Making predictions in a changing world: The benefits of individual-based ecology

Ecologists urgently need a better ability to predict how environmental change affects biodiversity. We examine individual-based ecology (IBE), a research paradigm that promises better a predictive ability by using individual-based models (IBMs) to represent ecological dynamics as arising from how individuals interact with their environment and with each other. A key advantage of IBMs is that the basis for predictions-fitness maximization by individual organisms-is more general and reliable than the empirical relationships that other models depend on. Case studies illustrate the usefulness and predictive success of long-term IBE programs. The pioneering programs had three phases: conceptualization, implementation, and diversification. Continued validation of models runs throughout these phases. The breakthroughs that make IBE more productive include standards for describing and validating IBMs, improved and standardized theory for individual traits and behavior, software tools, and generalized instead of system-specific IBMs. We provide guidelines for pursuing IBE and a vision for future IBE research

Use of the t -Distribution to Construct Seismic Hazard Curves for Seismic Probabilistic Safety Assessments

Seismic probabilistic safety assessments are used to help understand the impact potential seismic events can have on the operation of a nuclear power plant. An important component to seismic probabilistic safety assessment is the seismic hazard curve which shows the frequency of seismic events. However, these hazard curves are estimated assuming a normal distribution of the seismic events. This may not be a strong assumption given the number of recorded events at each source-to-site distance. The use of a normal distribution makes the calculations significantly easier but may underestimate or overestimate the more rare events, which is of concern to nuclear power plants. This paper shows a preliminary exploration into the effect of using a distribution that perhaps more represents the distribution of events, such as the t-distribution to describe data. The integration of a probability distribution with potentially larger tails basically pushes the hazard curves outward, suggesting a different range of frequencies for use in seismic probabilistic safety assessments. Therefore the use of a more realistic distribution results in an increase in the frequency calculations suggesting rare events are less rare than thought in terms of seismic probabilistic safety assessment. However, the opposite was observed with the ground motion prediction equation considered

Survival of fish impinged on a rotary disk screen

An impingement survival study was conducted to determine 48-h survival of fish impinged on a modified rotary disk screen equipped with fish protection features. The rotary disk screen was installed for a technology evaluation at the cooling-water intake structure of the North Omaha Station located on the Missouri River in Omaha, Nebraska. Hatchery-raised fish and native fish collected from the Missouri River were released in batches into the rotary disk screen bay and collected with a system that was constructed to recover fish from the screen\u27s vacuum system. That system was designed to remove fish from the rotary disk screen and return them to the river. Screen performance was assessed in April and August, representing spring and summer environmental conditions. The 48-h survival rates of hatchery-raised fathead minnow Pimephales promelas, channel catfish Ictalurus punctatus, and bluegills Lepomis macrochirus and a group of mixed native species approached 100%. Survival rates were not statistically different between test groups and controls, indicating that impingement did not contribute to the observed mortality. High survival rates of impinged fish removed from the screen indicated that the rotary disk screen would reduce impingement losses at the North Omaha Station, where losses due to impingement on the existing vertical traveling screens are assumed by the U.S. Environmental Protection Agency to approach 100% because the screens lack fish protection features. Our study results suggest that the rotary disk screen tested could be considered an alternative technology under section 316(b) of the Clean Water Act, which requires power plants to install the best technology available to reduce impingement. Use of hatchery-reared fish and native fish collected from the river assured that an adequate number of fish were tested to provide statistically reliable results and allowed the use of controls to account for mortality due to handling stresses experienced by test fish