Influence of fish on the breeding of the red-necked grebe Podiceps grisegena (Boddaert, 1783)

I determined whether selection of breeding sites by thered-neckedgrebe Podiceps grisegena (Boddaert, 1783) was affectedbycompetition for food with fish. During 1987–89, ten ponds inScania, southern Sweden were investigated, five with(breedingsites) and five without breeding red-necked grebe(non-breedingsites). I quantified the biomass of fish and macrozoans(here:larger invertebrates and small vertebrates) and measured thephysical and chemical conditions of the ponds.Breeding sites had significantly lower relative fish abundancethannon-breeding sites. They were either devoid of fish or hadonly nine-spined sticklebackPungitius pungitius. The biomass (dry weight) ofmacrozoans,many of which represent a food resource for grebes, was 16timesgreater at breeding than at non-breeding sites. The physicalandchemical conditions of the ponds did not differsignificantly.These results are consistent with the hypothesis thatcompetitionfor macrozoans occurs between red-necked grebe and fish andthat adense population of many fish species caused red-necked grebestoavoid otherwise acceptable breeding sites.     

Elemental signatures of human diets from the Georgia Bight

Multielement analysis was performed on bone samples extracted from the femora of 39 adults from three mortuary sites (Johns Mound, Santa Catalina de Guale, and Santa Catalina de Guale de Santa Meria) and time periods (late preagricultural, early contact, and late contact) in the Georgia Bight. This study was used to investigate whether elemental analysis would support or contradict other lines of data regarding diets and dietary change previously generated for the region. The data are in agreement with an earlier interpretation, based on stable isotopes, that dietary maize increases through time but fails to support the idea that marine resources decreased in importance. Rather, it appears that the wild plant food component of the diets decreases as maize increases in importance; throughout the sequence, marine resources comprise a significant portion of the diets. © 1995 Wiley-Liss, Inc.     

Changes in the behavior of the female short-tailed cricket,Anurogryllus muticus (De Geer) (Orthoptera: Gryllidae) following mating

InAnurogryllus muticus females, mating stimulates burrow construction, burrow provisioning, feeding, egg production, and egg-laying. Since mating often occurs before the ovaries are fully developed, the time span between mating and oviposition is used for increased food intake and the accumulation of nutrient reserves in the fatbody. Oviposition triggers maternal care of eggs and emerging hatchlings, and blocks egg consumption. Hatchling behavior is investigated. When hatchlings eat eggs, they prefer newly laid over older, embryonic eggs.     

The cholecystokinin antagonist,proglumide, increases food intake in the rat

Cholecystokinin, secreted in response to ingested food entering the duodenum, may play a role in limiting food intake. Inhibition of cholecystokinin should therefore induce an increase in food intake. Proglumide, a specific antagonist of cholecystokinin was used to block the satiety effect of a food preload in rats. A significant increase in food intake was obtained following proglumide injection, thus supporting the hypothesis that cholecystokinin, released by food in the duodenum, acts as a short-term satiety factor.     

Projections of world population and world food supply

This paper considers projections made about world population levels and world food production from 1945 to 1970, attempting to evaluate them in terms of actual levels of 1975. Most underestimated the population explosion of the past two decades; short-term estimates were more reliable than long-term ones; there was little variation in population estimates at any one time; and U. N. figures were generally the most useful. Projections of world food production were less satisfactory than those of population levels, as both data and measures were debatable. The research suggests some of the problems in evaluating the danger of world famine by examining projections of population and food supply mechanically and in isolation from the complex processes which affect these factors.     

Surfacing activity and food utilisation in the obligatory air-breathing fish ophiocephalus striatus as a function of body weight

Reared in cylindrical aquaria containing different depths of water (2.5 to 70 cm) the obligatory air-breathing fish Ophiocephalus striatus, belonging to different weight classes (0.1, 0.75, 10, 20 and 41 g), was forced to swim vertically a longer or shorter distance per surfacing. Surfacing frequency was a depth-dependent, activity in individuals weighing less than 20 g in all weight classes, the frequency was nearly 2 times more in the series fed ad libitum on fish muscle, than in the one where the fish were starved. Owing to the sustained surfacing activity and the consequent fatigue, the test individuals hung to the surface for a definite period. Neither frequency nor duration of hanging was depth-dependent. Mean hanging durations for the feeding series were 1.1, 3.8, 5.9, 7.9 and 8.8 hr/day in the 0.1, 0.75, 10, 20 and 41 g weight classes, respectively; the corresponding values for the starving series were 1.3, 15.0, 13.0, 12.7 and 12.8 hr/day. The distance swum by the feeding fish increased from 57 to 681 m/day and from 61 to 507 m/day in the 0.1 and 41 g individuals exposed to the minimum and maximum aquarium depths. Feeding rate, which was a depth-dependent activity, decreased from 280 to 113 g cal/g live fish/day with increasing weight. Rate and efficiency of conversion also decreased with increasing body weight; in larger fish conversion was dependent on volume rather than on depth of the aquarium. O₂ uptake of feeding fish was about 6 times higher than the starving ones of the tested weight classes at different aquarium depths.This paper is part of a thesis submitted by the author (from A.P.A. College, PALNI) to Madurai University in partial fulfillment of the requirement of the Ph. D. degree. Contribution No. 12 under a research scheme granted to Dr. T. J. Pandian by the UGC (New Delhi). The author is grateful to Dr. T. J. Pandian for valuable guidance, financial support and encouragements.     

Une etude sur clarias senegalensis val. dans la region du lac kossou (cote d'ivoire)

A study on Clarias senegalensis Val. in the region of Lake Kossou (Ivory Coast). Clarias senegalensis is the dominant silurid of the man-made lake Kossou and some smaller impoundments in the same region. Comparison of data spread over a five year period starting from 1970, some months before the dam was completed, reveals that the density of C. senegalensis dropped to the original level that existed in the river after reaching a peak in the years following the damming. This phenomenon which coincides with the impoverishment of the lake waters, is explained by the fact that C. senegalensis has its optimal habitat in poorly oxygenated waters, rich in organic matter. It is able to colonize this kind of productive waters thanks to the suprabranchial organ. In these optimal conditions it mainly feeds on aquatic insects and plankton.The fecundity of C. senegalensis may reach 20o ooo ripening eggs per female. Reproduction occurs during the rainy season in flooded savannas. Growth rates are very high and the age determinations show that, in the region of Kossou, C. senegalensis reaches an average standard length of 620 mm (2.7 kg) within three years.Our results are compared to literature data on other related species of the genus Clarias and the position of C. senegalensis within this generic complex is discussed.

     

Possible occurrence of character displacement in the sympatric skates Raja erinacea and R. ocellata (Pisces: Rajidae)

Synopsis Raja erinacea and R. ocellata are sibling species which are positively correlated with each other by occurrence and numerical abundance. In sympatry the species undergo interactive segregation; R. erinacea feeds on a higher percentage of epifauna and R. ocellata feeds on a higher percentage of infauna.An isolated allopatric population of R. ocellata occurs in the Gulf of St. Lawrence which is phenotypically intermediate between the sympatric populations of R. erinacea and R. ocellata in characters related to feeding e.g. size, number of tooth rows in the upper jaw, and shape of the upper jaw. It appears probable that the allopatric population represents the morphological state of R. ocellata before it became sympatric with R. erinacea; divergence in size, number of tooth rows, and shape of the upper jaw between the two species developed after establishment of sympatry. These divergences in character traits, related to feeding, reduced competition between the two sympatric species and permitted the present wide overlap in their ranges.Character displacement is evidently rare in demersal fishes inhabiting the flat and soft bottoms of the northwestern Atlantic because the three other pairs of sibling species that occur there are parapatrically distributed and thus would not compete for resources. Raja erinacea and R. ocellata may have been restrained from establishing parapatry by another species pair of skates (R. senta and R. radiata) which have a complementary distribution and similar feeding habits of R. erinacea and R. ocellata but which occur in deeper water.     

Diel food selection of pelagic Arctic charr, Salvelinus alpinus (L.), and brown trout, Salmo trutta L., in Lake Atnsjø, SE Norway

Patterns of diel food selection in pelagic Arctic charr, Salvelinus alpinus (L.) and brown trout, Salmo trutta L. were investigated in Lake Atnsjo, SE Norway, by gillnet sampling during July-September 1985. Arctic charr feed almost exclusively on zooplankton both day and night, while brown trout had a diurnal shift in diet. For this species zooplankton made up a considerable part of the diet in the daytime, while at night the diet consisted mainly of surface insect and chironomid pupae. Both species had a selective feeding mode on zooplankton during the day and night. Arctic charr had a higher gill raker number and a denser gill raker spacing compared with brown trout. Still, the differences in prey size between the two species were small. We argue that the observed differences in food selection between Arctic charr and brown trout can be explained by differing abilities to detect food items under low light conditions.