Animal movement rates as behavioural bouts

Johnson et al . ( Journal of Animal Ecology , 2002, 71 , 225–235) have proposed a new technique for identifying scales of movement in animals. Animals are located at certain time intervals, and movement rates between successive animal relocations are calculated. The null model of a nonscalar response predicts a decreasing linear relationship between log(frequency) vs. movement rate, while a scalar response predicts a monotonically decreasing curve with an inflection point at the separation between the processes. I tested this technique using three types of simulated movement paths: correlated random walks, directed walks, and movements in patchy habitat. None of the simulations showed the results expected by the technique. This occurs because the technique assumes that movement rates are exponentially distributed, which is highly unlikely. Thus before this technique can be applied to animal movement data we need to understand how spatial and temporal scale, as well as sampling interval, affect the frequency histogram of animal movement rates.     

The effects of NPK fertilization for nine years on boreal forest vegetation in northwestern Canada

Abstract. Plant productivity is limited by mineral nutrient availability in many boreal forest ecosystems. This study is an analysis of the growth responses of components of a boreal plant community (cryptogams, herbaceous and woody perennials, the dominant shrubs Salix glauca (grey willow) and Betula glandulosa (bog birch) and the dominant tree Picea glauca (white spruce), to the addition of an NPK fertilizer over a nine-year period. The study was carried out in a low-nutrient boreal forest ecosystem in the Yukon territory in northwestern Canada. The following predictions were tested: (1) that there would be an overall increase in abundance (measured either as cover, density, or dry mass) of all components of the vegetation, (2) that vegetation composition would change as more competitive species increased in abundance and (3) that initial community changes in response to fertilization would be transient. In general, all predictions were found to be true. Species composition changed rapidly in response to fertilizer. Graminoids (e.g. Festuca altaica) and some dicots (e.g. Mertensia paniculata and Achillea millefolium) increased in cover, while other dicots (e.g. Anemone parviflora), dwarf shrubs (e.g. Arctostaphylos uvaursi), bryophytes and lichens declined. There was a significant increase in the growth rate of the two dominant shrubs and of Picea, but not in the cone crop or seed production by Picea. Surveys after 1 or 2 years showed responses by the vegetation but more stable patterns of response did not emerge until after 5 or 6 years. There were consistent and directional changes in the percent cover of some of the herbaceous species on control plots. Growth rates of Salix and Betula varied considerably from year to year, independently of treatment. Long-term studies are essential if we are to understand the role of nutrient limitation in this ecosystem.