Matching Items (3)
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- All Subjects: Plant litter
- Creators: Ball, Becky
Description
Due to the nature of animals, even domesticated pets, animal scavenging of human remains is an important taphonomic factor. This area of study has, however, been undercounted in the current literature. The purpose of this study was to begin the first step in creating a taphonomic profile for urban / household animal scavenging as distinguishable from manmade tool marks. Using volunteered animals and regularly available tools, alterations were made on beef ribs in order to characterize the distinguishing profiles between the two groups. It was found that animal scavenging alterations, in the short term (20 minutes used in this study) have a distinctly different appearance than tool mark alterations. Animal scavenging has less visible alterations, consistent bite morphology across different species, and symmetrical cut marks along the midsection of the long bones. Ultimately, this study was a successful first step in furthering taphonomic alteration database research across various biomes and conditions.
ContributorsLittle, Cody Lee (Author) / Kobojek, Kimberly (Thesis director) / Falsetti, Anthony (Committee member) / Ball, Becky (Committee member) / School of Human Evolution and Social Change (Contributor) / School of Mathematical and Natural Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Arid and semiarid ecosystems (known as drylands) cover 45% of global land area and are predicted to expand to encompass half of the world’s land area by the end of the century. Litter decomposition plays a large role in nutrient and carbon cycling in dryland ecosystems, yet it remains poorly understood. Models that accurately predict decomposition in mesic ecosystems fail to accurately describe decomposition in drylands due to differing drivers of decomposition but also because litter in drylands accumulates around litter retention elements (LREs). LREs can be any object or surface that inhibits the movement vectors (e.g., wind) that push litter across drylands, creating a “pool” of litter around the LRE. Litter pooling increases the amount of mixing between litter and soil, creating a microclimate more conducive to microbial decomposition. Due to the increase in microbial decomposition, the decomposition rate for litter around LREs can be markedly different than that of litter not in LREs. To further understand how much litter accumulates in LREs, I studied the differences in litter accumulation between LREs and open areas in five drylands across the Southwestern United States. To do this, I visually analyzed photos of 424 litterbags to determine the cover percentages of four different types of organic litter (grass, broadleaf, reproductive, woody) and rock litter. Visual analysis of litterbags consisted of manually delineating the percent coverage of each of these litter categories. Litterbags had been placed in both open intercanopy areas as well as woody sub-canopy areas in which the plant canopy acted as the LRE. Additionally, 45 of these litterbags were randomly selected for analysis in the computer program FIJI (FIJI is Just ImageJ) to assess the litter area find the percent difference between visual and digital analysis. Areas underneath woody sub-canopies accumulated far more organic matter litter over time than open areas between canopies did but displayed a similar amount of rock litterbag cover. Shrub microsites also displayed far more varied litterbag cover percentages than open microsites. Data also suggested that litter does not always accumulate underneath shrubs or open intercanopy areas and may dissipate as time progresses. These results support the idea that litter accumulation varies throughout drylands, and that soil and litter mix frequently in LREs such as under woody plant canopies. The percent difference between FIJI analysis and visual analysis was generally negative, reflecting that visual estimation of litterbag cover was typically smaller than digital estimates. Cumulatively, litter was shown to accumulate much more around LREs and even move from them – supporting the idea that litter decomposition models need to account for litter movement in drylands to be accurate.
ContributorsNelson, Benjamin (Author) / Throop, Heather (Thesis director) / Ball, Becky (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2022-05
Description
Decay of plant litter represents an enormous pathway for carbon (C) into the atmosphere but our understanding of the mechanisms driving this process is particularly limited in drylands. While microbes are a dominant driver of litter decay in most ecosystems, their significance in drylands is not well understood and abiotic drivers such as photodegradation are commonly perceived to be more important. I assessed the significance of microbes to the decay of plant litter in the Sonoran Desert. I found that the variation in decay among 16 leaf litter types was correlated with microbial respiration rates (i.e. CO2 emission) from litter, and rates were strongly correlated with water-vapor sorption rates of litter. Water-vapor sorption during high-humidity periods activates microbes and subsequent respiration appears to be a significant decay mechanism. I also found that exposure to sunlight accelerated litter decay (i.e. photodegradation) and enhanced subsequent respiration rates of litter. The abundance of bacteria (but not fungi) on the surface of litter exposed to sunlight was strongly correlated with respiration rates, as well as litter decay, implying that exposure to sunlight facilitated activity of surface bacteria which were responsible for faster decay. I also assessed the response of respiration to temperature and moisture content (MC) of litter, as well as the relationship between relative humidity and MC. There was a peak in respiration rates between 35-40oC, and, unexpectedly, rates increased from 55 to 70oC with the highest peak at 70oC, suggesting the presence of thermophilic microbes or heat-tolerant enzymes. Respiration rates increased exponentially with MC, and MC was strongly correlated with relative humidity. I used these relationships, along with litter microclimate and C loss data to estimate the contribution of this pathway to litter C loss over 34 months. Respiration was responsible for 24% of the total C lost from litter – this represents a substantial pathway for C loss, over twice as large as the combination of thermal and photochemical abiotic emission. My findings elucidate two mechanisms that explain why microbial drivers were more significant than commonly assumed: activation of microbes via water-vapor sorption and high respiration rates at high temperatures.
ContributorsTomes, Alexander (Author) / Day, Thomas (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Ball, Becky (Committee member) / Hall, Sharon (Committee member) / Roberson, Robert (Committee member) / Arizona State University (Publisher)
Created2020