Because phytoplankton succession involves pulses of short duration and a degree unpredictability, most workers have argued against resource specialization by zooplankters. Yet, in Lake Mitchell, Vermont, two genera cladocerans (Bosmina Daphnia) coexist under nearly equilibrium conditions that involve an intriguing conflict. Daphnia can depress Bosmina, but apparently cannot exclude it, even though both share substantial portions available resources. This coexistence appears mediated the...

The copepod Epischura nevadensis selectively preys on zooplankton communities in a way that reduces the abundance of cladoceran Bosmina longirostris and favors larger‐bodied species. responds to this predation by behavioral morphological adjustments frustrate searching handling strategies predatory copepods; response implies considerable evolution between two antagonists. Predation copepods other freshwater invertebrates seems an important factor determining not only size composition lake...

Predatory copepods are not imprecise hunters: they capable of sophisticated behavior. Pelagic species ( Cyclops, Epischura ) usually sense approaching prey from a distance and must judge approach angle speed, reorient during attack, often vary their handling responses. Below certain crucial sizes that trigger avoidance responses in the predator, attack distances related to size speed. Cyclopoids predatory calanoids capture handle differently, morphology first maxillae reflects these modes....

In Union Bay, a temperate embayment in Seattle, Washington, USA two different kinds of predators maintain polymorphism the cladoceran Bosmina longirostris. The boundary separating these populations is unusual because it maintained freely mixing body water, and important its distinctness consequence trophic dynamics, result interactions visual (fish) grasping (copepods). Not only do fish directly affect morph composition by differentially removing more conspicuous morphs, they also indirectly...

Here we introduce a combined experimental and descriptive approach (termed resurrection ecology) to reconstructing historical perturbations, pointing out how direct tests with sediments hatched resting eggs complement the traditional calculation of microfossil fluxes. In Keweenaw Waterway, freshwater estuary off Lake Superior, turn‐of‐the‐century copper mining impacted resident biota. Remain fluxes document that diatom, rhizopod, Bosmina production all declined during stamp sand discharges...

Visual predation by fishes appear to have driven prey towards divergent extremes, with two of the alternative avenues dependent upon initial palatability. On one hand, selective initially large—bodied, strongly pigmented, and highly palatable zooplankton has selected for reduced conspicuousness (smaller body size at maturity, increased transparency tissues). other yet mildly unpalatable groups (e.g., water mites), enhanced distastefulness. At basis these diverging responses lies mouthing...

Taking an experimental approach to paleoecology, we evaluated the prey portion of Van Valen's Red Queen hypothesis by retrieving diapausing eggs from lake sediments for laboratory tests evolutionary responses. The consisted core samples Portage Lake (Michigan), which were dated a combination varve counts and radioisotope ( 137 Cs 210 Pb) techniques. sedimentary record documented several major environmental changes (mining, channeling, post‐1950s eutrophication) over past century. Remains...

An intimate relationship is apparent between fecudity and predator resistance in clones of the parthenogenic cladoceran Bosmina longirostris. Young certain possess spines slightly larger bodies, thicker carapaces, all which frustrate handling tactics predatory copepods. During periods abundant resources, purchased at considerable cost, since eggs developing young are carried n a restricted space, special brood chamber formed from dorsal portion carapace. The energy used development...

The cladoceran Bosmina Longirostris undergoes a peculiar egg—size cycle in Frains Lake. Females carry small eggs during summer, then switch to large late fall, the process more than doubling enclosed yolk volume. Winter generations mature at larger sizes, shift early spring. fluctuations egg size are not strongly associated with indirect measures of nutritional conditions. Rather, they seem part that produces young one seasons, another, primarily as response changing patterns predation.

We used the Rassoulzadegan-DeMott bead bioassay to evaluate ability of various pelagic microcrustaceans discriminate between particles on basis taste and size. The test examined zooplankton reactions fresh algal exudates adsorbed onto polystyrene microspheres. investigation shows that there is a marked dichotomy certain large-bodied freshwater in how they respond small particles; it confirms large daphnid cladocerans exhibit no discrimination for beads, whereas calanoid copepods continually...

Groundwater flow influenced epibenthic algal biomass and N:P ratios at a seepage lake (Sparkling Lake, Wisconsin). During seasonal studies, flux were positively associated ( r = 0.453; P < 0.001). Pore‐water soluble reactive phosphorus (SRP) concentrations (29.2–110.7 µg PO, liter −1 ), SRP fluxes, significantly higher high groundwater discharge sites than low (< 10.0 to 27.7 PO 4 ). ammonia (NH + ) lower (<10.0 566.0 NH recharge (61.4–1464.9 3 The coupling between pore‐water...

In mesotrophic Lake Mitchell, density fluctuations of Daphnia cause rapid shifts within algal assemblages, while total phytoplankton cell densities persist at comparable levels before and after grazer fluctuations. The shifting balance between naked flagellates several digestion—resistant species is evident in both seasonal patterns enclosure experiments. resistant helps explain asymmetrical demographic responses competing smaller bodied cladocerans to changes density. Shifts refractory...

Populations of the waterflea Bosmina undergo temporal replacement cycles (seasonal successions clones or closely—related sibling species) in many modern lakes, where long—featured winter are subsequently replaced by short—featured summer clones. Inspection lake sediment reveals that populations have also undergone long—term replacements. Remarkably well—preserved remains, heavily biased towards morphology production dynamics, document a progressive shift from late—glacial phenotypes to...

In the days of large lakes, populations cladocerans and rotifers often appear to undergo seasonal morphological changes. past, these transformations were thought reflect phenotypic plasticity within lineages (cyclomorphosis). However, in Union Bay Bosmina, clearly involve regular replacements (termed "taxocene cycles") by genetically different lineages. Bay, Washington, USA, selective predation both visually foraging blindly grasping predatrory copepods, combined with reproductive...

The range of divergence a character, as measured by the difference between its largest and smallest local sample means, is highly significant positively correlated with average local-sample standard deviation in all fish, lizard, snake, bird case histories studied. More important, two variables remain significantly when both are divided mean which eliminates contribution from relationship deviation. We conclude that those characters exhibit greater variation populations show extremes...

Summary The effects of the invasive bivalves Dreissena polymorpha (zebra mussel) and rostriformis bugensis (quagga on aquatic ecosystems, including Lake Michigan, are a topic current interest to scientists resource managers. We hypothesised that winter–spring phytoplankton bloom in Michigan is reduced at locations where fraction water column cleared per day by filter feeding approached net growth rate phytoplankton, when was not stratified. To test this hypothesis, we compared spatial...

Watercress (Nasturtium officinale) is a spring—stream macrophyte that possesses glucosinolates, which are hydrolyzed to feeding deterrent isothiocyanates when the enzyme myrosinase released by tissue damage. Previous studies indicated frequently associated aquatic shredders strongly prefer yellowed—senescent leaves over fresh—green foliage, because latter releases much more isothiocyanate than senescent watercress. When action of was blocked heating tissue, shredders' preference shifted...

Sotdé, Michael (Department of Biology, University California, San Diego, La Jolla, 92037) and Kerfoot, W. Charles (Museum Zoology, Michigan, Ann Arbor, 48104). On the climatic determination scale size in a lizard. Syst. Zool. 21:97–105.—The relation between climate was studied two northern groups Sceloporus gradosus. In western section, an area intense summer drought, 84 percent geographic variation number mid-dorsal scales explained multiple regression model by August rainfall annual pan...

The spiny cladoceran (Bythotrephes longimanus) is an invasive, predaceous zooplankter that expanding from Great Lakes coastal waters into inland lakes within a northern latitudinal band. In large, Boundary Water lake complex (largely Voyageurs National Park), we use two comparisons, 2-year spatial and 12-year temporal, to quantify seasonal impacts on food webs biomass, plus preliminary calculation of secondary production decline. Bythotrephes alters the biomass pattern by severely depressing...