Browsing by Author "Estades, Cristian F."

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    Contrasting seasonal and aseasonal environments across stages of the annual cycle in the rufous-collared sparrow, Zonotrichia capensis: Differences in endocrine function, proteome and body condition
    (2018) Gonzalez-Gomez, Paulina L.; Echeverria, Valentina; Estades, Cristian F.; Perez, Jonathan H.; Krause, Jesse S.; Sabat, Pablo; Li, Jonathon; Kultz, Dietmar; Wingfield, John C.
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    Effects of habitat loss, habitat fragmentation, and isolation on the density, species richness, and distribution of ladybeetles in manipulated alfalfa landscapes
    (WILEY, 2006) Zaviezo, Tania; Grez, Audrey A.; Estades, Cristian F.; Perez, Astrid
    1. Habitat loss and fragmentation are the main causes of changes in the distribution and abundance of organisms, and are usually considered to negatively affect the abundance and species richness of organisms in a landscape. Nevertheless, habitat loss and fragmentation have often been confused, and the reported negative effects may only be the result of habitat loss alone, with habitat fragmentation having nil or even positive effects on abundance and species richness.
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    Haematozoa in forest birds from southern Chile
    (2008) Merino, Santiago; Moreno, Juan.; Vasquez, Rodrigo A.; Martinez, Javier; Sanchez-Monsalvez, Inocencia; Estades, Cristian F.; Ippi, Silvina; Sabat, Pablo; Rozzi, Ricardo; Mcgehee, Steven
    The existence of latitudinal gradients in species richness and their abundance is known for many free living organisms but few cases have been reported for parasitic diseases. In addition, asymmetries between the Northern and Southern Hemispheres in several characteristics may affect the distribution and diversity of species at all ecological levels. In this respect, we study the distribution of several genera of blood parasites infecting birds along a latitudinal gradient that includes the world's southernmost forests ecosystems. Birds were mist-netted and sampled for blood in localities across Chile ranging from 33 degrees S to 55 degrees S during the years 2003-06. Overall, 26 bird species were sampled and 27 parasite lineages were identified. The latter belonged to three genera: Plasmodium (8), Haemoproteus (8) and Leucocytozoon (11). We found a positive significant relationship between prevalence and latitude for Leucocytozoon lineages and a negative relationship for Haemoproteus, Plasmodium and mixed infections. However, we did not find a significant relationship between parasite diversity and latitude. We found 18 lineages infecting only one species of host, and 19 lineages appear in only one of the localities of sampling. This pattern implies that some parasite lineages may evolve in isolation in some species/localities. In addition, specificity at the host-family level was only found for Haemoproteus lineages infecting birds in the family Emberizidae. Individuals of the long distance migrant bird white-crested elaenia (Elaenia albiceps), were found infected by the same parasite lineages in localities separated by 20 degrees of latitude. Infections by these lineages were detected in other sedentary birds including juveniles and nestlings of different bird species. Therefore, long distance migrants are able to distort the presence of latitudinal gradients of diseases due to the potential role of migrants in spreading infections. Geographical gradients in prevalence of avian haematozoa differ between parasite genera and hemispheres, probably in relation to the existence of appropriate vector-parasite-host interactions.
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    Is natural selection promoting sexual dimorphism in the Green-backed Firecrown Hummingbird (Sephanoides Sephaniodes)?
    (2009) Gonzalez-Gomez, Paulina L.; Estades, Cristian F.
    In many hummingbird species there is an opposite pattern of sexual dimorphism in bill length and other morphometric measures of body size. These differences seem to be closely related with differences in foraging ecology directly associated with a different resource exploitation strategy. The aim of this study was to assess if natural selection is acting on wing length and bill size in hummingbird males and females with different resource exploitation strategies (i.e., territorial males and non-territorial females). If competition for resources promotes sexual dimorphism as a selective pressure, males should be subjected to negative directional selection pressure for wing length and no selection pressure over bill size, while females should undergo positive directional selection pressure for both bill size and wing length. The morphometric data we collected suggests that there is no selection for wing length and bill size in male hummingbirds. In contrast, our females exhibited positive directional selection for both wing length and bill size. Although we cannot reject sexual selection acting on sexually dimorphic traits, this study suggests that natural selection may promote sexual dimorphism in traits that are closely related with hummingbird foraging ecology and resource exploitation strategies.