Browsing by Author "Cox, Robert D. (TTU)"
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Item Airborne environmental DNA metabarcoding detects more diversity, with less sampling effort, than a traditional plant community survey(2021) Johnson, Mark D. (TTU); Fokar, Mohamed (TTU); Cox, Robert D. (TTU); Barnes, Matthew A. (TTU)Background: Airborne environmental DNA (eDNA) research is an emerging field that focuses on the detection of species from their genetic remnants in the air. The majority of studies into airborne eDNA of plants has until now either focused on single species detection, specifically only pollen, or human health impacts, with no previous studies surveying an entire plant community through metabarcoding. We therefore conducted an airborne eDNA metabarcoding survey and compared the results to a traditional plant community survey. Results: Over the course of a year, we conducted two traditional transect-based visual plant surveys alongside an airborne eDNA sampling campaign on a short-grass rangeland. We found that airborne eDNA detected more species than the traditional surveying method, although the types of species detected varied based on the method used. Airborne eDNA detected more grasses and forbs with less showy flowers, while the traditional method detected fewer grasses but also detected rarer forbs with large showy flowers. Additionally, we found the airborne eDNA metabarcoding survey required less sampling effort in terms of the time needed to conduct a survey and was able to detect more invasive species than the traditional method. Conclusions: Overall, we have demonstrated that airborne eDNA can act as a sensitive and efficient plant community surveying method. Airborne eDNA surveillance has the potential to revolutionize the way plant communities are monitored in general, track changes in plant communities due to climate change and disturbances, and assist with the monitoring of invasive and endangered species.Item Canopy detection beyond the field: Colored backgrounds impact precision of Canopeo(2023) Hale, Gabriella A. (TTU); Cox, Robert D. (TTU); Ritchie, Glen (TTU)The development of Canopeo as a close-range remote sensor for measuring ground cover fraction (GCF) offered farmers and scientists an accurate, simple, low-cost tool for monitoring health and development throughout the plant lifecycle. However, a significant obstacle to image-based monitoring of plant performance is the difficulty of object distinction between plant and background sharing similar colors. The overall goal of this research was to test Canopeo's sensitivity for detecting GCF when plants were imaged on different colored backgrounds in a greenhouse environment. We therefore tested Canopeo's ability to detect plant versus non-plant pixels in each image (resolution 72 × 72) using ten complex flat backgrounds. Multicolored backgrounds resembling flooring which may be found in a greenhouse setting (concrete, brick painted white, natural wood plank, and wood painted white with scuffs) resulted in least amount of deviation (<0.46) when analyzed with the control (flat black) background. Canopeo overestimated GCF of Viburnum sp. and E. pinnatum cv. on a green background which resulted in the greatest amount of deviation (>20). Canopeo demonstrated greatest underestimation GCF for Viburnum sp. and E. pinnatum cv. on a red background. When GCF of the green background was omitted, the r2 value of 0.75, or goodness of fit, suggest approximately 75% of the sampling variation can be described by the background color and not experimental error. Canopeo is an easily accessible tool for researchers and farmers to monitor plant growth and development on a diversity of backgrounds beyond soil and field settings.Item Identifying ecologically relevant scales of habitat selection: Diel habitat selection in elk: Diel(2017) Roberts, Caleb P. (TTU); Cain, James W.; Cox, Robert D. (TTU)Although organisms make resource selection decisions at multiple spatiotemporal scales, not all scales are ecologically relevant to any given organism. Ecological patterns and rhythms such as behavioral and climatic patterns may provide a consistent method for identifying ecologically relevant scales of habitat selection. Using elk (Cervus canadensis) as an example species, we sought to test the ability of behavioral patterns to empirically partition diel scales for modeling habitat selection. We used model selection to partition diel scales by shifts in dominant behavior and then used resource selection probability functions to model elk habitat selection hierarchically at diel scales within seasons. Model selection distinguished four diel temporal partitions following elk crepuscular behavioral patterns: dawn, midday, dusk, and night. Across seasons, model-averaged coefficients indicated that elk shifted from selecting grassland cover at dawn/dusk, to selecting for greater canopy and forest cover at midday, and then to areas with greater herbaceous biomass at night. Top models changed between diel intervals in spring and fall but stayed the same across diel intervals in winter and summer. In winter, elk selected for southern aspects during midday, for unburned areas at dawn/dusk, and for areas burned within 1-3 yr at dawn/dusk and night. In spring, elk selected for northern aspects and for areas burned within 1-3 yr at midday, for areas farther from roads at dawn/dusk and midday, and for areas farther from water at midday. In summer, elk changed diel preferences for fewer covariates: At dawn/dusk and midday, elk selected for areas farther from water and avoided forest cover, and at night, elk selected for areas burned within 1-3 yr. In fall, elk selected for areas burned the previous year at dawn/dusk and night, for higher elevations at midday, and for areas closer water at night. Using behavioral patterns to identify ecologically relevant scales can help identify overlooked habitat requirements such as diel changes in preference for fire history, forage availability, and cover. We show that the ecological relevancy of a given scale (e.g., a diel temporal scale) can change throughout a given extent (e.g., across seasons).Item Influence of landscape-scale variables on vegetation conversion to exotic annual grassland in southern California, USA(2014) Cox, Robert D. (TTU); Preston, Kristine L.; Johnson, Robert F.; Minnich, Richard A.; Allen, Edith B.In California, USA, coastal sage scrub (CSS) vegetation is being converted to exotic annual grassland, and several causes have been suggested. In order to investigate the importance of environmental variables in the conversion and recovery of CSS, particularly nitrogen deposition within the context of historical fire intervals, we employed an information theoretic approach. Prior studies have not assessed both conversion and recovery, and did not analyze nitrogen critical load for vegetation type conversion. We included measures of climate, topography, vegetation, land use, nitrogen deposition, and fire in our analysis, and found that 34% of CSS study sites were converted to exotic grassland between 1930 and 2009. Converted sites had higher nitrogen deposition with a critical load of 11 kg N ha-1 yr -1, also had shallower slopes, and were more west-facing. A smaller number of sites (24%) recovered to CSS, and these sites had about 2.5 times more CSS and 4.5 times less grassland in the surrounding landscape. CSS conservation and restoration efforts are most likely to be successful when focused on sites with <11.0 kg N ha-1 yr -1 and low invasion of exotic grasses. Analyses such as this that identify important threats may be useful in region-wide plans to conserve unique vegetation types.Item Interactive effects of severe drought and grazing on the life history cycle of a bioindicator species(2018) Fritts, Sarah Rebecah; Grisham, Blake A. (TTU); Cox, Robert D. (TTU); Boal, Clint W. (TTU); Haukos, David A.; McDaniel, Patricia; Hagen, Christian A.; Greene, Daniel U.We used the lesser prairie-chicken (Tympanuchus pallidicinctus), an iconic grouse species that exhibits a boom–bust life history strategy, on the Southern High Plains, USA, as a bioindicator of main and interactive effects of severe drought and grazing. This region experienced the worst drought on record in 2011. We surveyed lesser prairie-chicken leks (i.e., communal breeding grounds) across 12 years that represented 7 years before the 2011 drought (predrought) and 4 years during and following the 2011 drought (postdrought). Grazing was annually managed with the objective of achieving ≤50% utilization of aboveground vegetation biomass. We used lek (n = 49) count data and covariates of weather and managed grazing to: (a) estimate long-term lesser prairie-chicken abundance and compare abundance predrought and postdrought; (b) examine the influence of annual and seasonal drought (modified Palmer drought index), temperature, and precipitation on long-term lesser prairie-chicken survival and recruitment; and (c) assess and compare the influence of grazing on lesser prairie-chicken population predrought and postdrought. Lesser prairie-chicken abundance was nearly seven times greater predrought than postdrought, and population declines were attributed to decreased survival and recruitment. The number of days with temperature >90th percentile had the greatest effect, particularly on recruitment. The population exhibited a substantial bust during 2011 and 2012 without a boom to recover in four postdrought years. Adaptive grazing positively influenced the population predrought, but had no effects postdrought. Results suggest that the severe drought in 2011 may have been beyond the range of environmental conditions to which lesser prairie-chickens, and likely other species, have adapted. Land management practices, such as grazing, should remain adaptive to ensure potential negative influences to all species are avoided. Increasing habitat quantity and quality by reducing habitat loss and fragmentation likely will increase resiliency of the ecosystem and individual species.Item Opportunities for Biodiversity Conservation via Urban Ecosystem Regeneration(2024) Perry, Gad (TTU); Cox, Robert D. (TTU)Conservation traditionally focuses on at-risk species and relatively intact ecosystems. As the human population and our global impact have risen, many more species and ecosystems are at risk and fewer intact ecosystems remain, with urbanization being a major contributing factor. Cities and their inhabitants are here to stay, and the prevalence of urbanization, often in the vicinity of areas of high conservation value, requires reconsideration of the conservation value of urban ecosystems and urban green spaces. Our aim is to explore the practical aspects of such actions. Urban ecosystem regeneration will require the incorporation of strategies for urban ecosystem regeneration into an overall conservation policy. The novel paradigm of urban ecosystem regeneration, advocated here, maximizes the capacity of urban spaces to support biodiversity while reducing undesirable outcomes and enhancing human wellbeing. The potential for cities to exacerbate biological invasion, climate change, and other ecosystem-degrading factors requires particular attention in devising a strategy for conservation in urban spaces, made essential by the predicted further spread of cities across the globe.Item Smoke water and heat influence emergence of shortgrass prairie species(2017) Cox, Robert D. (TTU); Chou, Yi Fang (TTU); Wester, David B. (TTU)Exposure to smoke can influence the germination of seeds in many fire-prone ecosystems, but this effect is not well studied in grasslands. Smoke treatments such as smoke water could be useful as management and restoration tools if the response of target species in natural settings is well understood. We tested eight species native to the southern High Plains region in Texas, USA, that were already known to respond to smoke water in the laboratory, for their responses in a less controlled glasshouse environment. We exposed seeds to smoke water, heat, or a combination of the two, sowed them into greenhouse flats, and observed and recorded emergence. Emergence of nearly all species was influenced by smoke water, with most species experiencing either lower emergence or longer times for emergence when exposed to high-concentration smoke water. Smoke water exposure enhanced emergence of broom snakeweed (Gutierrezia sarothrae [DC.] A. Gray) seeds, with more than twice as many treated seeds emerging than untreated seeds (germination of control seeds = 26% ± 4.39% SE; germination of treated seeds = 69% ± 4.62% SE). Because many species displayed different results in the glasshouse as compared to the laboratory, smoke treatments should be tested in the field before being used on a larger scale. Doing so will allow a better understanding of how target species might respond to smoke treatments with more realistic soils, fluctuating temperatures, and other complications encountered in the field.Item Understanding Grass Invasion, Fire Severity, and Acacia koa Regeneration for Forest Restoration in Hawaiʻi Volcanoes National Park(2021) Hamilton, Natalia P. (TTU); Yelenik, Stephanie G.; Durboraw, Tara D. (TTU); Cox, Robert D. (TTU); Gill, Nathan S. (TTU)With invasive grasses increasing wildfire occurrence worldwide, a better understanding of the relationships between native plants, fire, and invasive grass is needed to help restoration plans facilitate ecosystem resilience. Invasive grasses are particularly problematic for altering fire regimes in the tropics, yet in Hawaiʻi, restoration sites are often planted with monocultures of the native tree Acacia koa, which can promote grass growth via nitrogen fixation. This, combined with the difficulty of estimating pre-fire grass cover under thick canopies, complicates attempts to restore Hawaiian ecosystems. We studied the 2018 Keauhou Ranch Fire in Hawaiʻi to investigate three questions: (1) at what level of precision can pre-fire grass cover be accurately estimated from oblique aerial photos? (2) how are post-fire A. koa regeneration densities affected by fire severity? and (3) how are post-fire A. koa regeneration densities affected by pre-fire grass cover and its interaction with fire severity? We collected burn severity and post-fire regeneration data from 30 transects stratified across mid-elevation woodland, montane woodland, and montane shrubland communities. We evaluated visual estimates of pre-fire grass cover from oblique aerial imagery with quantitative in situ data from 60 unburned transects of the same cover types. Pre-fire estimates of grass cover categories were 67% accurate in montane woodland (n = 9) and 100% accurate in montane shrubland (n = 11), but only 20% accurate in mid-elevation woodland (n = 10). In montane woodlands with low pre-fire tree densities, A. koa regeneration densities were higher with increased fire severity, but this trend reversed when pre-fire tree densities were high. We detected no effect of pre-fire grass cover, nor its interaction with fire severity, on A. koa regeneration density. This indicates that restoration through the planting of A. koa may be successful in promoting fire-resilient A. koa forest, although there are potential issues to consider regarding the effects that A. koa’s grass promotion may have on other species within the ecosystem.