Periods Of Low Risk Research Articles

Phosphorus Sources and Management in Organic Production Systems

Organically produced fruit and vegetables are among the fastest growing agricultural markets. With greater demand for organically grown produce, more farmers are considering organic production options. Furthermore, there is an increasing interest in maintaining optimal production in an organic system, which involves appropriate nutrient management. The objectives of this review were to summarize the current state of our knowledge concerning effects of organic production systems on phosphorus (P) availability, describe P availability in common organically accepted P sources, and review best management practices that can reduce environmental risks associated with P management in organic systems. Organic production systems seek to improve soil organic matter and biological diversity, which may impact P cycling and P uptake by crops. Increases in organic matter will be accompanied by an increase in the organic P pool. Furthermore, management of cover crops and potentially enhanced arbuscular mycorrhizal fungi colonization from organic production practices can increase the availability of soil P pool (both organic and inorganic) by stimulating microbial activity and release of root exudates. This can help compensate for low soil P, but will not supersede the need to replace P removed by the harvested crop. Phosphorus fertilization in organic production systems entails balancing the P inputs with crop removal through selection and management of both nitrogen (N) and P inputs. Organic production systems that rely on manure or composts for meeting crop N demand will likely have a P surplus; therefore, P deficiencies will not be an issue. Systems using other N sources may have a P deficit, therefore requiring P supplementation for optimal plant growth. In such situations, maintenance P applications equal to crop removal should be made based on soil test recommendations. Primary organically approved P sources are phosphate rock (PR), manure, and compost. Phosphate rock is most effective at supplying P in soils with low pH (less than 5.5) and low calcium concentrations. Phosphate rock applications made to soils with pH greater than 5.5 may not be effective because of reduced PR solubility. Manure- and compost-based P has high plant availability, ranging from 70% to 100% available. Use of manures and composts requires extra considerations to reduce the risk of P loss from P sources to surface waters. Best management practices (BMPs) for reducing source P losses are incorporation of the manures or composts and timing applications to correspond to periods of low runoff risk based on climatic conditions. Organic production systems that use manures and composts as their primary N source should focus on minimizing P buildup in the soils and use of management practices that reduce the risks of P loss to surface waters. Evaluation of P loss risk with a P index will assist in identification of soil and management factors likely to contribute to high P loss as well as BMPs that can decrease P loss risks. BMPs should focus on controlling both particulate and dissolved P losses.

Predation risk allocation or direct vigilance response in the predator interaction between perch (Perca fluviatilis L.) and pike (Esox lucius L.)?

Abstract – Predation risk allocation hypothesis predicts that a prey's response to predator depends on prey's previous experience on predator. Here we tested whether the group of three perch respond differentially to pike, predator of perch, depending on the timing of high constant (HC) and high unpredictable (HU) risk periods within low constant risk periods in short‐term (10 h) experiments, and whether the response is stronger during a HU risk period than during a HC risk period. Perch clearly erected the dorsal fin in response to predation risk treatments (pike odour only, odour and visible pike). Decrease in activity and increase in shoaling behaviour were observed mainly during high risk periods. However, the perch's responses to pike did not differ statistically between periods of various levels of predation risk or depending on the timing of high risk situations within constant low risk periods, and thus, suggesting that perch respond mainly to changes in the current predation risk.

The effects of temporal variation in predation risk on anti-predator behaviour: an empirical test using marine snails.

Foraging animals must often balance the conflicting demands of finding food and avoiding predators. Temporal variation in predation risk is expected to influence how animals allocate time to these behaviours. Counterintuitively, the proportion of time spent foraging during both high- and low-risk periods should increase with increasing time exposed to high risk. We tested this prediction using intertidal marine snails (Littorina spp.) that were exposed to temporal variation in perceived predation risk from crabs (Cancer productus and Cancer magister). Our results were consistent with those predicted for high-risk, but not low-risk, periods. During high-risk periods, a greater number of snails foraged (versus those that left the water or remained in their shells) as time at high perceived risk increased. For low-risk periods, there was no relationship between the number of snails foraging and time at high risk. This might be due to snails in all treatments foraging maximally in the low-risk periods. As a consequence, the difference in the number of snails foraging between high- and low-risk periods decreased with increasing time subject to high risk. These results indicate that the commonly used protocol of exposing foragers to a single pulse of heightened risk might tend to overestimate their typical investment in anti-predator behaviour.

Temporal Variation in Danger Drives Antipredator Behavior: The Predation Risk Allocation Hypothesis

The rapid response of animals to changes in predation risk has allowed behavioral ecologists to learn much about antipredator decision making. A largely unappreciated aspect of such decision making, however, is that it may be fundamentally driven by the very thing that allows it to be so readily studied: temporal variation in risk. We show theoretically that temporal variability in risk leaves animals with the problem of allocating feeding and antipredator efforts across different risk situations. Our analysis suggests that an animal should exhibit its greatest antipredator behavior in high-risk situations that are brief and infrequent. An animal should also allocate more antipredator effort to high-risk situations and more feeding to low-risk situations, with an increase in the relative degree of risk in high-risk situations. However, the need to feed leaves an animal with little choice but to decrease its allocation of antipredator effort to high-risk situations as they become more frequent or lengthy; here, antipredator effort in low-risk situations may drop to low levels as an animal allocates as much feeding as possible to brief periods of low risk. These conclusions hold under various scenarios of interrupted feeding, state-dependent behavior, and stochastic variation in risk situations. Our analysis also suggests that a common experimental protocol, in which prey animals are maintained under low risk and then exposed to a brief "pulse" of high risk, is likely to overestimate the intensity of antipredator behavior expected under field situations or chronic exposure to high risk.

Seedcorn Maggot (Diptera: Anthomyiidae) Phenology in Central Iowa and Examination of a Thermal-Unit System to Predict Development Under Field Conditions

Two generations of seedcorn maggots (SCM)occurred in central Iowa in 1980 and 1981. In both years, overwintering flies appeared in late April (at 181/198°Dc; 1980–1981) and the F1 generation appeared in early June (at 494/490 degree-days C; 1980–1981). SCM were uncommon or absent in the summer and fall, strongly suggesting aestivation by flies in the F2. Air temperatures were useful in predicting SCM development in the field; however, both air and soil temperatures overestimated SCM development. Our results indicate that low-risk planting periods could be identified with additional knowledge of SCM population biology.

A correlational study of neural tube defects and infectious diseases

This paper presents a study of the relationship between levels of community-reportedinfectious diseases (measles, rubella, influenza, mumps, scarlet fever, hepatitis A, and salmonella) and rates of neural tube defects (anencephalus and spina bifida) in Los Angeles County during 1968–77. Cases of anencephalus and spina bifida were ascertained from vital records, and rates of the infectious diseases under study were obtained from county Communicable Disease reports. No statistically significant correlation was observed between the quarterly trends of infectious diseases and neural tube defects over the study period. No relationships were observed between the seasonal patterns of neural tube defects and the diseases. Using periods of elevated disease activity to determine hypothetical high- and low-risk periods for conceiving infants with these defects, none of the rate ratios was significantly elevated above unity for any of the infectious diseases under study. Because of limitations in study design, accuracy of case identification, and accuracy of disease reporting, our results cannot be interpreted as disproving a role for these infectious diseases in the etiology of neural tube defects. Nevertheless, our results do indicate that such associations as may exist are not strong enough to be reflected in community health data.