AME 42:293-310 (2006)  -  doi:10.3354/ame042293

ABSTRACT: Pond physicochemical characteristics and bottom-up effects were more important than top-down effects in governing ciliate community structure in 2 adjacent intermittent ponds in Southern Ontario, Canada. The ciliates showed a bimodal seasonal pattern with abundances peaking early and late in the hydroperiods, and the communities showed a strong seasonal succession of species—only 15% of the 162 ciliate species were present throughout the hydroperiods. Less than half of the species occurred in both ponds. Adding riparian leaf litter to large pond enclosures affected several physicochemical variables, increased bacterial abundance, and promoted the appearance of particular species—many of which are known to be associated with nutrient- or organic matter-enriched conditions. This treatment resulted in higher ciliate abundance (mainly small-sized bacterivores) and lower ciliate diversity in mid-hydroperiod in one of the ponds. The removal of plant litter generally produced effects in the physicochemical variables that were opposite to those seen in the leaf litter addition, and resulted in a 15% decrease in the proportion of ciliate bacterivores in one pond. The effects of top-down manipulations (i.e. prevention of aerial colonization of insects) were minor. Many treatment effects were season-, and pond-specific. The measured environmental variables (including pond and treatments) explained half of the variation in ciliate abundance, one-third of the species diversity, and one-fifth of the species composition. Pond characteristics and the leaf litter additions were the most important factors for determining ciliate abundance (together with chlorophyll a), diversity (together with dissolved oxygen), and community composition (together with season).

KEY WORDS: Ciliates · Seasonal succession · Temporary ponds · Resource addition · Resource removal · Predator exclusion · Seasonal succession · Top-down · Bottom-up