Increased niche differentiation between two Conochilus species over 33 years of climate change and food web alteration
Limnol. Oceanogr., 50(2), 2005, 421-426 | DOI: 10.4319/lo.2005.50.2.0421
ABSTRACT: Long-term data from Lake Washington are used to ask whether zooplankton population dynamics can be predicted on the basis of abiotic gradients and potential food resources. I used Dynamic Linear Models to examine effects of fluctuations in temperature and five algal groups on population dynamics of two rotifer species over a 33-yr period in which climate has warmed, anthropogenic nutrient loading has changed dramatically, and Daphnia has become established. Dynamics of the colonial rotifers Conochilus hippocrepis and Conochilus unicornis were both best predicted by temperature and the density of single-celled bacterio- and phytoplankton smaller than 10 mm, but their seasonal peaks have become dramatically offset toward fall and spring, respectively, in recent years. Both species have been extirpated from the summer months in which they once flourished, seemingly because of midsummer declines in their food resources, which have been depressed by Daphnia since its establishment. However, climate warming has increased the length of the plankton growing season in Lake Washington, such that spring and fall offer greater abundance of food resources for Conochilus, offsetting modern exclusion of Conochilus from midsummer months. Additionally, greater distinction in temporal niches presumably has reduced possibilities for intrageneric competition, and both Conochilus species have achieved higher mean annual abundances in recent years.