Compositional response of Amazon forests to climate change

Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate-induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long-term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO₂ concentrations): maximum tree size, biogeographic water-deficit affiliation and wood density. Tree communities have become increasingly dominated by large-statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry-affiliated genera have become more abundant, while the mortality of wet-affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry-affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate-change drivers, but yet to significantly impact whole-community composition. The Amazon observational record suggests that the increase in atmospheric CO₂ is driving a shift within tree communities to large-statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

Cross sectional survey of perpetrators, victims, and witnesses of violence in Bogotá, Colombia

OBJECTIVES

To establish the prevalence and distribution of witnesses, victims, and perpetrators of different types of violence in the general population and the proportion of victims consulting health services or reporting the incident to authorities.

METHODS

Cross sectional survey of a random sample of 3007 inhabitants between the ages of 15 and 60 in the city of Bogotá, Colombia, in 1997, based on a face to face interview.

RESULTS

Age adjusted past year prevalence of witnesses, victims, and perpetrators of physical aggression was 61%, 27%, and 27%, respectively, while lifetime prevalence of witnesses, victims, and perpetrators of assault with a weapon in this population reached 70%, 55%, and 5.8%. Between 11% and 67% of the victims consulted a health service and less than 32% reported the incident to an authority. Those involved in most types of physical violence tended to be young, male, from lower middle social classes, with some degree of secondary education, and single or divorced.

CONCLUSIONS

Prevalence of witnesses and victims of violence in this sample appears to be high, while perpetrators constitute a small proportion. Violence is not equally distributed throughout the population suggesting the possibility of identifying a population at higher risk for the development of intervention programmes.

Pathways to marijuana use among adolescents: cultural/ecological, family, peer, and personality influences

OBJECTIVE

To examine the linkages, cultural/ecological factors, and major psychosocial risk factors as they relate to drug use in a sample from Colombia, South America.

METHOD

The participants were 1.687 adolescents living in mixed urban-rural communities in Colombia, South America. An individual interview was administered to youths in their homes by Colombian interviewers. The scales used were based on item intercorrelations grouped into the following risk categories: (1) adolescent personality, (2) family traits, (3) peer factors, and (4) cultural/ecological variables.

RESULTS

Pearson correlations were computed for each variable and the frequency of marijuana use. Results show that each of the domains was related to adolescent marijuana use, with some notable gender differences. As regards the interrelation of domains, a mediational model was operative.

CONCLUSIONS

Findings support a family interactional theory. The domains of family, personality, and peer factors had a direct effect on the adolescents' marijuana use. Implications for prevention are also addressed.