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T R Royama - One of the best experts on this subject based on the ideXlab platform.
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factors governing feeding rate Food Requirement and brood size of nestling great tits parus major
2008Co-Authors: T R RoyamaAbstract:SUMMARY Observations were made on feeding rates and Food-consumption of nestling Great Tits Parus major mainly in Larch plantations at lake Yamanaka, Japan. Feeding frequencies were recorded by an automatic recorder. There were marked differences between early and late broods; the feeding frequencies were twice as great in early than in late broods of the same size. No clear tendency was observed in the variations of feeding frequencies in relation to brood size. There was, however, a clear inverse relationship between the frequencies and the average size of Food brought to the nests. The males' share in terms of feeding frequencies is described. These figures, however, did not follow the males' contribution in terms of weight of Food, which was nearly always higher than the females'. It is pointed out that feeding frequencies are far too variable to be used as a true index of Food consumption by nestlings, and are not reliable. Attempts were made to measure the weight of Food; the method is described. The average weight of Food brought by males was lighter in early than in later broods. The total weight of Food was estimated. The trend of daily Food consumption per chick was similar to that of the chick's growth curve. It was found that up to about the tenth day of the nestling period daily Food-intake per chick increased linearly as body weight increased. At some nests, rate of defaecation was observed. This was at first low, but it increased steeply on the third day, with a steady increase thereafter. By comparing the rates of Food intake, faeces output, and weight increment of a chick, it was found that only 20–30% of digested matter (the difference between Food-intake and faeces-output was used up daily (for body temperature regulation various external effort, etc.). The factors responsible for this high efficiency of growth in nestlings are discussed. There was a clear inverse relationship between the total weight of Food brought per chick per day and the brood size. This is largely because the heat-loss is greater in small than in large broods, so that a chick from a small brood in fact needs more energy to maintain its body temperature after a certain age than one from a large brood. This is discussed in detail. Factors which caused variations in size of Food are discussed in relation to feeding frequencies. It is pointed out that, because of the inverse relationship between energy Requirement by each chick and brood size, the total Food Requirement by a brood as a whole did not vary directly in proportion to the brood size. An estimation showed that a b/3 still required about 75% of the total Food required by a b/8. A smaller brood is less advantageous than expected to parents feeding nestlings when they encounter adverse conditions, e.g. Food shortage in the habitat, or a lack of help by their mates, etc. On the other hand, it is suggested that once they have left the nest, the Food-demand by a brood of fledglings the parents have to feed, so that, in the fledging period, in times of Food shortage it would certainly be advantageous to have fewer young. It is suggested that, although fledglings may consume three to four times as much Food as nestlings, the parents, in providing this Food, would not work proportionately harder, since the parents' efficiency of providing Food could be higher in feeding the fledglings, which always follow the parents as they are hunting, than in feeding the nestlings to which Food has to be brought. On this basis, the adaptive significance of the length of the nestling period in nidicolous species is discussed in relation to clutch size, brood size and Food Requirement.
C. M. Lessells - One of the best experts on this subject based on the ideXlab platform.
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Warmer springs lead to mistimed reproduction in great tits (Parus major)
1998Co-Authors: Marcel E. Visser, Joost M. Tinbergen, A. J. Van Noordwijk, C. M. LessellsAbstract:In seasonal environments, the main selection pressure on the timing of reproduction (the ultimate factor) is synchrony between offspring Requirements and Food availability. However, reproduction is initiated much earlier than the time of maximum Food Requirement of the offspring. Individuals should therefore start reproduction in response to cues (the proximate factors), available in the environment of reproductive decision making, which predict the later environment of selection. With increasing spring temperatures over the past decades, vegetation phenology has advanced, with a concomitant advancement in the reproduction of some species at higher trophic levels. However, a mismatch between Food abundance and offspring needs may occur if changes in the environment of decision making do not match those in the environment of selection. Date of egg laying in a great tit (Parus major) population has not advanced over a 23-year period, but selection for early laying has intensified. We believe that this is the first documented case of an adaptive response being hampered because a changing abiotic factor affects the environment in which a reproductive decision is made differently from the environment in which selection occurs.
H Shimauchi - One of the best experts on this subject based on the ideXlab platform.
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population biomass feeding respiration and growth rates and carbon budget of the scyphomedusa aurelia aurita in the inland sea of japan
2005Co-Authors: H ShimauchiAbstract:We investigated the seasonal occurrence, wet : dry : carbon : nitrogen weight ratios, population biomass, gastric pouch contents, and rates of feeding, growth and respiration of the scyphomedusa Aurelia aurita in the central part of the Inland Sea of Japan. Aurelia aurita medusae began to appear in January/ February as ephyrae, reached annual maximum body size in July/August, and disappeared, presumably due to death, by November. Initial slow growth in early spring was followed by a period of exponentialgrowth(meangrowthrate:0.069d � 1 )betweenAprilandJuly.IntheOndoStrait,whichis characterized by strong tidal mixing, the A. aurita population (mean carbon biomass: 66.0 mg C m � 3 ) overwhelmingly dominated the zooplankton-community biomass (mean biomass of micro- and mesozooplankton: 23.7 mg C m � 3 ) between May and early August The gastric content analysis revealed that A. aurita ate almost all micro- and mesozooplankters, of which small copepods were most important. On the basis of digestion time for small copepods (60 min) and their abundance in the gastric pouch of field-collected A. aurita, we determined the weight specific feeding rates and clearance rates. The former increases linearly with increasing copepod abundance, but the latter was relatively constant irrespective of the Food supply. We also measured the respiration rates of A. aurita and expressed them as functions of body weight and temperature. These physio-ecological parameters enabled us to construct the carbon budget of the A. aurita population typical of early summer in the Ondo Strait. Predicted population-feeding rate (6.07 mg C m � 3 d � 1 ) was higher than the population-Food Requirement for both metabolism and growth (4.55 mg C m � 3 d � 1 ), indicating that Food supply was sufficient to sustain the observed growth rate. This feeding rate was equivalent to 26% of microand mesozooplankton biomass, a significant impact on zooplankton.
Marcel E. Visser - One of the best experts on this subject based on the ideXlab platform.
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Warmer springs lead to mistimed reproduction in great tits (Parus major)
1998Co-Authors: Marcel E. Visser, Joost M. Tinbergen, A. J. Van Noordwijk, C. M. LessellsAbstract:In seasonal environments, the main selection pressure on the timing of reproduction (the ultimate factor) is synchrony between offspring Requirements and Food availability. However, reproduction is initiated much earlier than the time of maximum Food Requirement of the offspring. Individuals should therefore start reproduction in response to cues (the proximate factors), available in the environment of reproductive decision making, which predict the later environment of selection. With increasing spring temperatures over the past decades, vegetation phenology has advanced, with a concomitant advancement in the reproduction of some species at higher trophic levels. However, a mismatch between Food abundance and offspring needs may occur if changes in the environment of decision making do not match those in the environment of selection. Date of egg laying in a great tit (Parus major) population has not advanced over a 23-year period, but selection for early laying has intensified. We believe that this is the first documented case of an adaptive response being hampered because a changing abiotic factor affects the environment in which a reproductive decision is made differently from the environment in which selection occurs.
Carolyn W Burns - One of the best experts on this subject based on the ideXlab platform.
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feeding response of nyctiphanes australis euphausiacea to various nanoplankton sizes and taxa
2003Co-Authors: Graeme J Haywood, Carolyn W BurnsAbstract:Nanoplankton (2 to 20 µm) are a substantial fraction of the plankton in the sea, where they form a potential Food source for zooplankton. Monocultures of 12 nanoplankton taxa of different cell size and 1 species of Thalassiosira (microplankton) were offered to Nyctiphanes australis to determine whether they would be consumed and, if so, determine rates of clearance and ingestion by the euphausiid. N. australis ingested very small cells (3.5 to 5.4 µm equivalent spherical diameter) at rates ≤ 5 × 10 5 cells h -1 . A total of 8 nanoplankton taxa were consumed at rates that provided N. aus- tralis with its minimum Food Requirement of 2% body carbon d -1 , and so could maintain it when microplankton abundance is low. Our results suggest that N. australis can detect and avoid unpalat- able Food such as the chlorophytes Dunaliella and Nannochloris, but is susceptible to the toxic dinoflagellate Alexandrium minutum.