To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species nuimber increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?

https://science.sciencemag.org/content/sci/185/4145/27.full.pdf

Resource Partitioning in Ecological Communities

[1] Many lakes show vertical stratification of their water masses, at least for some extended time periods. Density differences in water bodies facilitate an evolution of chemical differences with many consequences for living organisms in lakes. Temperature and dissolved substances contribute to density differences in water. The atmosphere imposes a temperature signal on the lake surface. As a result, thermal stratification can be established during the warm season if a lake is sufficiently deep. On the contrary, during the cold period, surface cooling forces vertical circulation of water masses and removal of gradients of water properties. However, gradients of dissolved substances may be sustained for periods much longer than one annual cycle. Such lakes do not experience full overturns. Gradients may be a consequence of external inflows or groundwater seepage. In addition, photosynthesis at the lake surface and subsequent decomposition of organic material in the deeper layers of a lake can sustain a gradient of dissolved substances. Three more geochemical cycles, namely, calcite precipitation, iron cycle, and manganese cycle, are known for sustaining meromixis. A limited number of lakes do not experience a complete overturn because of pressure dependence of temperature of maximum density. Such lakes must be sufficiently deep and lie in the appropriate climate zone. Although these lakes are permanently stratified, deep waters are well ventilated, and chemical differences are small. Turbulent mixing and convective deep water renewal must be very effective. As a consequence, these lakes usually are not termed meromictic. Permanent stratification may also be created by episodic partial recharging of the deep water layer. This mechanism resembles the cycling of the ocean: horizontal gradients result from gradients at the surface, such as differential cooling or enhanced evaporation in adjacent shallow side bays. Dense water parcels can be formed which intrude the deep water layer. In the final section, stratification relevant physical properties, such as sound speed, hydrostatic pressure, electrical conductivity, and density, are discussed. The assumptions behind salinity, electrical conductance, potential density, and potential temperature are introduced. Finally, empirical and theoretical approaches for quantitative evaluation from easy to measure properties conclude this contribution.

https://www.eoas.ubc.ca/~mjelline/453website/eosc453/E_prints/newfer09/boehrer_stratlakeRG08.pdf

Stratification of lakes

The size-efficiency hypothesis, first proposed in 1965 by Brooks & Dodson (24), has profoundly influenced the direction of research in aquatic ecology since its publication.3 The size-efficiency hypothesis (SEH) is an attempt to explain the commonly observed inverse relationship between the abundances of smalland of large-bodied herbivorous zooplankton in freshwater lakes. The SEH was originally stated as follows:

The Size-Efficiency Hypothesis and the Size Structure of Zooplankton Communities

Interstitial water profiles of SeO42−, SeO32−, SO42−, and Cl− in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO42− occurred under anaerobic conditions, was more rapid with H2 or acetate, and was inhibited by O2, NO3−, MnO2, or autoclaving but not by SO42− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO2. A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters.

Selenate Reduction to Elemental Selenium by Anaerobic Bacteria in Sediments and Culture: Biogeochemical Significance of a Novel, Sulfate-Independent Respiration

The paper considers the extent to which salinity determines the structure of biological communities (composition and species richness and diversity) in saline lakes, ie inland bodies of water with salinities in excess of 3 g l-1 It also considers the extent to which oxygen, ionic composition, pH, hydrological patterns (degree of permanence and impermanence of water), geographical position, palaeoclimatic events, chance, human intervention, and biological interactions especially predation determine biological communities in salt lakes It suggests that salinity is less significant as a determinant of community structure in salt lakes than has been assumed

Salinity as a determinant of the structure of biological communities in salt lakes

Collections of algae, mainly planktonic, were made from 41 saline lakes in southern Saskatchewan ranging in salinity from 3.2 to 428 g l-1. Algae in 7 phyla, 8 classes, 42 families, 91 genera and 212 species and varieties were identified. Fourteen species were restricted to hypersaline (50 g l-1) waters and eleven of these were diatoms. In general, species diversity was inversely related to lake salinity. Algae that were important community constituents over a broad spectrum of salinities were the green algae Ctenocladus circinnatus, Dunaliella salina and Rhizoclonium hieroglyphicum, the blue-green Lyngbya Birgei, Microcystis aeruginosa, Oscillatoria tenuis, O. Utermoehli and Nodularia spumigena and the diatoms Melosira granulata, Stephanodiscus niagarae and Chaetoceros Elmorei. In general green algae were dominant when lake salinity exceeded 100 g l-1 although diatoms played important roles in most of these highly saline lakes except for Patience Lake.

The distribution and abundance of algae in saline lakes of Saskatchewan, Canada

For more than fifty years man has been trying to measure primary production rates of waters varying from fresh to saline and from inland to marine. From indirect methods such as phytoplankton counts and measurement of chlorophyll concentrations to direct methods employing oxygen and carbon-14 light and dark bottle techniques and even diurnal oxygen changes, scientists have attempted to ascertain the actual and potential productivity of aquatic ecosystems. Not only has there been the problem of what a particular technique is actually measuring, there has also been the problem of how accurately the measurement represents the dynamics of the real system. Considerable controversy has always been associated with the choice of method, the frequency of measurement, the length of production incubations, and the comparison of results employing different methods.

Primary production in saline lakes

Vascular macrophyte species richness decreases with increasing salinity Only three species of submerged plants (Potampgeton pectinatus, Ruppia maritima, R occidentalis) tolerate hypersaline waters (> 50 g l-1, total of ionic constituents) Eight emergent species occur in more saline habitats but only five (Scirpus maritimus var paludosus, Distichlisstricta, Puccinellia nuttalliana, Scirpus americanus, Triglochin maritima) occur commonly over a range of saline lakes into the hypersaline category Usually, species tolerant of high salinities are found over the entire saline spectrum and even extend into subsaline waters (> 3 g l-1) and thrive there A major increase in the number of species occurs below 5 g l-1 As the water recedes plants such as Salicornia rubra, Suaeda calceoliformes, Hordeum jubatum and Sonchus arvensis invade

Aquatic macrophytes in saline lakes of the Canadian prairies

For more than fifty years man has been trying to measure primary production rates of waters varying from fresh to saline and from inland to marine. From indirect methods such as phytoplankton counts and measurement of chlorophyll concentrations to direct methods employing oxygen and carbon-14 light and dark bottle techniques and even diurnal oxygen changes, scientists have attempted to ascertain the actual and potential productivity of aquatic ecosystems. Not only has there been the problem of what a particular technique is actually measuring, there has also been the problem of how accurately the measurement represents the dynamics of the real system. Considerable controversy has always been associated with the choice of method, the frequency of measurement, the length of production incubations, and the comparison of results employing different methods. This paper will not try to resolve these problems. Rather I will present the results of various scientists who have worked on saline lakes and compare them using the parameters employed today. The variability of primary production in saline waters will be discussed as well as variability in various related parameters. Wetzel (1975) has indicated that almost as much of the world's inland waters are saline as

5. Primary production in saline lakes: A review

The geology and physiography, climate, soils and vegetation of the saline lakes region of southern Saskatchewan are briefly reviewed. The location and morphometry of 60 saline lakes was determined. Some of them are large (307 km2) but mean depths do not exceed 10 m and many are very shallow. Light penetration varied considerably from very turbid shallow lakes to Redberry Lake where the 1% light level was below 16.5 m. Light extinction coefficients for the entire water column of deeper lakes (7) varied from 0.256 to 2.558.



Shallow lakes failed to stratify thermally but a dozen deeper lakes stratified for at least several months. Higher salinity tends to prolong stratification. Thermal stratification augmented chemical stratification in two meromictic lakes. Maximum temperature up to 30 °C in very saline shallow waters was recorded while temperatures as low as-3 °C occurred under the ice. Freezing was delayed and thawing accelerated in more saline lakes. Annual heat budgets varied from 3350 to 13,900 g cal cm-2 in seven lakes.



Oxygen concentration was reduced below thermoclines and was virtually absent below the ice in very shallow lakes and, at times, in a very productive lake.

U. Theodore Hammer

Papers

The distribution and abundance of algae in saline lakes of Saskatchewan, Canada

Primary production in saline lakes

Aquatic macrophytes in saline lakes of the Canadian prairies

5. Primary production in saline lakes: A review

The Saline Lakes of Saskatchewan II. Locale, Hydrography and other Physical Aspects