Consumer versus resource control and the importance of habitat heterogeneity for estuarine bivalves

The relative influence of consumers (top down) and resources (bottom up) on the distribution and abundance of organisms remains a key question in ecology. We examined the relationships between consumer and resource variables along a productivity gradient for a dominant predator-prey interaction in a marine soft-sediment system. We 1) quantified density and size of the clam Macoma balthica (prey species) in six replicate sites at each of four habitat types (shallow mud, deep mud, muddy sand and detrital mud) in the Rhode River, Chesapeake Bay. We selected one habitat type of high food availability and clam density (shallow mud) and another of low food availability and clam density (muddy sand) for manipulative experiments. Then, we 2) measured M. balthica survival and growth through transplants, 3) measured food availability as sedimentary organic carbon content, 4) quantified predator density, and 5) calculated predator foraging efficiency in the two habitat types. Clam density in the four habitat types differed and was related to sedimentary carbon availability and predator density. One of the habitats, detrital mud, appeared to be a population sink because it only held juvenile Macoma that never survived to reproductive age. Macoma size and growth, and predator (mainly blue crab Callinectes sapidus) densities were positively correlated with productivity and were higher in shallow mud than muddy sand. In contrast, Macoma mortality, local \u27interaction strength\u27, and predator foraging efficiency were lower in the productive habitat (shallow mud). Thus, predation intensity was inversely correlated with productivity (food availability); consumer and resource effects differed by habitat type; and, at a relatively small spatial scale, consumer and resource forces jointly determined population dynamics in this soft-sediment marine system

Density-dependent predation by blue crabs upon infaunal clam species with contrasting distribution and abundance patterns

Adult infaunal clams (Macoma balthica) persist at low densities in sandy and muddy habitats in Chesapeake Bay, USA, despite intense predation by blue crabs Callinectes sapidus; another infaunal soft-shelled clam (Mya arenaria) only persists in sandy habitats. We hypothesized that the persistence of M. balthica and M. arenaria in certain habitats was due to blue crabs exhibiting a type III (sigmoid) functional response whereby the risk of mortality is reduced at low clam densities. Laboratory experiments assessed functional responses (prey consumption predator-1 as a function of prey density) of large male blue crabs to 6 densities of M. balthica as a function of sediment type (sand and mud) and tank size (54.6 cm and 97.2 cm diameter). These results were compared with previous experiments with M. arenaria. Abundances of blue crabs, M. balthica, and M. arenaria were measured 4 to 10 times yr-1 from 1979 to 1986 at both sand and mud stations in the mesohaline zone of Chesapeake Bay. Laboratory functional response results were then related to seasonal habitat-specific abundance patterns of M. balthica and M. arenaria in the field. With the exception of M. balthica in mud, abundances of M. arenaria and M. balthica decreased as blue crab abundance increased during the summer. When blue crabs reached their peak abundances in July, M. balthica was predominant in mud whereas M. arenaria numbers dropped to zero in mud and persisted in sand at similar low densities to M. balthica in sand. In the laboratory, blue crabs exhibited density-dependent (type III) functional responses to M. balthica irrespective of sediment type and tank size, even though mortality rates of clams were significantly higher in sand than mud. Differences in habitat-specific burial depth probably accounted for the differential survival of M. balthica in sand and mud. Thus, M. balthica obtained a relative refuge from blue crab predation at low densities similar to those in the field near the end of the seasonal period of active predation. Previous laboratory experiments with blue crabs indicated a type III functional response to M. arenaria in sand and an inversely density-dependent type II response to M. arenaria in mud. Thus, the collective laboratory and field evidence from this study and others strongly suggests that blue crabs are critical determinants of species- and habitat-specific prey persistence in marine soft-bottom communities, and that analysis of predator functional and aggregative responses may help to explain much of the spatial variation of clam abundance patterns in the mesohaline zone of Chesapeake Bay

Density-dependent predation, habitat variation, and the persistence of marine bivalve prey

The persistence of prey encountering intense predation varies by species, prey density, and habitat type; however, the collective impact of these factors has rarely been tested experimentally in natural marine systems. Using the thin-shelled clams Mya arenaria and Macoma balthica as prey, and the main epibenthic predator of whole adult clams, the blue crab Callinectes sapidus, we conducted a series of experiments in Chesapeake Bay tributaries that (1) links field abundance and distribution of bivalve prey species with habitat-specific mortality patterns; (2) represents the first comprehensive field test of species-specific, habitat-specific, and density-dependent mortality for subtidal, soft-bottom, deep-burrowing prey; and (3) thereby enables development of a conceptual model to be used as a heuristic tool linking predator-prey dynamics, habitat type, and evolutionary defense tactics for marine benthos. In 15 years of field monitoring, Mya was more common in sand than mud habitats, and Macoma was widely distributed and at higher densities than Mya in mud and sand. In field experiments, mortality of both Mya and Macoma was density dependent in those habitats where the clams are common. The blue crab population in the field exhibited a type III guild functional response on Mya in sand, and on Macoma in both mud and sand. Mortality was lower in sand than mud for Mya, and similar in mud and sand for Macoma, correlating with the high abundances of Mya in sand and Macoma in sand and mud. The persistence of large juvenile and adult bivalves when confronted with intense predation derived substantially from a low-density refuge from predation that varied in a species-specific manner with habitat type, demonstrating the species-specific importance of density and habitat to clam survival. We developed a conceptual model detailing the relative importance of behavior, morphology, habitat features, and the basic components of predator-prey interactions to the survival of bivalve molluscs. At one extreme are bivalve molluscs, such as oysters, that emphasize morphological refuges that increase the predator\u27s handling time. At the other extreme are bivalves, such as Mya and Macoma, that reduce predator encounter rates. The model is intended to be used as a heuristic tool to develop testable hypotheses

Vitamin D supplementation and breast cancer prevention : a systematic review and meta-analysis of randomized clinical trials

In recent years, the scientific evidence linking vitamin D status or supplementation to breast cancer has grown notably. To investigate the role of vitamin D supplementation on breast cancer incidence, we conducted a systematic review and meta-analysis of randomized controlled trials comparing vitamin D with placebo or no treatment. We used OVID to search MEDLINE (R), EMBASE and CENTRAL until April 2012. We screened the reference lists of included studies and used the “Related Article” feature in PubMed to identify additional articles. No language restrictions were applied. Two reviewers independently extracted data on methodological quality, participants, intervention, comparison and outcomes. Risk Ratios and 95% Confident Intervals for breast cancer were pooled using a random-effects model. Heterogeneity was assessed using the I2 test. In sensitivity analysis, we assessed the impact of vitamin D dosage and mode of administration on treatment effects. Only two randomized controlled trials fulfilled the pre-set inclusion criteria. The pooled analysis included 5372 postmenopausal women. Overall, Risk Ratios and 95% Confident Intervals were 1.11 and 0.74–1.68. We found no evidence of heterogeneity. Neither vitamin D dosage nor mode of administration significantly affected breast cancer risk. However, treatment efficacy was somewhat greater when vitamin D was administered at the highest dosage and in combination with calcium (Risk Ratio 0.58, 95% Confident Interval 0.23–1.47 and Risk Ratio 0.93, 95% Confident Interval 0.54–1.60, respectively). In conclusions, vitamin D use seems not to be associated with a reduced risk of breast cancer development in postmenopausal women. However, the available evidence is still limited and inadequate to draw firm conclusions. Study protocol code: FARM8L2B5L

Understanding young adult physical activity, alcohol and tobacco use in community colleges and 4-year post-secondary institutions: A cross-sectional analysis of epidemiological surveillance data

<p>Abstract</p> <p>Background</p> <p>Young adults experience many adverse health behavior changes as they transition from adolescence into adulthood. A better understanding of the relationships between health promoting and risky health behaviors may aid in the development of health promotion interventions for various types of young adult post-secondary students. Therefore, the purpose of this study was to examine associations between alcohol and tobacco use and physical activity among 2-year and 4-year college students.</p> <p>Methods</p> <p>Cross-sectional analyses were conducted using 2007 survey data, collected as part of an on-going post-secondary health surveillance system in Minnesota. Students were randomly selected to participant from 14 Minnesota colleges and universities (six 2-year community and/or technical colleges, eight 4-year post-secondary institutions). The 2007 surveillance data included 9,931 respondents.</p> <p>Results</p> <p>The prevalence of demographic characteristics and health behaviors (e.g., physical activity, tobacco use) differed between young adults attending 2-year and 4-year post-secondary institutions; in general, those attending 2-year institutions are representative of more at-risk populations. Overall, higher levels of moderate, vigorous and strengthening physical activity were associated with higher levels of alcohol consumption and lower levels of smoking. In general, despite the disparities in the prevalence of these risk behaviors, the associations between the behaviors did not differ substantially between 2-year and 4-year post-secondary populations.</p> <p>Conclusions</p> <p>These findings illustrate links between leading risk behaviors. Interventions targeting multiple risk behaviors among young adults may warrant further consideration. Overall, future research is needed to support and inform young adult health promotion efforts that may be implemented in a wide array of post-secondary institutions.</p

Middle Segment Pancreatectomy: A Useful Tool in the Management of Pancreatic Neoplasms

Small, benign, or low-grade malignant tumors located in the neck of the pancreas are usually treated with enucleation. However, if enucleation is too risky because of possible damage of the main pancreatic duct, standard pancreatic resections are performed. Such operations can lead to impaired long-term exocrine–endocrine function. Middle segment pancreatectomy consists of a limited resection of the midportion of the pancreas and can be performed in selected patients affected by tumors of the pancreatic neck. Middle segment pancreatectomy is a safe and feasible procedure for treating tumors of the pancreatic neck; in experienced hands it is associated with no mortality but with high morbidity, even if the rate of “clinical” pancreatic fistula is about 20%. Moreover, it allows a surgeon to preserve pancreatic parenchyma and consequently long-term endocrine and exocrine pancreatic function

Trial Publication after Registration in ClinicalTrials.Gov: A Cross-Sectional Analysis

Joseph Ross and colleagues examine publication rates of clinical trials and find low rates of publication even following registration in Clinicaltrials.gov

Genetic variability of the neogregarine apicystis bombi, an etiological agent of an emergent bumblebee disease

The worldwide spread of diseases is considered a major threat to biodiversity and a possible driver of the decline of pollinator populations, particularly when novel species or strains of parasites emerge. Previous studies have suggested that populations of introduced European honeybee (Apis mellifera) and bumblebee species (Bombus terrestris and Bombus ruderatus) in Argentina share the neogregarine parasite Apicystis bombi with the native bumblebee (Bombus dahlbomii). In this study we investigated whether A. bombi is acting as an emergent parasite in the non-native populations. Specifically, we asked whether A. bombi, recently identified in Argentina, was introduced by European, non-native bees. Using ITS1 and ITS2 to assess the parasite's intraspecific genetic variation in bees from Argentina and Europe, we found a largely unstructured parasite population, with only 15% of the genetic variation being explained by geographic location. The most abundant haplotype in Argentina (found in all 9 specimens of non-native species) was identical to the most abundant haplotype in Europe (found in 6 out of 8 specimens). Similarly, there was no evidence of structuring by host species, with this factor explaining only 17% of the genetic variation. Interestingly, parasites in native Bombus ephippiatus from Mexico were genetically distant from the Argentine and European samples, suggesting that sufficient variability does exist in the ITS region to identify continent-level genetic structure in the parasite. Thus, the data suggest that A. bombi from Argentina and Europe share a common, relatively recent origin. Although our data did not provide information on the direction of transfer, the absence of genetic structure across space and host species suggests that A. bombi may be acting as an emergent infectious disease across bee taxa and continents