![]() Because adaptations often are similar in geographically disjunct arid and semiarid communities, there are unusual opportunities for studying convergent properties among taxonomically unrelated organisms.Ĭonvergence among organisms in several geographically separated warm deserts was emphasized by Orians and Solbrig (1977). Inhabitants in such areas demonstrate a variety of adaptations to aridity, including water independence, novel metabolic and photosynthetic pathways, nocturnal activity, use of burrows or other thermal refuges, and summer torpor. Because intervals between ENSO events are long and responses are slow, long-term studies are essential for understanding such effects in semiarid or arid systems.Įnvironmental conditions in arid systems, including extremes in temperature, insolation, evapotranspiration, and precipitation, present unusual challenges for organisms. Therefore, we suggest that instead of exclusive top-down or bottom-up control, this system undergoes shifting control, with relatively greater importance of biotic interactions in wet years and of resource limitation in dry ones. ![]() However, periodic El Niño Southern Oscillation (ENSO) events caused several high rainfall episodes during this interval, resulting in large “bottom-up” increases in both plants and animals. We documented important “top-down” predation effects on some small-mammal species, and small-mammal effects on some plant species resulting from experimental exclusions. Using a large-scale field manipulation, we monitored changes in small mammals, plants, and vertebrate predators. For 13 years, we studied the role of biotic interactions, including predation, herbivory, and interspecific competition, in a semiarid thorn scrub community in north-central Chile.
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