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71.
Jamie N. Womble Gail M. Blundell Scott M. Gende Markus Horning Michael F. Sigler David J. Csepp 《Marine Biology》2014,161(6):1361-1374
Foraging theory predicts that animals will adjust their foraging behavior in order to maximize net energy intake and that trade-offs may exist that can influence their behavior. Although substantial advances have been made with respect to the foraging ecology of large marine predators, there is still a limited understanding of how predators respond to temporal and spatial variability in prey resources, primarily due to a lack of empirical studies that quantify foraging and diving behavior concurrently with characteristics of prey fields. Such information is important because changes in prey availability can influence the foraging success and ultimately fitness of marine predators. We assessed the diving behavior of juvenile female harbor seals (Phoca vitulina richardii) and prey fields near glacial ice and terrestrial haulout sites in Glacier Bay (58°40′N, ?136°05′W), Alaska. Harbor seals captured at glacial ice sites dived deeper, had longer dive durations, lower percent bottom time, and generally traveled further to forage. The increased diving effort for seals from the glacial ice site corresponded to lower prey densities and prey at deeper depths at the glacial ice site. In contrast, seals captured at terrestrial sites dived shallower, had shorter dive durations, higher percent bottom time, and traveled shorter distances to access foraging areas with much higher prey densities at shallower depths. The increased diving effort for seals from glacial ice sites suggests that the lower relative availability of prey may be offset by other factors, such as the stability of the glacial ice as a resting platform and as a refuge from predation. We provide evidence of differences in prey accessibility for seals associated with glacial ice and terrestrial habitats and suggest that seals may balance trade-offs between the costs and benefits of using these habitats. 相似文献
72.
Simon W. Townsend Markus Zöttl Marta B. Manser 《Behavioral ecology and sociobiology》2011,65(10):1927-1934
Socio-demographic factors, such as group size and their effect on predation vulnerability, have, in addition to intrinsic
factors, dominated as explanations when attempting to understand animal vigilance behaviour. It is generally assumed that
animals evaluate these external factors visually; however, many socially foraging species adopt a foraging technique that
directly compromises the visual system. In these instances, such species may instead rely more on the acoustical medium to
assess their relative risk and guide their subsequent anti-predator behaviour. We addressed this question in the socially
foraging meerkat (Suricata suricatta). Meerkats forage with their head down, but at the same time frequently produce close calls (‘Foraging’ close calls). Close
calls are also produced just after an individual has briefly scanned the surrounding environment for predators (‘Guarding’
close calls). Here, we firstly show that these Guarding and Foraging close call variants are in fact acoustically distinct
and secondly subjects are less vigilant (in terms of frequency and time) when exposed to Guarding close call playbacks than
when they hear Foraging close calls. We argue that this is the first evidence for socially foraging animals using the information
encoded within calls, the main adaptive function of which is unrelated to immediate predator encounters, to coordinate their
vigilance behaviour. In addition, these results provide new insights into the potential cognitive mechanisms underlying anti-predator
behaviour and suggest meerkats may be capable of signalling to group members the ‘absence’ of predatory threat. If we are
to fully understand the complexities underlying the coordination of animal anti-predator behaviour, we encourage future studies
to take these additional auditory and cognitive dimensions into account. 相似文献
73.
Eliecer Díaz Christine Güldenzoph Markus Molis Christopher McQuaid Martin Wahl 《Marine Biology》2006,149(6):1301-1311
Variabilities in the responses of several South African red and green macroalgae to direct grazing and the responses of one green alga to cues from grazers were tested. We used two feeding experiments: (1) testing the induced responses of three red and one green algae to direct grazing by mesograzers and (2) a multi-treatment experiment, in which the direct and indirect effects of one macrograzer species on the green alga Codium platylobium were assessed. Consumption rates were assessed in feeding assays with intact algal pieces and with agar pellets containing non-polar extracts of the test algae. Defensive responses were induced for intact pieces of Galaxaura diessingiana, but were not induced in pellets, suggesting either morphological defence or chemical defence using polar compounds other than polyphenols. In contrast, exposure to grazing stimulated consumption of Gracilaria capensis and Hypnea spicifera by another grazing species. In the multi-treatment experiment, waterborne cues from both grazing and non-grazing snails induced defensive algal traits in C. platylobium. We suggest that inducible defences among macroalgae are not restricted to brown algae, but that both the responses of algae to grazers and of grazers to the defences of macroalgae are intrinsically variable and complex. 相似文献
74.
Tobias Türcke Stefan Norra Doris Stüben Zsolt Berner Markus Leosson 《Environmental Sciences Europe》1999,11(3):127-133
Different sources of traffic immissions (tyres, soot, oil, asphalt, plastic, paint) were analysed for stable carbon and sulphur isotope ratios. The aim of this study is to investigate whether these isotope ratios can be used to evaluate the environmental impact of traffic immitted harmful substances in roadside soils. The δ13C values of technical materials are between -30‰ and -18‰ (PDB). They can be distinguished by their δ13C value because of specific production methods. The δ13C value of asphalt is between -23 and -18‰, soot shows values from -27 to-22‰ Moreover, soot of different fuel have different carbon isotope ratios. Plastic, paint and oil have similar δ13C from -30 to -27‰ Carbon isotope ratios of automobile tyres are around -26‰ Traffic impact on the carbon isotope composition is reflected in δ13C values of various carbon spezies found in street sediments and road side soils. These δ13C values correlate to concentrations of lead and platinum. Although δ34S values of technical materials are between -6 and +8‰ it was not possible to characterise samples according to their Sulphur isotopic compostion. 相似文献
75.
We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat.
The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then
characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was
the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary
layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical
modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates
that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats
and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
76.
The neonatal incidence rate of Down syndrome (DS) is well-known to accelerate strongly with maternal age. This non-linearity
renders mere accumulation of defects at recombination during prolonged first meiotic prophase implausible as an explanation
for DS rate increase with maternal age, but might be anticipated from chromosomal drive (CD) for trisomy 21. Alternatively,
as there is selection against genetically disadvantaged embryos, the screening system that eliminates embryos with trisomy
21 might decay with maternal age. In this paper, we provide the first evidence for relaxed filtering stringency (RFS) to represent
an adaptive maternal response that could explain accelerating DS rates with maternal age. Using historical data, we show that
the proportion of aberrant live births decrease with increased family size in older mothers, that inter-birth intervals are
longer before affected neonates than before normal ones, and that primiparae exhibit elevated levels of DS incidence at higher
age. These findings are predicted by adaptive RFS but cannot be explained by the currently available alternative non-adaptive
hypotheses, including CD. The identification of the relaxation control mechanism and therapeutic restoration of a stringent
screen may have considerable medical implications. 相似文献
77.
Many regions of the world are predicted to experience water scarcity due to more frequent and more severe droughts and increased water demands. Water use efficiency by plants can be negatively affected by soil water repellency (SWR). It is timely to review existing techniques to remedy SWR. Ideally remediation addresses the origins of a problem. However, the fundamental mechanisms of how and why SWR develops are still poorly understood. In this review it was hypothesized that SWR occurs where the balance of input-decomposition of organic matter is impaired, due to either increased input or decreased decomposition rates of hydrophobic substances. Direct and indirect strategies to remedy SWR were distinguished. While direct remediation aims at abolishing the causes of SWR, indirect strategies seek to manage sites with SWR by treating its symptoms. The 12 reviewed strategies include applying surfactants, clay, slow-release fertilizers, lime, and fungicides, bioremediation of SWR through stimulating earthworms, choosing adapted vegetation, irrigation, cultivation, soil aeration and compaction. Some of the techniques have been applied successfully only in laboratory experiments. Our review highlights that it is not straightforward to cure SWR based on easily measurable and site-specific soil and vegetation properties, and that long-term, large-scale field experiments are required to improve the understanding of the evolution of SWR as cornerstone to develop cost-effective and efficient remediation strategies. We also identified current research gaps around the diagnosis and prevention of SWR. 相似文献
78.
An assertion deeply rooted in the ornithological literature holds that sex-specific mortality causes a sex ratio disparity
(SRD) between complete and incomplete broods. Complete broods are thought to reflect the primary sex ratio before any bias
introduced by developmental mortality. Contrary to this view, however, complete and incomplete broods should exhibit identical
sex ratio distributions even when the sexes experience differential mortality, as shown in the classic paper of Fiala (Am
Nat 115: 442–444, 1980). Therefore, in partially unsexed samples, primary sex ratio biases cannot be distinguished from biases
caused by differential mortality. In addition, complete broods do not represent primary sex ratio more accurately than incomplete
ones and might even be misleading. Despite Fiala’s prediction, SRD does occur in some empirical studies. We show that this
pattern could arise if (1) primary sex ratio affects chick mortality rates independently of sex (direct effect), (2) primary
sex ratio covaries with a variable that also affects mortality rate, or (3) sex differential mortality covaries with overall
mortality rate (indirect effects). Direct effects may cause stronger SRD than indirect ones with a smaller and opposite bias
in the overall sex ratio and could also lead to highly inconsistent covariate effects on brood sex ratios. These features
may help differentiate direct from indirect effects. Most interestingly, differences in covariate effects between complete
and incomplete broods imply that influential variables are missing from the analysis. 相似文献
79.
80.
Mathias Gadegast Ulrike Hirt Dieter Opitz Markus Venohr 《Regional Environmental Change》2012,12(3):571-580
Studies of nutrient emissions into surface waters are usually only performed for years in recent decades. However, estimating nutrient emissions for the more distant past enables us to identify the main factors responsible for the increasing nutrient contamination since the end of the nineteenth century. We focussed on the Oder River System for 1875–1944, divided into 10-year periods. Nutrient emissions into surface waters were calculated with the model MONERIS (MOdelling Nutrient Emissions in RIver Systems). For seven different pathways and eight sources, the total nitrogen (TN) emissions were quantified. The TN-emissions into the surface waters for 1880 amounted to 25,300 t?year?1, and by 1940, this value had almost doubled to 46,600?t?year?1. In 1880, 57% of TN-emissions into the surface waters derived from urban systems, due to the high amount of untreated waste water. In 1940, only 34% of TN-emissions into surface waters derived from urban systems, despite a population growth of about 27% since 1880; point sources via newly constructed waste water treatment plants (WWTPs) increased from 4% (1880) to 26% (1940). During the study period, the main changes in diffuse TN-emissions from agriculture were caused by inorganic fertilizer application and nitrogen deposition, while TN-emissions via urban sources were shifted to point sources due to population growth and the construction of new WWTPs. Furthermore, estimated TN-concentrations could make a contribution to construct benchmarks for nutrient concentrations according to the physiochemical properties to implement the European Water Framework Directive (WFD 2000). 相似文献