Current brood size and residual reproductive value predict offspring desertion in the burying beetle Nicrophorus vespilloides

Life-history theory suggests that offspring desertion can be an adaptive reproductive strategy, in which parents forgo the costly care of an unprofitable current brood to save resources for future reproduction. In the burying beetle, Nicrophorus vespilloides, parents commonly abandon their offspring to the care of others, resulting in female-only care, male-only care, brood parasitism, and the care of offspring sired by satellite males. Furthermore, when there is biparental care, males routinely desert the brood before larval development is complete, leaving females behind to tend their young. We attempted to understand these patterns of offspring desertion by using laboratory experiments to compare the fitness costs associated with parental care for each sex and the residual reproductive value of the 2 sexes. We also tested whether current brood size and residual reproductive value together predicted the incidence of brood desertion. We found that males and females each sustained fecundity costs as a consequence of caring for larvae and that these costs were of comparable magnitude. Nevertheless, males had greater residual reproductive value than females and were more likely than females to desert experimental broods. Our results can explain why males desert the brood earlier than females in nature and why female-only care is more common than male-only care. They also suggest that the tipping point from brood parasitism or satellite male behavior to communal breeding (and vice versa) depends on the value of the current brood relative to residual reproductive value. Copyright 2009, Oxford University Press.

Transformações da terra: para uma perspectiva agroecológica na história Transformation of the land: towards an agroecological perspective in history

O artigo discute a constituição do campo da história ambiental, que se deu nos anos 70 em meio aos debates sobre a crise ecológica e a eclosão do movimento ambientalista. Esta história não aceita a noção de que as sociedades humanas não produzem alterações ambientais significativas, e interpela as condições específicas dessa interação recorrente. O sistema agroecológico representa um dos casos mais típicos de rearranjo da atividade humana sobre os ecossistemas naturais, em uma relação complexa de interação entre plantas nativas, vegetação forasteira, fertilidade dos solos e diversas práticas agrícolas. O itinerário dessas mudanças é essencial para se compreender a história do ponto de vista ambiental<br>This article discusses the formation of the field of environmental history which originated in the 1970s in the middle of the debates on the ecologic crisis and the emergence of the environmental movement. This history rejects the notion that human societies do not cause significant environmental alterations and analyzes the specific conditions of that recurring interaction. The agroecologic system is one of the most typical cases of the intervention of human activity on natural ecosystems in a complex interaction between indigenous plants, exotic vegetation, fertility of the soil and diverse agricultural practices. The roadmap of these changes is essential to understand history from the view point of the environment