Biology (Bryn Mawr)

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Now showing 1 - 5 of 6
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    Spatially Explicit Disturbance Histories of Forested Sites Within the National Ecological Observatory Network
    (2022) Olivares-Mejia, Samantha; Record, Sydne
    Land use and disturbance history play a large role in understanding our environment as they can have long lasting effects on composition of modern ecosystems. This research aims to collate land use and disturbance histories for forested sites within the National Ecological Observatory Network (NEON). Although the network has standardized monitoring techniques for sites across the country, it does not have any spatially explicit data on disturbance history. This research intends to bridge this knowledge gap to enhance the context of ecological analyses based on NEON data. A total of 59 data products were created for 75% of the forested NEON sites, 80% of which depict disturbance history and 20% depicting land cover information. This research highlights the importance of open data, proper data management practices, and collection of spatially explicit disturbance data to be a routine part of the land management process.
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    Acclimation to Drought and Cold Stress in Holly (Ilex): Evergreen Tolerance and Deciduous Escape
    (2022) Northing, Poppy C.; Grossman, Jake J.
    Exploration of the differences between physiological adjustment in evergreen and deciduous trees can help us gain a better understanding of how temperate ecosystems will fare under anthropogenic climate change. I compared foliar osmotic adjustment and stomatal conductance of a deciduous and an evergreen species of Ilex over the growing and dormant season in order to explore differential adjustment strategies with respect to leaf habit. I found that the hollies showed distinct drought tolerance across the year and utilized different methods of managing winter water stress consistent with their respective leaf habits. Evergreen I. opaca demonstrated osmotic adjustment throughout the growing season and into the dormant season while maintaining stable rates of gas exchange. In contrast, deciduous I. verticillata showed osmotic adjustment only during the growing season, then ceased adjustment once the dormant season arrived. Instead, I. verticillata protects itself from cold, dry winter conditions through down-regulation of gas exchange in conjunction with leaf color change and senescence. These results confirm our hypotheses that evergreen and deciduous species regulate themselves differently, and highlight the differences in the impacts that climate change will have on temperate trees based on their leaf habit.
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    T. H. Morgan, Nettie M. Stevens, and the Trouble with Aphids
    (2022) Johnson, Claire; Davis, Gregory K. (Biologist)
    When one considers the greatest discoveries in the history of biology, one is naturally drawn to think of well-known model organisms, such as mice or Drosophila melanogaster, which have been the backbone for most contemporary discoveries. Yet, along the way, there have been many other organisms—marine and terrestrial—that have bolstered our understanding of genotype-by- environment interactions (called polyphenisms) and organismal development. Aphids are one of these organisms. Aphids are particularly interesting for their cyclically parthenogenetic lifecycle: phases of female-only asexual reproduction in spring and summer, and male and female sexual reproduction in winter. It appeared to many that the determination of sex was due to environmental factors such as temperature or nutritional supply. Thomas Hunt Morgan, Chair of Biology at Bryn Mawr College from 1891-1904, chose to study aphids and their close relatives because he thought they would provide evidence in his favor in a long-standing conflict regarding the chromosomal theory of sex determination to which he was opposed, instead believing that the cytoplasm was at the heart of heredity and development. In 1905, he encouraged his former Ph.D. student at Bryn Mawr, Nettie M. Stevens, to study aphid development—specifically, the production of males, asexual females, and sexual females. In 1906, Morgan studied the development of a close relative of aphids, phylloxerans. Both he and Stevens committed the same crucial oversight. What had been overlooked and how? The complex lifecycle and biology of aphids may be the culprit. In 1908 and 1909, respectively, Morgan and Stevens—prompted by the former—revisited their own previous works and corrected their oversights. The back-and-forth communication between Morgan and Stevens during their studies of phylloxerans and aphids, respectively, arguably primed Morgan to be able to accurately apply the concept of sex linkage to his discovery of the famous mutant, white-eyed fly. He came to accept the truth of the chromosomal theory of sex determination in Drosophila, the very theory he had vigorously opposed.
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    Everything but the carbon sink: Cessation of N enrichment allows for rapid recovery of carbon cycling processes in a New England salt marsh
    (2019) Drew, Sophia E.; Mozdzer, Thomas J.
    Salt marshes provide critical ecosystem services, including storm protection, water filtration, wildlife habitat, and carbon sequestration. Nutrient pollution poses a major threat to these ecosystems as runoff from agricultural fields and wastewater systems delivers high loads of nitrogen and other nutrients. Several studies have shown that N enrichment alters carbon cycling processes in salt marshes, but there has been little work done to determine the capacity for recovery with reduction of N loading. Here we found that ecosystem respiration and decomposition processes returned to reference levels one year after cessation of nitrate addition in a chronically enriched Massachusetts salt marsh. Our results suggest that land management practices that reduce N loading in coastal systems may allow for rapid recovery of carbon cycling processes in enriched marshes.
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    Ground-Dwelling Macroinvertebrate Biodiversity as a Determinant of Forest Health in Morris Woods
    (2016) Fleet, Caroline; Record, Sydne
    The edge effect is a phenomenon that occurs when two or more ecosystems overlap to form a ‘border’ environment that is ecologically different from the surrounding biome. The nature and magnitude of the edge effect can be elucidated through direct examination of a myriad of environmental and biotic factors, including macroinvertebrate diversity, soil temperature, and canopy coverage. Extensive pitfall trapping, canopy coverage assays, and soil temperature probing were conducted in interior and edge plots in Morris Woods, a relatively small temperate forest in suburban SE Pennsylvania. No significant differences appeared to manifest within measurements of soil temperature (Tinterior = 15.63 oC; Tedge = 16.23 oC; 2-­‐tailed SEM1, p > 0.05) and canopy coverage (Cinterior = 91.64%; Cedge = 88.31%; 2-­‐tailed SEM, p > 0.05) between the edge and interior plots, though observable differences in macroinvertebrate abundance (Ninterior = 179; Nedge = 262), species richness (Rinterior = 2.127; Redge = 1.259), and species diversity (Dinterior = 0.5864 ; Dedge = 0.4151) were evident. Results also indicated that the interior plot supports more macroinvertebrate taxa and more environmentally sensitive taxa than the edge plot, indicating that that the interior plot likely exhibits higher niche richness, though the factors of soil temperature and canopy coverage did not appear to account for these differences.