Test for the effects of 60-Hz magnetic fields on fecundity and development in Drosophila

Ramirez et al (1983) reported reduced egg laying by Drosophila melanogaster and reduced survival of those eggs to adulthood when adult flies were exposed to magnetic fields. In a similar study, no effects from exposures of Drosophila to 1-mT, 60-Hz magnetic fields were found.     

Retention of suspended sediment and phosphorus on a freshwater delta, South Lake Tahoe, California

The Upper Truckee River and Trout Creek, two major tributaries inflowing to Lake Tahoe, join to form what was historically the largest wetland in the Sierra Nevada mountain range that separates California and Nevada (USA). In the 1950s the delta floodplain of the Upper Truckee River was greatly reduced in area (38%) by urban development and the diversion of the river into a single excavated channel. Conversely, Trout Creek still flows through a wide marsh system with significant overbank flooding before entering Lake Tahoe. This study hypothesized that river channel reaches that are not incised within the delta floodplain retain more sediment and nutrients as a result of greater floodplain connectivity, compared to more incised and excavated reaches. Suspended sediment (SS) and total phosphorus (TP) load data from the delta formed by the Upper Truckee River and Trout Creek were collected using flow stage sensors, turbidometers and depth-integrated samples. During the spring snowmelt flow events monitored in 2003, SS load was reduced by 13–41% for the Upper Truckee River and by 68–90% for Trout Creek. Similar reductions in TP load were observed: 13–32% for the Upper Truckee River and 61–84% for Trout Creek. Monitoring of Trout Creek indicated a reduction in load per unit volume of 20–34% in a moderately incised reach versus a reduction of 51–77% in a non-incised marsh reach containing lagoons, braided channels and backwater areas created by a beaver dam. Smaller particle sizes, <10 μm, were retained in the lower marsh reach with similar efficiencies as larger particle sizes. If retention rates from the Trout Creek portion of the marsh are applied to the Upper Truckee River, sediment loading to Lake Tahoe for 2003 would have been reduced by 917 tons of SS.     

Global distribution patterns provide evidence of niche shift by the introduced African dung beetle Digitonthophagus gazella

The establishment of cattle ranches throughout the world has prompted the release of dung beetles as biological control agents that reduce pasture fouling and control dung-breeding flies. One of these beetles, Digitonthophagus gazella (Fabricius) (Coleoptera: Scarabaeidae), that is native to southeast Africa, has been introduced into the Americas, Australia, and New Zealand. Distribution records for this species have been used to develop climate models of potential future establishment. Recent studies, however, identify D. gazella as a complex of seven species. Taking into account this revision, and the clear identification of the records belonging to the actual D. gazella, we developed environmental models to identify factors that have contributed to the establishment of this species across regions and habitats. We compared the environmental conditions of D. gazella in its native range against those in the regions where the species has or has not established. Our results indicate that D. gazella is still absent in certain parts of Central and South America and parts of Africa where it could potentially establish. We speculate that its distribution in Africa is limited by competitive exclusion. The introduction of D. gazella in America is relatively recent, such that the full extent of its distribution has probably yet to be realized. In Australia and North America, D. gazella is present in regions not predicted according to its native environmental conditions. This discrepancy may reflect a lack of competitive exclusion, phenotypic plasticity, and/or genetic adaptation. Our analyses suggest that the species has the ability to adapt to a wide range of environmental conditions that are extremely different from those in their native region. The species represents a useful case study to indicate that an introduced species may expand its realized niche beyond what is expected based on apparent environmental limits in the species native range.     

Aboveground plant production and nutrient content of the vegetation in six peatlands in Alberta,Canada

We examined the effects of water level, surface water chemistry, and climatic parameters on aboveground primary plant production, and the tissue nutrient concentrations in the dominant herb species in a bog, three fens, and two marshes. In the fens, total NPP correlated best with NO ₃ ^- and total phosphorus surface water concentrations in 1993 and 1994. Total NPP in the marshes correlated best with alkalinity in 1993, and with soluble reactive phosphorus in 1994. Climatic parameters, such as mean annual growing season temperature, growing degree days, and precipitation, had the most notable effect on moss growth, whereas shrub and herb production correlated significantly with the water level relative to the moss surface. Herb production correlated positively and shrub production correlated negatively with the water level relative to the moss surface. Tissue nutrient concentrations of carbon (C), nitrogen (N), and total phosphorus (TP), and the C:N quotient in Carex lasiocarpa exhibited similar trends in the fens and the marshes. Carbon tissue concentrations in C. lasiocarpa remained unchanged, whereas N and TP tissue levels decreased throughout the growing season. In the site with the highest NPP and presumably the highest stand density, C. lasiocarpa exhibited the highest tissue N and TP levels. Furthermore, TP tissue concentrations in C. lasiocarpa were substantially higher in the marshes than in the fens. Tissue nutrient concentrations in Eriophorum vaginatum in the bog showed variable response patterns. N tissue levels increased, whereas tissue TP concentrations decreased from late June to late August. In the bog, E. vaginatum exhibited similar tissue TP levels to C. lasiocarpa in the fens; however, they were both substantially lower than those found in C. lasiocarpa from the marshes.