Browsing by Author "Cofré, H"

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    Effects of habitat fragmentation on bird species in a relict temperate forest in semiarid Chile
    (2000) Cornelius, C; Cofré, H; Marquet, PA
    We analyzed the structure and composition of a bird assemblage in a fragmented relict temperate forest located in northcentral Chile (Fray Jorge National Park). In terms of species composition, the bird assemblage we found in Fray Jorge was more similar to southern temperate forest sites, located more than 1200 km south of Fray Jorge, than to localities found in nearby scrub habitats. The relict character and long-term isolation of the Fray Jorge forest provides a natural experiment with which to establish the potential long-term effects of fragmentation and isolation on southern Chilean temperate forests. Between May 1996 and March 1997, we conducted seasonal surveys of birds in six forest fragments, ranging in size from 0.5 to 22.5 ha, at Fray Jorge. The number of bird species at each forest fragment was positively correlated with fragment area during all seasons. The relict forest system had a steeper species-area slope than that reported for similar temperate-forest bird assemblages in forest fragments within Chiloe Island and for islands across the Chiloe Archipelago in southern Chile. In this regard, this bird fauna resembled a depauperate oceanic archipelago. This difference in area effects is likely a consequence of the minimization of rescue effects because of the absence of large source forest areas nearby and the long-term isolation of the system. In addition, the distribution of species among forest fragments in Fray Jorge was not random, showing a nested subset pattern. Thus, some species occur across all fragments, regardless of their area, and therefore are less affected by habitat fragmentation and less prone to local extinction. These results suggest that, for south-temperate forest birds, large fragments (or reserves) should afford better protection against extinction than small forest patches.
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    Large temporal and spatial scales in the structure of mammalian assemblages in South America
    (1999) Marquet, PA; Cofré, H
    We analyze the distribution of body masses for 701 species of South American terrestrial mammals at different spatial resolutions from continental to biome, to local habitat scales. Previous studies on North American mammals suggest that body size distributions are highly modal and right skewed at continental scales, but become more uniform as spatial scale decreases. We show, in general, that these patterns also hold for the body size distribution of South American terrestrial mammals. However, we also found some striking differences attributable to the history of this biota and related to the Great American Biotic Interchange (GABI). At continental scales the distribution of body masses for South American mammals is highly right skewed and possesses several modes. One mode corresponds to species derived from North American ancestors, while a second mode, towards larger size, is characteristic of the South American stock. The same pattern is apparent at biome and local habitat scales. We found support for the progressive flattening of the distributions as spatial scale decreases, but they do not become as flat (indistinguishable from log-uniform) as they do in North America. However, the pattern is stronger for species of South American origin. Our results indicate that there is a strong historical component affecting the macroecological structure of contemporary assemblages at different spatial scales. Body size distributions can provide valuable information on the ways biotas built up.