Intraspecific variation in a predator affects community structure and cascading trophic interactions

Intraspecific phenotypic variation in ecologically important traits is widespread and important for evolutionary processes, but its effects on community and ecosystem processes are poorly understood. We use life history differences among populations of alewives, Alosa pseudoharengus, to test the effects of intraspecific phenotypic variation in a predator on pelagic zooplankton community structure and the strength of cascading trophic interactions. We focus on the effects of differences in (1) the duration of residence in fresh water (either seasonal or year-round) and (2) differences in foraging morphology, both of which may strongly influence interactions between alewives and their prey. We measured zooplankton community structure, algal biomass, and spring total phosphorus in lakes that contained landlocked, anadromous, or no alewives. Both the duration of residence and the intraspecific variation in foraging morphology strongly influenced zooplankton community structure. Lakes with landlocked alewives had small-bodied zooplankton year-round, and lakes with no alewives had large-bodied zooplankton year-round. In contrast, zooplankton communities in lakes with anadromous alewives cycled between large-bodied zooplankton in the winter and spring and small-bodied zooplankton in the summer. In summer, differences in feeding morphology of alewives caused zooplankton biomass to be lower and body size to be smaller in lakes with anadromous alewives than in lakes with landlocked alewives. Furthermore, intraspecific variation altered the strength of the trophic cascade caused by alewives. Our results demonstrate that intraspecific phenotypic variation of predators can regulate community structure and ecosystem processes by modifying the form and strength of complex trophic interactions.     

Festering food: chytridiomycete pathogen reduces quality of Daphnia host as a food resource

When parasitic infections are severe or highly prevalent among prey, a significant component of the predator's diet may consist of parasitized hosts. However, despite the ubiquity of parasites in most food webs, comparisons of the nutritional quality of prey as a function of infection status are largely absent. We measured the nutritional consequences of chytridiomycete infections in Daphnia, which achieve high prevalence in lake ecosystems (>80%), and tested the hypothesis that Daphnia pulicaria infected with Polycaryum laeve are diminished in food quality relative to uninfected hosts. Compared with uninfected adults, infected individuals were smaller, contained less nitrogen and phosphorus, and were lower in several important fatty acids. Infected zooplankton had significantly shorter carapace lengths (8%) and lower mass (8-20%) than uninfected individuals. Parasitized animals contained significantly less phosphorus (16-18% less by dry mass) and nitrogen (4-6% less) than did healthy individuals. Infected individuals also contained 26-34% less saturated fatty acid and 31-42% less docosahexaenoic acid, an essential fatty acid that is typically low in cladocera, but critical to fish growth. Our results suggest that naturally occurring levels of chytrid infections in D. pulicaria populations reduce the quality of food available to secondary consumers, including planktivorous fishes, with potentially important effects for lake food webs.     

THE IMPORTANCE OF BEAVER TO WETLAND HABITATS AND WATERFOWL IN WYOMING1

ABSTRACT: Beaver (Castor canadensis) are habitat‐modifying keystone species, and their activities broadly influence many other plants and animals. Beaver are especially important to waterfowl in the western U.S. where riparian and wetland habitats comprise less than 2 percent of the landscape yet provide habitat for greater than 80 percent of wildlife species. Wyoming is currently ranked sixth of the 50 states in the size of its breeding waterfowl population, and beaver ponds may play a significant role in providing habitat for these birds. The objectives of this research were to: (1) identify streams in Wyoming where beaver are currently present, extirpated, or used to manage riparian habitat; (2) identify areas where beaver could be relocated to create wetlands and improve riparian habitat; (3) compare wetland surface areas between areas that have beaver with those that did not; and (4) compare waterfowl numbers in areas with and without beaver. Using a survey of 125 land managers in Wyoming, we found that beaver have been removed from 23 percent (6,497 kin) of the streams for which managers had direct knowledge (28,297 kin). The same managers estimated that there are over 3,500 km of streams where beaver could improve habitat conditions. The riparian width in streams with beaver ponds averaged 33.9 m (95 percent CI = 25.1–42.7 m) in contrast to 10.5 m (CI = 8.6–12.4 m) in streams without beaver. During waterfowl surveys we counted 7.5 ducks/km (CI = O.9–14.4 ducks/kin) of stream in areas with beaver ponds and only O.1 ducks/km (no CIs calculated) of stream in similar areas without beaver present. Beginning in 1994, we restored beaver to 14 streams throughout Wyoming in an effort to create wetlands and improve riparian habitat. Waterfowl have been quick to respond to these important habitats. We feel that beaver restoration and management can be used to improve habitat in drainages where conflicts with other land uses are minimal.     

Ecological principles,biodiversity, and the electric utility industry

The synthetic field of conservation biology uses principles derived from many different disciplines to address biodiversity issues. Many of these principles have come from ecology, and two simple ones that seem to relate to many issues involving the utility industry are: (1) Everything is interconnected (and should usually stay that way), and (2) We can never do merely one thing. The first principle can be applied to both the biotic and physical environments that are impacted by industrial activities. Habitat fragmentation and the loss of physical and biotic connectedness that results are frequently associated with transmission rights-of-way. These problems can be reduced—or even turned into conservation benefits—by careful planning and creative management. The second principle applies to the utility industry's programs to deal with carbon released by burning fossil fuels. Ecological knowledge can allow these programs to contribute to the preservation of biodiversity in addition to addressing a pollution problem. Without careful ecological analyses, industry could easily create new problems while implementing solutions to old ones.     

Prenatal diagnosis of Pallister–Killian syndrome: Resolution of cytogenetic ambiguity by use of fluorescent in situ hybridization

We report a case of Pallister-Killian syndrome initially diagnosed prenatally as tetrasomy 21. A 33-year-old primiparous woman was noted at 24 weeks' gestation to have moderate polyhydramnios. Ultrasonography showed diminished fetal stomach filling, hydronephrosis, and prominence of the cisterna magna. Cytogenetic analysis of cultured amniocytes was initially interpreted as mosaic tetrasomy 21: 46,XX/47,XX,+i(21q). The patient was then referred to our centre for genetic counselling. At 34 weeks' gestation, a dysmorphic infant was delivered and died within 30 min. Physical features were consistent with the Pallister-Killian syndrome. Renal, gastrointestinal, and central nervous system anomalies were found at post-mortem examination. Analysis of peripheral lymphocytes revealed 5 per cent of cells with a marker chromosome, while 92 per cent of cultured fibroblasts had this same marker. Fluorescent in situ hybridization (FISH) using an alpha-satellite probe for chromosomes 13 and 21 failed to hybridize to the marker, while a chromosome 12 centromeric probe unequivocally identified it as an i(12p). Use of FISH can provide rapid, specific prenatal diagnosis of ambiguous marker chromosomes and improve prenatal counselling.     

A comparison of polycyclic aromatic hydrocarbon and petroleum hydrocarbon uptake by mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) in Hong Kong coastal waters

The ability of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) to accumulate polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons (PHCs) from five sites in Hong Kong's coastal waters was compared. Mussels consistently had higher levels of contaminants, but their utility was limited at one highly polluted site due to mortality. Mussels and SPMDs ranked sites differently in terms of individual contaminant levels. Although SPMDs overcome many of the disadvantages of using living organisms to measure contaminants in marine waters, they cannot be used as "mimics" due to different PAH and PHC accumulation patterns.     

Some biologically important low molecular weight organic acids in the sediments of Loch Eil

The isolation of biologically important low molecular weight organic acids from organically enriched sediments in Loch Eil, Scotland, was carried out by extraction of pore water with acidified ethyl acetate. High concentrations of acetic acid, up to 1.8 mg g^-1 dry weight of sediment were found at Station E-24. Propionate, butyrate, valerate, lactate and traces of succinate were also found. Succinate was present in significant amounts, 42.2 g g^-1 dry weight of sediment at Station E-70, which received a higher input of organic matter than E-24. Both propionate and succinate were absent from a control station in the Lynn of Lorne where the sediment was low in carbon compared with Loch Eil. In experimental tanks, acetate levels increased as the input of organic carbon (as cellulose) was increased up to a load level of 1.5 g m^-2 day^-1. Above this, acetate decreased and succinate appeared. Succinate was not detected in low-loaded tanks. Experiments with sieved mud showed a vertical distribution of the different acids with depth. Lactate and succinate reached highest concentration in the 0 to 3 cm layer, acetate at 3 to 6 cm and propionate at 6 to 9 cm. The results are discussed in relation to the role of these acids as food sources and as indicators of biochemical pathways taking place in sediments with different carbon input levels.     

Achondrogenesis type II (Langer–Saldino) in association with jugular lymphatic obstruction sequence

The prenatal diagnosis of achondrogenesis in association with cystic hygroma is described. Ultrasound findings of severe short-limbed dwarfism, decreased vertebral ossification, and normal ossification of the calvarium were all consistent with achondrogenesis type II. Although the unusual finding of associated cystic hygroma raised the suspicion of a concurrent chromosome abnormality, the karyotype of both fetal lymphocytes and fetal fibroblasts was normal. Autopsy confirmed dilated lymphatic channels in the basal endothelial layer of the skin, cystic hygroma, and coarctation of the aorta. Although previously unreported, we suggest that the features of this case of achondrogenesis indicate an association with lymphatic stasis and jugular lymphatic obstruction sequence in this syndrome.