How Transient Patches Affect Population Dynamics: The Case of Hypoxia and Blue Crabs

Transient low-oxygen patches may have important consequences for the population dynamics of estuarine species. We investigated whether these transient hypoxic patches altered population dynamics of the commercially important blue crab (Callinectes sapidus) and assessed two alternative hypotheses for the causal mechanism. One hypothesis is that temporary reductions in habitat due to hypoxia increase cannibalism. The second hypothesis is that crab population dynamics result from food limitation caused by hypoxia-induced mortality of the benthos. We developed a spatially explicit individual-based model of blue crabs in a hierarchical framework to connect the autoecology of crabs with the spatial and temporal dynamics of their physical and biological environments. Three primary scenarios were run to examine the interactive effects of (1) hypoxic extent vs. static and transient patches, (2) hypoxic extent vs. prey abundance, and (3) hypoxic extent vs. cannibalism potential. Static patches resulted in populations limited by egg production and recruitment whereas transient patches led to populations limited by the effects of cannibalism and patch interactions. Crab survivorship was greatest for simulations with the largest hypoxic patches which also had the lowest prey abundance and lowest crab densities. In these simulations, nearly all crab mortality was accounted for by aggression, not starvation. In addition, increased prey abundance had little influence on crab abundance and dynamics, and massive reductions in prey abundance (\u3e 50%) were necessary to decrease crab abundance, survival, and egg production. Our analyses suggest that cannibalism coupled with decreased egg production determined key aspects of crab demography. Specifically, decreased cannibalism potential resulted in a food-limited crab population with long development times and high adult crab densities whereas increased cannibalism potential led to low adult crab densities with higher individual egg production rates. Our analyses identified several key knowledge gaps, including the nature of crab-crab cannibalism and the role of refuges from predation. Several experiments are suggested to test model predictions and to improve understanding of ecosystem-population linkages for this estuarine species

Evidence of Climate-Induced Range Contractions in Bull Trout \u3ci\u3eSalvelinus confluentus\u3c/i\u3e in a Rocky Mountain Watersehd, U.S.A.

Many freshwater fish species are considered vulnerable to stream temperature warming associated with climate change because they are ectothermic, yet there are surprisingly few studies documenting changes in distributions. Streams and rivers in the U.S. Rocky Mountains have been warming for several decades. At the same time these systems have been experiencing an increase in the severity and frequency of wildfires, which often results in habitat changes including increased water temperatures. We resampled 74 sites across a Rocky Mountain watershed 17 to 20 years after initial samples to determine whether there were trends in bull trout occurrence associated with temperature, wildfire, or other habitat variables. We found that site abandonment probabilities (0.36) were significantly higher than colonization probabilities (0.13), which indicated a reduction in the number of occupied sites. Site abandonment probabilities were greater at low elevations with warm temperatures. Other covariates, such as the presence of wildfire, nonnative brook trout, proximity to areas with many adults, and various stream habitat descriptors, were not associated with changes in probability of occupancy. Higher abandonment probabilities at low elevation for bull trout provide initial evidence validating the predictions made by bioclimatic models that bull trout populations will retreat to higher, cooler thermal refuges as water temperatures increase. The geographic breadth of these declines across the region is unknown but the approach of revisiting historical sites using an occupancy framework provides a useful template for additional assessments

Dataset for the article: Metal contamination and food web changes alter exposure to upper trophic levels in upper Blackfoot River basin streams, Montana

Reduced invertebrate abundance and diversity are common responses to heavy metals contamination in mining-impacted streams. The resulting changes in community composition may have implications for metals accumulation and transfer through the food web. We investigated how changes in invertebrate community composition (abundance, species richness, and food web complexity) influence metals bioaccumulation and exposure risk to upper trophic levels along a contamination gradient in the upper Blackfoot River basin, Montana. Invertebrate species richness exhibited the strongest decline with increasing sediment metals concentrations, driven by the loss of metals-sensitive taxa. These changes in invertebrate community composition resulted in a decline in the proportion of invertebrates in the scraper functional feeding group, likely influencing dietary metals exposure to the invertebrate community. Additionally, invertebrates with a strong propensity-to-drift increased with sediment contamination, potentially facilitating metals transfer to fish and higher trophic levels through predation. By using invertebrate exposure values (invertebrate abundance x metals concentrations), we found that moderately contaminated sites in our study area produced both the highest invertebrate exposure values and the highest metals concentrations in fish tissues. Our results indicate that considering both changes in invertebrate community composition and metal concentrations is an important step towards understanding and evaluating potential toxic effects to upper trophic levels in mining-impacted streams. Geographic location: Upper Blackfoot River, Montana and tributaries in the vicinity of the Upper Blackfoot Mining Complex Associated data and attachments (files available below): Water quality [Water_quality.csv] Fine sediment metals [Fine_sediment_metals.csv] Invertebrate community composition [Invertebrate_community_composition.csv] Invertebrate metals concentrations [Invertebrate_metals.csv] Fish tissue metals [Fish_metals.csv] Fish population estimate [Fish_population.csv] Site descriptions [Site_descriptions.csv] Site map [Site_map.pdf] (see Download button above

Toward a more ecologically informed view of severe forest fires

We use the historical presence of high-severity fire patches in mixed-conifer forests of the western United States to make several points that we hope will encourage development of a more ecologically informed view of severe wildland fire effects. First, many plant and animal species use, and have sometimes evolved to depend on, severely burned forest conditions for their persistence. Second, evidence from fire history studies also suggests that a complex mosaic of severely burned conifer patches was common historically in the West. Third, to maintain ecological integrity in forests born of mixed-severity fire, land managers will have to accept some severe fire and maintain the integrity of its aftermath. Lastly, public education messages surrounding fire could be modified so that people better understand and support management designed to maintain ecologically appropriate sizes and distributions of severe fire and the complex early-seral forest conditions it creates

Evaluating older drivers’ skills

The Contracting Officer's Technical Representative for this project was Dr. Kathy Sifrit.Research has demonstrated that older drivers pose a higher risk of involvement in fatal crashes at intersections than younger drivers. Age-triggered restrictions are problematic as research shows that the majority of older people have unimpaired driving performance. Thus, it has become important to be able to identify which drivers are at risk of crashes and apply driving limitations based on this risk (instead of age alone). The objective of this project was to review the report from the 2003 University of Florida Consensus Conference as well as other important documents on similar topics, and to interview experts to obtain information about the strengths and weaknesses of these specialist-administered screening and assessment tools, self-screening instruments and training methods. This report will help to guide future research by highlighting tools and methods commonly used by clinicians that have not yet been adequately evaluated and those which may already be recommended for use. The goal was not to reach consensus but to provide a rich background from the literature combined with expert opinions in an attempt to guide decisions and research goals related to these evaluation tools.National Highway Traffic Safety Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/98832/1/102948.pd