Collaborative Research: LTREB: Experimental determination of trophic dynamics and energy flows in a semiarid habitat in Chile.

University Of California-Davis, Davis CA

Investigators

Abstract

Long-term environmental research provides context that shorter-term efforts lack. Data collected over extended periods allows researchers to quantify the influence of fleeting or episodic factors that simply elude short-term efforts. This project started in 1989 as an experimental investigation of the importance of biotic interactions in a semiarid thorn scrub community in Bosque Fray Jorge National Park, Chile. While a role of predation was documented in early years, the overwhelming role of episodic rainfall (especially El Niño-associated rains) became clear in the first decade of work. Through the second and third decades the study focused on the relative role of biotic vs. abiotic influences, the role of invasive plans and rabbits, and the impact of extended drought conditions. Now the longest-running experimental field research program of its kind, this project has documented significant but limited effects of small mammal herbivory, and significant effects of invasive species and rainfall (and its absence) on populations of both plants and small mammals. The current research adds novel and sophisticated assessment of energy flow (from plants through consumers to predators) as a function of rainfall and hydrologic conditions, and advanced modeling of long-term population dynamics to identify mechanisms underlying changes in community stability observed in this highly variable system. Data collected at this site will be used to improve outreach efforts on the natural history and ecology of the National Park and the surrounding region, and will also be included in IsoCamp (isocamp.org), a two-week short course on stable isotope biogeochemistry and ecology for graduate students and postdoctoral researchers. This project is centered on 20 experimental grids (75x75 m) in which the following activities occur: (1) small mammals are sampled monthly (4 days/month); (2) cover by shrubs is measured every three months, and that of ephemeral plants monthly during the growing season; (3) soil samples are taken every 4 months to estimate seed density; and (4) fox scat and owl pellets are collected monthly from the site and nearby roosts to characterize their diets. Whereas exclusions of one small mammal herbivore (the degu) had limited effects, installation of all‐small mammal exclusions in 2002 demonstrated strong effects on several plant species. Superimposed on these effects were dramatic responses of plants, small mammals, and predators to increased precipitation during 8 El Niño/high rainfall events. North-central Chile has experienced severe drought conditions for over a decade, but forecasters predict more frequent and intense El Niño events, suggesting extreme temporal variation in abiotic conditions. This project will continue to track the interactive roles of environmental change and invasive species, but adds novel integration of stable isotopes, fecal DNA metabarcoding, and empirical dynamic modeling to better characterize how trophic structure is influenced by temporally varying energy flows. Key foci over the next 5 years include: (1) How are plants and small mammals influenced by the presence and abundance of invasive lagomorphs?; (2) How does variation in the availability of fast-growing ephemeral herbs and slow-growing perennial shrubs influence dietary breadth and niche partitioning among small mammals?; (3) Does omnivory facilitate individual- and population-level niche partitioning during boom-bust population cycles?; (4) How does multichannel energy flow and temporal variation in trophic structure affect small mammal community stability? These goals are being pursued through extensive collaboration with multiple investigators at multiple institutions in Chile and the United States. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.