Propagule Pressure and Stream Characteristics Influence Introgression: Cutthroat and Rainbow Trout in British Columbia

Hybridization and introgression between introduced and native salmonids threaten the continued persistence of many inland cutthroat trout species. Environmental models have been developed to predict the spread of introgression, but few studies have assessed the role of propagule pressure. We used an extensive set of fish stocking records and geographic information system (GIS) data to produce a spatially explicit index of potential propagule pressure exerted by introduced rainbow trout in the Upper Kootenay River, British Columbia, Canada. We then used logistic regression and the information-theoretic approach to test the ability of a set of environmental and spatial variables to predict the level of introgression between native westslope cutthroat trout and introduced rainbow trout. Introgression was assessed using between four and seven co-dominant, diagnostic nuclear markers at 45 sites in 31 different streams. The best model for predicting introgression included our GIS propagule pressure index and an environmental variable that accounted for the biogeoclimatic zone of the site (r2¼0.62). This model was 1.4 times more likely to explain introgression than the next-best model, which consisted of only the propagule pressure index variable. We created a composite model based on the model-averaged results of the seven top models that included environmental, spatial, and propagule pressure variables. The propagule pressure index had the highest importance weight (0.995) of all variables tested and was negatively related to sites with no introgression. This study used an index of propagule pressure and demonstrated that propagule pressure had the greatest influence on the level of introgression between a native and introduced trout in a human-induced hybrid zone

Renesting Decisions and Annual Fecundity of Female Dickcissels (Spiza americana) in Illinois

ABSTRACT.-Renesting decisions and annual fecundity are crucial for interpreting other demographic information, yet are infrequently reported. We used radiotelemetry to monitor female Dickcissels (Spiza americana) throughout the 1999 and 2000 breeding seasons in southeastern Illinois. Overall fecundity (regardless of whether females remained in the study area throughout the breeding season) was 0.61 ± 0.13 female fledglings per year. Of females that remained within the study area, 94% fledged young (1.25 ± 0.15 female fledglings per year). Most females (62%) that experienced nest failure emigrated from the study area (moved \u3e10 km) in 2.8 ± 0.6 days; others (36%) initiated subsequent nests in 8.5 ± 0.8 days. After fledging ~1 young, 95% of females ceased breeding for the season. Successful and failed nest sites were indistinguishable on the basis of vegetative characteristics. Moreover, replacement nests had similar vegetative characteristics and were similar distances from habitat edges, compared with initial nests, which suggests that female Dickcissels do not or cannot improve nest-site characteristics in response to nest failure. We observed two behaviors unusual in female Dickcissels: one bird that fledged two broods in one season, and the return of five females banded in 1999 to the study site in 2000

Renesting Decisions and Annual Fecundity of Female Dickcissels (Spiza americana) in Illinois

ABSTRACT.-Renesting decisions and annual fecundity are crucial for interpreting other demographic information, yet are infrequently reported. We used radiotelemetry to monitor female Dickcissels (Spiza americana) throughout the 1999 and 2000 breeding seasons in southeastern Illinois. Overall fecundity (regardless of whether females remained in the study area throughout the breeding season) was 0.61 ± 0.13 female fledglings per year. Of females that remained within the study area, 94% fledged young (1.25 ± 0.15 female fledglings per year). Most females (62%) that experienced nest failure emigrated from the study area (moved \u3e10 km) in 2.8 ± 0.6 days; others (36%) initiated subsequent nests in 8.5 ± 0.8 days. After fledging ~1 young, 95% of females ceased breeding for the season. Successful and failed nest sites were indistinguishable on the basis of vegetative characteristics. Moreover, replacement nests had similar vegetative characteristics and were similar distances from habitat edges, compared with initial nests, which suggests that female Dickcissels do not or cannot improve nest-site characteristics in response to nest failure. We observed two behaviors unusual in female Dickcissels: one bird that fledged two broods in one season, and the return of five females banded in 1999 to the study site in 2000

Testing road surface treatments to reduce erosion in forest roads in Honduras

Using forest roads produces more erosion and sedimentation than any other forest or agricultural activity. This study evaluated soil losses from a forest road in central Honduras over two consecutive years. We divided a 400-m segment of road into 8 experimental units, each 50 m in length. Four units were treated with Best Management Practices (BMPs) and four were left untreated. The BMP treatments included reshaping the road prism, installing culverts and reshaping of road ditches, compacting 20-cm layers of the road tread, crowning the road surface (3% slope, double drainage), longitudinal sloping (less than 12%), and adding a 10-cm layer of gravel (crush size = 0.63 cm). Soil movement was measured daily during the rainy seasons. The highest soil loss occurred in the control road, around 500 m³km-1 per year, while the road treated with BMP lost approximately 225 m³km-1 per year. These results show that road surface erosion can be reduced up to 50% with the implementation of surface treatments.Los caminos forestales producen mas erosion y sedimentación que cualquier otra actividad agrícola o forestal. En la parte central de Honduras, las perdidas de suelo producidas en la superficie de caminos forestales fueron evaluadas por dos años consecutivos. En la superficie del camino, se establecieron 400 m de camino en los cuales se colocaron ocho unidades experimentales de 50 m de longitud. Cuatro unidades fueron tratadas, mientras que cuatro no fueron tratadas y se dejaron como testigos. Los tratamientos aplicados fueron: conformado del prisma del camino, instalación de alcantarillas y limpieza y conformado de cunetas, compactación en capas de 20 cm con material selecto, bombeo de la superficie del camino con una pendiente transversal doble de 3%, una pendiente longitudinal menor del 12% y una capa de 10 cm de grava triturada (a 1/4 inch = 0.63 cm). Los movimientos de suelo fueron medidos durante las estaciones de lluvia. Los resultados finales mostraron que las perdidas de suelos en los segmentos no tratados fueron de alrededor de 500 m³km-1 por año, mientras que en los segmentos tratados resultó cerca de 225 m³km-1 por año, mostrando que la erosion de la superficie del camino puede ser reducida hasta en un 50% con tratamientos de la superficie

Annual accomplishment report--1992 : Fish Habitat Relationships Program /

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