RESUMO
Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.
Assuntos
Carbono/metabolismo , Ecossistema , Cadeia Alimentar , Nitrogênio/metabolismo , Fósforo/metabolismo , Animais , Belize , Biomassa , Carbono/análise , Invertebrados/fisiologia , Nitrogênio/análise , Fósforo/análise , Árvores/fisiologia , Áreas AlagadasRESUMO
OBJECTIVES: To identify factors associated with effective AIDS behavior change among injecting drug users (IDU) in different national settings. DESIGN: Cross-sectional surveys of IDU, with determination of HIV status. Trends in city HIV seroprevalence among IDU also used to validate effectiveness of behavior change. SETTING AND PARTICIPANTS: Subjects recruited from drug-use treatment programs and outreach efforts in Bangkok, Thailand (n = 601), Glasgow, Scotland (n = 919), New York City, USA (n = 2539), and Rio de Janeiro, Brazil (n = 466). RESULTS: Evidence for the effectiveness of self-reported risk reduction was available for all cities. Univariate followed by multiple logistic regression analyses were used to identify factors associated with self-reported AIDS behavior change. Separate analyses were conducted for each city. Talking about AIDS with drug-using friends was significantly associated with behavior change in all four cities. Talking with sex partners about AIDS, educational level, knowing that someone can be HIV-infected and still look healthy, and having been tested previously for HIV were each significantly associated with behavior change in three of the four cities. CONCLUSIONS: Despite the substantial differences in these national settings, there were common factors associated with effective risk reduction. In particular, risk reduction appears to occur through social processes rather than through individual attitude change. HIV prevention programs need to explicitly incorporate social processes into their work.