Stream drift,size-specific predation,and the evolution of ovum size in an amphibian

Summary A stream-breeding race of small-mouthed salamanders (Ambystoma texanum) in central Kentucky produces ova that are twice as large as those of a pond-breeding race found nearby. Embryos of stream-breeders also hatch at a more advanced developmental stage than those of pond-breeders. Morphological evidence indicates that stream-breeders were derived from pond-breeding stock. Assuming that differences between stream and pond-breeders reflect evolutionary change, and that the ancestral pond stock that invaded streams was similar to extant pond-breeders, we examined three hypotheses that might explain changes in ovum size and stage at hatching following the invasion of streams. (1) Larger ovum size evolved indirectly as a consequence of selection for rapid development which minimizes mortality risk from stream drying. (2) Increased ovum (hatchling) size and stage at hatching of stream-breeders are adaptations to resist stream current. (3) Increased ovum (hatchling) size and stage at hatching are adaptations to reduce predation on hatchlings from stream invertebrates. The results of field and laboratory studies only support hypotheses (2) and (3). Hatchlings that were relatively large or at a more advanced developmental stage had slower drift rates and were less vulnerable to predation by Phagocata gracilis, a flatworm abundant in streams in central Kentucky. Developmental and growth parameters were not correlated significantly with ovum size in populations of either geographic race. Differences in degree of parental care among races also cannot explain variation in ovum size since both races abandon their eggs immediately after oviposition.     

Striking convergence in the mouthpart evolution of stream-living algae grazers

This scanning-electron microscopic study demonstrates the convergent evolution of the mouthparts of various herbivorous stream animals (insects from different orders, an isopod, snails, fish, and a tadpole) feeding on epilithic algal pastures. This food source is rich but is often difficult to harvest. Nevertheless, a large number of species can live on it because they have evolved highly specialized mouthparts. There are four functional problems that an algae grazer has to solve: the algae must be removed from the stone, they have to be collected and crushed, and a current shield is needed to prevent the water flow sweeping away the food. Among the 30 algae grazers examined in this study, a limited number of morphological solutions have been found for each of these adaptational problems. There are multiple evolutionary pathways for mouthpart adaptation and even closely related species have often evolved different types of tools for the same function. This refects the existence of a certain amount of evolutionary scope. Such freedom of evolution is present, however, only at the beginning of the adaptiogenesis of an algae grazer. Once one of the evolutionary pathways is taken, further improvement of the mouthparts is possible only by the refinement of the ‘chosen’ type of tools. The consequence of this is that a large number of astonishing convergences have occurred in algae grazers that have independently trodden the same evolutionary pathway.     

Limnology of a hypertrophic reservoir storing wastewater effluent for agriculture at Kibbutz Na'an,Israel

The reservoir investigated collects domestic and agricultural effluents after primary and secondary treatment. Despite the high concentration of organic matter (mean BOD⁵ = 60 mg l^–1), the reservoir does not deteriorate to produce obnoxious, anaerobic conditions. During a one year period, dissolved oxygen levels fluctuated widely but presented a long term dynamic stability, based on diffusion from the air during the winter mixing and on algal — bacterial — zooplankton equilibrium during the summer stagnation. The system, rich in organic and inorganic nutrients exhibited a much higher self-regulatory cability, than would be expected from its extreme enrichment. A hypothesis is proposed to explain the dynamic equilibrium achieved under extremely hypertrophic conditions.Human Environmental Sciences Division, School of Applied Science and Technology     

Morphological variation in Kellicottia longispina

The lengths of the body, the posterior spine and the three longest anterior spines were measured for 25 specimens of Kellicottia longispina from each of the eight lakes distributed from Imikpuk at Point Barrow, Alaska (latitude 71° 15) to Lake Washington (latitude 47° 38). Collections were available for more than two dates from six of the lakes. Temperature ranged from 1.2° to 18 °C. Mean lengths and ratios were examined in relation to latitude and temperature. Each population differed from the others in some aspect of absolute size, variability, or shape as expressed by the ratios of the dimensions. The population from Point Barrow is similar but not identical to Olofsson's var. heterospina.     

Chemical limnology of two artificial lakes used for both stormwater management and recreation

The aims of this study were to document the mainly chemical behaviour of two linked artificial lakes used for both stormwater management and recreation in the new town of Craigavon. Further, the understanding of their behaviour should help in their management and the design of other similar lakes.The lake mean total phosphorus (73 µg P l^–1), nitrate (0.50 mg N l^–1) and chlorophyll a (25 µg l^–1) concentrations, Secchi depth (1.2 m) and the estimated total phosphorus loading (1.98 g m^–2 a^–1) all classify the main lake as eutrophic. An important source of the phosphorus load on the lakes is the urban area of Craigavon (52% of the total load). The interrelationships between total phosphorus, chlorophyll a and Secchi depth in the main lake are similar to those in natural ones. In addition, the lake follows the total phosphorus load — trophic state relationships (lake total phosphorus and chlorophyll a concentrations and Secchi depth) found to apply elsewhere. These two points indicate that the artificial lakes in Craigavon behave similarly to natural ones.     

Effects of suspensoids (turbidity) on penetration of solar radiation in aquatic ecosystems

In mainland Australia and in southern Africa, the aridity of the climate and sparse vegetative cover increase the susceptibility of the soils to erosion, and as a consequence surface waters are usually turbid. The inanimate suspensoids in such waters, the tripton fraction of the limnologist, are responsible for virtually all the light scattering, and also, by virtue of the yellow-brown humic materials adsorbed on their surface, for a substantial part of the light absorption. Spectral absorption data for suspensoids in terms of theirin situ absorption coefficient values, and the contribution of suspensoids to absorption of photosynthetically available radiation (PAR) are given for certain Australian water bodies.To understand the effect of suspensoids on attenuation of the solar flux with depth, the scattering coefficient must also be known, and this can be determined from the nephelometric turbidity or from up- and down-welling irradiance measurements. The effect of particle size on scattering efficiency is discussed.An equation expressing the vertical attenuation coefficient for downward irradiance as a function of absorption coefficient, scattering coefficient and solar altitude is presented, and is used to explore the effects of absorption due to dissolved colour and suspensoids, and the effects of scattering by suspensoids, on the penetration of PAR.Suspensoids, by increasing the rate of attenuation of the solar flux with depth, can greatly diminish the euphotic depth of a water body, with a consequent decrease in the ratio of the euphotic to the mixed depth: thus turbidity can reduce productivity of a water body substantially below that which might be expected on the basis of nutrient availability. Shallow turbid waters of low intrinsic colour can, however, be highly productive. By diminishing the depth of the layer within which solar energy is dissipated as heat, suspensoids can greatly modify the hydrodynamic behaviour of water bodies, and this also has far-reaching ecological consequences.Suspensoids drastically impair the visual clarity of water, a fact of major significance for the aquatic fauna, as well of aesthetic significance for humanity. The reciprocal of the Secchi depth is more correctly thought of as a guide to the vertical contrast attenuation coefficient rather than to the vertical attenuation coefficient for irradiance. The reflectivity of a water body, being at any wavelength proportional to the backscattering coefficient divided by the absorption coefficient, is highly dependent on the concentration, and optical character, of the suspensoids present. This has implications not only for the appearance (colour, muddiness) of the water to an observer, but also for the remote sensing of water composition by air- or satellite-borne radiometric sensors.     

Limnology and plankton periodicity of Jos Plateau water reservoir,Nigeria, West Africa

Limnological data (Dec. 1980–Jan. 1982) on the plankton and water chemistry of Lamingo Dam, located within the Jos biotite granite area of the Plateau State (Nigeria) are presented. The water-body falls in Beadle's (1981) category I of African lakes (conductivity < 40 µS cm^–1). Alkalinity (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3914!\[\bar x\] = 0.3 meq l^–1), principally composed of bicarbonates, dominated the anions % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaK4waiaajI% eacaqIdbGaaK4tamaaxababaGaeyOeI0caleaacaaIZaaabeaakiaa% b6dacaqIdbGaaKiBaiaaj2cacaqG+aGaaK4uaiaaj+eadaqhaaWcba% GaaKinaaqaaiaajkdacaqITaaaaOGaaKyxaaaa!4657!\[\user1{[HCO}\mathop -\limits_3 {\text{ > }}\user1{Cl - }{\text{ > }}\user1{SO}_\user1{4}^{\user1{2 - }} \user1{]}\]The plankton were characterized by a moderate standing crop of phytoplankton, and zooplankton were, generally, very limited in species and abundance. The order of dominance for the categories of phyto and zooplankton was: [Bacillariophyceae > Chlorophyceae > Dinophyceae] and [Rotifera > Crustacea] respectively. A diel cycle was characterized by nocturnal upward migration of the zooplankton, and the reverse behaviour in the phytoplankton.Interrelations between the biotic assemblages of plankters and various physical and chemical variables are discussed.     

Depth distribution of Campostoma grazing scars in an Ozark stream

Synopsis Campostoma spp., widespread and abundant herbivorous minnows of eastern North America, produce distinctive grazing scars when feeding on algae attached to natural substrates in streams. These scars are particularly prominent upon the low growth forms of blue-green algae that dominate the attached algal flora of many upland streams. In one stream pool in the Ozark uplands of Oklahoma, numbers and sizes of grazing scars coincided with numbers and sizes of individual Campostoma that occurred across a depth gradient, demonstrating that the information contained in the scars can provide quantification of microhabitat use and grazing intensity of these important herbivores. The results also support the hypothesis that in environments free of aquatic predators, larger fish use deeper parts of available stream habitats, particularly if threats from terrestrial or avian predators exist.