Date of Award
Doctor of Philosophy
Fifteen biennial species co-existed in an abandoned gravel pit near London, Ontario. Investigations were performed to identify variations in their regeneration characteristics. Once identified, variations were compared to attempt to explain these species' co-existence in this habitat. Mean net seed production per plant, mean seed weight per species, and dispersal of diaspores by wind, water, and animals were determined for each species. Mean seed production per plant ranged from 119 to 22,425. Mean weight per seed per species ranged from 0.07mg to 13.03mg. Mean weight per seed varied throughout the growing season in each of thirteen species. Diaspores of eight species had no morphological adaptation for dispersal, five were adapted for wind dispersal, and two for external carriage by animals. Diaspores of all species floated; those of thirteen floated after agitation. Greater numbers of diaspores of two species adhered to a dry groundhog pelt whereas numbers of those of thirteen species adhered to a wet pelt. The biennial seed rain within the study area was assessed using a grid of sticky traps. The biennial seed bank was assessed through collection and subsequent incubation of soil cores. Viable ungerminated seeds present in two collections were extracted. Both seed rain and seed bank were dominated by two taxa. Six species formed persistent, and two transient, seed banks. Seeds of six species were nondormant; a portion of those of four were nondormant, and those of five were innately dormant. Seeds of each species were sown in both sparsely and densely vegetated plots. Seedling emergence was greater in dense plots for four species but in sparse plots for the others. Mean percentage seedling establishment ranged from 0 to 83% in sparse plots and from 0 to 92% in dense plots. Seeds of all species were sown into a range of gap sizes and soil textures. More seedlings of five taxa established on medium to fine textures whereas more seedlings of six species established on medium to coarse textures. More seedlings of all species established in the three largest gaps. These species differed in every life history characteristic investigated.
Threadgill, Paul Frederick, "Variations In The Biennial Life History Strategy Among 15 Ruderal Species In An Abandoned Gravel Pit Near London, Ontario" (1986). Digitized Theses. 1563.