A trophic cascade triggers collapse of a salt-marsh ecosystem with intensive recreational fishing

Overexploitation of predators has been linked to the collapse of a growing number of shallow-water marine ecosystems. However, salt-marsh ecosystems are often viewed and managed as systems controlled by physical processes, despite recent evidence for herbivore-driven die-off of marsh vegetation. Here we use field observations, experiments, and historical records at 14 sites to examine whether the recently reported die-off of northwestern Atlantic salt marshes is associated with the cascading effects of predator dynamics and intensive recreational fishing activity. We found that the localized depletion of top predators at sites accessible to recreational anglers has triggered the proliferation of herbivorous crabs, which in turn results in runaway consumption of marsh vegetation. This suggests that overfishing may be a general mechanism underlying the consumer-driven die-off of salt marshes spreading throughout the western Atlantic. Our findings support the emerging realization that consumers play a dominant role in regulating marine plant communities and can lead to ecosystem collapse when their impacts are amplified by human activities, including recreational fishing.     

Proving the Authenticity of Ancient DNA by Comparative Genomic Hybridization

 In PCR-supported amplification of ancient, degraded DNA, contamination with contemporary DNA can lead to false-positive results, which frequently give rise to discussions in which the mere existence of ancient DNA is doubted. Our confirmation of ancient DNA using comparative genome hybridization (CGH) eliminates these doubts. Unlike PCR methods, CGH requires no amplification of the DNA to be analyzed if adequate amounts of specimen DNA is used. Thus, false results traceable to contaminations are practically ruled out. The examples provided here prove the authenticity of ancient DNA for a 250-year-old and a 3000-year-old sample. At the same time, the CGH of ancient DNA offers the chance to gain insight into the pattern of DNA degradation and to monitor the preservation of certain chromosomal segments. Received: 10 May 1999 / Accepted in revised form: 29 July 1999     

Improvements in anisotropic models of single tree effects in Cartesian coordinates

For anisotropic density functions of e.g. fruit or leaf dispersal, most mathematical research is only done in polar coordinates. However, in software solutions aiming to derive inverse models for real world dispersal data, Cartesian coordinates may be preferred for several reasons. Thus, we introduce an anisotropic model in Cartesian coordinates following the approach in Wälder et al. (2009) with the von Mises approach. By introducing a correction factor, we thereby consider the fundamental attribute, that the integral over a density function with respect to the Cartesian coordinates has to be equal 1. It may have been overlooked so far that guaranteeing for this attribute needs different approaches whether working in polar or Cartesian coordinates. One result is that our approach can be used also for other anisotropic models rather than models from the von Mises approach.     

How application of agricultural waste can enhance soil health in soils acidified by tea cultivation: a review

Environmental Chemistry Letters - Tea is one of the world’s most consumed beverages and an important crop of many developing countries. Intensive tea cultivation has negative impacts on soil...