Beta diversity at different spatial scales: plant communities in organic and conventional agriculture.

Biodiversity studies that guide agricultural subsidy policy have generally compared farming systems at a single spatial scale: the field. However, diversity patterns vary across spatial scales. Here, we examined the effects of farming system (organic vs. conventional) and position in the field (edge vs. center) on plant species richness in wheat fields at three spatial scales. We quantified alpha-, beta-, and gamma-diversity at the microscale in 800 plots, at the mesoscale in 40 fields, and at the macroscale in three regions using the additive partitioning approach, and evaluated the relative contribution of beta-diversity at each spatial scale to total observed species richness. We found that alpha-, beta-, and gamma-diversity were higher in organic than conventional fields and higher at the field edge than in the field center at all spatial scales. In both farming systems, beta-diversity at the meso- and macroscale explained most of the overall species richness (up to 37% and 25%, respectively), indicating considerable differences in community composition among fields and regions due to environmental heterogeneity. The spatial scale at which beta-diversity contributed the most to overall species richness differed between rare and common species. Total richness of rare species (present in < or = 5% of total samples) was mainly explained by differences in community composition at the meso- and macroscale (up to 27% and 48%, respectively), but only in organic fields. Total richness of common species (present in > or = 25% of total samples) was explained by differences in community composition at the micro- and mesoscale (up to 29% and 47%, respectively), i.e., among plots and fields, independent of farming system. Our results show that organic farming made the greatest contribution to total species richness at the meso (among fields) and macro (among regions) scale due to environmental heterogeneity. Hence, agri-environment schemes should exploit this large-scale contribution of beta-diversity by tailoring schemes at regional scales to maximize dissimilarity between conservation areas using geographic information systems rather than focusing entirely at the classical local-field scale, which is the current practice.     

Demands of effective PCDD/PCDF-analysis in environment and production control. Aims of an analytical laboratory to meet legal and toxicological requirements. Critical approach to detection limits

Attainable or obtained detection limits play an important role in the discussion of trace analysis of polychlorinated dibenzo-p-dioxins and -furans. Now-a-days state of the art is based as well on highly developed instrumental techniques as on sophisticated clean up methods. However, with this state of the art is not connected, necessarily, a defined level of detection limits. Comparison of detection limits obtained in various laboratories are difficult. Reasonable comparisons imply knowledge about definitions, ways of quantitation, strategies of improvement, their limitations, and the substances under investigations. Measures to improve detection limits and their limitations are interdependent in a complex manner. Examples are given in this presentation.

The group analysis of the degrees of chlorination of the dibenzo-p-dioxins and -furans deteriorates the detection limits with respect to the single isomer determitation because of the higher influence of the residual matrix. Particulary, these topics should be taken into consideration when planning and executing analytical work for regulatory enforcement and legal purposes.     

The roles of echolocation and olfaction in two Neotropical fruit-eating bats, Carollia perspicillata and C. castanea, feeding on Piper

We studied the echolocation and foraging behavior of two Neotropical frugivorous leaf-nosed bats (Carollia perspicillata, C. castanea: Phyllostomidae) in a flight cage. To test which cues Carollia uses to detect, identify, and localize ripe Piper fruit, their preferred natural food, we conducted experiments under semi-natural conditions with ripe, unripe, and artifical fruits. We first offered the bats ripe fruits and documented their foraging behavior using multiflash stereophotography combined with simultaneous sound recordings. Both species showed a similar, stereotyped foraging pattern. In searchflight, the bats circled through the flight cage in search of a branch with ripe fruit. After finding such a branch, the bats switched to approach behavior, consisting of multiple exploration flights and the final approach when the bats picked up the fruit at its tip and tore it off in flight. Our behavioral experiments revealed that odor plays an important role in enabling Carollia to find ripe fruit. While foraging, Carollia always echolocated and produced multiharmonic, frequency-modulated (FM) signals of broad bandwidth, high frequency, short duration, and low intensity. We discriminated an orientation phase (mostly a single pulse per wingbeat) and an approach phase (groups of two to six pulses per wing beat). We conclude from the bats' behavioral reaction to real and artificial fruit as well as from characteristic patterns in their echolocation behavior that during exploration flights, Carollia changes from primarily odor-oriented detection and initial localization of ripe fruit to a primarily echo-oriented final localization of the position of the fruit. Received: 27 March 1997 / Accepted after revision: 28 February 1998     

Prenatal diagnosis of Huntington's disease (HD): Experiences with six cases and PCR

In the course of a 2-year predictive testing programme for Huntington's disease (HD), six couples from a total of 52 applicants requested prenatal testing. In each case, the pregnancy was in the first or second trimester when the couples were referred for DNA diagnosis. In five cases, exclusion testing was offered; in one case, a person at risk with an increased risk of being a gene carrier requested prenatal diagnosis. In all cases, informative markers for prenatal testing could be determined. Whenever possible, the newer technique of polymerase chain reaction (PCR) for D4S125 was applied to perform rapid prenatal diagnosis. Two couples withdrew before chorionic villus sampling was undertaken; prenatal diagnosis was completed in the remaining four cases. After exclusion testing, two pregnancies were determined to have an increased risk and two fetuses to have a low risk of being HD gene carriers.