Long-term research in Bosque Fray Jorge National Park: Twenty years studying the role of biotic and abiotic factors in a Chilean semiarid scrubland

Abstract

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.

Agricultural landscapes as habitat for birds in central Chile

“…Temperate agroecosystems follow seasonal abiotic variations that may influence wildlife communities due to the availability of food resources [24,25]. In the Himalayas, Elsen et al [26] demonstrated the importance of low intensity agriculture (small farms with diverse annual crops, orchards and small woodlots) for increasing abundance of forest birds during winter.…”

Estudios socio-ecológicos de largo plazo en los sitios fundadores de la red LTSER-Chile: desafíos y oportunidades para el futuro

“…El énfasis que se ha dado a la investigación de largo plazo en cada sitio refleja esta diversidad, como se constata en las tres síntesis de las investigaciones publicadas recientemente (Rozzi et al 2006, Carmona et al 2010, Gutiérrez et al 2010. En su primera etapa de existencia, no obstante la institucionalidad adquirida por la red LTSER-Chile, la diversidad de enfoques ha marcado la aproximación de estudios a largo plazo en cada sitio.…”

“…Los resultados de este estudio han permitido detectar el rol clave de la variación interanual en las precipitaciones, lo cual contradice la hipótesis inicial que postulaba a las interacciones bióticas como elementos moduladores en la dinámica de estas comunidades. Es esencial notar que luego de 26 años de estudio, muchas de las hipótesis y percepciones iniciales acerca de la estructura y dinámica de este sistema semiárido de Chile, no solamente cambiaron, sino que requirieron modificaciones en la aproximación experimental y en el monitoreo (Gutiérrez et al 2010). Este experimento ha cambiado a lo largo del tiempo bajo un enfoque de monitoreo adaptativo (Lindenmayer y Likens 2009).…”

“…En el PNFJ el monitoreo establecido en el experimento de exclusión de herbívoros y carnívoros (ver sección Parque Nacional Bosque Fray Jorge) se ha complementado con estudios experimentales de corto plazo (Gutiérrez et al 2010). Por otro lado, dada la importancia de la neblina en el mantenimiento del bosque relicto de PNFJ (Del Val et al 2006), se ha refinado la escala temporal y espacial de las mediciones de neblina.…”

“…Durante el primer quinquenio de existencia de la LTSER-Chile, esta complementariedad favoreció la creatividad para establecer estudios ecosistémicos pioneros en la evaluación de procesos bióticos y abióticos (Gutiérrez et al 2010, Carmona et al 2010, y en la integración transdisciplinaria de la ética ambiental (Rozzi et al 2013).…”