quantitative and experimental investigation of foodweb dynamics in intermittent freshwater ponds.
Published: 2006
Language: eng
Number of pages: 287
ISBN-13: 9780494218525
Description: The purpose of this study was to identify community-regulating mechanisms in intermittent ponds by contrasting the effects from foodweb manipulations to the natural temporal and spatial variations in four ponds. The ponds differed in depth, hydroperiod length, water chemistry, and community structure: the longer duration pond was dominated by collector-gatherers and had more high trophic level taxa compared with the shorter-duration pond that was dominated by collector-filterers. A 'false start' of the hydroperiod had a strong negative influence on the abundance of zooplankton and higher trophic levels throughout the hydroperiod.The addition versus removal of resources (i.e., leaf litter) in large pond enclosures affected the physicochemical variables in the ponds and generated shifts in the basal resources (e.g., chl a, bacteria, ciliates). The resource addition resulted in lower biomass of many insect taxa, whereas the resource removal had the opposite effects: the magnitudes of the responses were correlated with the substrate and vegetation in the ponds. The addition of invertebrate predators (i.e., odonates and coleopterans) had a negative impact on large zooplankton and dipterans, and indirectly, affected lower trophic levels in the ponds (e.g., bacteria, protozoans, and microcrustaceans). The odonates and coleopterans affected different prey taxa, but both preferred larger-sized prey. Aerial colonization was one of the most influential factors for maintaining intermediate and higher trophic levels in the ponds, whereas the use of enclosures prevented horizontal within-pond movements and significantly reduced abundances of many zooplankton taxa. The low trophic levels in the ponds were most strongly affected by the resource manipulations whereas higher trophic levels were more affected by colonization patterns and predatory intensity.Although the pond characteristics, seasonal development, and annual differences were of greater importance than biological factors for shaping the physicochemical characteristics, bottom-up and top-down effects in the ponds were both clear. The effects from the food web manipulations appeared weak in comparison to the natural variation due to the high temporal and spatial variability within the food webs. All manipulations resulted in responses that propagated through the food chains and demonstrated that the trophic links in intermittent ponds are strong.
Notes: Source: Dissertation Abstracts International, Volume: 68-01, Section: B, page: 0068.

Thesis (Ph.D.)--University of Toronto, 2006.

Electronic version licensed for access by U. of T. users.