Cohabitation of three Hieracium species in relation to the spatial heterogeneity in an old pasture

Publisher Website
Google Scholar
Abstract
Three closely related species, Hieracium floribundum. H. pratense, and H. florentinum, are found in Wellington County and they frequently grow together in old pastures near Guelph, Ontario. In the 60 × 60 m study area, the maximum difference in elevation per metre was 0.5 m. Each species occupied a distinctive but a highly overlapping position in the available niche space as determined by relief exposure and influenced by competition. Although all three species were found on slopes facing in any direction, each was significantly associated with a particular exposure. Hieracium floribundum and H. pratense were positively associated with northwest- and north-facing slopes, respectively. These two vegetatively reproducing species displaced H. florentinum from northern slopes when they came into contact. Hieracium florentinum had the broadest niche over the range of exposures but was positively associated only with south-facing slopes. The small variations in relief resulted in higher maximum temperatures and higher accumulated degree-hours on southwest than on northeast slopes. We concluded that the spatial heterogeneity of the old pasture was sufficiently high and that temperature differences were great enough to account for the cohabitation of the three species. The conclusions drawn from the study area are extrapolated and used to explain the distribution pattern within the county.