Revista Chilena de Historia Natural 83 (1): 69-98, 2010
Long-term research in Bosque Fray Jorge National Park: Twenty years studying the role of
biotic and abiotic factors in a Chilean semiarid scrubland
Since 1989, we have conducted a large-scale ecological experiment in semiarid thorn
scrub of a national park in north-central Chile. Initially, we focused on the role of biotic interactions including predation, interspecific
competition, and herbivory in small mammal and plant components of the community. We utilized a reductionist approach with
replicated 0.56 ha fenced grids that selectively excluded vertebrate predators and/or larger small mammal herbivores such as the
degu, Octodon degus. Although we detected small transitory effects of predator exclusions on degu survival and numbers,
other species failed to show responses. Similarly, interspecific competition (i.e., degus with other small mammals) had no detectable
numerical effects (although some behavioral responses occurred), and degu-exclusions had relatively small effects on various plant
components. Modeling approaches indicate that abiotic factors play a determining role in the dynamics of principal small mammal
species such as O. degus and the leaf-eared mouse (Phyllotis darwini). In turn, these are mainly
related to aperiodic pulses of higher rainfall (usually during El Niño events) which trigger ephemeral plant growth; a food addition
experiment in 1997-2000 verified the importance of precipitation as a determinant of food availability. Since 2004, we have expanded
long-term monitoring efforts to other important community components including birds and insects in order to understand effects of
abiotic factors on them; we report some of the first results of comprehensive surveys on the former in this region. Finally, we recently
shifted focus to documenting effects of exotic lagomorphs in the park. We installed additional treatments selectively excluding small
mammals, lagomorphs, or both, from replicated grids in order to evaluate putative herbivore impacts. In conjunction with increased
annual rainfall since 2000, we predict that introduced lagomorphs will have increasing impacts in this region, and that more frequent El
Niños in conjunction with global climatic change may lead to marked changes in community dynamics. The importance of long-term
experimental studies is underscored by the fact that only now after 20 years of work are some patterns becoming
evident.
Key words:
birds, Chilean desert,
ephemeral plants, LTER, small mammals
