Decrease In Food Supply Research Articles

Les paléocommunautés profondes sur fond rocheuxdu Pléistocène méditerranéen. Description et essai d'interprétation paléoécologique

Dredgings and in situ observations (from the submersibleCYANA) undertaken in different areas of the Mediterranean Sea show that communities, chiefly composed of sponges and/or scleractinians and serpulids have colonized rocky bottoms, of subsea bathyal relief features, i.e. as far as 2500–3000 m. These faunas, not very diversified are now fossilized. There are some regional and local variations in thedensity of populations but, in several sites, particularly in the Tyrrhenian Sea and along the Malta escarpment, concentration in individuals can be high. In this case, their skeletons constitute the frame of decimetric to metric edifices of constructed limestones. The paleocommunities are contemporaneous withthe last cold climatic phase of the Pleistocene. Their development might have been favoured by the presence of deep-currents. The latters initiated superficial and early cementations which have affected associated micritic material during periods of absence of sedimentation. The disappearance of these Mediterranean assemblages is probably related to several concomitant factors; in particular to an increase in temperature of deep-waters and to a decrease in food supply.

The distribution of Heterotrissocladius oliveri Saether (Diptera: Chironomidae) in Lake Michigan

Fifty one chironomid species were identified from 504 samples collected at depths ranging 8 to 267 m in Lake Michigan, U.S.A. Heterotrissocladius oliveri Saether occurred in 32% of these samples and had an average abundance of 22 m−2 which was similar to other estimates from the Great Lakes. Maximum average lake-wide density was at 30 to 60 m (41 m−2). At depths ≥60 m, H. oliveri was the dominant chironomid species comprising 75% of total Chironomidae. The substrate preference of H. oliveri differed within each depth regime considered: at 30–60 m, 2–3 ϕ; at 60–120 m, 3–5 ϕ, 7–9 ϕ; and at 120–180 m, 6–8 ϕ. Abundance was notably reduced at all depths in substrates characterized as medium silt (5–6 ϕ). On a lake-wide basis, the distribution pattern suggested H. oliveri was most numerous from 30 to 60 m along the southwestern, eastern, and northern shorelines and at 60–120 m depths along the southern and eastern shorelines. Increased abundance in the South Basin was concurrent with evidence of increased sedimentation at 60 to 100 m. However, in several other areas of the lake, high densities were associated with medium to very fine sands relatively free of silts and clays. This observation suggested occurrence of H. oliveri was minimally affected by sediment type.Widely variable, but generally elevated water temperatures likely prevent H. oliveri from establishing a substantial population density at depths < 30 m. With increased depth, temperature fluctuation is negligible and food is more stable, though the source is variable. Factors limiting abundance of H. oliveri at depths ≥30 m were related to decreased food supply due to distance from shore, food sources of lower value (clays), and, most importantly, to reproductive replenishment.Although still oligotrophic in nature, high density occurrences in both high and low sedimentation areas of the lake suggest the trophic indicator status of H. oliveri might be broader than previously thought.

Larval Competition Between the Introduced Vector of Dengue Fever in Australia, Aedes-Aegypti (L), and a Native Container-Breeding Mosquito, Aedes-Notoscriptus (Skuse) (Diptera, Culicidae)

The introduced vector of dengue, Aedes aegypti, has disappeared from New South Wales at the same time as the indigenous Ae. notoscriptus has increasingly intruded into the domestic environment. Laboratory investigations of larval survival and development rates for both species, alone and in various combinations, at two temperatures under varying conditions of density and food, were conducted to test the hypothesis that the latter species had a competitive advantage. For both species, in intra- and interspecific competition, survival declined markedly, and development rate increased considerably, with increasing density and decreasing food in intra- and interspecific competition. Decrease in food supply had relatively greater effect than increase in larval density, although combining both had the greatest effects. Although the native Ae. notoscriptus had a marginal advantage over the introduced Ae. aegypti at 22�C, the situation was reversed at 28�C. Overall, however, the predominant species in mixed cultures was usually advantaged. The hypothesis was not proved, although the results indicated that Ae. notoscriptus may have a competitive advantage over Ae. aegypti in cooler areas when the former species is predominant.

Growth and reproduction of the bay scallop, Argopecten irradians (Lamarck) at its southern distributional limit

Growth and reproduction in a Florida population of bay scallop, Argopecten irradians (Lamarck), existing at the southern limit of its distribution, was monitored over a 3-yr period. Somatic growth accompanied increasing water temperature between May and August, when maximum mantle, digestive gland, and adductor muscle weights and indexes were observed. From July through September, reproductive development was correlated with a decline in adductor muscle weight and index. Maximum gonad weight, gonad index, and oocyte diameter were found in late September and early October. Spawning commenced at this time in conjunction with decreasing water temperature. In comparison to more northern populations, the reproductive cycle of the Florida bay scallop occurs later in the year and is characterized by a higher gametogenic initiation temperature, a decreased maximum gonad index and decreased oocyte diameter, and a shift in reproductive energy resources from digestive gland (available food) to adductor muscle (pre-stored reserves). Increased metabolic rate associated with higher temperature and coupled with decreased food supply results in the Florida bay scallop having less energy available for reproduction, ultimately limiting its southern distribution.

Effects of temperature on the energy budgets of Hydra pseudoligactis.

Dry matter, nitrogen, and energy budgets were determined for laboratory cultures of Hydra pseudoligactis reared at 10, 15, 20, and 25° C, and fed freshly collected zooplankton. Maximum specific feeding rates increased from 0.24 to 0.91 (KJ food/KJ Hydra) with increasing rearing temperature. The corresponding growth rates increased from 0.14 to 0.29 but gross (growth/ingestion), net (growth/(ingestion-egestion)), and assimilation (gross/net) efficiencies decreased with increasing temperatures. The requisite food densities to maintain maximum ingestion rates (when permitted to feed for 3 hrs day-1) increased from 0.0056 to 0.021 KJ of zooplankton/KJ of Hydra. The combination of increasing energy requirements, decreasing food supply, and efficiencies of food utilization, with increasing water temperatures may contribute to the rapid declines of Hydra populations that are often observed in temperate lakes.

The Social Regulation of Population Density and Age-Sex Distribution in the Toque Monkey

The Social Regulation of Population Density and Age-Sex Distribution in the Toque Monkey

Environmental factors affecting growth and survival of juvenile western rock lobsters Panulirus longipes (Milne-Edwards)

The effects of temperature, photoperiod, oxygen, food supply, crowding, and autotomy of limbs have been measured under controlled conditions in aquaria. Growth rate increased with temperature to a maximum 26� C above which both growth rate and survival declined. Varying the length of photoperiod did not affect growth rate or survival, except that the growth rate was depressed significantly in continuous darkness. A mild deficiency of oxygen (60-67 % saturation) resulted in a smaller size increment at a moult; depression to 47-55 % saturation caused deaths at ecdysis. Daily feeding was necessary to maintain maximum rate of growth. The fist response to decreased food supply was a reduction in frequency of moulting. More severe shortage of food also depressed growth increment per moult. Feeding rates and conversion ratios have been measured. Frequency of moulting (and hence growth rate) was depressed markedly when juveniles were held in isolation. At a moult replacing two lost limbs, the growth rate was not affected; replacement of four limbs reduced that moult increment. Single loss of up to four limbs did not result in an earlier moult, but repetitive loss of two or more limbs at or immediately after each ecdysis led to precocious moulting. The impact of these and other components of the environment (shelter, salinity, turbidity, competitors and predators) upon juveniles during the 4 years spent on shallow coastal reefs is discussed. Food supply is emerging as the dominant factor determining growth and survival in the wild population.

THE SOCIABLE WEAVER, PART 3: BREEDING BIOLOGY AND MOULT

Summary Maclean, G. L. 1973. The Sociable Weaver, Part 3: Breeding biology and moult. Ostrich 44: 219–240. Rain or some associated phenomenon is the principal Zeitgeber releasing breeding in the Sociable Weaver. The species does not breed in the absence of rain. The same nest chambers are used for breeding as are used for roosting throughout the year. The Sociable Weaver is monogamous. The clutch size varies from two to six eggs, larger clutches being more common after good rains than in relatively poorer breeding periods. Food supply may therefore be the proximate factor regulating clutch size. Replacement clutches are not necessarily smaller than first clutches. The mean clutch size within a breeding period decreases with an apparent decrease in food supply. The parents share parental duties about equally. Up to four successive broods may be raised in a single breeding period; a breeding period may last up to nine months and may occur at any time of the year according to the somewhat erratic rainfall wh...

Ecological Factors Influencing the Breeding Season Schedule of Western Sandpipers (Calidris mauri) in Subarctic Alaska

Studies of the breeding system ecology of the Western Sandpiper (Calidris mauri) were conducted in the summers of 19661969 on the Yukon-Kuskokwim Delta in western Alaska. Western Sandpipers arrive as soon as the snow begins to melt, establish territories on heath tundra, pair and nest once. Second nestings are restricted to replacement clutches. As soon as breeding is completed, the adults shift to coastal habitats, begin molt, and by early to mid-July move S on migration. Young mauri follow about 2 to 3 weeks later. After their arrival on Pacific coast feeding areas, the adults continue their prebasic molt, completing it by late October. The single nesting and early departure of Western Sandpipers from the breeding areas are related to a decreasing food supply in an otherwise favorable environment. The only other congener sympatric with mauri on the Delta, C. alfpina, follows an identical breeding schedule, but remains longer in the N, occupying riverbank and intertidal habitats, and completes its molt before migrating S in late September. This extended residence of alpina in Alaska is possible because it is able to exploit marine invertebrates there during late summer, whereas mauri apparently is not. Therefore, the changes in food abundance near the nesting areas and the lack of suitable food supply in midsummer are the primary factors influencing the scheduling of breeding season events in Western Sandpiper populations.