Relationships between plant species richness and grazing intensity in a semiarid ecosystem.

Plant species richness is an important property of ecosystems that is altered by grazing. In a semiarid environment, we tested the hypotheses that (1) small-scale herbaceous plant species richness declines linearly with increasing grazing intensity by large ungulates, (2) precipitation and percent sand interact with grazing intensity, and (3) response of herbaceous plant species richness to increasing intensity of ungulate grazing varies with patch productivity. During January-March 2012, we randomly allocated 50, 1.5-m × 1.5-m grazing exclosures within each of six 2500 ha study sites across South Texas, USA. We counted the number of herbaceous plant species and harvested vegetation in 0.25-m2 plots within exclosures (ungrazed control plots) and in the grazed area outside the exclosures (grazed treatment plots) during October-November 2012-2019. We estimated percent use (grazing intensity) based on the difference in herbaceous plant standing crop between control plots and treatment plots. We selected the negative binomial regression model that best explained the relationship between grazing intensity and herbaceous plant species richness using the Schwarz-Bayesian information criterion. After accounting for the positive effect of precipitation and percent sand on herbaceous plant species richness, species richness/0.25 m2 increased slightly from 0% to 30% grazing intensity and then declined with increasing grazing intensity. Linear and quadratic responses of herbaceous plant species richness to increasing grazing intensity were greater for the least productive patches (<15.7 g/0.25 m2) than for productive patches (≥15.7 g/0.25 m2). Our results followed the pattern predicted by the intermediate disturbance hypothesis model for the effect of grazing intensity on small-scale herbaceous plant species richness.

Fracking pond restoration in the western Rio Grande Plains, Texas: Stockpiled topsoils may not be necessary, but seeding helps.

Soil disturbances that accompany energy development can damage local habitats. Prior to oil and gas extraction, it is commonly recommended that topsoil stockpiles be created to aid future restoration. Our study area, a retired fracking pond in the western Rio Grande Plains, Texas, was restored in 2017 with stockpiled topsoil that was collected in 2013. We segregated the existing stockpile into three layers that were ∼1.5 m in thickness and distributed these layers, along with a non-amended control surface (consisting of former subsoil that made up the perimeter of the fracking pond), in strips over the restoration area. Each of the four surfaces was seeded with a mixture of (1) 13 native grasses, (2) 13 native grasses plus an annual warm-season grass cover crop, or (3) non-seeded. We monitored plant density and species composition two through five years post-restoration. The non-amended control surface had higher seeded grass density during the final 2 sampling periods; stockpiled surfaces seldom differed from each other. Previous year's competing plant density had little effect on restoration success. Providing supplemental seed initially increased seeded plant density but benefits diminished over time; adding a cover crop was not advantageous. Changes in community composition over time were similar on stockpile surfaces but more variable than observed on the control surface. Results suggest that stockpiling topsoil may not be necessary, but that supplemental seeding was beneficial, to restoration success.

If you build it, will they come? A comparative landscape analysis of ocelot roadkill locations and crossing structures.

Wildlife-vehicle collisions can have a substantial influence on the mortality rates of many wildlife populations. Crossing structures are designed to mitigate the impact of road mortality by allowing safe passage of wildlife above or below roads, and connect to suitable areas on both sides of the road. Ocelots (Leopardus pardalis) are a federally endangered felid in the United States, with remnant populations of <80 individuals remaining in the Lower Rio Grande Valley of South Texas. Vehicle collisions are the greatest known source of mortality for ocelots in Texas. Crossing structures designed for ocelot use have been implemented throughout South Texas since the 1990s, however, ocelots rarely use them. We compared landscape characteristics between ocelot crossing structures and ocelot-vehicle collision sites. We quantified the spatial distribution of woody and herbaceous cover types surrounding ocelot crossing structures (n = 56) and ocelot-vehicle collision sites (n = 26) at multiple spatial extents and compared landscape metrics between these location types. The landscape surrounding ocelot crossing structures had 17-22% more open herbaceous cover >1,050 m from the road, and 1.2-5.8 ha larger herbaceous patches >450 m from the road compared to ocelot-vehicle collision sites. Additionally, many crossing structures installed during the 1990's are situated >100 km away from an extant ocelot population. Results from this study can guide conservation planners to place future road crossing structures in areas more likely to be used by ocelots. Our results also emphasize that reliable scientific data must be used for effective mitigation efforts. In the absence of data, post-installation assessments can improve the placement of future structures.

Occurrence of mesocarnivores in montane sky islands: How spatial and temporal overlap informs rabies management in a regional hotspot.

Interspecific interactions among mesocarnivores can influence community dynamics and resource partitioning. Insights into these interactions can enhance understanding of local ecological processes that have impacts on pathogen transmission, such as the rabies lyssavirus. Host species ecology can provide an important baseline for disease management strategies especially in biologically diverse ecosystems and heterogeneous landscapes. We used a mesocarnivore guild native to the southwestern United States, a regional rabies hotspot, that are prone to rabies outbreaks as our study system. Gray foxes (Urocyon cinereoargenteus), striped skunks (Mephitis mephitis), bobcats (Lynx rufus), and coyotes (Canis latrans) share large portions of their geographic ranges and can compete for resources, occupy similar niches, and influence population dynamics of each other. We deployed 80 cameras across two mountain ranges in Arizona, stratified by vegetation type. We used two-stage modeling to gain insight into species occurrence and co-occurrence patterns. There was strong evidence for the effects of elevation, season, and temperature impacting detection probability of all four species, with understory height and canopy cover also influencing gray foxes and skunks. For all four mesocarnivores, a second stage multi-species co-occurrence model better explained patterns of detection than the single-species occurrence model. These four species are influencing the space use of each other and are likely competing for resources seasonally. We did not observe spatial partitioning between these competitors, likely due to an abundance of cover and food resources in the biologically diverse system we studied. From our results we can draw inferences on community dynamics to inform rabies management in a regional hotspot. Understanding environmental factors in disease hotspots can provide useful information to develop more reliable early-warning systems for viral outbreaks. We recommend that disease management focus on delivering oral vaccine baits onto the landscape when natural food resources are less abundant, specifically during the two drier seasons in Arizona (pre-monsoon spring and autumn) to maximize intake by all mesocarnivores.

EFFECT OF PRESCRIBED FIRE ON THE VIABILITY OF BAYLISASCARIS PROCYONIS EGGS.

Baylisascaris procyonis is a zoonotic parasite that can cause serious health issues in their intermediate hosts. Eggs of the parasite are shed in the feces of raccoons (Procyon lotor), the definitive host, and can remain viable in the environment for years. Temperatures at 49 C are the LD50 for B. procyonis eggs. Our objective was to determine the effect of prescribed fire as a lethal control technique for B. procyonis eggs. Aliquots of 1,000 viable B. procyonis eggs were placed on the soil surface and at a depth of 2 cm within 10×10 m grass plots consisting of approximately 2,000 kg/ha and 4,000 kg/ha fuel loads. In addition, aliquots of 1,000 viable B. procyonis eggs were placed at 0, 0.7, 1.2, and 1.8 m from the fire's edge and within a 1 m2 circle of bare ground on the leading edge, center of circle, and trailing edge of the fire of similar plots. Prescribed fire killed B. procyonis eggs on the soil surface up to 0.7 m from the fire's edge at fuel loads of 4,000 kg/ha but was ineffective at depths of 2 cm. Fuel loads of 2,000 kg/ha killed only 50% of B. procyonis eggs on the soil surface at the fire's edge but was not effective killing eggs at greater distances or at soil depths. Prescribed fire can be used to reduce the quantity of B. procyonis eggs on the soil surface within an environment but will not be effective in eradicating the parasite eggs.

EFFICACY OF WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS) TREATMENT FOR CATTLE FEVER TICKS IN SOUTHERN TEXAS, USA.

White-tailed deer (Odocoileus virginianus) serve as a host for cattle fever ticks (Rhipicephalus [Boophilus] microplus and Rhipicephalus [Boophilus] annulatus; CFTs); therefore, deer are a concern for CFT control programs in southern Texas, US. Systemic (oral delivery of ivermectin) and topical (permethrin on pelage) treatment devices have been developed for white-tailed deer; however, the efficacy of these treatment options has not been determined for CFTs in southern Texas. Our objectives were to evaluate the effectiveness of CFT treatment strategies by 1) measuring exposure rates of deer to the acaricides permethrin and ivermectin, 2) determining the relationship between CFTs on deer and exposure to the acaricides, and 3) determining if photos from remote cameras at medicated bait sites can be used as a measure of acaricide treatment. We captured 327 deer at four sites in southern Texas. Deer visitation to medicated bait sites was monitored using remote cameras from March 2010 to February 2012. There was no relationship between the presence of permethrin and the probability of being infested with CFTs (P≥0.336). The probability of infestation with CFTs decreased as serum ivermectin levels increased for male (n=18, P=0.098) and female (n=33, P<0.001) deer. Our results indicate ivermectin may be more effective in treating CFTs than permethrin; thus it would be worthwhile to develop topical acaricides other than permethrin for treating white-tailed deer in southern Texas.

Hydrology and Soil Manipulations of Iron-Rich Ditch Mesocosms Provide Little Evidence of Phosphorus Capture within the Profile.

Agricultural drainage ditches function as first-order streams and affect nutrient management. Soil mesocosms from a ditch featuring a vertical (increasing upward) gradient in iron (Fe) and phosphorus (P) were subjected to hydraulic and soil treatments. These manipulations mimicked aspects of dredging and controlled drainage and inspected the soil release and retention of P. Treatments did not remove P from simulated groundwater. Throughput water either gained in P (lack of dredging, especially under Fe-reducing conditions) or had P concentrations indistinguishable from input water (dredging). Undredged mesocosms, when Fe-reducing, released Fe and P simultaneously. Simultaneous release of P and Fe from our Fe-reducing mesocosms indicates a mechanism whereby P capture occurs by Fe precipitation upon emergence to aerated surficial waters. Upwelling and surficial phases of ditch hydrology and the lowering of the ditch surface on dredging complicate interpretation of traditional means of describing ditch P retention and release.

Assessing Potential Environmental Contamination by Baylisascaris procyonis Eggs from Infected Raccoons in Southern Texas.

Baylisascaris procyonis is a large ascarid of raccoons (Procyon lotor) and is a zoonotic threat. We documented the potential rate a raccoon population can contaminate their environment with B. procyonis eggs. We estimated the population size of raccoons using a 9 × 7 trapping grid of Havahart traps, identified locations of raccoon scats through systematic searches, and enumerated the distance B. procyonis eggs passively travel from site of origin upon scat decay. During an 8-week capture period, the raccoon population was estimated to be 19.6 ± 1.3 raccoons within the 63-ha study area (1 raccoon/3.2 ha). There were 781 defecation sites, of which 744 (95.3%) were isolated sites and 37 (4.7%) were latrine sites. Fifty-three (6.8%) defecation sites occurred in areas associated with human structures (commensal zone). Of the noncommensal sites, 9 (1.2%) and 719 (98.8%) sites were identified as latrine sites and isolated scats, respectively. More latrine sites were located within the commensal zone (p < 0.0001, [Formula: see text]) than proportionately available space. Twenty-five raccoon scats containing B. procyonis eggs were allowed to decay on level bare soil by way of simulated rain events, 13 were allowed to desiccate naturally in the environment, and 12 were allowed to desiccate and, subsequently, experience a simulated 1 cm rain event; eggs were found 49 ± 6, 28 ± 8, and 68 ± 8 cm from the initial scat location, respectively. We calculated that a single B. procyonis-infected raccoon could contaminate 0.03 ± 0.01 ha/year with B. procyonis eggs. Our findings indicate that B. procyonis represents a substantial risk to humans in areas where infected raccoons and humans co-occur.

Permeability and Viability of Baylisascaris procyonis Eggs in Southern Texas Soils.

Baylisascaris procyonis is a nematode whose definitive host is the raccoon ( Procyon lotor ). Adult parasites are not particularly pathogenic to raccoons; however, larvae in intermediate hosts can cause visceral, ocular, and neural larva migrans. Humans serve as dead-end hosts, and pathological responses are similar to those found in infected intermediate hosts. Infected raccoons expose intermediate hosts through their feces, which can contain millions of B. procyonis eggs. Our objective was to determine how the quantity and viability of B. procyonis eggs in soil changed over time within different soil texture, moisture, and sun exposure. To examine egg survival and movement through soil we placed 100 B. procyonis eggs on 100 squares in 48 boxes representing a full factorial treatment of soil texture, moisture, and sun level. We monitored egg percolation and survival for 2 yr, removing (at 0, 1, 3, 6, 12, 18, and 24 mo) 5 squares from each box and counting the number of viable eggs at each depth in the soil column. Dry soils were mainly impermeable; even after 2 yr, >60% of B. procyonis eggs remained on the surface of all soil textures. Wet soils were more permeable than dry soils, but even in wet sandy soils where the greatest egg movement occurred, it required 1 yr before 60% of eggs transitioned from the soil surface to the next soil depth. For all soil textures, moistures, sun exposures, and depths, >92% of B. procyonis eggs remained viable after 2 yr in the southern Texas environment. Therefore, high exposure risk exists for potential hosts because B. procyonis eggs remain viable on or near the soil surface for at least 2 yr.

Environmental Temperatures in Southern Texas, USA: Implications for Survival of Baylisascaris procyonis Eggs.

Baylisascaris procyonis is an intestinal nematode of raccoons ( Procyon lotor ). Within intermediate hosts, larvae can cause visceral, ocular, and neural migrans. Humans, especially children, have become infected after ingestion of larvated eggs at raccoon latrines. Eggs of B. procyonis have a thermal death point of 62 C. During 2012, we assessed the likelihood of thermal lethality on B. procyonis eggs in southern Texas. We recorded temperature every 30 min with data loggers placed on the ground in full sun and in the shade, buried 5 cm underground and the ground surface exposed to full sun or in shade, in attics with and without exhaust fans, in woodpiles, in sheds, in tree crevices, and in cars parked in the sun. Such locations represented common raccoon latrine sites or locations where B. procyonis eggs could be found. In addition, data loggers placed about 135 cm above the ground in full sun and in shade were used as controls to acquire ambient temperature. The hottest month was August (maximum 44 C), with 15 d that exceeded 38 C. However, only the car reached the lethal temperature limit, and only for 1 h. Southern Texas has one of the warmest climates in the contiguous US; however, it is unlikely that the southern Texas climate is hot enough to kill B. procyonis eggs.

Soil nitrate nitrogen dynamics after biosolids application in a tobosagrass desert grassland.

Dormant-season application of biosolids increases desert grass production more than growing season application in the first growing season after application. Differential patterns of NO3-N (plant available N) release following seasonal biosolids application may explain this response. Experiments were conducted to determine soil nitrate nitrogen dynamics following application of biosolids during two seasons in a tobosagrass [Hilaria mutica (Buckl.) Benth.] Chihuahuan Desert grassland. Biosolids were applied either in the dormant (early April) or growing (early July) season at 0, 18, or 34 dry Mg ha(-1). A polyester-nylon mulch was also applied to serve as a control that approximated the same physical effects on the soil surface as the biosolids but without any chemical effects. Supplemental irrigation was applied to half of the plots. Soil NO3-N was measured at two depths (0-5 and 5-15 cm) underneath biosolids (or mulch) and in interspace positions relative to surface location of biosolids (or mulch). Dormant-season biosolids application significantly increased soil NO3-N during the first growing season, and also increased soil NO3-N throughout the first growing season compared to growing-season biosolids application in a year of higher-than-average spring precipitation. In a year of lower-than-average spring precipitation, season of application did not affect soil NO3-N. Soil NO3-N was higher at both biosolids rates for both seasons of application than in the control treatment. Biosolids increased soil NO3-N compared to the inert mulch. Irrigation did not significantly affect soil NO3-N. Soil NO3-N was not significantly different underneath biosolids and in interspace positions. Surface soil NO3-N was higher during the first year of biosolids application, and subsurface soil NO3-N increased during the second year. Results showed that biosolids rate and season of application affected soil NO3-N measured during the growing season. Under dry spring-normal summer precipitation conditions, season of application did not affect soil NO3-N; in contrast, dormant season application increased soil NO3-N more than growing season application under wet spring-dry summer conditions.

Fire and grazing effects on wind erosion, soil water content, and soil temperature.

Selective grazing of burned patches can be intense if animal distribution is not controlled and may compound the independent effects of fire and grazing on soil characteristics. Our objectives were to quantify the effects of patch burning and grazing on wind erosion, soil water content, and soil temperature in sand sagebrush (Artemisia filifolia Torr.) mixed prairie. We selected 24, 4-ha plots near Woodward, OK. Four plots were burned during autumn (mid-November) and four during spring (mid-April), and four served as nonburned controls for each of two years. Cattle were given unrestricted access (April-September) to burned patches (<2% of pastures) and utilization was about 78%. Wind erosion, soil water content, and soil temperature were measured monthly. Wind erosion varied by burn, year, and sampling height. Wind erosion was about 2 to 48 times greater on autumn-burned plots than nonburned plots during the dormant period (December-April). Growing-season (April-August) erosion was greatest during spring. Erosion of spring-burned sites was double that of nonburned sites both years. Growing-season erosion from autumn-burned sites was similar to nonburned sites except for one year with a dry April-May. Soil water content was unaffected by patch burn treatments. Soils of burned plots were 1 to 3 degrees C warmer than those of nonburned plots, based on mid-day measurements. Lower water holding and deep percolation capacity of sandy soils probably moderated effects on soil water content and soil temperature. Despite poor growing conditions following fire and heavy selective grazing of burned patches, no blowouts or drifts were observed.