DSpace Angular :: Browsing by Author "Marquet, PA"

Browsing by Author "Marquet, PA"

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Conservation of temperate forest birds in Chile
(2002) Reid, S; Cornelius, C; Barbosa, O; Meynard, C; Silva-García, C; Marquet, PA
We characterize the bird assemblage of an isolated relict temperate rainforest (Santa Ines) in terms of its structure, composition and dynamics. The relict character and long-term isolation of this forest remnant, immersed in a matrix of semiarid scrub, provide a natural experiment to assess the consequences of long-term isolation and forest area reduction for temperate bird species. Bird surveys were conducted in a forest fragment and the surrounding scrub matrix between April 1999 (austral autumn) and October 2000 (austral spring) on a seasonal basis. Within the forest fragment we distinguished two microhabitat types: creeks and areas far from creeks (i.e. slopes). A total of 36 species were recorded in the study site, of which 21 were inside the relict forest. Highest bird abundance and richness were recorded during winter and spring, and these were always higher in creek plots rather than slope plots. Comparisons between this assemblage and those distributed in the continuous temperate forest (located more than 900 km southwards) indicate that this bird assemblage shares more similarities, with regard to bird species composition, to southern temperate forest localities and to other relict forests, than to nearer scrub habitats. However, there are eight species, endemic to temperate forests in southern South America, missing from our system. In this regard, our analyses indicate that these eight endemic species should be of great conservation concern and will likely be the ones that will go extinct first if the fragmentation of the temperate forest continues.
Darwinian fitness and reproductive power: Reply
(1996) Brown, JH; Taper, ML; Marquet, PA
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.
El Nino events, precipitation patterns, and rodent outbreaks are statistically associated in semiarid Chile
(1999) Lima, M; Marquet, PA; Jaksic, FM
In the last two decades, several researchers have noted rodent population outbreaks in semiarid South America, in association with unusually high precipitation that seemingly concurs with Ei Nino events. To date, no studies have been conducted to determine the statistical relationships between ENSO (El Nino Southern Oscillation) events. increased precipitation, and rodent irruptions. Here we show that: 1) there is a statistical association between ENSO events and increased precipitation in the semiarid region of northern Chile, 2) the occurrence or rodent outbreaks in that region is statistically related with the precipitation levels of the same year; 3) the multi-annual patterns of the total annual precipitation levels and population abundance of those rodents Juring the summer are positively associated. The putative chain of effects seems to start with unusually high rainfall brought by ENSO to semiarid environments. which thus respond with increased primary productivity (herbage and seeds), which then fuels the rodent outbreaks.
Geographic energetics of the Andean mouse, Abrothrix andinus
(1999) Bozinovic, F; Lagos, JA; Marquet, PA
we measured basal metabolic rate, thermal conductance, body temperature, and temperature differential of three populations of the Sigmodontine-rodent Abrothrix andinus in three different habitats of the Andean range of northern Chile. Individuals from the three habitats were good thermoregulators, were capable of maintaining a high mass-independent temperature differential, and were able to survive the cold ambient temperatures during the night. We compared our data with:previously published information on seasonal energetics of another population of A. andinus in the Andean range of central Chile and with species of the genus Abrothrix in a Mediterranean climate. Energetics of Abrothrix did not vary in response to different climatic conditions, which favored the hypothesis that it was a fixed character probably reflecting a common ancestor of Andean origin or radiation along the Andes Mountains.
Global gap analysis
(2004) Rodrigues, ASL; Akçakaya, HR; Andelman, SJ; Bakarr, MI; Boitani, L; Brooks, TM; Chanson, JS; Fishpool, LDC; Da Fonseca, GAB; Gaston, KJ; Hoffmann, M; Marquet, PA; Pilgrim, JD; Pressey, RL; Schipper, J; Sechrest, W; Stuart, SN; Underhill, LG; Waller, RW; Watts, MEJ; Yan, X
Protected areas are the single most important conservation tool. The global protected-area network has grown substantially in recent decades, now occupying 11.5% of Earth's land surface, but such growth has not been strategically aimed at maximizing the coverage of global biodiversity. In a previous study, we demonstrated that the global network is far from complete, even for the representation of terrestrial vertebrate species. Here we present a first attempt to provide a global framework for the next step of strategically expanding the network to cover mammals, amphibians, freshwater turtles and tortoises, and globally threatened birds. We identify unprotected areas of the world that have remarkably high conservation value (irreplaceability) and are under serious threat. These areas concentrate overwhelmingly in tropical and subtropical moist forests, particularly on tropical mountains and islands. The expansion of the global protected-area network in these regions is urgently needed to prevent the loss of unique biodiversity.
How do species really divide resources?
(1996) Taper, ML; Marquet, PA
We show that the relationship between variance in population energy use and variance in species abundance depends critically on the model of causal relationships among metabolic rate, body size, and population density assumed, provided that they specify alternative paths of error propagation. It has been claimed that the allometric relationship between population density and body size indicates that species within communities use resources less equitably than would be inferred from a particular species abundance distribution. Our analysis of 41 local bird communities shows that this claim is supported only if it is assumed that both body size and metabolic rate are a consequence of population density. A more realistic model that assumes a causal role for body size as affecting metabolic rate and population density provides estimates of variance in population energy use that closely match the pattern of variance in population density. This implies that the apportionment of individuals and resources, among species, are equivalent processes.
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.
Peridomestic small mammals associated with confirmed cases of human hantavirus disease in southcentral Chile
(2004) Torres-Pérez, F; Navarrete-Droguett, J; Aldunate, R; Yates, TL; Mertz, GJ; Vial, PA; Ferrés, M; Marquet, PA; Palma, RE
Cases of human hantavirus disease have been reported in Chile since 1995, most of them in people living in rural and periurban areas. We conducted a peridomestic study of small mammals to evaluate the relationships between the presence of rodents with antibodies to Andes virus confirmed human cases of hantavirus pulmonary syndrome in southcentral Chile. The results of 20 sampled sites, which involved the capture of 272 mice over an 18-month period, showed the occurrence of 10 small mammal species, of which Oligoryzomys longicaudatus was the only seropositive species for hantavirus, with an intra-specific serologic rate of 10.4%.
Phylogenetic and biogeographic relationships of the mouse opossum Thylamys (Didelphimorphia, Didelphidae) in southern South America
(2002) Palma, RE; Rivera-Milla, E; Yates, TL; Marquet, PA; Meynard, AP
Nucleotide sequence data from the mitochondrial cytochrome b gene were used to evaluate the phylogenetic relationships among mouse opossum species of the genus Thylamys. Based on approximately 1000 bp in five of the six species of the genus and including different localities for some of the species, we concluded that T. macrura from the subtropical forests of eastern Paraguay is the most primitive taxon. Subsequent radiation of the genus is explained mainly via founder effect speciation. This evolutionary scenario would account for the speciation of T pusilla, T venusta, T pallidior, and T elegans in the Chaco, southern Bolivia and northern Argentina, the Andean Altiplano, the Coastal Desert of Chile, and coastal Peru, respectively. Calibration of a molecular clock set the Pleistocene as the period for the differentiation of Thylamys species. The molecular results confirm the strong genetic connection between populations that inhabit the "pre-cordillera" of northern Chile (T pallidior) and the canyons that run through the Atacama Desert to the lowlands in northern Chile. Our results confirm the occurrence of two Thylamys species in Chile, T. pallidior and T. elegans, within and south to the Atacama Desert, respectively. (C) 2002 Elsevier Science (USA). All rights reserved.
Phylogeography of Oligoryzomys longicaudatus (Rodentia: Sigmodontinae) in temperate South America
(2005) Palma, RE; Rivera-Milla, E; Salazar-Bravo, J; Torres-Pérez, F; Pardiñas, UFJ; Marquet, PA; Spotorno, AE; Meynard, AP; Yates, TL
Phylogeographic relationships were evaluated at the intraspecific level using nucleotide sequence data from the mitochondrial cytochrome b gene of representative specimens of "colilargo" (Oligoryzomys longicaudatus) from 31 localities, along its distributional range over a large part of the western Andes and southern Argentina. Based on approximately 1,000 base pairs (bp), we recognized a single species on both the Chilean and the Argentinean side as far as at least latitude 51degreesS, rejecting the subspecific distinctiveness of longicaudatus and philippi. We thus placed the latter in full synonymy with O. longicaudatus as earlier studies proposed, and enlarged its range as far as Torres del Paine, about 51degreesS. The occurrence of subspecies in this range is doubtful given the low sequence divergence values and the absence of significant associations between haplotypes and their geography. Additionally, we hypothesized that the entrance of this species into the Chilean side of the Andes mountains occurred through the Patagonian forests of southern Argentina, with further dispersal to the north from the south.
The introduced Hawaiian avifauna reconsidered: Evidence for self-organized criticality?
(1996) Keitt, TH; Marquet, PA
Over the last century, many bird species have been introduced into the Hawaiian islands. The data indicate a scenario in which island communities build up to a critical number of species, above which avalanches of extinction occur. Plotting the distribution of extinction event sizes approximates a power-law in accordance with the notion of a self-organized critical system. The lengths of time between introduction and extinction for different species also exhibit power-law scaling. These results suggest that ecological communities are not characterized by a well defined equilibrium, but rather by a detailed balance which is minimally stable to perturbations such that the introduction of species can trigger extinction cascades. (C) 1996 Academic Press Ltd
Vegetation in an altitudinal gradient along the Rio Loa in the Atacama Desert of northern Chile
(1998) Gutiérrez, JR; López-Cortes, F; Marquet, PA
Six sites between 0 m and 4000 m were sampled for plant and soil chemical characteristics along the Rio Loa, Atacama Desert, Chile. Sites located between 0 m and 1500 m showed lower species richness, higher plant cover and higher herbaceous productivity than the upper part of the altitudinal gradient. The number of species varied non-linerly with precipitation along the altitudinal gradient. Plant cover and herbaceous productivity in the lowlands is characterized by the Pluchea absinthioides-Distichlis spicata association of anthropic origin. We propose that vegetation structure along the altitudinal gradient has been affected by past and present human activities, and climatic and edaphic factors. (C) 1998 Academic Press.

Browsing by Author "Marquet, PA"

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