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Texas Tech University (TTU) 2018

The effects of land use and climate change on playa wetlands and their invertebrate communities

Starr, Scott McKinley

Titre : The effects of land use and climate change on playa wetlands and their invertebrate communities

Auteur : Starr, Scott McKinley

Université de soutenance : Texas Tech University (TTU)

Grade : Doctor of Philosophy (PhD) 2018

Résumé
Climate and land-use changes are the primary threats to playa wetlands and their invertebrate communities. Playas are ephemeral, depressional wetlands that are the primary form of surface water in the Southern High Plains of North America, an area that has experienced recent land-use changes that may affect playas. I used remotely sensed imagery to assess changes in land use in five categories (agriculture, rangeland/grassland, fallow, developed, and water) and playa inundation in Texas on six dates during the late growing season over 23 years. A decrease in the number of wet playas was observed over that span, and significant differences among land uses were found between and within years around dry and wet playas. Mean patch size and overall area of rangeland/grassland increased over time, possibly due in part to conservation efforts in the area. Other land-use types consequently decreased, but agriculture remained one of the dominant land-use types throughout. Because playas are crucial habitats, these changes have likely affected regional biodiversity. Playa-associated biodiversity is largely comprised of birds, amphibians, and invertebrates. The Familiar Bluet (Hexapoda : Odonata, Coenagrionidae, Enallagma civile) was selected as a model organism to study the effects of environmental changes on playa invertebrates. Odonates are good model organisms to study ecological and evolutionary concepts because of their amphibious life history, which makes them sensitive to both aquatic and terrestrial environmental changes. Enallagma civile is a habitat generalist with a widespread distribution throughout the New World that has been underutilized in research. I summarized its life history and described lab husbandry techniques in an overview of the species as a potential model organism for studies on environmental subjects like climate change effects on elevated water temperature. Current climate change predictions estimate increased air temperatures across the Southern High Plains, putting many organisms at risk from environmental changes affecting nymph and adult life stages. Increased air temperatures can lead to elevated water temperatures, but experiments are lacking on responses in terms of development or survival. Enallagma civile was used to examine these effects. Eggs were collected and reared under four water temperature regimes (26, 32, 38, and 41°C). Nymph body measurements after molts, development rate, and deaths were recorded daily. Nymphs in the two hotter treatments were smaller and had lower survivorship whereas individuals in the cooler temperatures generally survived to adulthood and were larger. Individuals reared at 32°C emerged the quickest, going from egg to adult in 26 days. Elevated temperatures can thus be both advantageous and detrimental, causing concern for aquatic invertebrates in the future. In conclusion, these studies have demonstrated how land-use and climate changes are threats to playa wetlands and biota. With rangeland/grassland increasing over time, the frequency of playa wetland inundation may continue to decrease due to interactions between land use and overland water flow during precipitation events. With decreases in playa inundation frequencies and effects of climate change, playa invertebrate communities are threatened due to infrequent standing water and elevated water temperatures. By understanding how land-use and projected climate changes are currently effecting playa wetlands, it will allow for better comprehension and management of current and future alterations.

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Page publiée le 10 novembre 2018