Effects of simulated herbivory on growth and reproduction of two beach annuals, Cakile edentula and Corispermum hyssopifolium
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Authors: K. E. Gedge, and M. A. Maun
Date: 1992
Journal: Canadian Journal of Botany
Volume: 70
Number: 12
Pages: 2467-2475
Summary of Methods: Four experiments (two field, two greenhouse) were conducted at The University of Western Ontario and at Lake Huron [Pinery Provincial Park (43° 15’ N, 81° 50’ W), Port Franks (43° 15’ N, 81° 51’ W)]to examine how Cakile edentula var. lucustris (sea rocket) and Corispermum hyssopifolium (bugseed) responded to simulated and natural defoliation. Field trial one, wild plants were monitored for actual level of herbivory from June through July and the degree of utilization was recorded as one of six categories (0-5, 5-25, 25-50, 50-75, 75-95, 95-100%). Field trial two, involved manually applying five defoliation treatments (control, 25%, 50%, 75%, and 100% leaf removal) to wild C. edentula and Cor. hyssopifollium in July and August. Plants were harvested at maturity, and data was collected for mortality, biomass production, number of fruits and seed mass. Greenhouse study one, plants received one of five defoliation treatments [control (no defoliation), 25 %, 50%, 75%, and 100% leaf removal] applied at five age groups for C. edentula, and three age groups for Cor. hyssopifollium. Greenhouse study two, plants were raised and transplanted to an infected cabbage field to test response to insect herbivory. Plants were assigned a defoliation category (same as field study) and removed from field to be grown to adulthood in the greenhouse once assigned level of herbivory was reached. Data was collected for how quickly the plant reached assigned level of damage, biomass production, number of fruits produced, and seed mass.
Article Summary / Main Points: Field trial one, no conclusions about the effects of herbivores on Cor. hysopifollium at Pinery could be drawn due to low plant populations. Wild plants of C. edentula received little grazing (primarily insect) damage early, but nearly all plants received some herbivory by the end of July. Whitetail deer were the primary cause of herbivory greater than 25%. Browsing affected plant productivity, but did not appear to threaten plant populations. Field trial two, manual defoliation of C. edentula resulted in no mortality at any treatment level or dates with little effect upon biomass production, though early defoliation seed mass was decreased . High levels of natural mortality on Cor. hysopifollium resulted in an inability to assess wild plant mortality at different defoliation levels. Defoliation before flowering resulted in increased biomass production (compensatory growth) for all treatments except control and complete leaf removal (100%). Defoliation after flowering resulted in decreased biomass production at 25% and 75% of leaf removed while August defoliation decreased seed production. Greenhouse study one, flowering was delayed for C. edentula on all plants when treated before flowering and when seedlings and juveniles received 100% defoliation. Fruit production was decreased when leaf removal was greater than 40%. Plant height declined with increasing leaf removal. Biomass and seed production decreased when Cor. hysopifollium was completely defoliated at six weeks. Greenhouse study two, greenhouse plants introduced into infected cabbage fields were quickly colonized by insects with complete defoliation occurring within eleven days. Biomass, fruit production, and seed mass were not affected by level of defoliation.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: Not Applicable
Agrovoc Control Words: Riparian zones Grazing Wildlife
Article Review Type: Refereed
Article Type: Scientific Synthesis
Keywords: cakile edentula, corispermum hyssopifolium, white-tailed deer, odocoileus virginianus, defoliation intensity, defoliation stage, compensatory response, intermediate growth
Annotation: C. edentula and Cor. hyssopifolium evade herbivory through low population density and are able to overcompensate when low levels of herbivory occur. Whitetail deer browsing resulted in the highest levels of herbivory to wild plants and increasing deer populations could pose a threat to plant populations. Study has limited application to the intermountain west region.
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