Filling the gaps: A comprehensive understanding of diets and ecosystem interactions within the modern and fossil small mammal communities of Meade Basin, Kansas

The modern Great Plains ecosystem began shifting from a woodland biome to a grassland in the Miocene. Stable isotope analysis (SIA) of a diverse community of local consumers, in this case small mammals, provides both a paleoenvironmental record of the shift from woodland C3 biomass to grassland C4 biomass, and a paleoecological record of species interactions and community dynamics. The Meade Basin in southwestern Kansas contains a rich and fairly complete fossil record of a Great Plains small mammal community throughout the past 5 million years. SIA of fossil tooth enamel from Meade small mammals has revealed interesting dietary patterns among, and within, major lineages of rodents and lagomorphs. Yet, an incomplete understanding of ecosystem interactions in the modern small mammal community hinders our interpretation of these fossil isotopic datasets. Until now, the majority of the modern Meade dataset was derived from 5 years of live trapping across a range of prairie microhabitats, and this sample is inherently biased towards small bodied and nocturnal species. The goal of this project is to fill taxonomic gaps in the modern sample, and provide a complete interpretation of current small mammal dietary ecology that is directly comparable to the fossil data. Our samples are derived from biologic (owl pellets, raptor nests and prairie dog burrows), and anthropogenic (road kill) collections, which contain remains of previously under sampled taxa within the small mammal community. Preliminary results have already highlighted the importance of this work. For example, prairie dogs are the highest C4 grass consumers in the modern community, and without them we would underestimate the use of C4 resources by small mammals. As another example, rabbits have predominantly been mixed C3-C4 to strongly C3 plant consumers throughout the past 5 million years, and that diet appears to be maintained today. Our complete isotopic dataset consists of results for more than 50 specimens, and yields a comprehensive understanding of species and ecosystem interactions among small mammals in the Great Plains today

Comparing 40-year sediment records of aquatic ecosystem evolution in two large lakes in the blast zone of Mount St. Helens

The 1980 eruption of Mount St. Helens dramatically altered the surrounding landscape, removing vegetation and impacting hydrology. The pyroclastic debris flow partially filled Spirit Lake and dammed Coldwater Creek, creating Coldwater Lake. Spirit Lake was sterilized by the eruption, and fallen trees from the blast washed into the lake forming a floating log mat covering 20% of the surface. While significant research has gone into understanding the history of ecosystem recovery in Spirit Lake, nearby Coldwater Lake has not been studied as extensively. These two lakes provide a unique opportunity to study how volcanic eruptions alter freshwater environments. Recent research at Spirit Lake has focused on spatial heterogeneity in the post-eruption lake ecosystem related to patterns of log mat coverage, and our current work at Coldwater Lake provides an important point of comparison in a lake without the influence of woody debris. In order to study the evolution of the Coldwater Lake ecosystem, we collected four sediment cores (~30 centimeters each), extruded and sectioned the cores, and analyzed diatom abundance and diversity, and carbon and nitrogen biogeochemistry through time. These sediment records reflect changes in lake conditions, such as water chemistry, and in aquatic ecology. Our data show a substantial increase in diatom abundance and diversity through time, with highest levels in the top 15 centimeters of the cores. The percent carbon and nitrogen also increases in younger core sediments. Coldwater Lake displays some spatial variability in diatom abundance between deeper and shallower locations in the lake, but benthic taxa are dominant across the lake. Coldwater Lake has a lower ratio of pelagic to benthic diatom taxa than Spirit Lake, implying that Coldwater Lake is more nutrient poor. The differences between the two lakes can likely be mainly explained by the differences in their geologic formations, and both have come to ecological equilibrium

Termites Create Spatial Structure And Govern Ecosystem Function By Affecting N-2 Fixation In An East African Savanna

The mechanisms by which even the clearest of keystone or dominant species exert community-wide effects are only partially understood in most ecosystems. This is especially true when a species or guild influences community-wide interactions via changes in the abiotic landscape. Using stable isotope analyses, we show that subterranean termites in an East African savanna strongly influence a key ecosystem process: atmospheric nitrogen fixation by a monodominant tree species and its bacterial symbionts. Specifically, we applied the N-15 natural abundance method in combination with other biogeochemical analyses to assess levels of nitrogen fixation by Acacia drepanolobium and its effects on co-occurring grasses and forbs in areas near and far from mounds and where ungulates were or were not excluded. We find that termites exert far stronger effects than do herbivores on nitrogen fixation. The percentage of nitrogen derived from fixation in Acacia drepanolobium trees is higher (55-80%) away from mounds vs. near mounds (40-50%). Mound soils have higher levels of plant available nitrogen, and Acacia drepanolobium may preferentially utilize soil-based nitrogen sources in lieu of fixed nitrogen when these sources are readily available near termite mounds. At the scale of the landscape, our models predict that termite/soil derived nitrogen sources influence \u3e50% of the Acacia drepanolobium trees in our system. Further, the spatial extent of these effects combine with the spacing of termite mounds to create highly regular patterning in nitrogen fixation rates, resulting in marked habitat heterogeneity in an otherwise uniform landscape. In summary, we show that termite-associated effects on nitrogen processes are not only stronger than those of more apparent large herbivores in the same system, but also occur in a highly regular spatial pattern, potentially adding to their importance as drivers of community and ecosystem structure

Probabilistic patterns of interaction: the effects of link-strength variability on food web structure

Patterns of species interactions affect the dynamics of food webs. An important component of species interactions that is rarely considered with respect to food webs is the strengths of interactions, which may affect both structure and dynamics. In natural systems, these strengths are variable, and can be quantified as probability distributions. We examined how variation in strengths of interactions can be described hierarchically, and how this variation impacts the structure of species interactions in predator-prey networks, both of which are important components of ecological food webs. The stable isotope ratios of predator and prey species may be particularly useful for quantifying this variability, and we show how these data can be used to build probabilistic predator-prey networks. Moreover, the distribution of variation in strengths among interactions can be estimated from a limited number of observations. This distribution informs network structure, especially the key role of dietary specialization, which may be useful for predicting structural properties in systems that are difficult to observe. Finally, using three mammalian predator-prey networks ( two African and one Canadian) quantified from stable isotope data, we show that exclusion of link-strength variability results in biased estimates of nestedness and modularity within food webs, whereas the inclusion of body size constraints only marginally increases the predictive accuracy of the isotope-based network. We find that modularity is the consequence of strong link-strengths in both African systems, while nestedness is not significantly present in any of the three predator-prey networks.Institute of Geophysics and Planetary PhysicsInstitute of Geophysics and Planetary PhysicsUC-Santa Cruz Committee-On-ResearchUCSanta Cruz CommitteeOnResearchNational Science Foundation Graduate Student Fellowship (NSFGRF)National Science Foundation Graduate Student Fellowship (NSF-GRF)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP

Diets of coastal and inland Western Fence Lizard populations in Washington State

The Western Fence Lizard (Sceloporus occidentalis) is a species of spiny lizard with a large range across western North America and has a generalist insectivorous diet. There are often behavioral and morphological variations between S. occidentalis populations, which can be influenced by local climate and habitat, as well as by diet (such as trophic level). Using a stable isotope analysis approach, our study examines the role of marine derived nutrients in S. occidentalis populations at an inland, coastal forest and beach habitat study site in Washington State. Beach lizards on the Puget Sound had variable and significantly greater δ15N values than the other populations, suggesting they feed on marine prey with individuals sourcing between 10-50% of their diet from marine sources. The similar δ15N values of coastal forest and inland lizards suggest they feed on similar trophic levels, and that coastal forest lizards do not rely on marine prey despite the population\u27s proximity to the beach (~1000 m). Spatial subsidies across ecosystem boundaries have important impacts on species interactions and food web dynamics. Our study documents a unique spatial subsidy in which marine nutrients and energy from the Puget Sound ecosystem enter the terrestrial food web via beach dwelling Western Fence Lizards. Because of this important energy exchange, changes to marine ecosystems can have consequences for Puget Sound lizard populations by influencing nutrient and energy flow via prey availability