Habitat and food resources use by birds in different landscapes of the State of São Paulo: an historical and isotopic approach

• Autor(a) principal: Navarro, Ana Beatriz
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/91/91131/tde-10032020-110903/
• topic: Anthropocene; Antropoceno; Ecologia trófica; Isótopos estáveis; Land use changes; Mudanças no uso do solo; Stable isotopes; Trophic ecology

The anthropogenic impacts caused by human expansion over areas of original forests pose strong threats to birds\' existence, altering the habitat and resource use by the species. Isotopic analysis of carbon (measured by δ13C) and nitrogen (measured by δ15N) can be very usefull providing information on spatial and temporal modifications influencing birds\' diet and habitat use. The main objective of this study was to measure isotopic modifications of carbon and nitrogen in tropical forest birds facing several historical anthropogenic impacts. This study was carried out in the state of São Paulo due to the intense human expansion and devastation of the original forests, especially in the 20th century. We obtained samples from wing feathers of several species that compose the following guilds: frugivore, granivore, insectivore, nectarivore and omnivore, from alive birds in the field and from specimens in the museum collection. We grouped individuals according to the following criteria: 1) historical individuals (collected until 1970) were separated from the recent ones (collected from 1985 to 2012), 2) recent individuals (from 2001 to 2019) were separated according to their presence in human- modified landscapes (HMLs; less or equal to 30% of forest cover) or in natural landscapes (NLs; equal or over 47% of forest cover). Individual samples were isotopically analyzed to obtain δ13C and δ15N values. We calculated the isotopic niche width of each guild within the different groups through the SIBER package in R. In addition, we compared the mean values of δ13C and δ15N between the guilds of each group through the Student\'s t-test or Wilcoxon signed-rank test. In both comparisons, historical and landscape approaches, the results showed significant differences in the isotopic niches widths of the guilds of each group. In the historical approach, all guilds had their niche widths declined over the years. In the landscape approach, almost all guilds had smaller niches when present in HMLs, except the granivores. The mean δ13C values in both approaches showed that birds prefer to forage in the forests and have a small mixture with resources from the agricultural matrix. The mean δ15N values differed between groups, showing the direct effects of anthropogenic impacts on birds\' diet. Although the analyzed species are still found in nowadays\' HMLs, most of them showed a high dependence on forest remnants as habitat and food source. Considering that the niche is formed by variables linked to the habitat use and diet, the reduction in niche width of guilds might pose a threat to the survival of these species in HMLs. Additionally, we observed that anthropogenic impacts derived from land use changes, such as fertilizer use and habitat homogenization, might be influencing the differences in δ15N values. Thus, in general, it became clear that the human expansion over a region of tropical forest has directly affected the isotopic ecology of birds.