Relative growth rate and the grazing optimization hypothesis
Relative growth rates and the grazing optimization ..
Coastal marshes on the north shore of Akimiski Island constitute the most important brood rearing habitat for geese. In the late 1970s, these coastal marshes were dominated by Puccinellia phryganodes and Carex subspathacea (Martini and Glooschenko 1984, Jefferies et al. 2006), both of which are high quality forage plants for geese (Gadallah and Jefferies 1995a, b). However, these coastal habitats have been progressively degraded over time by the foraging activities of large numbers of staging and nesting geese, and habitat loss was most pronounced from 1985-1993, when more than 5000 ha of coastal marsh were lost on Akimiski Island (Jefferies et al. 2006). Based on the decline in harvest rates of juvenile Canada Geese, we hypothesize that the goose-habitat relationship on Akimiski Island reached a tipping point starting in about 1986, presumably because abundance of Canada Geese and their broods exceeded carrying capacity of brood rearing areas, which led to declines in gosling growth and postfledging survival. Habitat loss may have continued through 2000 (Jefferies et al. 2006), and although some forage species increased in abundance between 1998-2008, the magnitude of changes was small, and above-ground biomass remained low (Kotanen and Abraham 2013). Despite this, we found that first-year survival rates of Canada Geese increased over the course of our study, and increased survival was associated with increases in gosling size. We attribute the increase in gosling size to increases in per capita forage caused by the overall decline in abundance of nesting Canada Geese. The 1990-2010 annual decline was about 585 breeding Canada Geese per year: linear regression with a log link P
M.I DyerRelative growth rates and the grazing optimization hypothesis
In this study, we examined plant traits and soil properties in response to different grassland management strategies in the Northern Tibetan Plateau. The specific aims are: (1) to reveal the impact of different grassland managements on plant traits and soil properties and to test the grazing optimization hypothesis; (2) to test the isometric partitioning theory on different alpine species under varying grassland management patterns; and (3) to explore the effects of grazing stress on clonal growth.