Weston H Nowlin

Texas State University | TxSt · Department of Biology

It is unclear if geographic distributions of animals are behaviorally mediated or simply maintained by ecologically-driven deleterious effects on fitness. Furthermore, it is not well known how behaviors that may affect geographic distributions and responses to environmental stressors evolve. To explore this, we examined behavioral and physiological...

Headwater streams and springs and their resident biotas are vulnerable to a broad range of anthropogenic stressors. Especially notable among those stressors are urbanization , eutrophication, excessive groundwater withdrawals, mining, hydraulic fracturing ("fracking") associated with petroleum development, the introduction of non-native taxa, and t...

Organisms living in environmentally stable ecosystems are hypothesized to exhibit narrow environmental tolerance ranges; however, previous experiments testing this prediction with invertebrates in spring habitats are equivocal. Here we examined the effects of elevated temperatures on four riffle beetle species (family: Elmidae) native to central an...

The Rio Grande cooter (Pseudemys gorzugi) is an imperiled freshwater turtle native to the southwestern United States and northeastern Mexico. Previous studies investigating P. gorzugi diet have focused on the population occupying the Black River drainage in southeastern New Mexico, while Texas populations have remained unexamined. During the summer...

We studied population density, population size, and reproductive seasonality of the Phantom Tryonia, Tryonia cheatumi (Pilsbry, 1935). This endangered freshwater snail is found only in the San Solomon Spring system, a cienega, or karst-based, arid-land freshwater spring system, in western Texas, USA. We sampled populations at seven locations in the...

Marine species from the Gulf of Mexico often have higher mercury (Hg) concentrations than conspecifics in the Atlantic Ocean. Spatial differences in Hg sources, environmental conditions, and microbial communities influence both Hg methylation rates and the bioavailability of Hg to organisms at the base of the food web. Mercury bioaccumulates within...

Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for population coexistence in these presumably low resource env...

Although freshwater systems comprise a small portion of land surface, they play a pivotal role in landscape carbon (C) cycling. Carbon processing by heterotrophic bacteria is critical, contributing to ecosystem production and dissolved organic carbon (DOC) processing. Riverine bacterial C metabolism is related to a diversity of factors, including (...

A long-standing hypothesis in subterranean biology posits that organisms living in poor resource subsurface habitats can withstand long periods of bioenergetic shortages due to an innate reduced metabolic rate when compared to their epigean counterparts. However, previous studies have proposed that caves with ample energy resources may not evolve o...

Sex identification of many species of adult riffle beetles (Coleoptera: Elmidae) has relied historically upon removal and examination of genitalia, which leads to death if examined individuals are initially alive. This process and its consequences present a substantial problem if investigators intend to study live beetles in captivity, or if an inv...

Terrestrial organisms such as shoreline spiders that consume prey from aquatic food webs can be contaminated with methyl mercury (MeHg). However, no studies have examined the relationship between MeHg contamination of shoreline spider taxa and the proportion of aquatic and terrestrial prey in their diets. The present study had two objectives: 1) de...

Macroinvertebrates are widely used as bio-indicators in streams and rivers, and it is usually assumed that their community composition is primarily controlled by local environmental conditions. We examined the distribution of macroinvertebrates within the Guadalupe River basin (3256 km²) in Central Texas across physiographic gradients. Spatial anal...

Zebra mussels, Dreissena polymorpha, have recently invaded Central Texas. More information is needed to predict their spread in this region and inform management decisions. In this study, we examined riverine zebra mussel dispersal from, and settlement downstream of, a recently invaded reservoir, Lake Belton. Veliger samples and settlement of juven...

To better understand the interaction between the abundance and composition of bacterial communities, physicochemical conditions, and bacterial metabolic function, we studied the patterns of bacterial community composition and metabolic function in relation to nutrients, land use, and network position in a large subtropical river. Composition varied...

The prevailing paradigm in subterranean ecology is that below-ground food webs are simple, limited to one or two trophic levels, and composed of generalist species because of spatio-temporally patchy food resources and pervasive energy limitation. This paradigm is based on relatively few studies of easily accessible, air-filled caves. However, in s...

The Lost Pines Ecoregion in East Central Texas is an ecologically unique area composed of a diverse set of terrestrial and aquatic organisms, many of which are on the western edge of their ranges within Texas. We assessed the diversity, abundance, and occurrence of aquatic invertebrates in small wetland ponds located on the Griffith League Ranch, a...

Habitat loss is one of the most critical factors affecting the loss of species. However, habitat conservation of many threatened species is performed with incomplete information on habitat requirements and trophic ecology, thus presenting a challenge to designing and implementing recovery plans. The San Marcos salamander ( Eurycea nana ) is a feder...

Non‐native invasive species ( NNIS ) are a global issue whose introduction into novel ecosystems can fundamentally alter nutrient recycling and storage. It is therefore important to understand factors that affect the abundance and distribution of NNIS and their effects on ecosystems. We investigated how nutrient enrichment and herbivorous armoured...

Sympatric species are expected to exhibit specialisation that reduces interspecific competition in environments with food resources that exhibit little spatial or temporal variation in availability, while sympatric species in more unpredictable environments should exhibit generalised feeding strategies to exploit a wide range of variable resources....

Riverine ecosystems are linked to their watersheds, and both land use and physiographic environmental conditions influence nutrient dynamics and water quality. We assessed aquatic nutrients and their relationship with land use and physiographic conditions at multiple spatial scales in the Brazos River watershed (Texas, USA) to examine the interacti...

Insects emerging from aquatic environments provide a critical energy subsidy to consumers in terrestrial ecosystems, but emergent insects may also expose terrestrial consumers to aquatic contaminants like methylmercury (MeHg), the so-called “dark side of subsidies.” We used a series of field surveys and experiments to explore how predatory fish and...

Methyl mercury (MeHg) is one of the most hazardous contaminants in the environment; it adversely affects the health of both wildlife and humans. Recent studies have demonstrated that aquatic insects biotransport MeHg and other contaminants to terrestrial consumers, but the factors that regulate the flux of MeHg out of aquatic ecosystems via emergen...

Native consumers play a vital role in maintaining ecosystem functioning, but species invasion may alter these processes. We hypothesized that the individual effects of large-bodied native and invasive consumers on ecosystem functioning and invertebrate community assemblages differ from the interactive effects. In the San Marcos River (Texas, USA),...

Background/Question/Methods The introduction of species to novel habitats is often cited as one of the largest and most pervasive anthropogenic impacts on ecosystems. Upon introduction, some species become invasive, dominating community biomass and alter community and ecosystem processes. In particular, introduction of non-native fishes is a glob...

Background/Question/Methods Stream and river ecosystems are intimately connected to adjacent terrestrial habitats through the exchange of organic matter, nutrients, and organisms. Traditionally, it was thought that the dominant directionality of the movement of inorganic and organic matter (OM) was from terrestrial to stream habitats; however, th...

The red imported fire ant Solenopsis invicta (RIFA) is an invasive species found throughout the southern and southeastern United States. Since its introduction, RIFA has been shown to negatively affect a wide range of native vertebrate and invertebrate species. The purposes of this study were to delineate the annual RIFA activity pattern, investiga...

Mercury is an environmental contaminant that negatively affects the health of vertebrate consumers such as fish, birds, and mammals. Although aquatic macroinvertebrates are a key link in the trophic transfer of Hg to vertebrate consumers, Hg contamination in macroinvertebrate communities has not been well studied. The purpose of the present study w...

Patterns of spatial variation of mercury and methylmercury (MeHg) were examined in sediments and muscle tissue of largemouth bass (Micropterus salmoides) from Amistad International Reservoir, a large and hydrologically complex subtropical water body in the Rio Grande drainage. The distributions of both Hg and MeHg were compared with environmental a...

The San Marcos River Observing System represents efforts by the River Systems Institute and Department of Biology at Texas State University to develop and maintain a high spatial and temporal resolution characterization and monitoring program within the Upper San Marcos River watershed (Texas), a spring-fed river system with substantial conservatio...

The genus Dionda (family Cyprinidae) consists of at least 12 species, all of which inhabit groundwater-dominated streams within the western Gulf slope drainages of North America. Purposes of this study were to quantify reproductive characters of two sympatric Dionda (D. argentosa and D. diaboli) and to assess relationships among life-history traits...

The Guadalupe bass, Micropterus treculii, is endemic to streams of central Texas and occurs primarily in the Edwards Plateau. We investigated the trophic ecology of Guadalupe bass using gut content data as well as carbon and nitrogen stable isotopes. We also sampled potential prey items to determine whether or not diet differences among populations...

Background/Question/Methods Determining sources of organic matter (OM) to aquatic communities has been a central focus of aquatic ecology. In riverine ecosystems, spatial resource subsidies can occur among habitats within a river and between riverine and terrestrial ecosystems. This study examines OM sources in an arid river ecosystem, the Rio Gr...

Background/Question/Methods Riverine ecosystems are a vitally important link between terrestrial and aquatic ecosystems, but the relationships between patterns of land-use/land cover (LULC), in-stream nutrient dynamics, and riverine ecosystem function are often complex. Rivers are sites of major biogeochemical processes, providing important ecosy...

Background/Question/Methods The purpose of this study was to examine mercury (Hg) in macroinvertebrate communities from grassland ponds with and without fish communities. We sampled macroinvertebrates from five ponds with fish and five ponds without fish, at the LBJ National Grassland in north Texas, USA. Results/Conclusions Ponds without fis...

Background/Question/Methods Rivers are critical in the transport and transformation of carbon (C) and inorganic nutrients exported from terrestrial landscapes, with suspended bacteria potentially playing a critical role. Suspended bacteria actively participate in organic carbon cycling and reallocation. Differential bacterial mediation of carbon o...

Plankton nutrient limitation and deficiency were assessed in six coastal and four interior lakes and reservoirs in British Columbia. Ultimate nutrient limitation was defined as occurring over longer time scales (months to years) and represented the potential attainable biomass or yield. Proximate nutrient deficiency reflected plankton physiological...

Introduced suckermouth catfishes (Family Loricariidae) are now established in a number of spring-influenced streams in North America but their impacts on native biota are not well documented. Purposes of this study were to quantify gut contents of the loricariid Hypostomus plecostomus from the San Marcos River in central Texas and to evaluate the r...

Ideas on how various measures of nutrient limitation relate to plankton biomass and species composition are re-examined. While long-term and multi-lake studies typically focus on determining overall biomass, seasonal studies are more focused toward understanding species composition. We use physiological assays to assess short-term nutrient deficien...

Background/Question/Methods: Project Flowing Waters is an NSF GK-12 program founded on the interdisciplinary theme of water, emphasizing the integration of water-related sciences research and inquiry-based teaching. ","serif";">The focal point of the program, the San Marcos River ecosystem, is a unique natural laboratory that permits integration o...

Mercury (Hg) contamination of aquatic ecosystems is a global environmental problem. Data are abundant on Hg contamination and factors that affect its bioaccumulation in lake communities, but comparatively little information on riverine ecosystems exists. The present study examines fish Hg concentrations of the Lower Rio Grande/Rio Bravo del Norte d...

We tested the hypothesis that nutrient sequestration and carbon flow through heterotrophic bacteria is relatively highest in oligotrophic systems and decreases with trophic state in 17 reservoirs in Texas and Ohio, U.S.A. The percentage of particulate carbon (C), nitrogen (N), and phosphorus (P) in bacteria (, 1 mm) was highest in oligotrophic rese...

Many freshwater ecosystems receive allochthonous resource subsidies from adjacent terrestrial environments. In eastern North American forests, geographic broods of periodical cicadas emerge every 13 to 17 y to breed, and local abundances can sometimes be .300 individuals/m 2 . Most individuals avoid predation, senesce after breeding, and become a r...

Resource pulses affect productivity and dynamics in a diversity of ecosystems, including islands, forests, streams, and lakes. Terrestrial and aquatic systems differ in food web structure and biogeochemistry; thus they may also differ in their responses to resource pulses. However, there has been a limited attempt to compare responses across ecosys...

Environmental mercury (Hg) contamination represents a serious threat to humans and wildlife. Humans have greatly altered the Hg cycle by releasing Hg via coal-fired power plants, mining, and industrial activities; approximately half of global Hg emissions are from humans. In the present study, I examined Hg contamination and fluxes at three sites i...

Periodical cicadas emerge from below ground every 13 or 17 years in North American forests, with individual broods representing the synchronous movement of trillions of individuals across geographic regions. Due to predator satiation, most individuals escape predation, die, and become deposited as detritus. Some of this emergent biomass falls into...

1. Limnologists have long acknowledged the importance of phosphorus (P) in determining the organism biomass and productivity of lake ecosystems. Despite a relatively large number of studies that have examined P cycling in lake ecosystems, there remain several substantial methodological issues that have impeded our understanding of P cycling in limn...

Periodical cicadas emerge from below ground every 13 or 17 years in North American forests, with individual broods representing the synchronous movement of trillions of individuals across geographic regions. Due to predator satiation, most individuals escape predation, die, and become deposited as detritus. Some of this emergent biomass falls into...

Large-bodied animals in stream ecosystems, such as fish and macro-crustaceans, often play substantial roles in nutrient cycling and organic matter processing. However, little is known about the individual and combined impacts of native and non-native animals on stream ecosystem processes. We experimentally investigated the effects of exotic herbivo...

Top–down control of phytoplankton biomass through piscivorous fish manipulation has been explored in numerous ecological and biomanipulation experiments. Piscivores are gape-limited predators and it is hypothesized that the distribution of gape sizes relative to distribution of body depths of prey fish may restrict piscivore effects cascading to pl...

We examined the biomass-dependent effects of common carp (Cyprinus carpio) on water quality in 10 ponds at the Eagle Mountain Fish Hatchery, Fort Worth, Texas, USA. Ponds contained 0–465kgha−1 of common carp. We measured limnological variables at weekly intervals for four weeks in early summer, after which ponds were drained and the biomass of fish...

1. Nutrients released from lake sediments can influence water column nutrient concentrations and planktonic productivity. We examined sediment nutrient release [soluble reactive phosphorus (SRP) and ammonia (NH)] at two sites in a eutrophic reservoir (Acton Lake, OH, U.S.A.) that differed in physical mixing conditions (a thermally stratified and an...

Stratification and thermal regimes of a reservoir with fluctuating water levels were compared to a natural lake of similar morphometry and trophic status over a two-year period (2000–2001) in coastal British Columbia, Canada. We compared the timing and duration of stratification, summer heat budgets and heat fluxes in two morphometrically contrasti...

Factors controlling algal abundance and carbon fixation form a cornerstone of aquatic ecology. Central among these are light, nutrients, and grazers. We measured 14C fixation over one year in six coastal BC lakes that differed in trophic status and grazer community structure. The lakes in our study were never covered with ice, so mixing due to wind...

Most knowledge of direct and indirect effects of zooplanktivorous fish has come from studies in which a treatment with a zooplanktivore is compared to a fishless control. However, effects of a zooplanktivore may be different in the presence of other fish species because the other fish have direct and indirect effects that may alter the effects of t...

[Abstract Not Available]