Bridging the gap between ecology and evolution: integrating density regulation and life-history evolution.

Early demographic models of life-history evolution were formulated in a density-independent framework and saw extrinsic sources of mortality, such as predation, as the primary driving force that shaped the evolution of life-history traits. The evidence for density dependence in nature motivated theoreticians to build models that incorporated population regulation. These later generations of models acknowledge that demographic mechanisms of population regulation and extrinsic mortality interact with one another and predict a wide variety of life-history responses. Such ecologically realistic models require knowledge of the demographic traits and life-stages most affected by density. Despite the vast empirical literature characterizing population regulation, and a wealth of methods to analyze it, such mechanistic understanding is rare. Ecological experiments whereby density is manipulated can be a powerful tool to disentangle the life-history determinants of population regulation. Here we review published density-manipulation experiments and highlight how they can be coupled with existing analytical tools to extract the mechanistic information needed for evolutionary models of life histories.

How does diet influence the reproductive seasonality of tropical freshwater fish?: A case study of a characin in a tropical mountain river

Seasonal breeding of tropical freshwater fish may be synchronized with periods of high food consumption. We explored this hypothesis by studying the relationship between diet and reproductive activity of Creagrutus guanes (Teleostei, Characidae). Our results showed that C. guanes had a generalist and omnivorous diet dominated by aquatic insects (mainly Diptera larvae) and seeds. Creagrutus guanes did not show intersexual or ontogenetic variation in diet. Peaks of feeding activity during rainy months were not synchronized with breeding in dry months. Our results do not support the hypothesis that the reproductive season has to be synchronized with high food consumption. We discussed the hypothesis fat reserves may be an important factor for the desynchronization of peaks of feeding and reproduction as explanation of seasonal breeding of this species.(AU)

A reprodução sazonal de peixes tropicais de água doce pode estar sincronizada com períodos de alto consumo de alimento. Nós examinamos esta hipótese estudando a relação entre dieta e atividade reprodutiva de Creagrutus guanes (Teleostei, Characidae). Nossos resultados mostraram que C. guanes teve uma dieta generalista e onívora, com predominância de insetos aquáticos (principalmente larva de Diptera) e sementes. Creagrutus guanes não apresentou variação intersexual ou ontogenética na dieta. Picos de atividade alimentar durante os meses chuvosos não foram sincronizados com atividade reprodutiva nos meses secos. Nossos resultados não sustentam a hipótese de que a estação reprodutiva está sincronizada com o consumo elevado de alimento. A reserva de gordura pode ser um fator importante para a dessincronização de picos de alimentação e reprodução (a reserva de gordura pode influenciar a ausência de sincronia entre os picos de alimentação e reprodução). São apresentadas hipóteses alternativas para a explicação de desova sazonal da espécie(AU)