Publications

Submitted
Submitted.
2017
Hendrickson, Dean A., Jack Johnson, Peter Sprouse, Sarah Howard, Gary P. Garrett, Jean K. Krejca, Andrew Gluesenkamp, et al. 2017. “Discovery of the Mexican Blindcat, Prietella phreatophila, in the U.S., and an update on its rangewide conservation status.” Proceedings of the Texas Academy of Sciences. Mary Hardin Baylor University, Belton, Texas. Publisher's VersionAbstract
Mexican blindcat, Prietella phreatophila, was described in 1954 from a single locality in Northern Coahuila, México. Long listed as endangered by the Mexican federal government, it was listed by the U.S. Fish and Wildlife Service as a foreign endangered species in 1970, and the most recent (1996) update of its assessment for the IUCN Red List considers it endangered as well. Explorations in the late 1990s discovered many new localities extending nearly to the international border, and a captive population established provided insights into the species’ basic biology and behavior. In 2016 the species was discovered in a cave in the Amistad National Recreation Area (ANRA), just north of the Río Grande in Texas. The 1970 listing instantly gave the TX population full protection under the U.S. Endangered Species Act. The species’ subterranean and mostly inaccessible habitat endows it with extremely low detectability and its actual range is likely broader than physical sampling of specimens has revealed. We review all prior and new knowledge of the species and its habitat to provide an updated international reassessment of its overall conservation status and threats, which most notably include aquifer depletion and contamination in both the Mexican and U.S. portions of its known range. A live captive population of two specimens collected in 1997 in Coahuila and one Texas specimen is now at the San Antonio Zoo, we are working with NPS to further explore ANRA caves and hope eventually to return to Coahuila to more fully update the species’ conservation status.
Pine, W. E., K. Limburg, B. Gerig, C. Finch, D. Chagaris, L. Coggins, D. Speas, and D.a. Hendrickson. 2017. “Growth of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River.” Journal of Fish and Wildlife Management 8 (1): 322–332. Publisher's VersionAbstract
Assessments of growth can provide information needed to understand how fish populations respond to changing environmental conditions and management actions, including ecosystem experimentation. We estimated growth rates and parameter uncertainty from otoliths of endangered Humpback Chub Gila cypha from the Colorado River in Grand Canyon, Arizona. We then compared growth of Humpback Chub \textless age 2 that were 1) occupying the mainstem Colorado River during a period of variable discharge and cooler water temperatures (1980–1998; epoch 1), 2) occupying the Colorado River during a period of moderate discharge variability and warmer water (2001–2011; epoch 2), and 3) occupying the unregulated Little Colorado River. Because growth rates of juvenile Humpback Chub (\textless age 2) may be more sensitive to changes in environmental conditions than adult fish, we used analysis of covariance and linear models to compare growth of juvenile fish (slopes) between epochs and capture sites (mainstem Colorado River vs. Little Colorado River). Our analysis of covariance results were ambiguous (age × epoch × site interaction; P = 0.06). However, individual linear regressions of size and age by epoch and site suggest biologically important differences in growth, as evidenced by slower growth in the Colorado River in epoch 1 than in epoch 2, and slower growth in the Colorado River compared with the Little Colorado River for all time periods. Overall our results 1) provide information on growth and growth variability useful for parameterizing models to assess population viability and 2) provide empirical information on how growth of juvenile and adult Humpback Chub growth may respond to changing environmental conditions.
Hendrickson, Dean A. 2017. “Utility of Mining of Diverse Historic and Current Data Sources for Insights into Distribution and Ecology ofAmerican Eels in the Gulf of Mexico and Its Tributaries.” F1000Research 6. Publisher's VersionAbstract
Compilation of basic occurrence records of American Eel in Texas revealed not only a general paucity of data, but also biases of different sources, and overall, inaccessibility of many different sources of useful records. Methodical searching, mining, normailization and basic data cleaning across a diversity of resources provided a much better picture of temporal and spatial occurrences of the species than had readily available sources. Similar data mining and sharing by all researchers and managers could greatly improve overall understanding of the species in the GoM and its tributaries, and help focus monitoring and research efforts.
2016
Hendrickson, Dean A., Adam E. Cohen, Ben Labay, Gary P. Garrett, Melissa Casarez, and F. Douglas Martin. 2016. “American Eel in Texas – what we do, don’t, and need to, know.” Kerrville, Texas, USA. Publisher's VersionAbstract
American Eel is undoubtedly one of the most studied freshwater fishes of North America. Many recent discoveries have added new insights that re-write important aspects of the “text book” knowledge of the species’ complex life history in ways that could have significant impacts on management. Despite all of this new information, debate about the species’ conservation status continues, and new threats, such as continued habitat loss and major clandestine fisheries driven by extremely high value in the global market, have further complicated management. Though USFWS recently decided that the species does not merit listing as “Endangered,” in 2012 Canada changed that country’s assessment of the species’ status from “Special Concern” (since 2006) to “Threatened” and IUCN upped its classification in 2013 to “Endangered.” Ontario has considered it “Endangered” since 2007. All U.S. Atlantic states vowed to work together to produce, in 1999, the American Eel Benchmark Stock Assessment, which mandated each state conduct standardized monitoring of recruitment and later, mandatory catch and effort monitoring. Given all that activity and data generation, it is remarkable that still so little is known about the populations of the Gulf of Mexico (GOM) and its tributary rivers that making any management decisions in that large, neglected part of the species’ range is virtually impossible. The Fishes of Texas Project team has been collating and improving the limited and scattered data on occurrences of the species in the region and concludes it important to promote a broad scale (Gulf of Mexico) collaborative community effort to acquire and share data and carefully curated specimens and, hopefully, develop a GOM-wide collaborative research and management plan like that implemented by Atlantic states. Here we’ll review the literature and state of knowledge about the species in Texas and GOM, and suggest ways to begin work toward such an effort.
Mayes, Kevin, and Dean A. Hendrickson. 2016. “The Enigmatic Eel – A Metamorphic Journey.” Texas Watersheds: Conservation news from headwaters to coast Spring 2016: 1–2. Publisher's VersionAbstract
The American eel, Anguilla rostrata, is an amazing catadromous (living in fresh water and spawning in the ocean) fish with a remarkable life history involving huge migrations. Immature adults, a.k.a. “yellow eel,” live in freshwater rivers, lakes, and estuaries, feeding on fishes and invertebrates for 5 to 20 years before making a remarkable, long-distance journey to the Atlantic Ocean to spawn in the depths of the Sargasso Sea (by the Bermuda Triangle).
Hendrickson, Dean A, Gary P Garrett, Ben J Labay, Adam E Cohen, and Melissa Casarez. 2016. Year 1 report for ‘Conserving Texas Biodiversity: Status, Trends, and Conservation Planning for Fishes of Greatest Conservation Need’. State Wildlife Grant Program. Austin, Texas, U.S.A.: Texas Parks and Wildlife Department, 1 - 177. Publisher's VersionAbstract
Substantive progress was made on all major Project Activities in this first year:Activity 1. Coordinate and Facilitate Science and Conservation Actions for Conserving Texas Biodiversity - We expanded and strengthened UT-TPWD coordination, transitioning the relationship between these partners into a much more collaborative one than was previously realized. The flow of data between TPWD and the Fishes of Texas Project (supported in part by this project) has become much more bi-directional. Many newly collected TPWD specimens, agency databases, legacy data products and reports, and feedback from resource managers are now beginning to contribute substantively to growth and diversity (now including non-specimen-vouchered records) of data served through the FoTX Project’s websites. Work on cleaning and normalizing of FoTX’s online specimen-vouchered database continued, and the updated FoTX occurrence and distribution data are being actively used. Most recently they were used by this project, together with expert (TPWD, UT and others’) opinions, to develop recommendations on conservation status of native fishes of Texas’ Species of Greatest Conservation Need for TPWD’s consideration in anticipated updates to the Texas Conservation Action Plan. Within two months of this report, a new and substantially larger and improved version of the FoTX website/database and related collection of images, field notes, and ancillary datasets, will be formally announced. Activity 2. Identify Priority Geographic Management Units for Conserving Fishes of Greatest Conservation Need - We used FoTX data in a systematic conservation area prioritization analysis to identify Native Fish Conservation Areas (NFCAs) for large portions of Texas where such comprehensive planning had not been previously carried out. Updated and new FoTX data for all Texas fish Species of Greatest Conservation Need (SGCN) were used in production of newly improved Species Distribution Models for input into this planning process, and the results of the planning exercise have already been integrated by TPWD into management prioritizations of both those species and the resultant NFCAs. Activity 3. Develop Monitoring and Conservation Plans for Native Fish Conservation Areas - Monitoring and conservation plans were delivered to TPWD for all NFCAs identified in Activity 2. Activity 4. Conduct Field-Based Surveys Detailed Biodiversity Assessments (i.e. Bioblitzing), and Citizen-Based Monitoring - Field surveys with detailed biodiversity assessments (“bioblitzes”) and citizen-based monitoring were conducted in three areas selected collaboratively by TPWD and FoTX Project staff from within the identified NFCAs: Nueces River headwaters, Big Cypress Bayou basin, and Village Creek basin. Along with this field effort, FoTX Project staff developed and circulated guidelines and best practices, and provided training for citizen-based monitoring that leverages iNaturalist for capture and reporting of photo-vouchered occurrence records in ways that will help assure scientifically useful data are obtained. All specimens acquired during these field efforts, and from many other routine specimen acquisitions from across the state (1845 total records/jars of specimens), were cataloged in the UT Fish Collection database. From there, these new records will soon be fed into GBIF, VertNet, FishNet2 and other major online data aggregators, including the online Fishes of Texas database.
2015
Hanna, Ashley H, Evan W Carson, Gary P Garrett, and John R Gold. 2015. “Conservation genetics of six species of genus Dionda (Cyprinidae) in the southwestern United States.” Monographs of the Western North American Naturalist 8: 1 - 25. Publisher's Version
Garrett, Gary P., Timothy W. Birdsong, Megan G. Bean, and Ryan McGillicuddy. 2015. “Guadalupe Bass Restoration Initiative,” 82: 379 - 386, 82, 379 - 386. Publisher's Version
Birdsong, T, MS Allen, JE Claussen, GP Garrett, TB Grabowski, J Graham, F Harris, A Hartzog, D Hendrickson, and RA Krause. 2015. “Native black bass initiative: Implementing watershed-scale approaches to conservation of endemic black bass and other native fishes in the southern United States.” Black Bass Diversity: Multidisciplinary Science for Conservation, edited by Michael D Tringali, James M Long, TIMOTHY W Birdsong, and Micheal S Allen, 82: 363 - 378. Bethesda, Maryland: American Fisheries Society, 82, 363 - 378.
Labay, Benjamin J, Dean A Hendrickson, Adam E Cohen, Timothy H Bonner, Ryan S King, Leroy J Kleinsasser, Gordon W Linam, and Kirk. O Winemiller. 2015. “Can species distribution models aid bioassessment when reference sites are lacking? Tests based on freshwater fishes.” Environmental Management. Publisher's VersionAbstract
Recent literature reviews of bioassessment methods raise questions about use of least-impacted reference sites to characterize natural conditions that no longer exist within contemporary landscapes. We explore an alternate approach for bioassessment that uses species site occupancy data from museum archives as input for species distribution models (SDMs) stacked to predict species assemblages of freshwater fishes in Texas. When data for estimating reference conditions are lacking, deviation between richness of contemporary versus modeled species assemblages could provide a means to infer relative biological integrity at appropriate spatial scales. We constructed SDMs for 100 freshwater fish species to compare predicted species assemblages to data on contemporary assemblages acquired by 4 independent surveys that sampled 269 sites. We then compared site-specific observed/predicted ratios of the number of species at sites to scores from a multimetric index of biotic integrity (IBI). Predicted numbers of species were moderately to strongly correlate with the numbers observed by the four surveys. We found significant, though weak, relationships between observed/predicted ratios and IBI scores. SDM-based assessments identified patterns of local assemblage change that were congruent with IBI inferences, however, modeling artifacts that likely contributed to over-prediction of species presence may restrict the stand-alone use of SDM-derived patterns for bioassessment and therefore warrant examination. Our results suggest that when extensive standardized survey data that includes reference sites are lacking, as is commonly the case, SDMs derived from generally much more readily available species site occupancy data could be used to provide a complementary tool for bioassessment.
Williams, Jack E, Daniel J Isaak, Jack Imhof, Dean A Hendrickson, and John R McMillan. 2015. “Coldwater Fishes and Climate Change in North America.” Elsevier.Abstract
Fishes of the family Salmonidae, including trout (Oncorhynchus), charr (Salvelinus), salmon (Oncorhynchus and Salmo), grayling (Thymallus) and whitefish (Prosopium), are expected to be particularly vulnerable to climate change because of their dependence on cold, clean water. Salmonids are among the most sought after fish by recreational anglers. In North America, their native range includes much of the continent from the Arctic Plains, along Pacific and Atlantic coasts, and throughout most mountainous regions (Behnke 2002). In Mexico, trout naturally occur in the mountainous regions of Baja California, and throughout the Sierra Madre Occidental as far south as the Rio Presidio and Rio Baluarte basins (Hendrickson et al. 2002). Brown trout (Salmo trutta) are native to Europe but have been broadly introduced in North America. Additionally, rainbow trout (O. mykiss) and brook trout (Salvelinus fontinalis) and other salmonids that are native to North America have been widely introduced into lakes, reservoirs, and river systems outside of their native ranges to increase angling opportunities.Climate change is likely to continue affecting salmonids throughout their ranges. Increasing air temperatures have been warming stream and lake temperatures (Schneider and Hook 2010; Asaak et al. 2012) with impacts ranging from growing stress and metabolic rates to loss of lower elevation habitats as waters warm (Eby et al. 2014; Keefer and Caudill 2015). Warmer conditions will also impact salmonids through changes in winter precipitation and altered flow regimes (Haak et al. 2010). Disturbance events, such as wildfires, floods, and drought, are likely to increase as well (Westerling et al. 2006) with resulting stream sedimentation (Goode et al. 2012). Many existing stressors for salmonids are likely to be made worse by climate change (Williams et al. 2015). For instance, non-native fishes, which now prey on and compete with native salmonids, are likely to increase in numbers and distributions as climate changes (Rahel and Olden 2008; Lawrence et al. 2014). The synergies that emerge from the combined effects of these stressors will be hard to predict with accuracy but are likely to magnify the negative consequences of climate change for coldwater fishes in North America. The range of climate change impacts will not be equally harmful across all salmonid species. Although, all salmonids tend to be dependent on cold, clean water supplies, some species, such as bull trout (Salvelinus confluentus), Arctic grayling (Thymallus arcticus), and Dolly Varden (S. malma), are particularly sensitive to increasing temperatures and sedimentation (Selong et al. 2001; Jones et al. 2013). Changes in winter precipitation from snow to rain may impact fall-spawning species such as brook trout or brown trout to a greater degree than spring-spawning trout because of increased scouring of their egg beds (Wenger et al. 2011; Goode et al. 2013). Other species, such as California golden trout (O. aquabonita) and Lahontan cutthroat trout (O. clarkii henshawi), may occur in regions that are in the midst of sustained drought and particularly vulnerable to loss because of increasing isolation and small population size. Despite our understanding of climate-driven impacts and known sensitivity of salmonids to warming conditions, predictions of future ecological conditions are complicated by the interactions among climate, biological, and geological processes. None of these factors act in isolation. The degree that warming and changes in disturbances impact particular habitats and species depends on the resilience of the habitat or species in question, including the interactions of biological, geomorphic and hydrologic systems. Impacts from climate change are likely to be more severe where stream and lake conditions are degraded or fragmented and less severe where habitats are robust and interconnected (Rieman and Isaak 2010). Unfortunately, many habitats of native salmonids have a legacy of pollution and fragmentation caused by dams, water diversions, agricultural runoff, and roads. The majority of native trout and charr species and subspecies occupy less than 25% of their historical habitat (Trout Unlimited 2015). The purposes of this paper are to 1) review existing and likely future climate change impacts to salmonids in North America, 2) provide a primary bibliography for these impacts, and 3) describe how restoration can help trout adapt to climate change. The reader should keep in mind that the conservation status of most native salmonids already has declined as a result of the legacy of agricultural development, hydropower development, and the introduction of non-native species (Behnke 2002; Trout Unlimited 2015). Some taxa already are classified as vulnerable, threatened, or endangered by state, provincial, and federal agencies. Furthermore, as occupied habitat becomes increasingly fragmented and isolated, risks to climate-driven disturbances increase as well. Conservation efforts such as building artificial barriers to protect native trout from upstream invasions of non-native trout and warmwater fishes may result in further vulnerability to climate change because of range restrictions. Thus it is important to view increasing risk not just from the perspective of one or two factors but from the full variety of impacts that may accumulate over space and time.
Oldfield, Ronald G, Kapil Mandrekar, Xavier Nieves, Dean A Hendrickson, Prosanta Chakrabarty, Brook O Swanson, and Hans A Hofmann. 2015. “Parental care in the Cuatro Ciénegas cichlid, Herichthys minckleyi (Teleostei: Cichlidae).” Hydrobiologia 748 (1): 233 - 257. Publisher's VersionAbstract
Behavioral studies have often examined parental care by measuring phenotypic plasticity of behavior within a species. Phylogenetic studies have compared parental care among species, but only at broad categories (e.g., care vs. no care). Here we provide a detailed account that integrates phylogenetic analysis with quantitative behavioral data to better understand parental care behavior in the Cuatro Ciénegas cichlid, Herichthys minckleyi. We found that H. minckleyi occurs in a clade of sexually monochromatic or weakly dichromatic monogamous species, but that male and female H. minckleyi have dramatically different reproductive coloration patterns, likely as a result of sexual selection. Furthermore, we found that males are polygynous; large males guard large territories, and smaller males may attempt alternative mating tactics (sneaking). Finally, compared to the closely related monogamous Rio Grande cichlid, H. cyanoguttatus, males of H. minckleyi were present at their nests less often and performed lower rates of aggressive offspring defense, and females compensated for the absence of their mates by performing higher levels of offspring defense. Body color, mating system, and parental care in H. minckleyi appear to have evolved after it colonized Cuatro Ciénegas, and are likely a result of evolution in an isolated, stable environment.
García de Leon, Francisco J, Rocío I Rodríguez Martinez, and Dean A Hendrickson. 2015. “Genetic Analysis and Conservation Status of Native Populations of Largemouth Bass in Northeastern Mexico.” Black Bass Diversity: Multidisciplinary Science for Conservation, edited by MD Tringali, JM Long, TW Birdsong, and MS Allen, 635 - 657. Bethesda, Maryland, USA: American Fisheries Society, 635 - 657. Publisher's VersionAbstract

Largemouth Bass Micropterus salmoides ranges naturally in Mexico fromthe binational Rio Grande basin, including Cuatro Ciénegas valley in the state of Coahuila, southward and eastward through two adjacent Gulf Coast drainages, the Río San Fernando and Río Soto la Marina in Nuevo León and Tamaulipas. Within this range, Florida Bass ⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚ has been introduced into reservoirs in at least the Río Grande and Soto La Marina basins. To assess the conservation status of native Mexican bass, we study genetic variability within and among Largemouth Bass populations and the degree of genetic introgression by Florida Bass within them. We sampled numerous localities in Cuatro Ciénegas, the San Fernando and Río Soto la Marina basins, and Vicente Guerrero Reservoir, where Florida Bass was introduced. We examined restriction-fragment polymorphisms within the 12S and 16S ribosomal RNA mitochondrial DNA genes and genotypes at two allozyme and ⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚⬚- ment testing using the nuclear data. Largemouth Bass specimens possessed generally lower nuclear diversity, but higher mitochondrial diversity, than those of Florida Bass. Populations from Cuatro Ciénegas differed from those in the San Fernando and Soto la Marina basins. Nuclear analyses revealed three genetically pure populations in Cuatro Ciénegas (Charcos Prietos, Las Playitas, and Canal del Tío Julio), but hybrids in Río Garabatal and Mojarral Este. Another presumably pure Largemouth Bass population was found in Río El Tigre of the Soto La Marina drainage. Our results could be explained by geographic barriers, sexbiased dispersion, hybrid disadvantage, or selection for coadapted gene complexes. More extensive surveys are needed to fully assess the conservation status of native Largemouth Bass populations in México. We anticipate that these will reveal additional native diversity. Meanwhile, the remnant native populations delineated herein are important to protect and we advocate that their ranges be managed as genetic conservation areas.

French, Connor, Dean A Hendrickson, Adam E Cohen, and Brian R Langerhans. 2015. “Morphological divergence in multiple populations of Notropis oxyrhynchus.” Annual meeting of the TX Chapter American Fisheries Society. American Fisheries Society. Publisher's VersionAbstract

Sharpnose shiner, Notropis oxyrhynchus, was recently listedas federally endangered  Known from the Brazos and Colorado Rivers, but Colorado population believed to be introduced and now extinct  Our species distribution models indicate sufficient habitat for the species to occur in the Colorado (Fig. 3).  Our previous work (Fig. 1) to verify cyprinid museum specimens in the Colorado indicate 5 records of N. oxyrhynchus collected from 1884 to 1955 strongly suggesting nativity of the species (or a morphologically similar form) Visual examination of specimens from the Colorado suggest distinctive morphological (shape) differences compared to Brazos specimens  We hypothesized Colorado population might be a separate or incipient species

2014
Cohen, Adam E., Laura E. Dugan, Dean A. Hendrickson, F. Douglas Martin, Jonathan Huynh, Ben J. Labay, and Melissa J. Casarez. 2014. “Population of variable platyfish (Xiphophorus variatus) established in Waller Creek, Travis County, Texas.” The Southwestern Naturalist 59 (3): 413–419. Publisher's VersionAbstract
Abstract The variable platyfish (Xiphophorus variatus), native to Gulf Coast drainages of northern Mexico, is a popular aquarium fish with a long history of introduction globally. We document the first Texas occurrence of this species, and its persistence in highly urban Waller Creek in the city of Austin since at least 2004. The population appears to be limited to Waller Creek, having not yet been found in neighboring creeks where similar habitat exists. We observed individuals in situ and in the lab surviving in 7°C water, well below published thermal minima, and report its persistence through one of the coldest winters in Austin's recorded history. Its persistence may be due to a combination of its cold tolerance and the presence of thermal refuges. In the lab we found that individuals purchased in a local pet store and individuals from Waller Creek had the same cold tolerance. , Resumen El pez espada de Valles (Xiphophorus variatus), nativo de las cuencas afluentes del golfo de México del norte de México, es una especie popular de acuario con una historia larga de introducciones globales. Aquí documentamos la primera ocurrencia de la especie en Texas y su persistencia en un arroyo urbano, Waller Creek en la ciudad de Austin, a partir de por lo menos 2004. La población parece limitada a Waller Creek porque aún no se ha encontrado en arroyos cercanos con hábitat similar. Observamos individuos in situ y en el laboratorio sobreviviendo en agua de 7°C, mucho más frio que la mínima tolerancia termal publicada, y reportamos su persistencia a través de uno de los inviernos más fríos en la historia de Austin. Su persistencia puede ser atribuida a una combinación de su tolerancia al frío y existencia de refugios termales. En el laboratorio, individuos comprados en una tienda local de acuario e individuos de Waller Creek mostraron la misma tolerancia al frío.
Garrett, Gary P, and Robert J Edwards. 2014. “Changes in Fish Populations in the Lower Canyons of the Rio Grande,” 396 - 408. Chihuahuan Desert Research Institute Fort Davis, 396 - 408.
Carson, Evan W, Ashley H Hanna, Gary P Garrett, Robert J Edwards, and John R Gold. 2014. “Conservation genetics of cyprinid fishes in the upper Nueces River basin in central Texas.” The Southwestern Naturalist 59 (1): 1 - 8. Publisher's Version
Sanchez, Jessica L, Brian B Boutwell, Samuel T Hamontree, Gary P Garrett, Richard H Lewis, Ashley N Ragan, Michael Tobler, and Raelynn Deaton Haynes. 2014. “Reproductive characteristics of two Gambusia congeners in west Texas.” The Southwestern Naturalist 59 (3): 438 - 441. Publisher's Version
García de León, Francisco, Juan P Ramírez-Herrejon, Rafael García-Ortega, and Dean A Hendrickson. 2014. “Foraging patterns of four sympatric species of silversides (Atheriniformes: Atherinopsidae) in Lago de Pátzcuaro, Central Mexico.” Cuadernos de Investigación UNED 6 (1): 127 - 139. Publisher's VersionAbstract
Since Barbour proposed sympatric speciation to explain evolutionof silversides in the Lerma-Santiago basin, relatively little subsequent study has been done. We assessed foraging patterns of four sympatric silversides species (Chirostoma estor, Chirostoma grandocule, Chirostoma attenuatum and Chirostoma patzcuaro) in Lago de Pátzcuaro to understand resource partitioning and their sympatric coexistence. We assessed the abundance of invertebrate prey in three feeding habitats and measured physical and chemical habitat parameters at two study sites. Fish were collected during the wet (September 1987) and dry (March 1988) seasons; a total of 242 gut contents were analyzed. We evaluated the trophic guild of each species using the index of relative importance (IRI), prey selectivity with the Ivlev Electivity Index (E), dietary diversity using Shannon and Wiener diversity index (H’), and diet overlap using Morisita index. All silverside species were determined to be predaceous carnivores that feed mainly on nekton and periphyton. Dietary diversity and prey selectivity patterns were similar among species and diet overlap was >70%. Our data do not support the proposition that coexistence of these four fish species is maintained by dietary specialization. We hypothesize that sympatric coexistence of atherinopsids in Lago de Pátzcuaro is explained by food resource availability and ontogenetic variation in their diets. This study highlights the importance of analyzing ecological patterns and mechanisms as basic elements for designing conservation strategies of species flocks, especially under habitat loss and introduction of exotic species. Conservation efforts are urgent to preserve the rare evolutionary process of sympatric speciation (habitat segregation) that is occurring in other lakes in central Mexico, and probably already lost in the Lago de Pátzcuaro, as a result of poor management and inadequate conservation strategies.

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