Contract Research Findings: Invertebrates


Title:Diversity and abundance of unionid mussels in three sanctuaries on the Sabine River in northeast Texas
Journal/Year:Texas Journal of Science/2009
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Author(s):Neil B. Ford|Jessica Gullett|Marsha E. May
Abstract:Populations of freshwater mussels (Bivalvia: Unionidae) in Texas are declining for reasons that are primarily anthropogenic. The Texas Administrative Code lists 18 freshwater mussel sanctuaries ("no-take" areas) within Texas stream segments and reservoirs, with three being on the Sabine River in northeast Texas. Visits to each Sabine River sanctuary were made multiple times between April and September 2007 with two goals: to establish species richness by locating rarer species not found in earlier surveys and to collect unionid data that could be used to evaluate abundances among the sanctuaries. Using timed and density surveys (0.25 meter square quadrats) 1596 individuals of 18 unionid species were recorded. Densities ranged from means of over 21 per meter square in one sanctuary to 3.6 per meter square in the sanctuary nearest the dam at Lake Tawakoni. Because a range of sizes were found for several species at the two downstream sanctuaries, recruitment evidently occurs. One of the healthiest unionid populations in these areas was Fusconaia askewi, which is a species of concern in the Texas Wildlife Action Plan. The mussel beds were found only in small, isolated patches in any sanctuary and silting over beds with sand from bankfalls was evident throughout the river. Whether these sanctuaries will sustain all species within the upper Sabine River is questionable and it will be important to continue to monitor them.
Citation:Ford, N. B., J. Gullet, and M. E. May. 2009. Diversity and abundance of unionid mussels in three sanctuaries on the Sabine River in northeast Texas. Texas Journal of Science 61:279-294.

Title:Effects of summer and winter burning on vegetation and wildlife in a sand sagebrush/honey mesquite savanna
Journal/Year:Thesis/2009
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Author(s):Matthew W. Poole
Abstract:There is substantial information on the generalized effects of fire in some grassland ecosystems. However, studies addressing seasonality of fire are less common. The Rolling Plains have high climatic variability with periodic droughts; however, little information is available on the potential role of burning in these communities under these conditions. Therefore, I initiated a project to explore the effects of seasonality of fire on a sand prairie ecosystem. We established 5 blocks of 3 18-ha plots at Matador Wildlife Management Area (WMA) in Cottle County, Texas. Each plot, within a block, was randomly assigned to a summer burn (August), winter burn (February), or a control (no fire) treatment. Herbaceous vegetation cover and frequency were measured twice annually (May-June and August-September) using 0.1 m² quadrats, while woody cover was measured during late summer using the line-intercept method. Invertebrates, herpetofauna, and small mammals were sampled utilizing drift fence arrays during the spring and summer. Invertebrates were also sampled in late summer using sweep nets and small mammals were also sampled twice annually using Sherman live traps. Summer burning appeared to benefit forbs, species richness, evenness and diversity. In general, forbs were not affected by winter burning, but forbs were similar to grasses, in that individual species' responses to winter burning were variable. My results indicated that prescribed summer burning appears to be effective at reducing, but not eliminating sand sagebrush, honey mesquite, prickly pear, yucca, and total woody canopy cover. Summer burning was the most effective treatment at reducing honey mesquite and sand sagebrush, which may have promoted the observed increases in herbaceous vegetation by making resources, such as light and water, available to grasses and forbs. However, many of the wildlife species examined did not respond to the application of summer and winter burning, but responded to onset of drought conditions. Therefore, a combination of both summer and winter burning treatments are recommended for suppressing woody plant cover and increasing overall plant diversity by promoting desirable herbaceous species for a wide variety of wildlife and livestock. Longer term research on the effects of summer and winter burning on herbaceous and woody vegetation, especially in drought years, is needed to fully evaluate the effects of burning in the Rolling Plains of Texas.
Citation:Poole, M. W. 2009. Effects of summer and winter burning on vegetation and wildlife in a sand sagebrush/honey mesquite savanna. Thesis, West Texas A&M University, Canyon, USA.

Title:Impact of red imported fire ants on insect abundance as a food source for broods of the critically endangered Attwater's prairie-chicken
Journal/Year:TPWD Final Report/2009
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Author(s):Alejandro A. Calixto|Bart Drees|Mike Morrow|Donna Roach|Johnny Johnson
Management Implications:This preliminary study failed to document consistent and significant impacts of RIFA foraging on insects and other arthropods with the exception that numbers of pill bugs (Isoptera) were significantly higher and larger (mm) in RIFA reduced plots. It is possible that the study design for this preliminary study was inadequate to determine impacts on arthropod communities, especially with respect to duration of RIFA reduction as it relates to the life history of other arthropods. Because of the preliminary nature of this study, plot size and number of replications may have been inadequate to document effects of RIFA control. Additionally, factors other than RIFA (e.g., weather, poor drainage, genetic isolation, pesticide drift, etc.) may have contributed to low insect/arthropod abundance in this area. A more elaborated study that accounts for these design constraints should be considered for future efforts. Classification to lower taxonomic levels may be necessary for understanding RIFA impacts. RIFA and insect/arthropod assessments through the year, particularly in late fall and early spring, could perhaps better document the relationship between these groups and timing of RIFA reduction and subsequent re-invasion. Finally, the development of target-specific treatments for RIFA, particularly in areas where RIFA population densities are low in order to assure minimization of potential secondary impacts of insecticide baits on non-target species, would possibly improve the likelihood of documenting the effects of RIFA on local insect/arthropod assemblages and support implementation of RIFA as a management practice in this sensitive environment.
Citation:Calixto, A. A., B. Drees, M. Morrow, D. Roach, and J. Johnson. 2009. Impact of red imported fire ants on insect abundance as a food source for broods of the critically endangered Attwater's prairie-chicken. Texas Parks and Wildlife Department Final Report, Austin, USA.

Title:Microhabitat selection and natural history of three scorpions in a prescribed fire matrix
Journal/Year:Thesis/2010
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Author(s):Abigail Lynn Lubbers
Abstract:Given the terrestrial nature of scorpions, they are likely to be impacted by fires in the grassland systems they occupy. To better understand such impacts, I studied the effect of seasonality of prescribed fire on microhabitat selection and compared scorpion abundance, richness, and diversity across fire treatments for Centruroides vittatus, Vaejovis coahuilae, and V. russelli at a site in the southeastern Great Plains. To assess microhabitat selection, I measured microhabitat variables for actual scorpion locations and random locations. Analysis of Variance was used to compare use versus availability to determine the influence of fire and season on microhabitat availability, use and selection. Diversity was calculated using modified Simpson's and Shannon-Wiener diversity indices. In addition, natural history was examined for C. vittatus, V. coahuilae, and V. russelli. Analysis of Variance was used to compare age structure and sexual dimorphism. Chi-square tests were used to determine if the sex ratio differed from 1:1. Regressions were used to determine if weather variables had an effect on abundance and diversity. Centruroides vittatus did not select for any aspect of its microhabitat, while V. coahuilae and V. russelli selected for a higher percentage of bare ground. Vaejovis coahuilae and total scorpion captures were highest in summer-burned plots and lowest in unburned plots while C. vittatus captures, diversity, and evenness were lowest in summer-burned plots and highest in unburned plots. Based on current trends, burning would seem to favor the burrowing species (Vaejovis coahuilae) at the expense of the climbing species (Centruroides vittatus). Results suggest that C. vittatus, V. coahuilae,and V. russelli are partitioning different aspects of their niches temporally, spatially, and morphologically.
Citation:Lubbers, A. L. 2010. Microhabitat selection and natural history of three scorpions in a prescribed fire matrix. Thesis, West Texas A&M University, Canyon, USA.

Title:Biogeography and conservation of freshwater mussels (Bivalvua: Unionidae) in Texas: patterns of diversity and threats
Journal/Year:Diversity and Distributions/2011
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Author(s):Lyubov E. Burlakova|Alexander Y. Karatayev|Vadim A. Karatayev|Marsha E. May|Daniel L. Bennett|Michael J. Cook
Keywords:biogeography|conservation|diversity|freshwater molluscs|human population density|Unionidae
Abstract:Geographic patterns of species distributions and the factors contributing to species endangerment are necessary for the development of integrative conservation strategies. Freshwater mussels Unionidae have among the highest levels of imperilment recorded in North America. This paper describes the biogeography and diversity of Unionidae along climate and habitat gradients in Texas, evaluates human impact, and identifies the hot spots of diversity and endemism that should be targeted for conservation. Unionids were surveyed in all major Texas river basins in 2003-2009. Multivariate statistics were used to test for differences in environmental parameters and among unionid assemblages in different bioprovinces, and to determine to what extent the multivariate pattern of species distribution was affected by environmental factors. To estimate human impact, we examined the relationship between human population density and the proportion of rare species, as well with the proportion of historically present species that persist in the watershed. Correlation between biotic and environmental similarity matrices indicated concordance in the differences among unionid assemblages and environmental factors that could cause these differences. Lake surface evaporation rate and percentage of forest cover in the watershed were among the most important parameters explaining the differences in unionid assemblages. Human population density was negatively correlated with the proportion of rare species. The proportion of species found live relative to the total number of live and relic species found in our surveys and to the number of historically known species decreased with the increase in human population density. Climate, landscape, geology, and land use type were important factors influencing unionid distribution patterns among biotic provinces. Increased human population density was associated with the loss of rare species over several decades, but this loss was not recognized because of a lack of assessing the conservation status of unionids.
Management Implications:We found East Texas, where almost every river supports from 17 to 28 species, to be the hot spot for the state’s unionid diversity. Considering growing development, deforestation on the watershed and water demand, we recommend protecting the Neches River, the core of this hot spot of diversity, by designating it to the National Wild and Scenic Rivers System. The Neches River qualifies for this system by having its segments in free-flowing conditions and by possessing an outstandingly remarkable wildlife value – the richest unionid fauna in the state. Several water-bodies in this province have witnessed a dramatic decline in diversity over the past decades, emphasizing the urgency of conservation efforts. At the beginning of the 20th century, the San Jacinto River was a home for 29 unionid species (Strecker, 1931), but because of extensive mining, deforestation, damming and urbanization, this river has become one of America’s most endangered rivers (American Rivers, 2006), and lost almost 70% of the former unionid diversity (Table 1). An even larger-scale conservation effort is necessary to preserve the hot spot of endemism in Central Texas, which is home to 85% of the state’s endemics. However, most of these endemics are currently threatened by acute droughts, human water alteration and urbanization (Burlakova et al., 2011). Another important area of endemism, the Rio Grande River, is one of the World’s top 10 rivers at risk, suffering from persistent drought, water over-extraction for irrigation and domestic consumption, an increase in border population and a decline in water quality (Wong et al., 2007). Although the survival of Rio Grande’s rare species greatly depends on the overall health of the river, special care should be given to protect the few remaining stretches of the river that support their populations. The protection of freshwater biodiversity is the ultimate conservation challenge largely because it is subject to severe competition among multiple human stakeholders (Dudgeon et al., 2006; Strayer & Dudgeon, 2010). This challenge is expected to increase in the near future because of a large demand for freshwater (Gleick, 2006). Efforts are currently underway in Texas to establish a system of protected areas for biodiversity (TPWD, 2010). Because of the ‘keystone’ role that mussels play in many freshwater ecosystems, they are well-known indicators of biological integrity and water and habitat quality (reviewed in Grabarkiewicz & Davis, 2008), and their abundance is a valuable predictor of diversity of other aquatic invertebrates (Aldridge et al., 2007). Thus, the protection of sites with a high diversity of Unionidae will ensure conservation of other freshwater taxa.
Citation:Burlakova, L. E., A. Y. Karatayev, V. A. Karatayev, M. E. May, D. L. Bennett, and M. J. Cook. 2011. Biogeography and conservation of freshwater mussels (Bivalvia: Unionidae) in Texas: patterns of diversity and threats. Diversity and Distributions 17:393-407.

Title:Endemic species: contribution to community uniqueness, effect of habitat alteration, and conservation priorities
Journal/Year:Biological Conservation/2011
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Author(s):Lyubov E. Burlakova|Alexander Y. Karatayev|Vadim A. Karatayev|Marsha E. May|Daniel L. Bennett|Michael J. Cook
Keywords:endemic species|rare species|Unionidae|community analysis|habitat alteration|conservation
Abstract:The biodiversity crisis, particularly dramatic in freshwaters, has prompted further setting of global and regional conservation priorities. Species rarity and endemism are among the most fundamental criteria for establishing these priorities. We studied the patterns of rarity and the role of rare species in community uniqueness using data on freshwater bivalve molluscs (family Unionidae) in Texas. Due to the large size and gradients in landscape and climate, Texas has diverse and distinct unionid communities, including numerous regional and state endemic species. Analysis of the state-wide distribution and abundance of Unionidae allowed us to develop a non-arbitrary method to classify species rarity based on their range size and relative density. Of the 46 Unionidae species currently present in Texas, 65% were classified as rare and very rare, including all state and regional endemics. We found that endemic species were a critical component in defining the uniqueness of unionid communities. Almost all endemics were found exclusively in streams and rivers, where diversity was almost double that of lentic waters. Man's ongoing alteration of lotic with lentic waterbodies favors common species, and dramatically reduces habitat for endemics, contributing to homogenization of unionid fauna. We identified hotspots of endemism, prioritized species in need of protection, estimated their population size, and recommended changes to their current conservation status.
Citation:Burlakova, L. E., A. Y. Karatayev, V. A. Karatayev, M. E. May, D. L. Bennett, and M. J. Cook. 2011. Endemic species: contribution to community uniqueness, effect of habitat alteration, and conservation priorities. Biological Conservation 144:155-165.

Title:Implications of coastal wetland management to nonbreeding waterbirds in Texas
Journal/Year:Wetlands/2012
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Author(s):Owen N. Fitzsimmons|Bart M. Ballard|M. Todd Merendino|Guy A. Baldassarre|Kevin M. Hartke
Keywords:aquatic invertebrates|marsh management|Texas coast|waterbirds
Abstract:Texas coastal marshes have declined in number and quality, prompting the widespread use of levees and water control structures to create or enhance coastal marsh habitat. In particular, management techniques that control water to provide fresh (< 0.5 ppt) and intermediate (0.5-5 ppt) marsh in a landscape dominated by brackish and saline marsh. However, research is needed to assess the effectiveness of these techniques in providing waterbird habitat. During 2007-09 along the central Texas Coast, we investigated the effects of marsh management on bird, plant, and aquatic invertebrate communities by comparing leveed areas within the coastal marsh that received water level and mechanical management, to adjacent nonmanaged marsh that received no hydrologic or mechanical manipulations. Managed marshes supported more bird species, greater waterbird densities, greater plant diversity, and greater aquatic invertebrate biomass than nonmanaged sites. However, nonmanaged wetlands supported greater densities and more species of secretive marsh birds (e.g., rails). Management of coastal marsh that reduces water salinities and suppresses plant succession appears to be a possible way to mitigate the effects of declines in fresh and intermediate marsh on nonbreeding waterbirds.
Management Implications:Our findings suggest that proper management of wetlands along the Texas coast can provide productive and diverse habitat for many wetland bird species. Greater invertebrate biomass and available energy, as well as greater seasonal variation in hydrology may have contributed to the higher bird species richness, bird diversity, and waterbird densities that we observed in managed wetlands. Marsh management techniques that reduce water salinities and suppress plant succession appear to create habitat for a suite of species that are not present in adjacent saltwater marshes. However, the value of nonmanaged marsh also was evident, as nonmanaged areas supported the majority of secretive marsh bird species (e.g., rails, bittern, sparrows) detected and greater marsh bird densities throughout the study. Future comparative studies should use extended monitoring efforts to account for broader temporal changes in plant and bird communities, and to better assess patterns across years. Also, investigating differences in foraging values of managed and nonmanaged marshes to different groups of waterbirds would help explain differences in their use, as aquatic invertebrates represent only a portion of the foods available to waterbirds in wetlands. Evaluating stopover duration, vital rates, or mass change of birds using managed and unmanaged marsh would allow a stronger assessment as to the quality of these habitats to migratory and wintering birds. Finally, major events such as hurricanes can provide valuable pre- and post event research opportunities, and future monitoring in these areas might provide clearer understanding of natural disturbances. Depending on specific objectives, managed wetlands on the Texas Coast can provide important habitat during crucial non-breeding periods to a large and diverse assemblage of birds, some of which are of high priority for conservation. Marsh management techniques present managers with an effective way to alleviate the negative effects of recent loss and degradation of freshwater and intermediate marsh on the Texas Coast (Moulton et al. 1997). The benefits of such practices are justification for the establishment of managed marshes in conjunction with the conservation of natural areas to improve habitat diversity for wetland birds at the local and landscape level on the Texas Coast.
Citation:Fitzsimmons, O. N., B. M. Ballard, M. T. Merendino, G. A. Baldassarre, and K. M. Hartke. 2012. Implications of coastal wetland management to nonbreeding waterbirds in Texas. Wetlands 32:1057-1066.

Title:Moist-soil managed wetlands and their associated vegetative, aquatic invertebrate, and waterfowl communities in east-central Texas
Journal/Year:Dissertation/2012
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Author(s):Daniel P. Collins, III
Citation:Collins, D. P, III. 2012. Moist-soil managed wetlands and their associated vegetative, aquatic invertebrate, and waterfowl communities in east-central Texas. Dissertation, Stephen F. Austin State University, Nacogdoches, TX, USA.

Title:State-wide assessment of unionid diversity in Texas
Journal/Year:TPWD Final Report/2012
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Author(s):Lyubov E. Burlakova|Alexander Y. Karatayev
Abstract:Field surveys of freshwater mussels (family Unionidae) were conducted in 2011-2012 at 126 sites in 11 rivers (Colorado, Frio, Guadalupe, Llano, Medina, Neches, Nueces, San Marcos, San Saba, Rio Grande, and Trinity), and in Brady Creek. The surveys concentrated on several rare Texas endemic species: Texas pimpleback, Texas fatmucket, Golden orb, smooth pimpleback, Texas fawnsfoot, and regional endemic Mexican fawnsfoot. We estimated the size of the Texas pimpleback, Texas fatmucket, Texas fawnsfoot, and smooth pimpleback populations in the San Saba River and found that some of the Texas endemic species (e.g., Texas fatmucket, Texas and Mexican fawnsfoot) are presently in dangerously low numbers. Considering the critical state of the Rio Grande River, and a number of Central Texas rivers suffering from drought and dewatering, appropriate conservation measures to save the remnant populations and preserve their habitat should be designed and carried out as soon as possible. We located sites on the Neches and Trinity rivers that are among the richest in the state in diversity and abundance of unionid bivalves, and additional sites for Texas endemic golden orb, smooth pimpleback and Texas pimpleback in the San Saba, Nueces, San Marcos and Guadalupe Rivers. We recommend these sites with abundant and diverse unionid assemblages for future monitoring and conservation. In addition, we analyzed historic and current distributional data for Texas pigtoe (Fusconaia askewi), Triangle pigtoe (F. lananensis), and Louisiana pigtoe (Pleurobema riddellii) collected during our 2003-2011 state-wide surveys and tested the genetic affinities of Fusconaia and similar species. Our study suggested that Triangle pigtoe is not a valid species, and it is likely that there is only one Fusconaia species (Texas pigtoe) currently present in Texas, thus simplifying conservation efforts. We found that the distribution range of both Texas pigtoe and Louisiana pigtoe has been reduced in the last 80 years. The present survey provided data required for successful management and conservation of freshwater molluscs (family Unionidae) in Texas.
Management Implications:The results of this study indicated that several rare Texas endemic species Texas pimpleback, Texas fatmucket, golden orb, smooth pimpleback, Louisiana pigtoe, Texas fawnsfoot and Mexican fawnsfoot still exist in Texas, and estimated the size of the Texas pimpleback, Texas fatmucket, Texas fawnsfoot, and smooth pimpleback populations in the San Saba River. However some of them (e.g., Texas fatmucket, Texas and Mexican fawnsfoot) are presently in dangerously low numbers. Considering the critical state of the Rio Grande River, and a number of Central Texas rivers suffering from drought and dewatering, all possible conservation measures to save the remnant populations and preserve their remaining habitat should be designed and carried out as soon as possible. We located sites on the Neches and Trinity rivers that are among the richest in the state in terms of diversity and abundance of unionid bivalves, and found additional sites for Texas endemic golden orb, smooth pimpleback and Texas pimpleback in the San Saba, Nueces, San Marcos and Guadalupe rivers. We recommend these sites for future monitoring and conservation. In addition, we found that triangle pigtoe (Fusconaia lananensis) is not a valid species, and it is likely that only one Fusconaia species (Texas pigtoe) is currently present in Texas, thus simplifying conservation efforts. Distribution range of both Texas and Louisiana pigtoe has been reduced in the last 80 years. The present survey provided data required for successful management and conservation of freshwater molluscs (family Unionidae) in Texas.
Citation:Burkalova, L. E., and A. Y. Karatayev. 2012. State-wide assessment of unionid diversity in Texas. Texas Parks and Wildlife Department Final Report, Austin, USA.

Title:New establishment and county records for Diorhabda spp. (Coleoptera: Chrysomelidae) and Coniatus splendidulus (Coleoptera: Curculionidae) in the Texas Panhandle and western Oklahoma
Journal/Year:Southwestern Entomologist/2013
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Author(s):G. J. Michels, Jr.|T. A. Royer|E. N. Jones|R. A. Lange|E. D. Bynum|D. C. Ruthven III|J. L. Tracy|J. B. Bible
Abstract:Cooperative projects by various national and state agencies in the last 10 years have resulted in the establishment of an effective saltcedar (Tamarisk sp.) biological control agent, the tamarisk beetle (Diorhabda spp.). Three species of tamarisk beetles have been established in different regions of Texas, typically based on their climatic adaptation. The beetles defoliate saltcedar over multiple seasons, weakening and, during 3 to 5 years, eliminating large stands of this invasive plant. Another saltcedar biological control agent, the splendid tamarisk weevil, Coniatus splendidulus F., is also established in the United States from undocumented introductions. Surveys of saltcedar for evidence of biological control in the eastern Texas Panhandle and western Oklahoma during the summer of 2012 following landowner reports of beetle infestations, and previous release efforts along the Canadian River in Texas resulted in new state and county records for Diorhabda carinata (Faldermann), D. elongata (Brullé), and C. splendidulus F. D. carinata x D. elongata hybrids were recorded for the first time in Oklahoma, from five western counties. In Texas, hybrids of D. carinata x D. elongata, D. carinata, D. elongata, and C. splendidulus were recorded from five, 16, one, and three eastern Panhandle counties, respectively. A history of the release efforts for establishment of Diorhabda spp. from 2004-2010 in the Texas Panhandle is included.
Citation:Michels, G. J., Jr., T. A. Royer, E. N. Jones, R. A. Lange, E. D. Bynum, D. C. Ruthven III, J. L. Tracy, and J. B. Bible. 2013. New establishment and county records for Diorhabda spp. (Coleoptera: Chrysomelidae) and Coniatus splendidulus (Coleoptera: Curculionidae) in the Texas Panhandle and western Oklahoma. Southwestern Entomologist 38:173-182.