• Introduction
• Why?
• Questions
• Methodology I
• Methodology II
• Results
• Conclusions
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INTRODUCTION

Since 1989, a team of national and foreign investigators has been conducting a long-term ecological field experiment in the semiarid zone of this national park.

Distinct groups of organisms are being studied including: 1) small mammals (more than 10 species of rats and mice, and one marsupial); 2) vertebrate predators (foxes, raptorial birds, snakes and lizards); 3) plants (shrub and herbaceous ephemerals); 4) birds (small passerines and several endemic nonpasserines); and 5) insects. 

We are focusing on the role of biotic interactions among these groups as well as that of abiotic factors.  Although mean annual rainfall is 120-140 mm, rainfall has varied considerably between years; since 1989 there have been five separate El Niño/high rainfall events with precipitation up to 356 mm.  During La Niña years (e.g., 1998, 2007), rainfall is as low as 11 mm.