514 research outputs found
Unexpectedly diverse forest dung beetle communities in degraded rain forest landscapes in Madagascar
Tropical forests, which harbor high levels of biodiversity, are being lost at an alarming speed. Madagascar, a biodiversity hotspot, has lost more than half of its original forest cover. Most of the remaining forests are small fragments of primary and secondary forest with differing degrees of human impact. These forests, as well as coffee and fruit plantations, may be important in supporting the forest-dependent biodiversity in Madagascar but this has been little studied. In Madagascar, dung beetles, which offer important ecosystem services, are largely restricted to forests. We examined the ability of fragmented and degraded forests to support dung beetle diversity, compared to the large areas of primary forest in eastern Madagascar. We found a general trend of a reduction of species with a loss of forest connectivity. In contrast, a higher level of forest disturbance was associated with higher species diversity. In several sites of low-quality forest as many or more species were found as in less disturbed and primary forests. The average size of dung beetles was smaller in the lower quality localities than in the primary forests. These findings suggest that many forest dung beetles in Madagascar are better adapted to forest disturbance than earlier expected, although they require some level of connectivity to surrounding forest. in Malagasy is available with online material.Peer reviewe
Deforestation and apparent extinctions of endemic forest beetles in Madagascar
Madagascar has lost about half of its forest cover since 1953 with much regional variation, for instance most of the coastal lowland forests have been cleared. We sampled the endemic forest-dwelling Helictopleurini dung beetles across Madagascar during 2002â2006. Our samples include 29 of the 51 previously known species for which locality information is available. The most significant factor explaining apparent extinctions (species not collected by us) is forest loss within the historical range of the focal species, suggesting that deforestation has already caused the extinction, or effective extinction, of a large number of insect species with small geographical ranges, typical for many endemic taxa in Madagascar. Currently, roughly 10% of the original forest cover remains. Speciesâarea considerations suggest that this will allow roughly half of the species to persist. Our results are consistent with this prediction
Smart Containers With Bidding Capacity: A Policy Gradient Algorithm for Semi-Cooperative Learning
Smart modular freight containers -- as propagated in the Physical Internet
paradigm -- are equipped with sensors, data storage capability and intelligence
that enable them to route themselves from origin to destination without manual
intervention or central governance. In this self-organizing setting, containers
can autonomously place bids on transport services in a spot market setting.
However, for individual containers it may be difficult to learn good bidding
policies due to limited observations. By sharing information and costs between
one another, smart containers can jointly learn bidding policies, even though
simultaneously competing for the same transport capacity. We replicate this
behavior by learning stochastic bidding policies in a semi-cooperative multi
agent setting. To this end, we develop a reinforcement learning algorithm based
on the policy gradient framework. Numerical experiments show that sharing
solely bids and acceptance decisions leads to stable bidding policies.
Additional system information only marginally improves performance; individual
job properties suffice to place appropriate bids. Furthermore, we find that
carriers may have incentives not to share information with the smart
containers. The experiments give rise to several directions for follow-up
research, in particular the interaction between smart containers and transport
services in self-organizing logistics.Comment: 15 page
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