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The Freshwater Mollusks of Mexico: Can We Still Prevent Their Silent Extinction?
Abstract
In this chapter, we provide an overview of the diversity of the Mexican freshwater mollusks (gastropods and bivalves). We outline their current status as one of the most imperiled group of animals in Mexico and we discuss necessary changes to stop their decline. The Mexican freshwater molluscan fauna is composed of 292 species, of which 195 are gastropods and 97 bivalves. Like many other aquatic invertebrates worldwide, members of both molluscan classes are rapidly declining in most regions of Mexico. These losses constitute a silent extinction during the Anthropocene resulting from water pollution, large diversions for irrigation of arid regions, hydropower production, and introductions of non-native species. The lack of historical data about molluscan distributions, especially of bivalves, makes it difficult to determine the full extent of these local and regional extinctions. However, a few case studies that include the methods of conservation paleobiology are used to show an alarming picture: the comparison of local sub-fossil records with recent data documents a dramatic loss of freshwater snail diversity of more than 80% in only a century. In light of this, it is becoming increasingly clear that current conservation efforts alone will not be enough to stop more extinctions. Climate change, especially increased frequency and intensity of regional drought, is known to decrease habitat quality. Dam removal along with more and larger protected areas and ecosystem restorations can reverse the trend of some of these potential species losses. We advocate a shift in consciousness so that natural scientific efforts are part of an integrated holistic solution that includes the ecological, economic, philosophical, and theological values for society.
... Since then, it has spread throughout Mexico (Counts, 1991;López et al., 2019;Naranjo-García & Castillo-Rodríguez, 2017). It can become the most prevalent mollusk in streams (Czaja et al., 2022;Tiemann et al., 2020), and threatens to alter biologically diverse aquatic ecosystems in Mexico (Czaja et al., 2023). ...
... First, we conducted qualitative freshwater mollusk surveys in the Grande, Pánuco, Papaloapan, and Usumacinta basins in the Mexican states of Chihuahua, San Luis Potosí, Veracruz, Tabasco, and Chiapas in 2017-2022 (see Inoue et al., 2020;Kiser et al., 2022;Tiemann et al., 2020). Second, we reviewed literature accounts of Corbicula in Mexico and shared drainages (Barba-Macías & Trinidad-Ocaña, 2017; Benson & Williams, 2021;Contreras-Arquieta & Contreras-Balderas, 1999;Counts, 1991;Counts et al., 2003;Czaja et al., 2022Czaja et al., , 2023Davis, 1980;Dinger et al., 2005;Fox 1970Fox , 1971Gutiérrez-Galindo et al., 1988;Hillis & Mayden, 1985;López-López et al., 2009, 2019Naranjo-García & Castillo-Rodríguez, 2017;Naranjo-García & Meza-Meneses, 2000;Naranjo-García & Olivera-Carrasco, 2014;Ramírez et al., 2022;Ramírez-Herrera & Urbano, 2014;Rico-Sánchez et al., 2020;Ruelas-Inzunza et al., 2007Tiemann et al., 2020;Torres-Orozco & Revueltas-Valle, 1996;Trinidad-Ocaña et al., 2018). Third, we gathered from the following natural history museums and collections: Colección ...
Corbicula spp. are one of the most prolific aquatic invasive species in the world and can have negative effects on aquatic ecosystems. We performed qualitative field surveys, examined literature accounts and natural history museum holdings, and accessed citizen science data sources to document the distribution of Corbicula in Mexico and shared drainages. Through 26 publications (N = 127 records), 312 museum holdings, and 446 iNaturalist records, we documented 885 records pertaining to Corbicula in Mexico and shared drainages with the USA. The first record of the species in Mexico was in 1969, and it has since been reported from 26 of the 32 Mexican states and most of the major river basins throughout the country. However, we suggest Corbicula are more prevalent in Mexico than we report in this work as it is often under sampled or under reported. Resumen Algunas especies de Corbicula son de las especies invasoras acuáticas más prolíficas del mundo y pueden tener efectos negativos en los ecosistemas acuáticos. En este trabajo, realizamos estudios de campo cualitativos, examinamos literatura y registros en museos de historia natural y, además, revisamos datos de ciencia ciudadana para documentar la distribución de Corbicula en México y cuencas compartidas con EUA. A través de 26 publicaciones (N = 127 registros), 312 registros de museos y 446 registros de iNaturalist, documentamos 885 registros pertenecientes a Corbicula en México. El primer registro en México de la especie en el país data de 1969 y, desde entonces, ha J.S. Tiemann et al. / Revista Mexicana de Biodiversidad 95 (2024): e955284 2 https://doi.org/10.22201/ib.20078706e.2024.95.5284
... However, the few available studies of insect decline have been conducted in highly humanised and well-studied regions, such as Germany and central California (Wagner et al., 2021). In more remote regions, and for other invertebrate groups, we know very little about population trends, and potential declines and extirpations may remain off the scientific and public radar (Cowie et al., 2022;Czaja et al., 2023). This is true for many groups of molluscs in terrestrial and freshwater ecosystems, including freshwater mussels (Bivalvia: Unionida), which, despite many warnings about their poor conservation status, still suffer from a lack of systematic monitoring and targeted conservation efforts (Lopes-Lima et al., 2018, with local and regional exceptions in North America and Europe. ...
Freshwater mussels are one of the most threatened animal groups in the world. In the European Union, threatened and protected mussel species are not adequately monitored, while species considered to be common and widespread receive even less attention. This is particularly worrying in the Mediterranean region, where species endemism is high and freshwater habitats are severely affected by water scarcity. In the absence of hard data on population trends, we report here a long-term comparison of freshwater mussel assemblages at 132 sites covering 15 different hydrological basins in Portugal. This study reveals a widespread decline of 60 % in the number of sites and 67 % in the overall abundance of freshwater mussels across Portugal over the last 20 years, indicating that all species are rapidly declining and threatened with extinction. These results show that current legislation and conservation measures are largely ineffective and highlight the importance of updating the Habitats Directive to enforce standard monitoring protocols for threatened species in the European Union and to extend monitoring to other freshwater species thought to be common and widespread. Efficient water management, restrictions on irrigation expansion in important biodiversity areas, mitigation of hydrological changes and loss of aquatic habitat connectivity caused by physical alterations are urgently needed to reverse these declining population trends. For the severely endangered species Margaritifera margaritifera, Potomida littoralis, and Unio tumidiformis, where populations are now critically low, more urgent action is needed, such as ex-situ conservation, protection of remaining populations and large-scale habitat restoration.
Near-time conservation palaeobiology uses palaeontological, archaeological and other geohistorical records to study the late Quaternary transition of the biosphere from its pristine past to its present-day, human-altered state. Given the scarcity of data on recent extinctions in the oceans, geohistorical records are critical for documenting human-driven extinctions and extinction threats in the marine realm. The historical perspective can provide two key insights. First, geohistorical records archive the state of pre-industrial oceans at local, regional and global scales, thus enabling the detection of recent extinctions and extirpations as well as shifts in species distribution, abundance, body size and ecosystem function. Second, we can untangle the contributions of natural and anthropogenic processes by documenting centennial-to-millennial changes in the composition and diversity of marine ecosystems before and after the onset of major human impacts. This long-term perspective identifies recently emerging patterns and processes that are unprecedented, thus allowing us to better assess human threats to marine biodiversity. Although global-scale extinctions are not well documented for brackish and marine invertebrates, geohistorical studies point to numerous extirpations, declines in ecosystem functions, increases in range fragmentation and dwindling abundance of previously widespread species, indicating that marine ecosystems are accumulating a human-driven extinction debt.
The malacofauna of the Sabinas River basin, Coahuila, North Mexico, was studied at 9 sites. In total, 21 native and 2 invasive species were found. Nineteen species were gastropods and 4 species were bivalves. One genus and 2 species of subterranean gastropods are endemic to the area. We report for the first time, a member of the family Amnicolidae in Mexico, Lyogyrus sp. Mexithauma cf. quadripaludium Taylor, 1966 and Juturniacoahuilae (Taylor, 1966) (Cochliopidae), previously known only as endemic in the neighboring Cuatro Ciénegas basin, were found for the first time outside of this basin. Also, Cincinnatiaintegra (Say, 1821) (Hydrobiidae), previously known in Mexico only from 1 relict site in San Luis Potosí state, was found living in Sabinas River. In all studied sites, the invasivespeciesMelanoides tuberculata (O. F. Müller, 1774) (Thiaridae) and Corbiculafluminea (O. F. Müller, 1774) (Cyrenidae) dominate the aquatic molluscan communities. Both molluscs are potential risks for native species, especially if the water pollution continues. At least 10 species from Sabinas River System are of special conservation significance (7 imperiled and 3 vulnerable), due to their endemism, extremely reduced habitat, or relict occurrence in Mexico.
This paper describes a new genus and species of subterranean gastropod from a karstic region near Viesca, Coahuila in northern Mexico. Shells of Phreatoviesca spinosa gen. nov. et sp. nov. were found in spring-deposited sediments near the outlet of a cave that dried up in the late 20th century. The new genus can be primarily distinguished conchologically from other phreatic genera by three remarkable characteristics: (i) prominent open coiling of the last whorl, (ii) shovel-shaped spine ornamentations on the teleoconch, and (iii) a coarsely honeycomb-like pitted protoconch structure. Since only dry shells were found, the new species could already be extinct. However, in view of the relative recent drying up of the spring, we consider that Phreatoviesca spinosa is possibly extant in the aquifers in or adjacent to the Viesca region.
Molluscs are among the most diverse and widespread animal groups in freshwater habitats. Unfortunately, like most freshwater taxa, they are decreasing dramatically and are now among the most threatened animals on Earth, with many species already extinct or on the brink of extinction. Here, we review our current knowledge on the biodiversity and conservation of freshwater molluscs using the concept of knowledge shortfalls. We focus on seven previously proposed key shortfalls to review and analyse existing knowledge gaps relating to (1) taxonomy, the Linnean Shortfall; (2) distribution, the Wallacean Shortfall; (3) abundance and population dynamics, the Prestonian Shortfall: (4) evolution, the Darwinian Shortfall; (5) abiotic tolerances, the Hutchinsonian Shortfall; (6) traits, the Raunkiaeran Shortfall; and (7) biotic interactions, the Eltonian Shortfall. In addition, we address a new shortfall, which relates to the application and effectiveness of conservation measures, including assessments, methods, funding, and policies, the Ostromian Shortfall. Based on our review, we provide recommendations and suggest pathways to overcome these existing shortfalls. This work also introduces the articles in this special issue of Hydrobiologia, which represent key contributions to the First International Freshwater Mollusk Conservation Society Meeting held in Verbania, Italy, in 2018.
The Cretaceous–Paleogene mass extinction event 66 million years ago eradicated three quarters of marine and terrestrial species globally. However, previous studies based on vertebrates suggest that freshwater biota were much less affected. Here we assemble a time series of European freshwater gastropod species occurrences and inferred extinction rates covering the past 200 million years. We find that extinction rates increased by more than one order of magnitude during the Cretaceous–Paleogene mass extinction, which resulted in the extinction of 92.5% of all species. The extinction phase lasted 5.4 million years and was followed by a recovery period of 6.9 million years. However, present extinction rates in European freshwater gastropods are three orders of magnitude higher than even these revised estimates for the Cretaceous–Paleogene mass extinction. Our results indicate that, unless substantial conservation effort is directed to freshwater ecosystems, the present extinction crisis will have a severe impact to freshwater biota for millions of years to come.
Many taxonomic groups successfully exploit groundwater environments and have adapted to a subterranean (stygobiotic) existence. Among these groups are freshwater gastropods (stygosnails), which represent a widespread and taxonomically diverse component of groundwater ecosystems in North America. However, owing to sampling difficulty and lack of targeted study, stygosnails remain among the most understudied of all subterranean groups. We conducted a literature review to assess the biodiversity and geographic associations of stygosnails, along with the threats, management activities, and policy considerations related to the groundwater systems they inhabit. We identified 39 stygosnail species known to occur in a range of groundwater habitats from karst regions in the United States and Mexico. Most stygosnails exhibit extreme narrow‐range endemism, resulting in a high risk of extinction from a single catastrophic event. We found that anthropogenically driven changes to surface environments have led to changes in local hydrology and degradation of groundwater systems inhabited by stygosnails such as increased sedimentation, introduction of invasive species, groundwater extraction, or physical collapse of water‐bearing passages. Consequently, 32 of the 39 described stygosnail species in the United States and Mexico have been assessed as imperiled under NatureServe criteria, and 10 species have been assessed as threatened under International Union for Conservation of Nature criteria. Compared with surface species of freshwater snails, stygosnail conservation is uniquely hindered by difficulties associated with accessing subterranean habitats for monitoring and management. Furthermore, only three species were found to have federal protection in either the United States or Mexico, and current laws regulating wildlife and water pollution at the state and federal level may be inadequate for protecting stygosnail habitats. As groundwater systems continue to be manipulated and relied on by humans, groundwater‐restricted fauna such as stygosnails should be studied so unique biodiversity can be protected.
The objective of this review is to update our previously published checklist of Recent freshwater mussel species and genera (Graf & Cummings, 2007, J. Molluscan Stud.: 291–314) to reflect the new data and research findings that have accumulated over the last decade. The MUSSEL Project Database was developed to synthesize the available taxonomic nomenclature, species ranges and published taxonomic hypotheses on genus–species combinations and synonymy. We have found 4,988 available species-group level nominal species representing 958 valid species in 192 genera worldwide, an increase of 118 species since 2007. The current patterns of species richness are discussed with regard to both taxonomy and geography, as is the general flux in the number of species recognized over time. A checklist is provided herein, with a bibliography to key faunistic and taxonomic references. The full dataset is maintained and updated on the MUSSEL Project Web Site (http://mussel-project.net/).
Before this study, researchers had not systematically surveyed the Río Conchos, a tributary of the Rio Grande located in northern Mexico, for freshwater mussels. The Texas hornshell, Popenaias popeii, an endangered species under the United States Endangered Species Act, occurs in the main stem of the Rio Grande near its confluence with the Río Conchos. The Texas hornshell's proximity to the Río Conchos prompted us to survey to determine whether P. popeii also occurs within the Conchos basin. Additionally, previous researchers described the Conchos disk, Disconaias conchos, from the Río Conchos but, to date, no one has reported live individuals of this species. The goal of this study was to determine the status of mussels within the Río Conchos basin and to provide a baseline for future monitoring efforts. We qualitatively surveyed 11 sites within the Río Conchos basin in May 2018. In total, we found two live individuals of the paper pondshell, Utterbackia imbecillis, at one site in the Río San Pedro, a tributary of the Conchos River, and as shells of recently live individuals at two sites in the Río Conchos. We found D. conchos as relict shells only at three sites, two in the Río Conchos and one in a tributary of the river at Coyame. The lack of live or fresh-dead material suggests that D. conchos is extinct. We also found live individuals of nonnative Asian clams (Corbicula spp.) at 10 sites. Sand and gravel mining, high organic pollution, and inadequate instream flows were evident throughout the basin and might explain the general absence of mussels. RESUMEN-El río Conchos, un afluente del río Bravo ubicado en el norte de México, nunca había sido examinado sistemáticamente en búsqueda de mejillones de agua dulce. El mejillón, Popenaias popeii, una especie en peligro de extinción bajo el Acta de Especies Amenazadas de los Estados Unidos, habita en la parte principal del río Bravo cerca de su confluencia con el río Conchos. Así mismo, por su cercanía al río Conchos, se inició la búsqueda para determinar si P. popeii también ocurre dentro de la cuenca del Conchos. Además, a la fecha no se ha reportado la existencia de individuos vivos de Conchos Disk, Disconaias conchos, cuyo origen sea el río Conchos. El objetivo de este estudio fue determinar el estado de los mejillones dentro de la cuenca del río Conchos y proporcionar la línea base para futuros esfuerzos de monitoreo. En mayo del 2018, realizamos una inspección cualitativa en 11 sitios de la cuenca del río Conchos. En total, encontramos dos individuos vivos de la Paper Pondshell, Utterbackia imbecillis, en un sitio del río San Pedro, afluente del Conchos, así como conchas recién muertas en dos sitios del río Conchos. Se encontraron conchas antiguas de D. conchos solo en tres sitios: dos en el río Conchos y una en un afluente del río en Coyame. La falta de D. conchos vivas o rastros frescos podría implicar que está extinta. También encontramos individuos vivos de la almeja asiática no nativa (Corbicula spp.) en 10 sitios. El minado de arena y grava, la alta contaminación orgánica y flujos alimentarios inadecuados de agua fueron evidentes en toda la cuenca y quizá expliquen la ausencia de mejillones.
With the biodiversity crisis continuing unchecked, we need to establish levels and drivers of extinction risk, and reassessments over time, to effectively allocate conservation resources and track progress towards global conservation targets. Given that threat appears particularly high in freshwaters, we assessed the extinction risk of 1428 randomly selected freshwater molluscs using the IUCN Red List Categories and Criteria, as part of the Sampled Red List Index project. We show that close to one-third of species in our sample are estimated to be threatened with extinction, with highest levels of threat in the Nearctic, Palearctic and Australasia and among gastropods. Threat levels were higher in lotic than lentic systems. Pollution (chemical and physical) and the modification of natural systems (e.g. through damming and water abstraction) were the most frequently reported threats to freshwater molluscs, with some regional variation. Given that we found little spatial congruence between species richness patterns of freshwater molluscs and other freshwater taxa, apart from crayfish, new additional conservation priority areas emerged from our study. We discuss the implications of our findings for freshwater mollusc conservation, the adequacy of a sampled approach and important next steps to estimate trends in freshwater mollusc extinction risk over time.
The inland waters of Mexico support a highly diverse group of freshwater fishes with high levels of endemism that occur across a broad range of aquatic habitat types. These aquatic ecosystems provide many direct (e.g., fisheries) and indirect (e.g., agricultural irrigation) benefits to people, and support local livelihoods and economies across Mexico. Freshwater ecosystems are undervalued and receive insufficient funding, political attention and protection. Developing interests and funding for freshwater species conservation is crucial for “bending the curve” to reduce and ultimately reverse freshwater biodiversity declines. Historical disregard for the health and sustainable use of freshwater ecosystems has resulted in alarming rates of loss in the quality and availability of aquatic habitat. This report presents the most recent information on the conservation status and distribution of freshwater fishes in Mexico, and examines the stressors that are driving their declining conservation status. Important conservation actions and considerations are also presented.
Five hundred and thirty-six species of freshwater fishes were assessed against the IUCN Red List Categories and Criteria, representing the most comprehensive assessment of freshwater biodiversity in Mexico to date. This assessment seeks to address the insufficient information available on freshwater fish conservation status, which has resulted in their inadequate representation in environmental planning and management. The full data set, including all species distribution maps, is freely available through the IUCN Red List website (www.iucnredlist.org).
Forty percent of all extant species assessed are threatened with extinction, assuming all Data Deficient species are threatened in the same proportion as those for which enough information was available. The most pervasive threats are related to habitat loss and degradation, which is driven primarily by unsustainable water use and widespread agricultural activity. Excessive extraction of groundwater and diversion of surface water for human consumption, industrial processes, and plantation agriculture has led to widespread flow reductions, reduced water tables, and subsequent drying of aquatic habitat, which is especially prevalent in the arid, endorheic spring systems of northern and central Mexico. Mexico’s vast hydroelectric infrastructure has altered the historical flow regime of many major rivers, blocking natural migration routes and fragmenting subpopulations of native fishes. Agricultural runoff, inadequate wastewater treatment, and industrial discharges have also resulted in increased
levels
We present an updated checklist of native Mexican freshwater gastropods with data on their general distribution,
hotspots of endemicity, threats, and for the first time, their estimated conservation status. The list contains 193 species,
representing 13 families and 61 genera. Of these, 103 species (53.4%) and 12 genera are endemic to Mexico, and 75
species are considered local endemics because of their restricted distribution to very small areas. Using NatureServe
Ranking, 9 species (4.7%) are considered possibly or presumably extinct, 40 (20.7%) are critically imperiled, 30
(15.5%) are imperiled, 15 (7.8%) are vulnerable and only 64 (33.2%) are currently stable. With 61 species in 21
genera, the Cochliopidae are the most diverse family, followed by the Planorbidae (37 species) and Pachychilidae
(31). Pachychilus is the most species-rich genus with 30 species. Despite the high number of imperiled species (84),
only 7 species (3.6%) are currently listed as endangered by the Mexican Secretariat of Environment and Natural
Resources. We identified 3 hotspots and 2 potential centers of gastropod endemicity. Our research serves as a first
step for determining priority areas for conservation of imperiled Mexican freshwater gastropods.
Despite their limited spatial extent, freshwater ecosystems host remarkable biodiversity, including one third of all vertebrate species. This biodiversity is declining dramatically: globally, wetlands are vanishing three times faster than forests, and freshwater vertebrate populations have fallen more than twice as steeply as terrestrial or marine populations. Threats to freshwater biodiversity are well documented but co-ordinated action to reverse the decline is lacking. We present an Emergency Recovery Plan to “bend the curve” of freshwater biodiversity loss. Priority actions include: 1) accelerating implementation of environmental flows; 2) improving water quality; 3) protecting and restoring critical habitats; 4) managing exploitation of freshwater ecosystem resources, especially species and riverine aggregates; 5) preventing and controlling non-native species invasions; and 6) safeguarding and restoring river connectivity. We recommend adjustments to targets and indicators for the Convention on Biological Diversity and the Sustainable Development Goals, and roles for national and international state and non-state actors.
*** This paper has been accepted for publication in BioScience. A link to the BioScience version will follow in due course ***
The decline of freshwater species diversity is
a worldwide phenomenon but it is especially
pronounced in arid regions such as in the
Chihuahuan Desert of Coahuila and Durango,
Northern Mexico. There are few historical data
on the distribution but no data on extinctions
of Mexican freshwater gastropods. In such
cases, paleontological data can be very helpful
and are often the only way to document past
distributions and local extinction or extirpation
events. This new paleoecological approach,
called Conservation Paleobiology, can provide
important perspectives in favor of conservation
of recent analogue ecosystems. The study site
contains subfossil (Late Holocene) deposits of
the Laguna District, a small area in Coahuila
and Durango. Here we describe a new species
and report several new records of subfossil
cochliopid, hydrobid, planorbid and neritid
gastropods. Most of these species (and some
genera) have not been known as fossil from
Mexico and all of them disappeared in very
recent times. Together with data from our
former paleomalacological studies, we present
herein an example of a “silent” local extirpation
in northern Mexico that began in the
Middle Holocene. This loss of species apparently
increased rapidly in the second half of
the 20th century. Of 32 species of freshwater
snails present in the area of study through the
Holocene only four (12.5%) are still extant.
At least 24 (75.0%) of them disappeared from
the area in the 20th century due to habitat
loss caused by anthropogenic activities. The
results show that especially hydrobiid species
with small geographic ranges (local endemics)
are highly sensitive and vulnerable to such
extirpation events. In this study area the extirpation
of freshwater snails happened silently
(unrecorded) while at the same time some
two hundred kilometers farther north, one
of the greatest recent hotspots of gastropods
diversity in North America remained in the
Cuatrociénegas Basin. The same imperilment
that led to local extirpation in the area of study
still threatens the freshwater snail communities
of the Cuatrociénegas valley.
This paper describes a new genus, two new species and new records of subterranean gastropods from the Sabinas and Álamos River, Coahuila, and the Nazas River, Durango, in northern Mexico. Phreatomascogosgregoigen. n. et sp. n. from Don Martín Basin, Coahuila, is described based on shells and opercula that show some morphological similarities with shells of Phreatodrobia Hershler & Longley, 1986 (Lithoglyphidae), which is a subterranean genus from neighboring area in Texas, United States. Conchologically, the new genus can be distinguished from Phreatodrobia and all other subterranean genera by a unique combination of characteristic shell morphology and opercula apomorphies. Balconorbissabinasensesp. n. (Cochliopidae) is the second species of this genus, which was previously known only from caves and associated subterranean habitats in Texas. The new record of Coahuilixparrasense , Czaja, Estrada-Rodríguez, Romero-Méndez, Ávila-Rodríguez, Meza-Sánchez & Covich, 2017 (Cochliopidae) from Durango and Coahuila is the first record of extant member of this genus out of its hitherto known habitat in the Cuatro Ciénegas basin, Coahuila. These records are remarkable because C.parrasense had been described recently as a fossil species. Shell morphologies of the new subterranean snails could be interpreted as possible evolutional adaptations to different hydrodynamic and other specific conditions in their habitat.
The species status assessment reports the results of the comprehensive biological status review for 14 aquatic springsnail species and provides a thorough account of each species’ overall viability and, therefore, extinction risk.
This paper describes 2 new species of phreatic gastropods from the Holocene deposits of Parras
and Viesca, Coahuila, northern Mexico. Both new fossil species belong to genera that today are known
living only from the Cuatro Ciénegas basin, Coahuila, Mexico, one of the hotspots of extant freshwater
gastropod diversity on the North American continent, frequently called the “Mexican Galapagos”.
Paludiscala thompsoni n. sp. was found in spring-deposited sediments at the outlet of caves near Viesca,
Coahuila, and is the first record of fossil shells of this genus. Our second new species, Coahuilix parrasense
n. sp., was collected in sediments of a dry channel near the town El Molino, Parras de la Fuente, Coahuila,
and its shell morphology has affinities with that of extant endemic cave snails from Cuatro Ciénegas.
Additionally, we present a new record from Parras de la Fuente of Phreatoceras taylori (Hershler &
Longley, 1987), previously known only from 2 sites in south-central Texas and Cuatro Ciénegas.
Antecedentes:
El aumento de la salinidad en los ecosistemas continentales es uno de los factores que influye en la distribución, abundancia y desarrollo de los organismos. Entender cómo varía la tolerancia al estrés ambiental entre po blaciones sirve para predecir los efectos del cambio climático en especies localmente adaptadas a su ambiente abiótico.
Objetivos:
Evaluar el efecto de la salinidad en cuatro especies de gasterópodos nativos y dos introducidos por medio de su CL50 y CL90, y TL50 y TL90 en el estado de Tabasco.
Métodos:
A fin de calcular CL50, CL90 y los rangos de tolerancia aguda a la salinidad de dichas especies, se probaron concentraciones de 0 a 15 g/L. Se utilizaron tres réplicas y un testigo para cada una con 20 gasterópodos por réplica. La mortalidad se contabilizó cada hora hasta las 12 horas. Se utilizó el número de moluscos activos como un índice de tolerancia a la salinidad.
Resultados:
Las especies que registraron el menor rango de tolerancia fueron Aroapyrgus clenchi ≤ 0.30 g/L, Pyrgophorus coronatus ≤ 1.00 g/L y las de mayor rango fueron Pomacea flagellata, Tarebia granifera y Melanoides tuberculata ≤ 5 g/L Mexinauta impluviata ≤ 6 g/L. Se encontró una correlación inversa y significativa entre la concentración y el tiempo letal.
Conclusiones:
La tolerancia aguda a la salinidad entre las especies introducidas Tarebia granifera y Melanoides tuberculata no mostró diferencias importantes con Mexinauta impluviata y Pomacea flagellata, pero sí con Pyrgophorus coronatus y Aroapyrgus clenchi, que presentaron una tolerancia menor.
Early historical records are included in this first national inventory
of species of mollusks introduced, whether intentionally
or not, into Mexico by humans. Of the 56 exotic-invasive mollusks
listed, 15 inhabit brackish and marine environments, 10
freshwater, and 31 are terrestrials. Thirty-six per cent of the
introduced species come from Europe and the Mediterranean,
18% from Asia-Australia-New Zealand, 46 % are cryptogenic,
coming from different regions of the planet, and the origin of
several others is uncertain. The best-represented families are
Mytilidae, Teredinidae (brackish and marine), Ampullariidae,
Thiaridae, and Planorbidae (freshwater), and Helicidae, Agriolimacidae,
Limacidae, Subulinidae, and Vallonidae (terrestrial).
They involve Mytilus galloprovincialis Lamarck, 1819, Pomacea
canaliculata, Lamarck, 1819, and Dreissena polymorpha (Pallas,
1771), species included among the world´s worst invasive species.
Some have become naturalized: three brackish and marine
species, six freshwater, and twelve terrestrial. The increase in
exchange of goods, services, and transport has assisted in the
transfer of species from distant places, as has intentional or
unintentional introduction of species of economic importance
(M. galloprovincialis, Crassostrea gigas (Thunberg, 1793),
C. sikamea (Amemiya, 1928)), without consideration of the
epibionts, endobionts, and endoparasites that may also be
introduced. Effective strategiesmust be developed to minimize
the potential impact of biological invasions and raise public
awareness of the problem; this must include the rigorous application
of more stringent regulations.
The importance of and threats to the biodiversity of Cuatro Ciénegas are hard to overstate. This relatively small valley harbors an exceptionally diverse and concentrated suite of native and endemic aquatic organisms that are endangered by rapidly accelerating, unsustainable uses of water resources in this and adjacent basins. Yet there also is reason for optimism, as you will soon read. In “Cuatro Ciénegas y su estado de conservación a través de sus peces”, Dr. Mauricio De la Maza-Benignos and his staff at Pronatura Noreste, A.C., introduce a provocative approach to conservation of aquatic biodiversity in Cuatro Ciénegas. Brief descriptions of the history and hydrology of the valley provide context, and technical (fishes) and heartfelt (bacteria) treatments of some of the valley’s iconic organisms demonstrate the scope of conservation concern. The innovative nature of this book first appears with a chapter on novel approaches to control of invasive species. The next three chapters, however, form the heart of the book, by articulating a holistic approach to conservation in which the authors introduce a Visual Index of Biological Integrity, which uses minimally intrusive methods to document biodiversity, and pair with a management plan that is anchored in legal recognition of the environment as a user of water resources. Publication of this book is invaluable because it not only documents a bold new approach to conservation in Cuatro Ciénegas, but also will serve as a model for conservation elsewhere.
Evan W. Carson
We describe two new species of the
genus Pyrgulopsis Call and Pilsbry
from subfossil spring deposits of Viesca,
Coahuila, in the northern part
of Mexico. The first species, P. paleominckleyi
sp. nov., has trochiform
shells with flat whorls and bulbous
shoulders. Extant endemic species
Pyrgulopsis minckleyi (Taylor) displayssimilar
shell features — this species
was originally described as Nymphophilus
minckleyi Taylor from the spring
complex of the Cuatrociénegas valley,
Coahuila. Some specimens of P.
paleominckleyi sp. nov. show wing-like
shoulders that have never been observed
among fossil or extant members
of the genus. In addition, shells
of the second new species from Viesca,
P. paleoacarinatus are similar to
P. acarinatus, which is other endemic
Pyrgulopsis species from Cuatrociénegas.
We suppose that both sub-fossil
springsnails of Viesca are sister species
or, likely, direct precursors of the
two extant endemic springsnails from
Cuatrociénegas valley.
Springsnails (genus Pyrgulopsis) are one of the most abundant and diverse members of the endemic western North American aquatic
biota. These tiny gastropods are imperiled by threats ranging from groundwater pumping to livestock grazing. During the past
25 years, this long-neglected element of biodiversity has emerged as a new focus of conservation-related activities, including
protection of several species under the Endangered Species Act and monitoring and habitat restoration efforts. Molecular investigations
have helped sharpen springsnail taxonomy and suggest that these animals cannot be managed using a priori assumptions of population
structure. Despite this progress, there is an urgent need for additional studies of springsnail natural history, taxonomy,
and genetics. The prospects for improving the protection and restoration of springsnail habitats are promising but are clouded
by the overarching threat of groundwater mining, which may be addressed best by broader conservation efforts focused on regional
groundwater-dependent ecosystems.
For over a decade the Chihuahuan Desert has been considered as a hotspot of biodiversity. The diverse aquatic ecosystems, espe-cially, are (and were) rich in mollusk species. The dunes of the Comarca Lagunera, Coahuila, Mexico, are of major importance due to the well-preserved remains of animals and plants in a paleolake that covered a vast area in the region. This paper is the first report of the paleolimnological investigations of the Paleolake Irritila ecosystems in northern Mexico. We determined more than 28 species of gastropods, bivalves, ostracods, algae and one aquatic plant. The dunes contain one of the richest and most diverse fauna of the late Quaternary of northern Mexico. The fossils indicate a permanent but shallow lake with moderate salinity and alkalinity (pH) higher than 8.5, most likely around 10. Most of the mollusks are distributed outside Mexico and restricted to northern latitudes (northern United States and Canada). Several of them are endemic to the southern United States (Florida, Nevada, and Texas). For the first time in North America, using the local fauna and flora preserved in dune sediments, we try to reconstruct the paleoenvironmental conditions in northern Mexico during the late Quaternary.
In this paper we analyse the degree of concordance in species richness and taxonomic distinctness (diversity) patterns among different freshwater taxonomic groups in order to test three long held patterns described in Mexican freshwater biogeography: 1. The aquatic biota of Mexico includes two distinct faunas, a rich Neotropical component in the south and a south-eastern region and a less rich Nearctic component towards central and northern latitudes of the country. 2. A hotspot of species richness and diversity has been recorded in the Usumacinta, including the Yucatan Peninsula. 3. The presence of two distinct biotas in Mexico, an eastern one distributed along the Gulf of Mexico slope, and a western one associated to the Pacific versant. We use species richness and taxonomic distinctness to explore patterns of diversity and how these patterns change between zoogeographical regions. This paper points out a clear separation between Neotropical and Nearctic drainage basins but also between eastern (Gulf of Mexico) and western (Pacific) drainage basins. Present data gives additional empirical support from freshwater biota for three long held beliefs regarding distributional patterns of the Mexican biota. The neotropical basins of Mexico are generally host to a richest and more diversified fauna, that includes more families, genera and species, compared to the less rich and less diverse fauna in the nearctic basins.
A study of richness and endemism of the freshwater fishes of Mexico, was carried out in order to identify hotspots and inform conservation efforts. This was done by mapping and overlaying individual species distributions by means of geographical information systems based on museum data. The study was able to confirm several previously proposed centres of freshwater fish richness (Southeastern Mexico, the Mesa Central, the Bravo-Conchos river system and the Panuco and Tuxpan-Nautla rivers). Seven areas with high ‘Corrected Weighted Endemism’ Index values were identified, with the valley of Cuatrociénegas recognized as a true centre. An alarming result was the identification of a “Ghost” centre of endemism (Llanos El Salado) in southwestern Nuevo León, where six endemic cyprinodont species are all ‘extinct’ or ‘extinct in the wild’. Forty-nine single site endemics that are distributed all over Mexico were identified. The Chichancanab lagoon in the border between Yucatan and Quintana Roo, where a flock composed of six endemic cyprinodonts is present needs special mention. Three hotspots of richness plus endemism were found in Mexico, the most important of which is the Mesa Central where impacts by human activities have had a detrimental effect on fish populations.
This is the first American Fisheries Society conservation assessment of freshwater gastropods (snails) from Canada and the United States by the Gastropod Subcommittee (Endangered Species Committee). This review covers 703 species representing 16 families and 93 genera, of which 67 species are considered extinct, or possibly extinct, 278 are endangered, 102 are threatened, 73 are vulnerable, 157 are currently stable, and 26 species have uncertain taxonomic status. Of the entire fauna, 74% of gastropods are imperiled (vulnerable, threatened, endangered) or extinct, which exceeds imperilment levels in fishes (39%) and crayfishes (48%) but is similar to that of mussels (72%). Comparison of modern to background extinction rates reveals that gastropods have the highest modern extinction rate yet observed, 9,539 times greater than background rates. Gastropods are highly susceptible to habitat loss and degradation, particularly narrow endemics restricted to a single spring or short stream reaches. Compilation of this review was hampered by a paucity of current distributional information and taxonomic uncertainties. Although research on several fronts including basic biology, physiology, conservation strategies, life history, and ecology are needed, systematics and curation of museum collections and databases coupled with comprehensive status surveys (geographic limits, threat identification) are priorities.
RESUMEN
esta es la primera evaluación sobre el estado que guarda la conservación de los gasterópodos (caracoles) de Canadá y los EE.UU., realizada por el Subcomité para los Gasterópodos (Comité de Especies Amenazadas) de la Sociedad Americana de Pesquerías. Esta revisión comprende 703 especies, pertenecientes a 16 familias y 93 géneros, de las cuales 67 se consideran extintas o probablemente extintas; 278 están en peligro, 102 amenazadas, 73 vulnerables, 157 cuentan con poblaciones estables y 26 especies presentan un estado taxonómico incierto. De la totalidad de la fauna, 74% de los gasterópodos se encuentran en alguna categoría de vulnerabilidad (amenazados, en peligro o vulnerables) o extintos, lo cual excede al nivel de amenaza al que está sujeto el grupo de los peces (39%) y los langostinos (48%), pero es similar al de los mejillones (72%). Comparando las tasas de extinción actuales contra las tasas de extinción de fondo en el grupo de los gasterópodos, se tiene que en la actualidad son las más altas registradas: 9,539 veces la tasa de extinción de fondo. Los gasterópodos son altamente susceptibles a la degradación y pérdida de hábitat, en particular aquellas especies endémicas cuya distribución está restringida a un solo manantial o a arroyos pequeños. La compilación realizada para esta revisión se dificultó por la falta de información sobre la incertidumbre en la distribución y taxonomía del grupo. Si bien se necesita desarrollar investigación en distintos frentes como biología básica, fisiología, estrategias de conservación, historias de vida y ecología, se consideran como prioridades la sistemática, curación de colecciones museográficas y bases de datos acopladas con muestreos sistemáticos integrales (para establecer límites geográficos, identificación de amenazas).
Recognition of biotic components constitutes the fi rst step toward a synthetic biogeographic theory. In Mexico we can characterize three main biotic components, each one having a particular combination of different biotic elements. The Nearctic component (Nearctic region) includes the arid subtropical areas in the north of the country, in the Californian, Baja Californian, Sonoran, Mexican Plateau and Tamaulipan biogeographic provinces. This component is dominated by the original element (Old Northern or Paleoamerican), together with one of more recent dispersal (Nearctic) and a third of ancient Neotropical origin. Vicariant events associated with the biotic evolution of the Nearctic component are related to the uplift of the Sierra Madre Occidental, which separated the Chihuahuan desert from the Sonoran and Mojave deserts; and the expansion of the Sea of Cortes, separating the Peninsula of Baja California from the continental mainland. The Transitional component (Mexican Transition Zone) includes basically montane areas in central Mexico, which are assigned to the Sierra Madre Oriental, Sierra Madre Occidental, Transmexican Volcanic Belt, Balsas basin and Sierra Madre del Sur biogeographic provinces. In this component, the Paleoamerican, Nearctic, Tropical Mesoamerican and Montane Mesoamerican elements coexist. Vicariant events associated with the biotic evolution of the Transitional component are the development of the Sierras Madre and the volcanism of the Transmexican Volcanic Belt. The Neotropical component (Neotropical region) includes humid and subhumid tropical areas of southern Mexico, assigned to the Mexican Pacifi c Coast, Mexican Gulf, Chiapas and Yucatan Peninsula biogeographic provinces. In it the Tropical Mesoamerican element predominates, but Nearctic and Antillean elements are also present. Vicariant events associated with the biotic evolution of the Neotropical component are related to the development of the isthmuses of Tehuantepec and Panama, and the inundation of the lowlands of Nicaragua and the Yucatan Peninsula.
Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates. Nonmarine mollusks (i.e., terrestrial and freshwater) are one of the most diverse and imperiled groups of animals, although not many people other than a few specialists who study the group seem to be aware of their plight. Nonmarine mollusks include a number of phylogenetically disparate lineages and species-rich assemblages that represent two molluscan classes, Bivalvia (clams and mussels) and Gastropoda (snails, slugs, and limpets). In this article we provide an overview of global nonmarine molluscan biodiversity and conservation status, including several case studies documenting the diversity and global decline of nonmarine mollusks. We conclude with a discussion of the roles that mollusks and malacologists should play in conservation, including research, conservation management strategies, and education and outreach.
We present a new map depicting the first global biogeographic regionalization of Earth's freshwater systems. This map of freshwater
ecoregions is based on the distributions and compositions of freshwater fish species and incorporates major ecological and
evolutionary patterns. Covering virtually all freshwater habitats on Earth, this ecoregion map, together with associated species
data, is a useful tool for underpinning global and regional conservation planning efforts (particularly to identify outstanding
and imperiled freshwater systems); for serving as a logical framework for large-scale conservation strategies; and for providing
a global-scale knowledge base for increasing freshwater biogeographic literacy. Preliminary data for fish species compiled
by ecoregion reveal some previously unrecognized areas of high biodiversity, highlighting the benefit of looking at the world's
freshwaters through a new framework.
Explanations for the coexistence of many closely related species in inland waters continue to be generated more than 50years
after Hutchinson’s question: why are there so many kinds of animals? This review focuses on the hypothesis that high species
diversity of freshwater gastropods results, in part, from predators maintaining biodiversity across a range of deep- and shallow-water
habitats. Invertebrate predators, such as aquatic insects, and leeches consume soft tissue of pulmonate snails by penetrating
shells of various shapes and sizes. Crayfish and large prawns chip around the shell aperture to enter thick shells and crush
small shells with their mandibles. Crabs use their strong chelae to crush thin and thick shells. Fishes with pharyngeal teeth
are major shell-breaking predators that combine with other vertebrate predators such as turtles and wading birds to increase
the diversity of gastropod communities by regulating the abundance of dominant species. Although the generalized diets of
most freshwater predators preclude tight co-evolutionary patterns of responses, there are combinations of predators that modify
gastropod behavior and shell morphology in aquatic assemblages of different ages and depths. This combination of invertebrate
and vertebrate predatory impacts led to competitive advantages among individual gastropods with different adaptations: (1)
less vulnerable shell morphologies and sizes; (2) predator-avoidance behaviors; or (3) rapid and widespread dispersal with
variable life histories. Some individuals develop thicker and/or narrow-opening shells or shells with spines and ridges. Other
thin-shelled species crawl out of the water or burrow to lower their risk to shell-breaking or shell-entering predators. Some
alter their age at first reproduction and grow rapidly into a size refuge. Fluctuations in water levels and introductions
of non-native species can change competitive dominance relationships among gastropods and result in major losses of native
species. Many different gastropod predators control species that are human disease vectors. Most snails and their predators
provide other ecosystem services such as nutrient cycling and transfer of energy to higher trophic levels. Their persistence
and diversity of native species require adaptive management and coordinated study.
KeywordsShell morphology-Aquatic insects-Leeches-Decapod crustaceans-Crabs-Crayfish-Fish-Omnivores-Invasive species-Disease ecology-Ancient lakes-Calcium-Water depth
• Efforts to describe spatial patterns of freshwater diversity and to evaluate their underlying factors have traditionally been focused on some animal groups (e.g. amphibians, fish or dragonflies). Despite being a dominant component in continental aquatic ecosystems and crucial for determining priority areas for conservation, broad‐scale data on gastropod total species, endemic and threatened species richness are limited. Based on these biodiversity indices, we identify global hotspots, extinction risk along the elevational gradient and the drivers of species richness patterns in the largest group of freshwater gastropods, the family Hydrobiidae.
• Given the strong dependency to a nonmarine aquatic environment, the observed richness patterns of extant hydrobiid species could be significantly influenced by large‐scale geography and dispersal processes as well as climatic conditions affecting continental ecosystems. Therefore, we tested several predictions for species richness derived from ecological and evolutionary hypotheses postulated for other freshwater groups.
• Based on a comprehensive literature and biodiversity database review, we compiled the number of total, endemic and threatened species per freshwater ecoregion. We classified ecoregions as hotspots if each biodiversity index was in the top 25% of its range and assessed the effect of 13 environmental and evolutionary factors on species richness using generalised linear models.
• We identified 906 species and 157 genera of Hydrobiidae showing mainly a Nearctic–Palearctic distribution and 19 biodiversity hotspots, most located across the Mediterranean Basin. In our data set, 83% of the species were endemic to a single ecoregion. Of the 43% non‐data deficient species, we found almost three times more threatened than non‐threatened species, and extinction risk peaked at 1,500 m a.s.l. Species richness was unequally distributed over biogeographic realms, increased with higher connectivity among ecoregions, and was negatively related with annual temperature range. Latitude and precipitation seasonality explained part of the richness variation by a nonlinear relationship.
• The identified hotspots correspond with those of other freshwater taxa. The hump‐shaped relationship of extinction risk with elevation is likely the consequence of decreasing natural and anthropogenic perturbations at higher elevations. Global hotspots of Hydrobiidae richness represent areas of climatic stability with medium precipitation and temperature seasonality that are well connected with other hydrological basins. Our results illustrate that both evolutionary and environmental factors determine these global patterns and that future changes of the latter factors may affect hydrobiid richness.
Co-extinctions are increasingly recognized as one of the major processes leading to the global biodiversity crisis, but there is still limited scientific evidence on the magnitude of potential impacts and causal mechanisms responsible for the decline of affiliate (dependent) species. Freshwater mussels (Bivalvia, Unionida), one of the most threatened faunal groups on Earth, need to pass through a parasitic larval (glochidia) phase using fishes as hosts to complete their life cycle. Here, we provide a synthesis of published evidence on the fish–mussel relationship to explore possible patterns in co-extinction risk and discuss the main threats affecting this interaction. We retrieved 205 publications until December 2015, most of which were performed in North America, completed under laboratory conditions and were aimed at characterizing the life cycle and/or determining the suitable fish hosts for freshwater mussels. Mussel species were reported to infest between one and 53 fish species, with some fish families (e.g., Cyprinidae and Percidae) being used more often as hosts than others. No relationship was found between the breadth of host use and the extinction risk of freshwater mussels. Very few studies focused on threats affecting the fish–mussel relationship, a knowledge gap that may impair the application of future conservation measures. Here, we identify a variety of threats that may negatively affect fish species, document and discuss the concomitant impacts on freshwater mussels, and suggest directions for future studies.
We describe 13 new, narrowly localized species of the aquatic gastropod genus Tryonia from springs in the Chihuahuan Desert (Chihuahua and Texas): T. allendae n. sp., T. angosturae n. sp., T. chuviscarae n. sp., T. contrerasi n. sp., T. julimesensis n. sp., T. metcalfi n. sp., T. minckleyi n. sp., T. molinae n. sp., T. oasiensis n. sp., T. ovata n. sp., T. peregrina n. sp., T. taylori n. sp.and T. zaragozae n. sp.. These novelties are distinguished by shell and other morphologic characters and are well differentiated genetically from each other and from other congeners (mtCOI sequence divergence >1.9%). We also provide two new records for T. seemani (Frauenfeld, 1863), which is distributed near the southern limit of the Chihuahuan Desert (Durango State) and previously had been thought to be possibly extinct. Bayesian analysis of a mtCOI dataset resolved two clades composed of novelties described herein: one (containing four species) is distributed in several drainages in Chihuahua, the other (containing three species) is a local species flock in the Río Conchos basin (also in Chihuahua) that lives in the warmest waters yet recorded for Tryonia (41-44°C). (The phylogenetic relationships of the other new species were not well supported.) Both of these clades contain sympatric species pairs; co-occurrence of Tryonia congeners previously had been reported only in Ash Meadows (southern Nevada). Some of the species described herein are from previously unsurveyed localities and may help delineate new areas of endemism within the Chihuahuan Desert. One of the new species (T. julimesensis) became extinct between 1991 and 2001 and another (T. oasiensis) disappeared from its single known locality shortly after it was first discovered in 2009 and also may be extinct. The other species treated herein are at risk of extirpation owing to the declining extent and condition of their unprotected habitats.
Lynn White's thesis, that the disenchantment of nature in the first chapter of Genesis led to reduced concern for the environment in the West, has received little empirical research at the level of individual differences in religious experience. In this study, we separated the effects of four different measures of religious experience on four different indexes of concern for the environment. Results offered substantial support for White's thesis: (a) belief in the Bible, and only belief in the Bible, predicted scores on all four indexes of environmental concern and did so in the direction expected by White's thesis; (b) this occurred independently of the effects of background items; (c) standard regression showed the effects of belief in the Bible to be independent of those of other measures of religious involvement on two indexes, and on the other two indexes stepwise regression showed the same thing; and (d) in only two of twelve cases did any other measure of religious experience significantly predict an index score independently of belief in the Bible.
ABSTRACT The fields of environmental ethics and of religion and ecology have been shaped by Lynn White Jr.'s thesis that the roots of ecological crisis lie in religious cosmology. Independent critical movements in both fields, however, now question this methodological legacy and argue for alternative ways of inquiry. For religious ethics, the twin controversies cast doubt on prevailing ways of connecting environmental problems to religious deliberations because the criticisms raise questions about what counts as an environmental problem, how religious traditions change, and whether ethicists should approach problems and traditions with reformist commitments. This article examines the critiques of White's legacy and presents a pluralist alternative that focuses religious ethics on the contextual strategies produced by moral communities as they confront environmental problems.
México is the southernmost country in North America, and extends into Central America, south of the Isthmus of Tehuantepec. The northern half of México is located on the Temperate belt and is arid in character (Nearctic), while the rest is within the Tropical belt (Neotropical). Climate varies from extremely temperate desert in the north, to tropical humid in the south. México has more than 500 freshwater fish species, about 271 of them country endemics, and approximately 48 endemics from binational basins. There are still some 30–40 fish species not yet described. There are 563 fish species colonizing coastal flood plain species. In addition to the numbers of colonizing fishes, the burden of introduced exotics has also been growing. In 1904, only 4 species were recognized as exotics; by 1997 the number had increased to 94, and by 2008 to 115. The main fish collections in Mexico are at IPN, UNAM, and UANL and are the most representative, being national in scope, although concentrated in the tropics, central region, and general in coverage, respectively. The decline of the native fish fauna has been in focus in recent years, usually as trend-in-time comparisons, where the loss of native forms and increase of exotics and/or colonizer species is evident in many basins, mainly in Río Balsas, Río Grande, and Río Lerma-Santiago. As a result, the numbers of species reported at some degree of risk have been increasing also, from 17 in 1963 to 192 in 2005. The trends in colonizers, exotics, and species at risk among Mexican fishes are parallel. The Index of Biological Integrity (IBI), in either its geographical, or historical form (IBIh), has been applied to the Rio Grande/Río Bravo basin, USA and México. IBIh values go between 0–91 (average 31). Alien species are regarded as detrimental. Overall, the IBI trends have been similar in all regions, starting from 70–95% in upper reaches, decreasing to less than 0–35% in the lower reaches of West central basins, and then down to 15% or less near the Lower Rio Grande delta. Several alien species of plecos have been recognized in the rivers Balsas, Grijalva-Río Usumacinta complex, and, also, one in the Rio Grande. Mexican rivers are notoriously dewatered in the northern half of the country. Until 1962, the Rio Grande had an average runoff of 12,000+ millions of cubic meters/year; however by 2002 it was less than 2% of that value. The river went nearly dry along the Big Bend region and was dry for months in the delta region, both in 2002 and 2004. The Rio Grande is mostly dry north of the Río Conchos junction, its main Mexican tributary, and other tributaries provide now between 1% (Río San Juan) and 20% (Río Conchos) of pre-1960 runoff. A modified Index of Biological Integrity for Rio Grande resulted in grades from 70 to 95% of the baseline in upper reaches, less than 35% in lower reaches, to less than 15% near the coast. The Texan version of the IBI was not representative as it suppresses data on euryhaline fishes. The reports of total toxics were masked, since the sum should have included both organics and heavy metals exceeding USA regulations to the total count, but only one of the two was included.
Geohistorical data and analyses are playing an increasingly important role in conservation biology practice and policy. In this review, we discuss examples of how the near-time and deep-time fossil record can be used to understand the ecological and evolutionary responses of species to changes in their environment. We show that beyond providing crucial baseline data, the conservation paleobiology perspective helps us to identify which species will be most vulnerable and what kinds of responses will be most common. We stress that inclusion of geohistorical data in our decision-making process provides a more scientifically robust basis for conservation policies than those dependent on short-term observations alone.
Freshwater biodiversity is the over-riding conservation priority during the International Decade for Action - 'Water for Life' - 2005 to 2015. Fresh water makes up only 0.01% of the World's water and approximately 0.8% of the Earth's surface, yet this tiny fraction of global water supports at least 100000 species out of approximately 1.8 million - almost 6% of all described species. Inland waters and freshwater biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms. Their conservation and management are critical to the interests of all humans, nations and governments. Yet this precious heritage is in crisis. Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much of the remaining biodiversity in fresh water will vanish before the 'Water for Life' decade ends in 2015. Why is this so, and what is being done about it? This article explores the special features of freshwater habitats and the biodiversity they support that makes them especially vulnerable to human activities. We document threats to global freshwater biodiversity under five headings: overexploitation; water pollution; flow modification; destruction or degradation of habitat; and invasion by exotic species. Their combined and interacting influences have resulted in population declines and range reduction of freshwater biodiversity worldwide. Conservation of biodiversity is complicated by the landscape position of rivers and wetlands as 'receivers' of land-use effluents, and the problems posed by endemism and thus non-substitutability. In addition, in many parts of the world, fresh water is subject to severe competition among multiple human stakeholders. Protection of freshwater biodiversity is perhaps the ultimate conservation challenge because it is influenced by the upstream drainage network, the surrounding land, the riparian zone, and - in the case of migrating aquatic fauna - downstream reaches. Such prerequisites are hardly ever met. Immediate action is needed where opportunities exist to set aside intact lake and river ecosystems within large protected areas. For most of the global land surface, trade-offs between conservation of freshwater biodiversity and human use of ecosystem goods and services are necessary. We advocate continuing attempts to check species loss but, in many situations, urge adoption of a compromise position of management for biodiversity conservation, ecosystem functioning and resilience, and human livelihoods in order to provide a viable long-term basis for freshwater conservation. Recognition of this need will require adoption of a new paradigm for biodiversity protection and freshwater ecosystem management - one that has been appropriately termed 'reconciliation ecology'.