Cranberry Lake Research Articles

Light Apparatus for Mesocosm Photo‐manipulation (LAMP): An inexpensive waterproof lighting device for within‐lake mesocosm experiments

Although light is a key biological driver, light additions to in‐lake experiments can be difficult, if not impossible. To address this problem, we developed an inexpensive Lighting Apparatus for Mesocosm Photo‐manipulation (LAMP), a device that can be deployed within experimental underwater enclosures to increase ambient light levels. Each apparatus consists of 12 Light Emitting Diode (LED) flashlights embedded within a watertight PVC frame. Through the use of a voltage regulator, each is wired to a 12V deep‐cycle marine battery. Twelve LAMPs were deployed during a 3.5‐week mesocosm experiment in Cranberry Lake in the Adirondack region of New York State and run 12 hours per day. LAMPs proved durable under harsh wind and weather conditions. Mesocosms with LAMPs had significantly higher average Photosynthetic Photon Flux Density (PPFD) in the water column than did controls (8% higher integrated Photosynthetic Active Radiation [PAR] over a 1.75 m depth, paired t test, P < 0.01). Other potential research applications for LAMPs include (1) testing light limitation in highly eutrophic systems where algal biomass may be self‐shading, (2) experimentation at depth (e.g., examination of light limitation at the deep chlorophyll maximum), (3) application at different depths or in water bodies where specific wavelengths have been naturally attenuated using LEDs with different spectral properties, (4) testing animal responses to light climate in the field, or (5) collection of macroinvertebrates or fish larvae in modified LAMP‐based light traps.

Direct and Indirect Interactions between an Invasive Alien Fish (Perccottus glenii) and Two Native Semi-aquatic Snakes

The ecological links of aquatic invasive fish and native reptiles are rarely studied. Thus, we analyzed the diet and helminth composition of a recently introduced invasive alien fish (the Rotan, Perccottus glenii) and of two native semi-aquatic snakes (the Dice Snake Natrix tessellata, the Grass Snake N. natrix) in Cranberry Lake, Russia. We also studied diet and helminthes of water frogs (Pelophylax spp.) as a potential mechanism of transmission of parasites. We identified 19 prey taxa and four helminthes for P. glenii, 21 and 24 for Pelophylax spp., and two and 16 for the snakes. The piscivorous N. tessellata has been feeding on P. glenii since its introduction and the subsequent elimination of native fish. Although we did not find P. glenii in the diet of the mainly frog-eating N. natrix, helminth analysis indicated that this snake may prey upon this fish. Both studied snakes contracted the parasitic tapeworm Ophiotaenia europaea from P. glenii. Therefore, the invasive fish and the native snakes demons...

Megacrystic Gore Mountain–type garnets in the Adirondack Highlands: Age, origin, and tectonic implications

Spectacular exposures of the world's largest megacrystic garnets (to 35 cm diameter) occur in a coarse-grained amphibolite at the Barton Garnet Mine in the Adirondack Highlands (Gore Mountain, New York State, USA). Over the years, numerous geologists have concluded that the large size of the garnets resulted from an influx of fluids during ca. 1050 Ma upper amphibolite facies metamorphism of a ca. 1155 Ma olivine metagabbro. The presence of fluids under such mid-crustal pressure-temperature conditions is anomalous and warrants explanation. Evidence indicates that the fluids were introduced along, and close to, a steep border fault that juxtaposes charnockite against the garnet ore at the southern margin of the mine. Granitic pegmatites and quartz veins are present in the border zone and locally intrude the garnet ore. Geochronology has played a critical role in resolving the genesis of the Gore Mountain garnets. Over the past 20 yr Sm-Nd and Lu-Hf techniques have been used to date the crystallization of the garnets as 1049 ± 5 Ma, an age that coincides with the termination of the contractional phase of the Ottawan orogeny, the onset of extensional orogen collapse, and the emplacement of the Lyon Mountain Granite. New U-Pb zircon age determinations of 1045 ± 7.5 (Barton Garnet Mine) and 1055 ± 7.4 (New York State Route 3 near Cranberry Lake) for Lyon Mountain granite pegmatites directly associated with megacrystic garnet amphibolites corroborate the synchronicity of emplacement of Lyon Mountain magmas and the growth of the garnet megacrysts. It is argued that during the ca. 1050 Ma extensional collapse of the Ottawan orogen, fluids gained access to extensional fault networks and interacted with country rocks. We further suggest that increasing temperature due to advected heat from Lyon Mountain Granite carried the Gore Mountain megagarnet amphibolite into granulite facies conditions that resulted in reactions between hornblende and garnet that produced orthopyroxene and calcic plagioclase intergrowths, both as symplectites and coarsely textured pods developed in pressure shadows. Geothermal modeling of garnet zoning in metapelites ([Storm and Spear, 2005][1]) and oxygen isotope zoning in titanite ([Bonamici et al., 2011][2]) require a short period of rapid cooling ca. 1050 Ma, which we interpret to be related to the extensional collapse of the Ottawan orogen at that time ([Rivers, 2008][3]; [McLelland et al., 2010a][4], [2010b][5]). Reconnaissance of the southern and central Adirondacks reveals that a number of megacrystic garnet occurrences similar to those at Gore Mountain are present in areas that contain both metagabbros and megacrystic garnet amphibolites, and we propose that all of these formed during orogen collapse, intrusion of Lyon Mountain Granite, and fluid-related alteration at high temperature. [1]: #ref-51 [2]: #ref-5 [3]: #ref-45 [4]: #ref-37 [5]: #ref-38

Robert Lewis Burgess 1931–2002

Robert Lewis Burgess 1931–2002

Using remote sensing image texture to study habitat use patterns: a case study using the polymorphic white‐throated sparrow (Zonotrichia albicollis)

ABSTRACTAim Ecological factors that vary along spatial scales can greatly influence the outcome of evolution. However, often it is difficult for researchers to identify significant ecological variables that might be associated with the geographical distribution of phenotypes and genotypes in nature. In this paper, we use remote sensing image texture analyses to investigate breeding territories of the white‐throated sparrow (Zonotrichia albicollis), a polymorphic passerine species that has been shown to segregate spatially according to morph. Our aim was to examine how an integrative measure of landscape feature, such as image texture, could be used to distinguish subtle differences in habitat use and, presumably, habitat selection.Location A population of white‐throated sparrows located 1.5 miles east of the Cranberry Lake Biological Station in the Adirondack Mountains of St Lawrence County, New York, was used in this study; the study site itself was approximately 1 km2.Methods We analysed 27 territories (16 white males; 11 tan males) to determine if image texture can be used to distinguish differences in vegetation and structure in territories of the two colour morphs. First (variance)‐ and second (homogeneity)‐order image texture measurements with three different window sizes were derived using the green, red, and near infrared bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. Texture was then placed into t‐tests to determine statistical differences between the territories of the two male morphs.Results Significant differences between the territories of the two morphs were found in both variance and homogeneity texture measures in the red and green ASTER bands in all three window sizes. There were no differences with any near infrared texture measures.Main conclusions Examination of first‐ and second‐order statistical measures indicated that the territories of tan males have significantly more spectral variance than the territories of white males, while white males’ territories are significantly more homogeneous. These findings are consistent with the previous finding of the morphs settling in ‘high’ and ‘low’ neighbour density habitats that differ with respect to the amount of useable area on their borders. Previous study has also suggested that white and tan male territories differ according to overall landscape structure, not vegetation composition. Therefore, we suggest that red and green spectra may be more useful when examining differences in territory structure and possibly territory quality of similar edge‐type species. Our results suggest that image texture is a useful tool for ecological and evolutionary modelling of the distributions of phenotypes/genotypes across landscapes.

DEVELOPMENT AND APPLICATION OF A MODFLOW PREPROCESSOR USING PERCOLATION THEORY FOR FRACTURED MEDIA1

ABSTRACT: The discrete heterogeneity of fracture distribution and hydraulic discontinuity are the primary difficulties in the modeling of flow in fractured media. The equivalent porous medium (EPM) approach, however, which has been frequently applied to simulate flow in fractured media due to its ease of use, ignores this. This practice results in some severe limitations such as hydraulic head averaging and an inability to handle preferred fluid pathways. The PMF package (a Preprocessor to MODFLOW for Fractured media) was developed employing percolation theory to address these limitations and to utilize the simplicity of the EPM approach at the same time. This preprocessor was applied to a fractured rock aquifer around Cranberry Lake in northern New Jersey. The calibration using hydraulic head observations, validation using water balance, and evaluation using residuals show that the model generated by the PMF package can provide a superior simulation of ground water flow to the EPM approach.

Seasonal and daily variations in concentrations of methyl-tertiary-butyl ether (MTBE) at Cranberry Lake, New Jersey

Methyl-tertiary-butyl ether (MTBE), an additive used to oxygenate gasoline, has been detected in lakes in northwestern New Jersey. This occurrence has been attributed to the use of gasoline-powered watercraft. This paper documents and explains both seasonal and daily variations in MTBE concentrations at Cranberry Lake. During a recent boating season (late April to September 1999), concentrations of MTBE typically exceeded 20 μg/L. MTBE concentrations varied daily from 12 to 24 μg/L over a 2-week period that included the Labor Day holiday. Concentrations were highest on weekends when there is more boat traffic, which had an immediate effect on MTBE mass throughout the lake. MTBE concentrations decreased to about 2 μg/L shortly after the end of the summer recreational season. The loss of MTBE can be accounted for by volatilization, with a half-life on the order of 10 days. The volatilization rate was modeled with the daily decrease in MTBE then the modeled rate was validated using the data from the seasonal decline.

Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack drainage, North Cascades, Washington

During the maximum late Wisconsin glaciation ca. 15 000 14C yr B.P., the Cordilleran Ice Sheet overwhelmed the Nooksack drainage of the northwestern Cascades, leaving only peaks higher than 2000 m above the ice surface. Ice-sheet flow over the Nooksack drainage and the adjacent Puget Lowland was essentially north-south. Rapid deglaciation between 14 500 and 12 500 14C yr B.P. resulted in dropping of the ice-sheet surface below ridge crests in the Nooksack drainage, and glacial activity thereafter became topographically controlled. Long valley glaciers in the upper Nooksack Valley were no longer connected to the Cordilleran Ice Sheet, and the source area changed from the main ice sheet to Mount Baker, Mount Shuksan, and the Twin Sisters Range. At that time, the margin of the remnants of the Cordilleran Ice Sheet was 30 km to the northwest, separated from the Nooksack Valley glaciers by several ridges 1200 m higher than the surface of the ice sheet. Moraines were built in all three forks of the Nooksack drainage, 25–45 km downvalley from their sources. The Middle Fork glacier stagnated 12 300 14C yr B.P. and deposited ice-contact drift that was later overridden when ice readvanced over ice-contact drift and deposited a prominent, 2-km-long, lateral moraine. Logs in a lateral moraine in the upper Middle Fork were dated at 10 680 ± 70 and 10 500 ± 70 14C yr B.P. The North Fork glacier, which originated at a large cirque on Mount Shuksan and was fed by glaciers from Mount Baker, extended to Kendall, where two moraines were deposited. Outwash from the younger moraine in the North Fork valley overlies glaciomarine drift, dated as 11 910 ± 80 14C yr B.P., and contains charcoal layers dated at 10 603 ± 69 and 10 788 ± 77 14C yr B.P. The South Fork glacier at its maximum was joined by ice from the Middle Fork and extended downvalley to Lake Whatcom and to Cranberry Lake. It retreated from its terminal position slightly before ca. 12 700 14C yr B.P.

Food processing by animals: do beavers leach tree bark to improve palatability?

Beavers store and consume tree parts in the bodies of water where they live. We examined whether such soaking renders food more palatable by leaching out undesirable compounds. In experiment 1, saplings of red maple, Acer rubrum (RM), were first soaked in a pond for periods of 2, 18, and 36 days, then offered to free-ranging beavers. Soaking for two days rendered RM slightly more acceptable to beavers. To further examine the time window around two days, RM sticks were soaked in distilled water in the laboratory for 1, 2, 4, and 6 days before presenting them to beavers (experiment 2). In experiment 3, twigs of three species were placed on land. Beavers placed RM in the water for 1 to 3 days before consuming the twigs. In experiment 4, sticks were provided in the water at Cranberry Lake Biological Station (CLBS). Most quaking aspen (QA) was consumed during the first night, and most witch hazel, Hamamelis virginiana (WH), during the third night. At Allegany State Park (ASP), no such difference was found. Twigs were provided in the water in experiment 5. At ASP, WH was taken after three days in the water, and at CLBS little WH was consumed, and only during the third night. A meta-analysis of all experiments shows that relatively more WH is consumed after two days than any other species. Experiment 6 traced the time beavers left their own harvested branches in the water. Unlike other tree species, WH remained in the water for two to four days before being consumed. Experiment 7 measured the phenolics leached into water from RM twigs and small pieces of bark soaked for 10 and 8 days, respectively. Shredded bark lost 50-60% of leachable phenolics into the water, and twigs 70-80%. We conclude that beavers can use water to leach undesirable compounds from their food. Although this effect was not robust, our study is the first of its kind.

Mating success in brood-guarding male rock bass,Ambloplites rupestris: the effect of body size

The hypothesis that variation in a paternal trait associated with offspring survival will result in female mate choice based on that trait was tested in rock bass,Ambloplites rupestris, a temperate fresh water fish with uniparental male care. The number of eggs acquired by 108 nesting male rock bass, in Cranberry Lake (New York State, U.S.A.), was estimated in two different spawning episodes that differed in the size structure of the nesting male stock. Early breeders (between the 4–7 June 1989) were mainly medium and large males (101–300 g), as compared to late breeders (between the 19–21 June 1989) which were mostly small (50–100 g). Because survival of larvae in rock bass is significantly lower in nests guarded by small males as compared to nests guarded by medium and large males, it was hypothesized that female mate choice should have been (1) size-based, and (2) more intense late in the season when the nesting stock was comprised mostly of small males. The results were consistent with these hypotheses. Variation in egg numbers per nest was significantly higher during the late spawning episode. In addition, egg number per nest were normally distributed during the early spawning episode, but were positively skewed and leptokurtic during the later episode. The correlation between male size and egg number was significant for both spawning episodes. However, during the late episode male size explained 23% of the variation in egg numbers versus only 8% of the variation during the earlier episode.

Reproductive Ecology of Tetraphis pellucida. I. Population Density and Reproductive Mode

Reproductive Ecology of Tetraphis pellucida. I. Population Density and Reproductive Mode

The upper Hadrynian Jeffers Group, Cobequid Highlands, Avalon zone of Nova Scotia: A back-arc volcanic complex

The upper Hadrynian Jeffers Group of the Cobequid Highlands (Avalon zone of northern Nova Scotia) consists of volcanic rocks of the Gilbert Hills Formation, interfingering deeper-water argillite of the Humming Brook Formation, and overlying turbidite lithic arkose and siltstone of the Cranberry Lake Formation. The Jeffers Group has a spatially inhomogeneous flat-lying cleavage, associated with thrust faults of late Hadrynian age that were in part reactivated during Carboniferous strike-slip motion on the Cobequid fault. The basal rocks of the Gilbert Hills Formation consist of felsic pyroclastics and minor mafic and felsic flows of the Lakelands facies, locally passing up into sandstone and marble, overlain by the Humming Brook Formation. Thrust over this sequence is the Harrington River facies of the Gilbert Hills Formation, comprising flows, ranging in composition from subalkalic basalt to rhyodacite, and pyroclastic rocks. Two groups of igneous rocks are distinguished geochemically. High-Ti basalts of the Lakelands facies and associated hypabyssal intrusions have tholeiitic character; enrichment in Ba, Rb, and K; flat light-REE spectra; little or no depletion in Nb and Ta; and high FeO t and Ti. They are associated with voluminous felsic rocks. The Harrington River facies has a calc-alkaline differentiation series from basalt to rhyodacite but with more enrichment in FeO t , P, Nb, and Zr than is found in typical calc-alkaline rocks. These two groups are also represented in hypabyssal rocks. The Jeffers Group rocks are compared geochemically with other predominantly continental back-arc basins in the Aegean Sea and Bransfield Strait. All three basins show the presence of a rock phase derived from partial melting of mantle only slightly modified by subduction processes (the Lakelands facies tholeiites of the Jeffers Group). They all also contain a more differentiated series showing more subduction-related chemical characteristics (the Harrington River facies of the Jeffers Group). Geochemical differences between these rocks and typical calc-alkali series are related to the lesser role of hydrous fluids in the back-arc basins. As a result, titanomagnetite and amphibole are not important fractionating phases, and Nb and Ta are not significantly depleted.

Mercury contribution to an adirondack lake

Elevated copper, lead, and zinc concentrations in the upper 10 to 20 cm of sediment sampled from Cranberry Lake, a large Adirondack lake, are attributed to atmospheric contributions. Pb-210 and pollen core data, however, suggest Cranberry Lake also received mercury discharges during the turn of the century when the area was the center of extensive lumbering and related activities. Elevated mercury concentrations in Cranberry Lake smallmouth bass derived from remobilization from mercury-contaminated bottom sediments which increased the bioavailability to Cranberry Lake organisms. Mercury remobilization and accumulation by fish are promoted by fluctuating pH values resulting from acid precipilation.

Barn Swallow Coloniality: A Net Cost for Group Breeding in the Adirondacks?

To explore the costs and benefits of groups living in a facultatively social bird, we studied the reproductive ecology of a marked population of Barn Swallows (Hirundo rustica) as the Cranberry Lake Biological Station in the Adirondack Mountains of New York State. Throughout its range, the Barn Swallow breeds solitarily or in small groups. From 1979 through 1985 we gathered reproductive and mortality data in colonies varying in size and density. Birds living in larger colonies tended to be younger and to breed later, on average, than solitary breeders. Breeding success was less for birds in large colonies than for birds breeding solitarily or in small groups. Larger colonies did not provide obvious benefits that offset the reduced reproductive success. Nests in larger colonies were infested more by a bloodsucking blow fly larva (Protocalliphora hirundo) than were nests in smaller colonies. The fraction of nests infested and the mean number of parasites per nestling also increased as the breeding season progressed. Since parasitism appeared to be the major source of nestling mortality, the increased parasite loads were probably the major cost of living in larger groups in our area. Birds in large colonies suffered a net reproductive loss relative to those breeding alone or in smaller groups. Thus, our data consistent with Snapp's (1976) conclusion that shortages of nesting habitat rather than direct benefits of group living are responsible for swallow coloniality.

Non-parental nest attendance in the barn swallow ( Hirundo rustica): helping or harassment?

During a long-term study of barn swallows in New York's Adirondacks, we observed many instances of third birds attending active nests. Most non-parental attendance involved unmated adult males that were not closely related to those they attended. There were no significant differences in the reproductive success of attended and unattended nests. Attendants showed little of the cooperative behaviour reported in earlier studies of other barn swallow populations. At Cranberry Lake, nest attendants behaved more often in ways that were detrimental to one or both breeders (e.g. attempting copulation with females, or committing infanticide). Our results indicate that non-parental nest attendance may be a competitive stragegy by which males gain information about, or access to, breeding sites and females. If this conclusion is correct, then the major difference between barn swallows and other species with more cooperative attendant (helper) systems may be that barn swallows live, in groups of non-relatives, where there are few indirect benefits to be gained by cooperation, while more cooperative species can interact socially with kin.

Cesium-137 sediment depth profiles and inventories in Adirondack Lake sediments

Depth distributions and inventories of137Cs (mCi km2) were determined in sediment from several fresh water lakes in the New York State Adirondack Preserve. Included were Big Moose and Darts Lakes, part of the North Branch of the Moose River system, as well as North, Sagamore, South, and Woods Lakes and the ‘seepage pond’, Tamarack Lake. Comparisons were made between the137Cs inventories in these lakes and large inpoundments in the Adirondacks (Hinkley, Great Sacandaga, Stillwater and Cranberry Lake Reservoirs) and other large impoundments and lakes located in various regions of the U.S., especially Cayuga Lake, Ithaca, NY.

Factors Affecting Nest and Site Fidelity in Adirondack Barn Swallows (Hirundo rustica)

AbstractDuring 1979-1983, I documented the natal and breeding dispersal of the Barn Swallow (Hirundo rustica) in the Cranberry Lake, New York, region of the Adirondacks by following the lifetime movements and breeding histories of individually marked birds. During the study, 847 birds were marked, and the movements of most were followed during the season they were marked. About 40% of the adults and 2% of the nestlings and juveniles were resighted or recaptured in two or more years. All recovered nestlings had dispersed from their natal colonies (median distance = 6.37 km). Most breeding adults remained faithful to previously used colonies, as well as to clusters within colonies, nests, and mates, when the latter were alive and available. Some individuals, however, did disperse. More females than males dispersed and usually moved farther both within and between breeding seasons. Males and, especially, females that had nested unsuccessfully with a particular mate in a particular location had a higher probability of deserting and dispersing than did successful breeders, both within and between breeding seasons. Old nests were reused at high frequencies for consecutive breeding attempts across breeding seasons. After successful first nests, breeders tended to move to secondary nests within 25 m of their first nests.

Barn swallow mobbing: Self-defence, collateral kin defence, group defence, or parental care?

We presented stimuli (human and stuffed owl) to a marked population of barn swallows ( Hirundo rustica) during the 1980–1982 breeding seasons at the Cranberry Lake Biological Station, Saint Lawrence County, New York. In experiment 1, we presented the stimuli at various distances from active nests during various stages of the reproductive cycle. Both the probability and intensity of mobbing varied during the breeding season, increasing with the probable reproductive value of young of the year and the degree of danger posed to them. Mobbing group sizes varied positively with local nest densities. In experiment 2, we analysed mobbing group structure in greater detail. Barn swallow mobbing groups usually contained active mobbers (those that emitted mobbing calls, and approached the stimulus closely, < 2 m, or even hit it) and passive mobbers (which were silent and flew in circles at greater distances, 2–10 m, from the stimulus). Passive mobbers were a random sample of the local population with respect to sex, age, nest location and reproductive status. This pattern is consistent with a hypothesis that passive mobbing, the less risky type, is a form of self-defence that reduces an actor's chance of being eaten, probably by providing information about the identity or probable behaviour of potential predators. Active mobbers were not a random sample of the source population. Mated birds and especially parents with nestlings were over-represented, while non-breeders, juveniles and incubators rarely mobbed actively. The seasonal changes in mobbing and the identity of active and passive mobbers are inconsistent with hypotheses that mobbing is a form of cooperative group defence or altruism conditioned by reciprocity or kin or group selection. These data are however consistent with other hypotheses, which propose that mobbing benefits the mate or the young. Even though active mobbers may be at risk, they benefit directly by increasing the personal component of their inclusive fitness, probably by alerting mates and young and defending them from predators. In this light the behavioural complex of mobbing appears to be a form of parental care (active) as well as self-defence (passive) and mate defence (active).

The 1976 A. LeRoy Andrews Bryological Foray

One hundred forty-nine species of mosses and 30 of hepatics were collected during the 1976 A. LeRoy Andrews Bryological Foray at Cranberry Lake and the bog at Sevey, New York State. The first A. LeRoy Andrews Bryological Foray was held 24-26 September 1976 at the Cranberry Lake Biological Station, Cranberry Lake, New York State. The foray, hosted by E. H. Ketchledge and organized by Nancy G. Slack and Richard H. Zander, was attended by 30 bryologists and their students. Participants came from five northeastern states and Michigan; a special guest was Gert Mogensen from Denmark. Habitats visited included the Station campus itself (where Anacamptodon splachnoides and Schistostega pennata were found), the rich woodland, streams and stream banks, the lake and pond shores and the limy cliffs near the shores of Cranberry Lake adjacent to the Station. In addition a group of bryologists especially interested in Sphagnum visited the bog (a poor fen) at nearby Sevey, New York; and William C. Steere found Dichelyma uncinatum on Catherine Island in Cranberry Lake. A list of species found in the Cranberry Lake region and at the bog at Sevey includes 149 species of mosses and 30 of hepatics. Of these, 12 mosses are not on the New York State checklist (Ketchledge, 1957), and an additional 30 species are new to the checklist for District 3 which includes Cranberry Lake. There is no similar checklist for hepatics. Taxa listed with an asterisk do not appear in the New York state checklist for District 3. Those marked with two asterisks do not appear in the New York State checklist. Bryophyta of the Cranberry Lake Region.

The Dynamics of Aquatic Systems: A Comparative Study of the Structure of Four Zooplankton Communities

This study compares the structure of the limnetic zooplankton communities of four very different lakes ranging from an oligotrophic Great Lake to a small dystrophic reservoir. Only filter feeding cladocerans and calanoid copepods are considered. Using Levins' Theory of the Niche analysis, I measured habitat overlap values for each species pair to determine to what extent habitat selection can explain the number of limnetic zooplankton species coexisting in these lakes and to what extent other factors, such as resource allocation or differential predation, must be invoked to explain the observed diversity. A substantial portion of the ecological overlap of zooplankton populations can be alleviated by habitat selection. Zooplankton communities are dominated by two to three species, in both numerical abundance and grazing intensity. In Lake Michigan (large, oligotrophic), habitat selection was the major mechanism of competitive coexistence and it was achieved by extensive vertical migrations (mean a = .47). In Gull Lake (small, mesotrophic), habitat selection via vertical migration also predominated (mean a = .37) as the major mechanism of competitive coexistence. Three species, Diaptomus sp., Daphnia retrocurva, and Daphnia galeata exhibited high habitat overlap coefficients. In Cranberry Lake, a dystrophic reservoir, most species possessed high overlap coefficients (mean a = .62) and minimal migration amplitudes. Diaptomus spp. and Daphnia catawba predominated. In Lake George, a medium—sized oligotrophic lake, mean habitat overlap was also high (mean 2 = .65). The three dominant species were Diaptomus sp., Diaphanosoma leuchtenbergianum and Daphina galeata. For the latter two communities, which possessed similar high and mean overlap values, the basic equation was weighted by the standing crop and turnover rate of phytoplankton. The spatial–temporal positioning of the Lake George populations were correlated with algal standing crop and turnover patterns while the Cranberry Lake populations were not.