The Relative Importance of Patch Area and Perimeter–Area Ratio to Grassland Breeding Birds

Habitat fragmentation has been implicated as a major cause of population decline in grassland birds. We tested the hypothesis that a combination of area and shape determines the use of grassland patches by breeding birds. We compared both species richness and individual species presence in 45 wet meadow grasslands in the floodplain of the central Platte River, Nebraska. Bird data were collected through the use of belt transects and supplemented by walking and listening outside transects. Our data supported our primary hypothesis that perimeter–area ratio, which reflects both the area and shape of a patch, is the strongest predictor of both individual species presence and overall species richness. The probability of occurrence for all six common species (Grasshopper Sparrows, Bobolinks, Upland Sandpipers, Western Meadowlarks, Dickcissels, and Red-winged Blackbirds) was significantly inversely correlated with perimeter–area ratio. The probability of occurrence of Grasshopper Sparrows, Bobolinks, Upland Sandpipers, and Western Meadowlarks was also correlated with area. We conclude that species richness is maximized when patches are large (\u3e50 ha) and shaped so that they provide abundant interior areas, free from the impacts of edges

The Relative Importance of Patch Area and Perimeter–Area Ratio to Grassland Breeding Birds

Habitat fragmentation has been implicated as a major cause of population decline in grassland birds. We tested the hypothesis that a combination of area and shape determines the use of grassland patches by breeding birds. We compared both species richness and individual species presence in 45 wet meadow grasslands in the floodplain of the central Platte River, Nebraska. Bird data were collected through the use of belt transects and supplemented by walking and listening outside transects. Our data supported our primary hypothesis that perimeter–area ratio, which reflects both the area and shape of a patch, is the strongest predictor of both individual species presence and overall species richness. The probability of occurrence for all six common species (Grasshopper Sparrows, Bobolinks, Upland Sandpipers, Western Meadowlarks, Dickcissels, and Red-winged Blackbirds) was significantly inversely correlated with perimeter–area ratio. The probability of occurrence of Grasshopper Sparrows, Bobolinks, Upland Sandpipers, and Western Meadowlarks was also correlated with area. We conclude that species richness is maximized when patches are large (\u3e50 ha) and shaped so that they provide abundant interior areas, free from the impacts of edges

Influence of Richness and Seeding Density on Invasion Resistance in Experimental Tallgrass Prairie Restorations

In recent years, agricultural producers and non-governmental organizations and agencies have restored thousands of hectares of cropland to grassland in the Great Plains of the United States. However, little is known about the relationships between richness and seeding density in these restorations and resistance to invasive plant species. We assessed the effects of richness and seeding density on resistance to invasive and other unseeded plant species in experimental tallgrass prairie plots in central Nebraska. In 2006, twenty-four 55 m × 55 m plots were planted with six replicates in each of four treatments: high richness (97 species typically planted by The Nature Conservancy), at low and high seeding densities, and low richness (15 species representing a typical Conservation Reserve Program mix, CP25), at low and high seeding densities. There was a significant negative relationship between richness and basal cover of unseeded perennial forbs/legumes and unseeded perennial/annual grasses, abundance of bull thistle (Cirsium vulgare), and the number of inflorescences removed from smooth brome (Bromus inermis) transplants. Invasion resistance may have been higher in the high richness treatments because of the characteristics of the dominant species in these plots or because of greater interspecific competition for limiting resources among forbs/legumes with neighboring plants belonging to the same functional group. Seeding density was not important in affecting invasion resistance, except in the cover of unseeded grasses. Increasing seed mix richness may be more effective than increasing the seeding density for decreasing invasion by unseeded perennial species, bull thistle, and smooth brome

Responses of predatory invertebrates to seeding density and plantspecies richness in experimental tallgrass prairie restorations

In recent decades, agricultural producers and non-governmental organizations have restored thousandsof hectares of former cropland in the central United States with native grasses and forbs. However,the ability of these grassland restorations to attract predatory invertebrates has not been well docu-mented, even though predators provide an important ecosystem service to agricultural producers bynaturally regulating herbivores. This study assessed the effects of plant richness and seeding density onthe richness and abundance of surface-dwelling (ants, ground beetles, and spiders) and aboveground(ladybird beetles) predatory invertebrates. In the spring of 2006, twenty-four 55 m × 55 m-plots wereplanted to six replicates in each of four treatments: high richness (97 species typically planted by TheNature Conservancy), at low and high seeding densities, and low richness (15 species representing a typ-ical Natural Resources Conservation Service Conservation Reserve Program mix, CP25), at low and highseeding densities. Ants, ground beetles, and spiders were sampled using pitfall traps and ladybird beetleswere sampled using sweep netting in 2007–2009. The abundance of ants, ground beetles, and spidersshowed no response to seed mix richness or seeding density but there was a significant positive effect ofrichness on ladybird beetle abundance. Seeding density had a significant positive effect on ground beetleand spider species richness and Shannon–Weaver diversity. These results may be related to differencesin the plant species composition and relative amount of grass basal cover among the treatments ratherthan richness

Risk Factors for Posttraumatic Stress Disorder Among Deployed US Male Marines

<p>Abstract</p> <p>Background</p> <p>Combat exposure has been reported as one of the strongest risk factors for postdeployment posttraumatic stress disorder (PTSD) among military service members. Determining the impact of specific deployment-related exposures on the risk of developing PTSD has not been fully explored. Our study objective was to explore the relationship between specific combat exposures and other life experiences with postdeployment PTSD.</p> <p>Methods</p> <p>This study consisted of male Marines who completed a Recruit Assessment Program (RAP) survey during recruit training at the Marine Corps Recruit Depot in San Diego, California as well as a follow-up survey several years after recruit training. Study participants included those Marines who deployed to the current operations in Iraq or Afghanistan between the baseline and follow-up surveys. Multivariable logistic regression was performed to determine which significant exposures and experiences were associated with postdeployment PTSD.</p> <p>Results</p> <p>Of the 706 study participants, 10.8% screened positive for postdeployment PTSD. Those who reported feeling in great danger of death (odds ratio [OR] = 4.63, 95% confidence interval [CI]: 2.46-8.73), were shot or seriously injured (OR = 3.51, 95% CI: 1.58-7.77), saw someone wounded or killed (OR = 2.47, 95% CI: 1.08-5.67), and baseline (before recruit training) prior violence exposures (OR = 2.99, 95% CI: 1.46-6.10) were at increased odds for reporting PTSD symptoms. Number of deployments, number of close friends or relatives reported at follow-up, and enlisted pay grade were also significantly associated with postdeployment PTSD.</p> <p>Conclusions</p> <p>Combat exposures, specifically the threat of death, serious injury, and witnessing injury or death are significant risk factors for screening positive for postdeployment PTSD among male Marines as well as violence exposures prior to entering the Marine Corps, which are independent of future combat exposures. A thorough history of lifetime violence exposures should be pursued when considering a clinical diagnosis of PTSD.</p

Responses of predatory invertebrates to seeding density and plantspecies richness in experimental tallgrass prairie restorations

In recent decades, agricultural producers and non-governmental organizations have restored thousandsof hectares of former cropland in the central United States with native grasses and forbs. However,the ability of these grassland restorations to attract predatory invertebrates has not been well docu-mented, even though predators provide an important ecosystem service to agricultural producers bynaturally regulating herbivores. This study assessed the effects of plant richness and seeding density onthe richness and abundance of surface-dwelling (ants, ground beetles, and spiders) and aboveground(ladybird beetles) predatory invertebrates. In the spring of 2006, twenty-four 55 m × 55 m-plots wereplanted to six replicates in each of four treatments: high richness (97 species typically planted by TheNature Conservancy), at low and high seeding densities, and low richness (15 species representing a typ-ical Natural Resources Conservation Service Conservation Reserve Program mix, CP25), at low and highseeding densities. Ants, ground beetles, and spiders were sampled using pitfall traps and ladybird beetleswere sampled using sweep netting in 2007–2009. The abundance of ants, ground beetles, and spidersshowed no response to seed mix richness or seeding density but there was a significant positive effect ofrichness on ladybird beetle abundance. Seeding density had a significant positive effect on ground beetleand spider species richness and Shannon–Weaver diversity. These results may be related to differencesin the plant species composition and relative amount of grass basal cover among the treatments ratherthan richness

Influence of Richness and Seeding Density on Invasion Resistance in Experimental Tallgrass Prairie Restorations

In recent years, agricultural producers and non-governmental organizations and agencies have restored thousands of hectares of cropland to grassland in the Great Plains of the United States. However, little is known about the relationships between richness and seeding density in these restorations and resistance to invasive plant species. We assessed the effects of richness and seeding density on resistance to invasive and other unseeded plant species in experimental tallgrass prairie plots in central Nebraska. In 2006, twenty-four 55 m × 55 m plots were planted with six replicates in each of four treatments: high richness (97 species typically planted by The Nature Conservancy), at low and high seeding densities, and low richness (15 species representing a typical Conservation Reserve Program mix, CP25), at low and high seeding densities. There was a significant negative relationship between richness and basal cover of unseeded perennial forbs/legumes and unseeded perennial/annual grasses, abundance of bull thistle (Cirsium vulgare), and the number of inflorescences removed from smooth brome (Bromus inermis) transplants. Invasion resistance may have been higher in the high richness treatments because of the characteristics of the dominant species in these plots or because of greater interspecific competition for limiting resources among forbs/legumes with neighboring plants belonging to the same functional group. Seeding density was not important in affecting invasion resistance, except in the cover of unseeded grasses. Increasing seed mix richness may be more effective than increasing the seeding density for decreasing invasion by unseeded perennial species, bull thistle, and smooth brome