Rusty crayfish (Orconectes rusticus) were first observed in Trout Lake, Wisconsin, in 1979 and took 19 years to completely disperse around the littoral zone, advancing at an average rate of 0.68 km·year–1. With the invasion of rusty crayfish, we found that fishes that share prey taxa with crayfish declined in numbers over time, but piscivorous fish species did not change in abundance. Snails declined from >10 000 to <5 snails·m–2 in one of the first invaded areas. Mean abundance of Odonata, Amphipoda, and Trichoptera decreased significantly lake-wide. Resident crayfish species nearly disappeared, although total crayfish abundance, driven by high abundances of rusty crayfish, continued to rise. Submerged macrophyte species richness declined by as much as 80% at some locations. Together these responses demonstrate dramatic long-term changes in the littoral zone biota of Trout Lake. Continued invasions of similar lakes in the region suggest that these impacts are occurring on a region-wide basis with potentially irreversible effects on communities and ecosystems. Only through long-term natural experiments such as this study can researchers ascertain the full extent of invasions and their impacts on community and ecosystem process that respond at spatial and temporal scales not captured in mesocosm studies.

Objectives-To investigate the eVect of diVerent durations of stretching (five or 15 seconds) on active and passive range of motion (ROM) in the lower extremity during a five week flexibility training programme. Method-Twenty four university sport club members (19 men, five women), with a mean (SD) age of 20.5 (1.35) years, were randomly assigned to one of three groups (two treatment and one control). The two treatment groups participated in a static active stretching programme three times a week for a five week period, holding each stretch for a duration of either five or 15 seconds. The total amount of time spent in a stretched position was controlled. The five second group performed each stretch nine times and the 15 second group three times resulting in a total stretching time of 45 seconds for both groups for each exercise. The control group did not stretch. Active and passive ROM were determined during left hip flexion, left knee flexion, and left knee extension before and after the training programme using an inclinometer. Results-Two factor within subject analysis of variance indicated no significant diVerence in ROM before and after the training programme for the control group. However, significant improvements in active and passive ROM (p<0.05) were shown in both treatment groups after the five week training programme. Two factor analysis of variance with repeated measures and post hoc analysis showed significant diVerences between the treatment groups and the control group for the improvements observed in active (p<0.05) and passive (p<0.05) ROM. The five and 15 second treatment groups did not diVer from one another when ROM was assessed passively, but significant diVerences were apparent for active ROM, with the 15 second group showing significantly greater improvements (p<0.05) than the five second group. Conclusion-These findings suggest that holding stretches for 15 seconds, as opposed to five seconds, may result in greater improvements in active ROM. However, sustaining a stretch may not significantly aVect the improvements gained in passive ROM. (Br J Sports Med 1999;33:259-263)

No abstract

Landscape boundaries and corridors are areas of small spatial extent relative to their large effects on ecological flows. The trend in ecological literature is to treat corridors and boundaries as separate phenomena on the landscape. This approach, however, misses a fundamental aspect they have in common: their strong influence on ecological flows. Corridors and boundaries exist at opposite ends of a permeability gradient, differing in their effects on rates and direction of flow. The position of landscape structures along this permeability gradient depends on attributes of both the flow and of the structure itself. We discuss boundaries and corridors in terms of mover specificity, scale, and effects on different levels of ecological organization, using rivers and streams to illustrate our points. We predict which structures will act as boundaries or corridors and at what spatial and temporal scales they are likely to be relevant. Considering the function of landscape structures across the boundary-corridor continuum will provide researchers and managers with a more complete, holistic viewpoint and will allow better strategies to attain conservation goals. Linderos y Corredores Como un Control de Flujo Ecológico Continuo: Lecciones de Ríos y ArroyosResumen: Los linderos y corredores de paisajes son áreas de extensión espacial pequeña con relación a la gran magnitud de sus efectos en los flujos ecológicos. En la literatura ecológica existe la tendencia de tratar a los corredores y a los linderos como un fenómeno separado en el paisaje. Sin embargo, esta estrategia pierde la característica común fundamental entre estos dos elementos: una fuerte influencia en los flujos ecológicos. Los corredores y los linderos existen a en extremos opuestos de un gradiente de permeabilidad, difieren en sus efectos en cuanto a las tasas y la dirección del flujo. La posición de estructuras del paisaje a lo largo de este gradiente de permeabilidad depende de los atributos tanto del flujo, como de la estructura en sí misma. Nosotros discutimos los linderos y los corredores en términos de especificidad del transportador, la escala y sus efectos en diferentes niveles de organización ecológica y utilizamos ríos y arroyos para ilustrar nuestros puntos. Predecimos cuales estructuras actuarían como linderos o corredores y a que escala espacial y temporal podrían ser relevantes. Considerando que la función de las estructuras del paisaje a lo largo de un continuo lindero-corredor proporcionará a los investigadores y manejadores un punto de vista mas completo e integral y dará cabida a mejores estrategias para alcanzar las metas de conservación.

Macrophyte harvesting often has been suggested as a way to improve fish growth and size structure in lakes with high densities of submergent macrophytes and stunted fish populations. However, previous experimental tests have provided no clear consensus on whether the technique works for management. We conducted a series of whole‐lake manipulations to test the effects of macrophyte removal on growth of bluegill and largemouth bass. We selected four lakes in southern and central Wisconsin for experimental manipulation and nine others for controls. In August 1994, we removed macrophytes from approximately 20% of the littoral zone by cutting a series of evenly spaced, deep channels throughout each treatment lake. In the first year after manipulation, we observed substantially increased growth rates of some age classes of both bluegill and largemouth bass in treatment lakes relative to controls. Growth rates of other age classes were less responsive to manipulation. We observed increased bluegill and largemouth bass growth despite rapid regrowth of macrophytes in our treatment lakes. By May 1996, fewer than 25% of the channels remained. Our results suggest that harvesting macrophytes in a series of deep channels may be a valuable tool for integrated management of fish and macrophytes.