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University of New Mexico (2018)

Seasonal Shifts in C3 and C4 Resource Use by a Small Mammal Community Under Changing Precipitation Regimes

Pershall Alaina D.

Titre : Seasonal Shifts in C3 and C4 Resource Use by a Small Mammal Community Under Changing Precipitation Regimes

Auteur : Pershall Alaina D.

Université de soutenance : University of New Mexico

Grade : Master of Science (MS) Biology 2018

Résumé
In light of climate change and projections of increasing temperatures and aridity in the North American southwest, it is essential to understand how consumer populations will respond to changes in the resource landscape. Rainfall varies in timing and intensity and therefore the timing, proportion, phenology, and abundance of C3 and C4 plant resources vary seasonally and annually. Here we examine rodent resource use in the Chihuahuan desert and focus on two distinct precipitation pulses in this system, where spring C3 plants increase production in response to winter rains and C4 plants respond to summer monsoons. We used the distinct carbon isotope ratios of the C3 and C4 plant photosynthetic types to quantify resource use and diet breadth by measuring δ13C in blood plasma and assessed relative trophic level by measuring δ15N. We compared resource use across three years with different precipitation regimes and C3 and C4 abundances. We observed a generally increasing use of C4 derived carbon, as C4 vegetation became more available and C3 decreased. However, diets were generally composed of a greater proportion of C3 derived carbon. Heteromyid rodents exhibited a greater overall reliance on C3 resources. When C3 resources were not available, we observed a division of resources among heteromyids, and the cricetid rodents maintained generally greater than 50% C4 use and higher peaks in C4 use. We observed a community wide shift to C3 resources when abundant, even in the presence of abundant C4 resources. Diet breadth was most constrained and dietary overlap was greatest when C3 plants were abundant and highly utilized. Onychomys arenicola, the most insectivorous species, showed the least variation in C3/C4 usage, greater reliance on C4 resources, and smallest diet breadth. In general, trophic level increases coincided with increased use of C4. Because of differences in physiology, C4 plants may outcompete important C3 plants under warmer drier conditions, changing the physical structure of the community and decreasing the nutritional quality and abundance of food resources. This could have a significant impact on consumer population size, species diversity, and competition in small mammals, which could have implications throughout the food chain.

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Page publiée le 6 novembre 2018