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651.
652.
Alexander Lukeneder Mathias Harzhauser Stefan Müllegger Werner E. Piller 《Marine Biology》2008,154(1):175-182
Stable isotopes (δ18O and δ13C) were measured in successive chambers of the aragonitic shells of the small deep-sea squid Spirula spirula (Linnaeus 1758) (class Cephalopoda, subclass Coleoidea, order Sepioidea, family Spirulidae) to determine whether their depth distributions
change with age. The spiral shells, ranging in diameter from 18 to 23 mm (30–38 chambers), were collected between 2000 and
2006 from beaches in six widely separated locations in three oceans, the Atlantic (Tobago and Canary Islands), Indian (Madagascar,
Maldives, and Perth, Australia), and Pacific Oceans (Ulladulla, Australia). The patterns for both isotopes were highly correlated
in specimens from all six sites. The δ18O data suggest that after hatching at depths >1,000 m at temperatures of 4–6°C, the squid migrate into shallower, warmer waters
at 12–14°C at depths of 400–600 m. Subsequently, the increasing δ18O values suggest a migration back into somewhat cooler, deeper habitats. The δ13C values also revealed three ontogenetic stages in all six specimens, including a major shift from positive to negative values,
which probably corresponds to sexual maturation, the initiation of reproduction, and concomitant changes in diet. In three
of the six specimens (from Tobago, Canary Islands, and Maldives) a fourth embryonic stage (not detected in the oxygen data)
was accompanied by markedly less positive δ13C values in the first few chambers. These data, combined with the scanty life history information from previous studies of
S. spirula, can be used to compare the habitat requirements of related extant and fossil cephalopod genera.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Indirect effects propagated through intervening species in a food web have important effects on community properties. Traditionally, these indirect effects have been conceptualized as mediated through density changes of the intervening species, but it is becoming increasingly apparent that those mediated through trait (phenotypic) responses also can be very important. Because density- and trait-mediated indirect effects have different properties, it is critical that we understand the mechanisms of transmission in order to predict how they will interact, and when or where they will be important. In this study, we examined the mechanisms and consequences of the lethal (density-mediated) and nonlethal (trait-mediated) effects of a larval odonate predator on a guild of four herbivore species (a larval anuran and three species of snails) and their resources. We also manipulated system productivity in order to explore the effects of environmental context on the transmission of these two types of indirect effects. We show that trait-mediated effects arising from the predator can be very strong relative to density-mediated effects on both the competing herbivores and the species composition and production of their resources. A number of these indirect effects are shown to be contingent on productivity of the system. We further present evidence that trait- and density-mediated indirect effects originating from a predator may be transmitted independently through different routes in a food web, particularly when spatial responses of the transmitting prey are involved. Finally, effects on prey growth due to trait responses to the predator varied from negative to positive in predictable ways as a function of time and indirect effects on the larger food web. These results indicate the important role that trait-mediated indirect effects can play in trophic cascades and keystone predator interactions, and we discuss how the mechanisms involved can be incorporated in theory. 相似文献
655.
Brose U Jonsson T Berlow EL Warren P Banasek-Richter C Bersier LF Blanchard JL Brey T Carpenter SR Blandenier MF Cushing L Dawah HA Dell T Edwards F Harper-Smith S Jacob U Ledger ME Martinez ND Memmott J Mintenbeck K Pinnegar JK Rall BC Rayner TS Reuman DC Ruess L Ulrich W Williams RJ Woodward G Cohen JE 《Ecology》2006,87(10):2411-2417
It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types. 相似文献
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659.
Sylke Ritter Werner H. Hauthal Gerd Maurer 《Environmental science and pollution research international》1995,2(3):153-160
Partition coefficients PO,w
(i) describing the distribution of a solute i onto coexisting phases of 1-octanol and water are needed in a large variety of
applications. They can be measured directly by HPLC as long as log PO,w
(i)≧ 3.5. For more hydrophobic substances, several experimental procedures have been proposed in the literature. The reliability
of those methods is questionable. Therefore, in the present work, PO,w
(i) is determined experimentally by three HPLC methods using reversed-phase HPLC [1]. Results from different procedures are compared
critically. The method of Braumann [2] proved to be superior over the OECD-guidelines [3]. It was therefore applied to determine
octanol/water partition coefficients for 23 substances at 25 °C. For eight of those substances (4-methylindole; 9-(hydroxymethyl)anthracene;
N-ethylcarbazol; ethylcyclohexane; trans-2-octene; l,l-dimethyl-(ethy])cyclohexane; heptylbenzene; 4-dodecyl-l,3-benzenediol)
no experimentally determined number for PO,w
(i) has been published before. 相似文献
660.