We assessed the effects of trophic structure on phosphorus (P) recycling by fishes, Chaoborus, and zooplankton in lakes with different food web configurations. Fishes in a piscivoredominated system recycled little P compared to that regenerated by zooplankton and Chaoborus. In a plan ktivore-dominated lake, excretion by fishes (especially young of year) dominated P recycling to algae; Chaoborus and zooplankton recycling was decreased due to intense predation by fishes. The sum of P incorporated into primary production and lost to sedimentation in the piscivore-dominated lake was only 77% of that in the planktivore-dominated lake, Our analyses suggest that the 30% greater primary production in the planktivore-dominated system may be accounted for by the greater than 40% increase in estimated P recycling that was directly due to differences in food web structure, Diel vertical migrations by Chaoborus concentrated P excretion in the epilimnion during night hours. In the plan ktivore-dominated system, Chaoborus migrations further affected spatial dynamics of P recycling by concentrating excreted P in the lower depths of the epilimnion. Diel vertical migrations by zooplankton had little effect on the spatial and temporal dynamics of P recycling except to dampen the effects of the Chaoborus migrations.
The documented range of the invasive and potentially pathogenic Asian fish tapeworm, Bothriocephalus acheilognathi Yamaguti, 1934 in the United States and Canada is updated based on examination of museum depositions and original field collections. Gravid specimens of B. acheilognathi were collected from the fathead minnow Pimephales promelas Rafinesque in Peter Lake, at the University of Notre Dame Environmental Research Center (UNDERC) Land o' Lakes, Wisconsin. A single immature specimen of the parasite was collected from a white bass, Morone chrysops (Rafinesque) in Lake Winnipeg, Manitoba, Canada. This is the first record of B. acheilognathi in Canada and extends its northern range in the interior of the continent by more than 600 miles over the last documented record. The previous record of B. acheilognathi in Canada, from the northern pikeminnow, Ptychocheilus oregonensis in British Columbia, is a misidentification of Eubothrium tulipai. Examination of selected records of intestinal cestodes from native cyprinids, in the Harold W. Manter Laboratory of Parasitology (HWML, n = 9) collection and in the United States National Parasite Collection (USNPC, n = 8), provided evidence of the parasite in Nebraska and possibly in the upper Colorado River basin. Introductions into Wisconsin-Michigan were due to the stocking of golden shiners, whereas the source of the introduction in Manitoba remains unknown.
We assessed the effect of sampling schedule on estimates of diet composition of an age-II+ cohort of largemouth bass Micropterus salmoides in a small lake in Michiganˈs upper peninsula. Our objectives were to determine the effects of sampling frequency on diet variance and on estimated prey consumption by the fish population. Sampling frequency ranged from 2 to 30 samples per 45-d sampling period in summer 1987. We determined the mean variance of an index of relative importance for each of six prey types as a function of sampling frequency. Estimates of mean rates of total population food consumption (based on percent wet weights of each prey type) were calculated with a generalized bioenergetics model. Feeding on each of three prey items (i.e., zooplankton, chironomids, and trichopterans) fluctuated irregularly over time, and intervals of 3–18 d between feeding bouts were determined from the data. Sampling frequency influenced the accuracy of consumption rate estimates. A minimum sampling frequency of three times per 45 d was necessary for accurate estimates of consumption rates for Chaoborus spp., for odonate naiads, and possibly for ephemeropterans. However, accurate estimates of consumption rates for zooplankton (Daphnia spp. and Holopedium gibberum), trichopterans, and chironomid pupae required more frequent sampling. Increased sampling did not decrease the intersample variance, but the error in estimates of consumption rates decreased with increased sampling frequency.
Diel vertical migration of zooplankton is influenced by a variety of factors including predation, food, and temperature. Research has recently shifted from a focus on factors influencing migration to how migration affects nutrient cycling and habitat coupling. Here we evaluate the potential for Daphnia migrations to incorporate metalimnetic productivity in a well-studied northern Wisconsin lake. We use prior studies conducted between 1985 and 1990 and current diel migration data (2008) to compare day and night Daphnia vertical distributions with the depth of the metalimnion (between the thermocline and 1% light depth). Daphnia migrate from a daytime mean residence depth of between about 1.7 and 2.5 m to a nighttime mean residence depth of between 0 and 2.0 m. These migrations are consistent between the prior period and current measurements. Daytime residence depths of Daphnia are rarely deep enough to reach the metalimnion; hence, metalimnetic primary production is unlikely to be an important resource for Daphnia in this system.
Abstract— We examined prey selection of largemouth bass ( Micropterus salmoides ), smallmouth bass ( M. dolomieu ), and yellow perch ( Percaftavescens ) by comparing diet overlap in a small, unexploited lake in Michigan, USA from 1988 to 1990. Niche hypervolume principles were applied to diet data as a means of assessing diet space for each species and the community as a whole. Largemouth bass occupied the largest proportion of community diet space (70.2%), followed by smallmouth bass (44.2%), and yellow perch (21.7%). The majority of community diet space (58.8%) was occupied by a single species, and 41.2% was shared by ≥ 2 species. Diet overlap was assessed by measuring the amount of diet space of one species occupied by the other species. Our analyses demonstrated that diet partitioning in a three species piscivore community is reflected in different use of the prey resource by co‐occurring species. Niche overlap of largemouth bass with smallmouth bass and yellow perch is strongly asymmetric, largely due to the ability of largemouth bass to effectively consume prey of terrestrial origin.
