3. We highlight the fact that, in recent years, freshwater fish distributions have already been affected by contemporary climate change in ways consistent with anticipated responses under future climate change scenarios: the range of most cold-water species could be reduced or shift to higher altitude or latitude, whereas that of cool- and warm-water species could expand or contract. 4. Most evidence about the effects of climate change is underpinned by the large number of studies devoted to cold-water fish species (mainly salmonids). Our knowledge is still incomplete, however, particularly due to taxonomic and geographic biases. 5. Observed and expected responses are well correlated among families, suggesting that model predictions are supported by empirical evidence. The observed effects are of greater magnitude and show higher variability than the predicted effects, however, indicating that other drivers of changes may be interacting with climate and seriously affecting freshwater fish. 6. Finally, we suggest avenues of research required to address current gaps in what we know about the climate-induced effects on freshwater fish distribution, including (i) the need for more long-term data analyses, (ii) the assessment of climate-induced effects at higher levels of organisation (e.g. assemblages), (iii) methodological improvements (e.g. accounting for uncertainty among projections and species' dispersal abilities, combining both distributional and empirical approaches and including multiple non-climatic stressors) and (iv) systematic confrontation of observed versus predicted effects across multi-species assemblages and at several levels of biological organisation (i.e. populations and assemblages).

Drivers and stressors of freshwater biodiversity patterns across different ecosystems and scales: a review

Abstract: The present review with focus on the last decade (2000–2010) aims to (i) collecting the major hypotheses explaining freshwater biodiversity patterns, (ii) identifying the main stressors affecting freshwater biodiversity, and (iii) revealing information gaps regarding ecosystem types, organism groups, spatial and temporal scales to highlight research needs to better propose sound conservation measures. The comparative analysis addresses six organism groups ranging from microorganisms to fish in basins, rivers, lakes, wetlands, ponds and groundwater. Short-term studies at ecoregion and catchment scale focusing on invertebrates, macrophytes and fish in Palaearctic and Nearctic regions dominated. The most frequent hypotheses tested were the landscape filter concept, the species–area relationship, the metacommunity concept. Dominating natural drivers were area, heterogeneity and disturbance. Land use, eutrophication and habitat destruction were identified as most important stressors. Generally, freshwater biodiversity declined in response to these stressors in contrast to increasing biodiversity determined by natural drivers across all ecosystems. Preferred organism groups were fish and invertebrates, most frequently studied in rivers, in contrast to smaller organisms (e.g. bacteria) and, e.g. groundwater being underrepresented. Hypotheses originating from the last century are still tested in freshwater research, while novel concepts are either missing or untested. Protection of freshwater biodiversity is the ultimate challenge since it supports valuable ecosystems services ensuring perpetuation of mankind. For that, comprehensive large-scale studies with holistic approaches are urgently needed.

Fish ecology in tropical streams

Abstract: Publisher Summary This chapter emphasizes the ecological responses of fishes to spatial and temporal variation in tropical stream habitats. It also discusses the steps to alleviate human impacts and restore degraded streams to protect the species of the fish. It reveals that freshwater fishes comprise 25% of the vertebrate species on earth. The South and Central American rivers and streams contain the greatest number of species on Earth, with recent estimates ranging as high as 8000 and 25% of global fish species richness. The highest fish species richness in the Neotropics is within the Amazon Basin. The ultimate environmental driver for variations in habitat quality and quantity, and hence breeding events, is probably stream hydrology. Tropical stream fishes occupy almost the entire spectrum of trophic niches that can occur in aquatic communities. Aquatic invertebrates are important food sources for stream fishes throughout the tropics. Terrestrial plants tissues, especially flowers, fruits, and seeds are very important resources for fishes in tropical streams. The primary threat to the ecological integrity of tropical streams and the long-term survival of their fish faunas is degradation of watersheds by a variety of human activities. The largest impact is from deforestation and conversion of land to agriculture besides over-fishing, dam construction, use of pesticides and herbicides, and introductions of exotic species, etc. Protection of vegetation cover, maintenance of the integrity of riparian zones, and reductions in point- and non-point-source pollution are essential components of conservation and management strategies for stream fishes.