TAMU-CC Theses, Dissertations, and Other Projects
Permanent URI for this communityhttps://hdl.handle.net/1969.6/1
Find theses, dissertations, and other projects completed by students of Texas A&M University-Corpus Christi. Associated files for theses, dissertations, and other projects, such as data sets and Honors Projects of Excellence, can also be found within this community.
Browse
Browsing TAMU-CC Theses, Dissertations, and Other Projects by Department "Biology"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Black mangrove recovery from freeze disturbance accelerated by nutrient enrichment(2023-05) Carr, Caleb Cappiello; Proffitt, C. Edward; Devlin, Donna; Withers, Kim; McCracken, ShawnDue to climate change, mild winters and fewer extreme freeze events at the temperate-tropical transition zone are allowing some species to migrate poleward, causing shifts in species dominance. In coastal Texas and some other sections of the GOM, woody encroachment by mangrove shrubs and trees into low latitude salt marsh leads to reduced salt marsh dominance likely through competition for light. A recent catastrophic (i.e., mangrove-killing) freeze event in Texas influenced the present regime shift by causing extensive mortality of mature, sapling, and seedling mangroves, alleviating salt marsh vegetation from competition for light. A key topic for study is assessing rate and extent of mangrove recovery following the freeze as a crucial factor impacting the direction, timing, and extent of the regime shift. Additionally, anthropogenic fertilization is predicted to increase and enrich estuaries and bays, resulting in various consequences, such as increased mangrove colonization and dominance, adding another potential impetus to the regime shift. To better understand how nutrient enrichment affects recovery following a catastrophic freeze, fertilization plots were used in a field experiment to ascertain how nitrogen (N) and phosphorus (P) affect black mangrove survival and growth, as well as, changes in the salt marsh vegetation. Other observational sites, with different high and low nutrient conditions, were employed to identify how the findings from the fertilization experiment translate to a larger scale and expand the inference space of the study. Results indicate that nutrient enrichment increased above-ground growth and reproductive output of mangroves, thus enhancing population recovery. Salt marsh species (mainly Batis maritima) reduced growth of mangrove seedlings via inferred competition, although marsh plants did not respond to fertilizer treatments with enhanced above-ground growth. Rather salt marsh was influenced by elevation and shading by mangrove canopy. The findings suggest that nutrient enrichment alters wetland plant dynamics and accelerates a regime shift from a salt marsh to a mangrove-dominated ecosystem, depending on the frequency and magnitude of future freeze events that can reset succession.Item Evaluating the use of drones for monitoring waterbird nest abundance and nest survival(2022-12) Mirzadi, Rostam; Gawlik, Dale; Stunz, Greg; Starek, MichaelSurveys of colonial waterbirds are used to monitor species’ population dynamics, contaminant levels, and to derive metrics that can be used to assess wetland ecosystem restoration and management. Previous studies have found that drone surveys provide accurate estimates of nest abundance and survival for ground-nesting waterbird species such as terns (Laridae Spp.), but drones have not been used to estimate survival for waterbirds nesting in a canopied marsh habitat, and potential sources of bias in drone surveys have not been examined in depth. We examined potential visibility biases associated with using a drone to survey colonies of wading birds (Ciconiiformes and Pelecaniformes) in marsh habitat in Florida in 2020 and 2021. Monthly nest counts and survival were compared between traditional (combination of fixed-wing aircraft and ground surveys) and drone survey methods. Ground-based and drone nest transect surveys were conducted to estimate survival and detection probabilities of each species and plumage color. Generalized linear mixed-effects models were used to quantify the degree to which visual occlusion of nests in?uenced detectability. Estimates of white-colored waterbird nests were significantly greater for drone surveys than those derived from traditional survey methods but estimates of dark-colored waterbirds from drone surveys were biased low. Variation in detection was best explained by canopy cover, plumage color, and nest stage. Overall, there was no difference between survival estimates from either method. However, drone-derived estimates of dark-colored waterbirds had lower accuracy. Our results suggest that drone surveys are a viable method to conduct monthly nest surveys and estimate survival of waterbirds breeding in marsh habitat, but researchers should consider their study area and species before choosing a survey method.