Global climate change and biotic-abiotic interactions in the northern Chilean semiarid zone: potential long-term consequences of increased El Niños

P.L. MESERVE; J.R. GUTIÉRREZ; D.A. KELT; M.A. PREVITALI; A. ENGILIS, JR.; W.B. MILSTEAD

Ocean circulation and El Niño: new research

Nova Science Publishers, Inc.

Lugar: Hauppauge, NY; Año: 2009; p. 139 - 162

Global climate change (GCC) has become a major focus in ecology as ramifications of environmental alteration grow increasingly evident. Although dispute remains about linkages, increased frequency, duration, and magnitude of El Niño events are a predicted consequence of GCC. In western South America, increased rainfall tends to occur during El Niño Southern Oscillation (ENSO) warm phases especially in semiarid zones of northwest Peru and north-central Chile; conversely, low rainfall occurs in other arid regions such as Australia and southern Africa. The implications of such changes for semiarid regions are multiple and complex. For example, increased rainfall leads to dramatic changes in ephemeral plant cover; however, in multiyear El Niño/high rainfall events, ephemeral cover often decreases in subsequent years, suggesting nutrient depletion. Many other organismal groups increase dramatically following El Niños, including small mammals, their predators, birds, and other components. The responses appear due to cascading-upwards effects of rainfall on productivity in regions which historically have been arid. A similar pattern holds for plant and animal groups elsewhere when unusually high rainfall occurs during El Niño years (e.g., North America). During ENSO cool (dry) phases (i.e., La Niña events), rainfall declines dramatically in the same regions with consequential negative effects on ephemeral plants and animals. In 1989, we initiated a large-scale manipulation in a national park in the north-central Chilean semiarid zone. Based on earlier work, we focused our attention on the role of biotic interactions in the community, specifically vertebrate predation, small mammal herbivory, and interspecific competition among members of the small mammal assemblage. Although we have documented some transitory effects of excluding vertebrate predators and small mammal herbivores from fenced, replicated live-trapping grids on small mammals and plants, respectively (e.g., “top-down” control), their responses to increased precipitation have been overwhelming, strongly implicating overall “bottom-up” control. In the last 19 years, five El Niño/ high rainfall events, differing in duration and intensity, have generated variable responses by plants, small mammals, birds, and insects. Potential consequences of increased duration and frequency of El Niños in the Chilean semiarid zone include changes in community dynamics, and greater impacts of introduced species as well as disease vectors and reservoirs.