Cross-scale determinants of palm species distribution

We investigate palm species distribution, richness and abundance along the Mokoti, a seasonally-dry river of southeastern Amazon and compare it to the patterns observed at a large scale, comprising the entire Brazilian territory. A total of 694 palms belonging to 10 species were sampled at the Mokoti River basin. Although the species showed diverse distribution patterns, we found that local palm abundance, richness and tree basal area were significantly higher from the hills to the bottomlands of the study region, revealing a positive association of these measures with moisture. The analyses at the larger spatial scale also showed a strong influence of vapor pressure (a measure of moisture content of the air, in turn modulated by temperature) and seasonality in temperature: the richest regions were those where temperature and humidity were simultaneously high, and which also presented a lower degree of seasonality in temperature. These results indicate that the distribution of palms seems to be strongly associated with climatic variables, supporting the idea that, by 'putting all the eggs in one basket' (a consequence of survival depending on the preservation of a single irreplaceable bud), palms have become vulnerable to extreme environmental conditions. Hence, their distribution is concentrated in those tropical and sub-tropical regions with constant conditions of (mild to high) temperature and moisture all year round.

Investigamos a distribuição, riqueza e abundância de espécies de palmeiras ao longo do Rio Mokoti, um rio sazonalmente seco do sudoeste da Amazônia, comparando posteriormente os resultados com os padrões observados em uma escala espacial mais ampla, englobando a totalidade do território brasileiro. Um total de 694 palmeiras pertencentes a 10 espécies foi amostrado na bacia do Rio Mokoti. Apesar das espécies terem mostrado padrões de distribuição diversos, a abundância e riqueza de palmeiras, além da área basal das árvores, foram significativamente superiores nas baixadas do que nas serras da região estudada, revelando uma forte influência de umidade sobre estes parâmetros. A análise englobando a escala espacial mais ampla também mostrou uma forte influência de pressão de vapor (uma medida de umidade do ar, modulada por temperatura) e sazonalidade sobre a temperatura: as regiões cuja riqueza de palmeiras foi mais alta foram aquelas onde a temperatura e a umidade foram simultaneamente altas, e que apresentaram menor sazonalidade na temperatura. Estes resultados indicam que a distribuição de palmeiras parece estar fortemente associada a fatores climáticos, apoiando a idéia de que ao adotar uma estratégia em que "todos os ovos são colocados em uma mesma cesta" (conseqüência da sobrevivência depender da preservação de um único broto insubstituível), as palmeiras tornaram-se vulneráveis a condições ambientais extremas. Desta forma, estas têm sua distribuição concentrada naquelas regiões tropicais e subtropicais com condições constantes tanto de temperatura (amenas a altas) como de umidade ao longo do ano.

Are vectors able to learn about their hosts? A case study with Aedes aegypti mosquitoes

The way in which vectors distribute themselves amongst their hosts has important epidemiological consequences. While the role played by active host choice is largely unquestioned, current knowledge relates mostly to the innate response of vectors towards stimuli signalling the presence or quality of their hosts. Many of those cues, however, can be unpredictable, and therefore prevent the incorporation of the appropriate response into the vector's behavioural repertoire unless some sort of associative learning is possible. We performed a wide range of laboratory experiments to test the learning abilities of the mosquito, Aedes aegypti. Mosquitoes were exposed to choice procedures in (1) an olfactomenter and (2) a 'visual arena'. Our goal was to determine whether the mosquitoes were able to associate unconditional stimuli (blood feeding, human breath, vibration and electrical shock) with particular odours (citral, carvone, citronella oil and eugenol) and visual patterns (horizontal or vertical black bars) to which they had been previously observed to be responsive. We found no evidence supporting the hypothesis that associative learning abilities are present in adult Ae. aegypti. We discuss the possibilities that the assays employed were either inappropriate or insufficient to detect associative learning, or that associative learning is not possible in this species