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1.
F. Veloso-Gomes F. Taveira-Pinto Luciana das Neves Joaquim Pais Barbosa Carlos Coelho 《Journal of Coastal Conservation》2004,10(1):43-52
The entire northwestern coast of Portugal is undergoing severe erosion and there are several areas at high risk of erosion.
Commonly considered as a problem—because it jeopardizes human development along the coast—erosion is indeed a natural process
of sediment redistribution. This paper presents a brief analysis of erosion driving forces and the subsequent state of vulnerability
that coastal segments between the mouth of the River Douro and Cape Mondego are facing. The paper also discusses erosion risk
levels, low or high, and the subsequent questions whether there are populations, economical assets or natural habitats at
risk and/or areas prone to coastal flooding. Main challenges and future trends along the study area are identified in the
light of understanding the underlying causes of conflicts and what realistically can be achieved given the morphodynamics
and hydrodynamic processes, human development established along this coastal segment and the existing policies. 相似文献
2.
Hamed Haddadi Andrew J. King Alison P. Wills Damien Fay John Lowe A. Jennifer Morton Stephen Hailes Alan M. Wilson 《Behavioral ecology and sociobiology》2011,65(8):1659-1668
Social Network Analysis has become an important methodological tool for advancing our understanding of human and animal group
behaviour. However, researchers tend to rely on arbitrary distance and time measures when defining ‘contacts’ or ‘associations’
between individuals based on preliminary observation. Otherwise, criteria are chosen on the basis of the communication range
of sensor devices (e.g. bluetooth communication ranges) or the sampling frequencies of collection devices (e.g. Global Positioning
System devices). Thus, researchers lack an established protocol for determining both relevant association distances and minimum
sampling rates required to accurately represent the network structure under investigation. In this paper, we demonstrate how
researchers can use experimental and statistical methods to establish spatial and temporal association patterns and thus correctly
characterise social networks in both time and space. To do this, we first perform a mixing experiment with Merino sheep (Ovis aries) and use a community detection algorithm that allows us to identify the spatial and temporal distance at which we can best
identify clusters of previously familiar sheep. This turns out to be within 2–3 m of each other for at least 3 min. We then
calculate the network graph entropy rate—a measure of ease of spreading of information (e.g. a disease) in a network—to determine
the minimum sampling rate required to capture the variability observed in our sheep networks during distinct activity phases.
Our results indicate the need for sampling intervals of less than a minute apart. The tools that we employ are versatile and
could be applied to a wide range of species and social network datasets, thus allowing an increase in both the accuracy and
efficiency of data collection when exploring spatial association patterns in gregarious species. 相似文献
3.
Angelika Hilbeck Joanna M McMillan Matthias Meier Anna Humbel Juanita Schläpfer-Miller Miluse Trtikova 《Environmental Sciences Europe》2012,24(1):1-12
Background
The Cefic Mixtures Industry Ad-hoc Team (MIAT) has investigated how risks from combined exposures can be effectively identified and managed using concepts proposed in recent regulatory guidance, new advances in risk assessment, and lessons learned from a Cefic-sponsored case study of mixture exposures.Results
A series of tools were created that include: a decision tree, a system for grouping exposures, and a graphical tool (the MCR-HI plot). The decision tree allows the division of combined exposures into different groups, exposures where one or more individual components are a concern, exposures that are of low concern, and exposures that are a concern for combined effects but not for the effects of individual chemicals. These tools efficiently use available data, identify critical data gaps for combined assessments, and prioritize which chemicals require detailed toxicity information. The tools can be used to address multiple human health endpoints and ecological effects.Conclusion
The tools provide a useful approach for assessing risks associated with combined exposures to multiple chemicals. 相似文献4.
Eric Deleersnijder Jean-Marie Beckers Eric J. M. Delhez 《Environmental Fluid Mechanics》2006,6(6):541-547
To understand why the findings of Deleersnijder et al. [(2006), Environ Fluid Mech 6: 25–42]—the residence time in the mixed layer in not necessarily zero at the pycnocline—are consistent with those of Delhez and Deleersnijder [(2006), Ocean Dyn 56:139–150]—the residence time in a control domain vanishes at the open boundaries of this control domain—, it is necessary to consider a control domain that includes part of the pycnocline, in which the eddy diffusivity is assumed to be zero. Then, depending on the behaviour of the eddy diffusivity near the bottom of the mixed layer, the residence time may be seen to exhibit a discontinuity at the interface between the mixed layer and the pycnocline. If such a discontinuity exists, the residence time is non-zero in the former and zero in the latter. This is illustrated by analytical solutions obtained under the assumption that the eddy diffusivity is constant in the mixed layer. 相似文献
5.
Dirk Bunke Wolfgang Reuter Frank Ebinger Ismene Jäger Klaus Schneider 《Environmental Sciences Europe》2003,15(3):208-212
Background
Aim and Scope. Implementation of the European Union White Paper on chemicals policy shall provide more safety and more transparency in chemicals use. In the past, when assessing existing commercial substances there was often a lack of information in the fields of application of the chemicals and the exposures arising in those contexts. The White Paper therefore calls for ‘shared responsibility’. Processors and commercial users of substances are to be involved much more closely in the risk evaluation process than has hitherto been the case. They are to provide data on substance applications and exposures, and, to some extent, they are also to carry out exposure assessments and risk assessments themselves. By analysing case studies, the paper highlights the consequences of this approach.Results and Discussion
Fear has often been voiced that these new tasks will completely overburden small and medium-sized enterprises. It is assumed that many chemicals are no longer available for smallvolume applications, as — for cost reasons — producers do not include these applications in their registration. The wording of the White Paper is not precise enough to be able to appraise the costs that will be associated with the required intensified communication. In this situation, it is essential to analyse prototypical substances and their applications in order to gain an improved understanding of the principle of shared responsibility.Conclusions
The concrete study of several product chains has shown that the flow of information required between producers and users is very likely feasible within the context of the REACH system. For the producers of chemicals, the intensified communication will presumably make it simpler to procure information in the fields of application and exposures. However, in order to avoid users being overburdened, it will be important that registration requirements and focuses are shaped in a manner doing justice to practical realities. Users will need to undertake community-wide efforts on an industry federation and branch level. In this context, the protection of company know-how also needs to be ensured.Recommendation and Outlook
In practice, implementation of the principle of shared responsibility can lead to intensified communication among the producers and users of chemicals. This can greatly facilitate exposure assessments and risk assessments. There is a need to develop manageable procedures that can also be implemented by small and medium-sized enterprises. Numerous proposals have been made in this context, and extensive reference material is now available. 相似文献6.
The role of ambient and enhanced ultraviolet-B radiation (UVB; 280 to 315 nm) in a natural sand-associated microbenthic community
was studied in a 3-week experiment by incubating intact sediment cores from a shallow bay in an outdoor flow-through system
with 27 aquaria. After sampling of initial cores, the remaining cores (one per aquarium) were given one of three treatments:
no, ambient, and moderately enhanced UVB, and sampled, nine at a time, after 5, 12, and 19 d. The response of the community
was studied by analysing algal and meiofaunal composition and biomass, chlorophyll a content, composition of pigments and fatty acids, and content of UV-absorbing compounds (state variables), as well as carbon
fixation and allocation, and bacterial productivity (rate variables). Among rate variables, significant effects of UVB-treatments
were found for carbon fixation and allocation, while bacterial productivity was not affected. For state variables, a significant
response was observed for the composition of microalgae and fatty acids, and for chlorophyll a content. The effect of treatments was mainly observed as differences in development with time (two-way analysis of variance,
treatment × time interaction). Towards the end of the experiment, the no-UVB treatment most often differed from one or both
of the two treatments with UVB exposure, the latter showing lower values. There were marked successional changes in the community,
irrespective of treatment. The microalgal community changed from being dominated by coccoid cyanobacteria and epipsammic diatoms
to a dominance of epipelic diatoms and filamentous cyanobacteria. The pattern of carbon allocation, as well as an increased
C/N ratio of the sediment, suggested limitation of growth, perhaps by nutrients, at the end of the experiment. This may possibly
have acted synergistically with UVB exposure to create the treatment effects. The new knowledge gained from our experiment
is that ambient UVB can exert a stress on the function of sand-associated microbenthic communities in shallow waters and that
this effect coincides with structural differences in the community. More experiments in natural or semi-natural systems are
needed to allow better prediction of microbenthic community-level responses to UVB.
Received: 11 November 1997 / Accepted: 12 June 1998 相似文献
7.
Kate S. Boersma Clifford H. Ryer Thomas P. Hurst Selina S. Heppell 《Behavioral ecology and sociobiology》2008,62(12):1959-1968
Animals balance feeding and anti-predator behaviors at various temporal scales. When risk is infrequent or brief, prey can
postpone feeding in the short term and temporally allocate feeding behavior to less risky periods. If risk is frequent or
lengthy, however, prey must eventually resume feeding to avoid fitness consequences. Species may exhibit different behavioral
strategies, depending on the fitness tradeoffs that exist in their environment or across their life histories. North Pacific
flatfishes that share juvenile rearing habitat exhibit a variety of responses to predation risk, but their response to risk
frequency has not been examined. We observed the feeding and anti-predator behaviors of young-of-the-year English sole (Parophrys vetulus), northern rock sole (Lepidopsetta polyxystra), and Pacific halibut (Hippoglossus stenolepis)—three species that exhibit divergent anti-predator strategies—following exposure to three levels of predation risk: no risk,
infrequent (two exposures/day), and frequent (five exposures/day). The English sole responded to the frequent risk treatment
with higher feeding rates than during infrequent risk, following a pattern of behavioral response that is predicted by the
risk allocation hypothesis; rock sole and halibut did not follow the predicted pattern, but this may be due to the limited
range of treatments. Our observations of unique anti-predator strategies, along with differences in foraging and species-specific
ecologies, suggest divergent trajectories of risk allocation for the three species. 相似文献
8.
Appraisal of visual assessments of habitat complexity and benthic composition on coral reefs 总被引:4,自引:0,他引:4
Visual assessments of topographic habitat structure and benthos on coral reefs were appraised using quantitative data collected
from 16 replicate surveys within each of 21 sites on Seychelles reefs. Results from visual assessments of reef benthos were
similar to those obtained using techniques frequently used to assess benthic complexity and composition. Visual estimates
of habitat topography were correlated with rugosity, reef height and holes of 10–70 cm diameter, whilst visual estimates of
benthic composition were very similar to those obtained from line intercept transects. Visual estimates of topography correlated
strongly with species richness of fish communities and explained 42% of the variation in these data. The relationship between
visual estimates of topography and species richness is strongest with fish 10–30 cm total length (TL), abundance of fish within
this size category also correlating positively with topographic visual assessments. Visual techniques are prone to observer
bias, however with regular training they can be used to quickly provide a reliable and effective means of assessing habitat
complexity and benthos on coral reefs. 相似文献
9.
Variations in embryo size and fatty acid (FA) dynamics during embryogenesis were evaluated in deep-sea pandalids and portunid
swimming crabs from the Portuguese continental margin and Madeira Island slope and compared with previous data on neritic
and deep-sea lobsters and shrimps (collected between February 2001 and March 2004). Inter-specific variations in embryo size
seem to be dictated primarily by phylogeny rather than by differences in reproductive or early life history traits. FA reserves
were significantly correlated with embryo size (P < 0.001). Principal component analysis revealed differences among three groups (1—neritic caridean shrimps, 2—deep-sea pandalids
of the genus Plesionika, and lobsters, 3—portunid crabs and the deep-sea pandalid Chlorotocus crassicornis, Costa 1871). Group 1 was clearly separated by PC1 mainly due to the higher percentage of essential C18 (linoleic and linolenic acids) and C20 (namely eicosapentaenoic) polyunsaturated FA (specific markers of primary producers). PC2 separated Group 2 from Group 3
due to differences in the percentage of several saturated FA (including odd-numbered FA—bacterial markers) and C18 monounsaturated FA (namely 18:1n − 9, a general marker of carnivory). Therefore, these differences among groups seem to result from distinctions in diet and
ecological niche. Intra-specific differences in FA composition between western and southern Plesionika martia martia (A. Milne-Edwards, 1883) populations may reflect higher water temperatures on the south sub-tropical coast. Lobster embryonic
development was more demanding of lipid energy than that of the other decapod species, which may reflect an evolutionary trend
in decapod taxa related to an increasing degree of lecithotrophy. However, a lower FA catabolism can be interpreted as an
enhanced independence of the newly hatched larvae from external energy sources. Higher FA content at hatching and, as a consequence,
a greater independence from the external environment should increase the chances of larval survival.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
10.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that frequently accumulate in soils. There is therefore a requirement to determine their levels in contaminated environments for the purposes of determining impacts on human health. PAHs are a suite of individual chemicals, and there is an ongoing debate as to the most appropriate method for assessing the risk to humans from them. Two methods predominate: the surrogate marker approach and the toxic equivalency factor. The former assumes that all chemicals in a mixture have an equivalent toxicity. The toxic equivalency approach estimates the potency of individual chemicals relative to the usually most toxic Benzo(a)pyrene. The surrogate marker approach is believed to overestimate risk and the toxic equivalency factor to underestimate risk. When analysing the risks from soils, the surrogate marker approach is preferred due to its simplicity, but there are concerns because of the potential diversity of the PAH profile across the range of impacted soils. Using two independent data sets containing soils from 274 sites across a diverse range of locations, statistical analysis was undertaken to determine the differences in the composition of carcinogenic PAH between site locations, for example, rural versus industrial. Following principal components analysis, distinct population differences were not seen between site locations in spite of large differences in the total PAH burden between individual sites. Using all data, highly significant correlations were seen between BaP and other carcinogenic PAH with the majority of r 2 values > 0.8. Correlations with the European Food Standards Agency (EFSA) summed groups, that is, EFSA2, EFSA4 and EFSA8 had even higher correlations (r 2 > 0.95). We therefore conclude that BaP is a suitable surrogate marker to represent mixtures of PAH in soil during risk assessments. 相似文献
11.
The study of correlations between different behaviours in a population—referred to as behavioural syndromes—has begun to flourish
during recent years. However, the evolutionary mechanisms that cause behavioural traits to vary non-independently from each
other are still poorly understood. Here, we bring behavioural syndromes into a new perspective, in which the phenomenon is
regarded at the individual level and on a continuous scale instead of as a population-level presence/absence trait. As the
correlation between behaviours is never perfect (i.e. r < 1), individuals are likely to vary in how consistently they behave. Therefore, we can predict that if behavioural syndromes
at the population level are results of natural selection, the consistency in a suite of behaviours—and not the behavioural
configuration per se—should be heritable and involve fitness advantages at the individual level. We define a variable that
describes the individual deviation from the hypothetical perfect correlation predicted by the syndrome. The use of such a
variable depicting the consistency of behaviours of individuals allows us to make solid evolutionary inferences about correlated
behaviours from patterns of individual instead of population variation. We suggest that, by adopting the concept of syndrome deviation, understanding the evolution of behavioural syndromes and, in particular, testing competing evolutionary hypotheses about
the origin of behavioural syndromes becomes possible in a more rigorous manner than before. 相似文献
12.
环境内分泌干扰物低剂量-效应研究进展 总被引:5,自引:2,他引:5
环境内分泌干扰物(EDCs)的低剂量-效应已成为生态毒理学界的研究热点.环境内分泌干扰物在接近或低于无可见不良效应浓度水平(NOAEL)时仍可诱发生物效应并存在非单调剂量-效应关系,这对现行的动物繁殖和发育毒理学检测规程以及环境内分泌干扰物风险评价的理论和方法提出了挑战.此外,由于环境中内分泌干扰物呈低剂量长期暴露的特征,研究低剂量-效应对正确进行生态风险评价具有重大的科学意义.在总结国内外相关研究的基础上,对当前环境内分泌干扰物低剂量-效应的研究进展进行了综述. 相似文献
13.
Jessica L. Adams Kari W. Camelio Matthew J. Orique Daniel T. Blumstein 《Behavioral ecology and sociobiology》2006,60(5):742-747
Antipredator behavior includes several qualitatively distinct activities, but few studies have determined the degree to which these activities are independent. If behaviors are not independent, then the nature of the relationship would illustrate potential performance constraints. We studied crimson rosellas (Platycercus elegans) and first focused on acoustic predator discrimination. We measured time allocation before and after playback of one of three experimental treatments (peregrine falcons—Falco peregrinus, wedge-tailed eagles—Aquila audax, and crimson rosellas) to determine whether or not rosellas discriminated predators from non-predators, and specifically whether or not they discriminated large from small predators. We then focused on the decision to flee. We experimentally approached subjects and measured the distance at which they oriented to us (alert distance) and the distance at which they fled (flight initiation distance; FID). We found that rosellas could distinguish among predators; however, there was no effect on general wariness as measured by FID. These two processes of antipredator behavior may, thus, be independent. 相似文献
14.
Most social primates live in cohesive groups, so travel paths inevitably reflect compromise: decision processes of individuals
are obscured. The fission–fusion social organisation of the chimpanzee, however, allows an individual's movements to be investigated
independently. We followed 15 chimpanzees (eight male and seven female) through the relatively flat forest of Budongo, Uganda,
plotting the path of each individual over periods of 1–3 days. Chimpanzee movement was parsed into phases ending with halts
of more than 20 min, during which individuals fed, rested or engaged in social activities. Males, lactating or pregnant females
and sexually receptive females all travelled similar average distances between halts, at similar speeds and along similarly
direct beeline paths. Compared to lactating or pregnant females, males did travel for a significantly longer time each day
and halted more often, but the most striking sex differences appeared in the organisation of movement phases into a day's
path. After a halt, males tended to continue in the same direction as before. Lactating or pregnant females showed no such
strategy and often retraced the preceding phase, returning to previously visited food patches. We suggest that female chimpanzee
movements approximate an optimal solution to feeding requirements, whereas the paths of males allow integration of foraging
with territorial defence. The ‘continually moving forwards’ strategy of males enables them to monitor their territory boundaries—border
checking—whilst foraging, generally avoiding the explicit boundary patrols observed at other chimpanzee study sites. 相似文献
15.
Predators can have significant nonlethal effects on prey by modifying prey behaviour through chemically mediated interactions.
We examined behavioural responses of wood frog (Ranasylvatica) and American toad (Bufoamericanus) tadpoles to both direct and indirect chemical signals associated with a predatory odonate (Anaxjunius). In laboratory trials, tadpoles of both species responded strongly to water conditioned with Anax nymphs by decreasing foraging rates, becoming immobile, and moving away from the stimulus. The responses to water conditioned
with starved Anax versus Anax that fed on conspecific tadpoles did not differ significantly; these results suggest that tadpoles rely primarily on direct
signals to detect odonates. Rana did not respond to water conditioned with conspecific tissue extracts, while Bufo responded with behaviours that were indistinguishable from those of tadpoles exposed to Anax chemicals. In a field experiment, the responses of R. sylvatica tadpoles to Anax chemicals were similar to those of tadpoles observed in the laboratory. Collectively, our data indicate that tadpoles of
both species use chemical cues to assess predation risk from other community members. Tadpoles can selectively distinguish
members who pose a threat, and only evacuate food patches or reduce foraging rates when in danger. These behaviours appear
to be adaptive and are consistent with the predictions of optimality theory.
Received: 1 August 1997 / Accepted after revision: 22 November 1997 相似文献
16.
M. DI MARCO L. BOITANI D. MALLON M. HOFFMANN A. IACUCCI E. MEIJAARD P. VISCONTI J. SCHIPPER C. RONDININI 《Conservation biology》2014,28(4):1109-1118
Assessing temporal changes in species extinction risk is necessary for measuring conservation success or failure and for directing conservation resources toward species or regions that would benefit most. Yet, there is no long‐term picture of genuine change that allows one to associate species extinction risk trends with drivers of change or conservation actions. Through a review of 40 years of IUCN‐related literature sources on species conservation status (e.g., action plans, red‐data books), we assigned retrospective red‐list categories to the world's carnivores and ungulates (2 groups with relatively long generation times) to examine how their extinction risk has changed since the 1970s. We then aggregated species’ categories to calculate a global trend in their extinction risk over time. A decline in the conservation status of carnivores and ungulates was underway 40 years ago and has since accelerated. One quarter of all species (n = 498) moved one or more categories closer to extinction globally, while almost half of the species moved closer to extinction in Southeast Asia. The conservation status of some species improved (toward less threatened categories), but for each species that improved in status 8 deteriorated. The status of large‐bodied species, particularly those above 100 kg (including many iconic taxa), deteriorated significantly more than small‐bodied species (below 10 kg). The trends we found are likely related to geopolitical events (such as the collapse of Soviet Union), international regulations (such as CITES), shifting cultural values, and natural resource exploitation (e.g., in Southeast Asia). Retrospective assessments of global species extinction risk reduce the risk of a shifting baseline syndrome, which can affect decisions on the desirable conservation status of species. Such assessments can help conservationists identify which conservation policies and strategies are or are not helping safeguard biodiversity and thus can improve future strategies. Una Evaluación Retrospectiva de la Declinación Global de Carnívoros y Ungulados 相似文献
17.
Sea surface colour data, derived from the Coastal Zone Colour Scanner (CZCS) archive, have been used to assess the space/time
variability of coastal plumes and run-off in the Mediterranean Sea. A time series of 2645 scenes, collected by the CZCS from
1979 to 1985, was processed to apply sensor calibration algorithms, correct for atmospheric contamination, and derive chlorophyll-like
pigment concentration. Individual images, remapped on a 1-km2 pixel grid, were generated for each available day, and then mean values calculated pixel by pixel to form monthly, seasonal
and annual composites. The results obtained must be taken with caution, due to the CZCS limitations in the quantitative assessment
of bio-optical pigments when high concentrations of dissolved organics or suspended sediments are present, e.g. along littorals
or within plumes. Marked differences appear in the distribution of water constituents between coastal zones and open sea,
northern and southern near-coastal areas, western and eastern sub-basins. The oligotrophic character of the basin contrasts
with areas of high concentration related to river plumes—Ebro (Ebre), Po, Rhone, Nile—, coastal run-off patterns, and persistent
mesoscale features (e.g. coastal filaments and eddies). Seasonal variability appears to be high, with higher concentrations
occurring over most of the basin in the cold season, when climatic conditions are favourable to coastal run-off and vertical
mixing. Atmospheric forcing (wind and rainfall over continental margins) could play an important role in establishing the
observed space/time distribution of water constituents. The impact of continental interactions (fluvial and coastal run-off),
or that of exchanges between coastal zone and open sea, could have paramount influence on the biogeochemical fluxes in the
entire basin. 相似文献
18.
Graphical models provide an important tool for facilitating communication between scientists, decision-makers, and statisticians—many
complicated ecological processes can be described in terms of “box-and-arrow” conceptual diagrams (e.g., Shipley in Cause
and correlation in biology: a user’s guide to path analysis, structural equations and causal inferences, Cambridge Universtiy
Press, Cambridge, 2000; Clark and Gelfand TRENDS in Ecology and Evolution 21:375–380, 2006). In particular, problems in landscape
ecology often involve modeling relationships among multiple physical and/or biological variables that may operate on differing
spatial scales (e.g., Rossi et al. in Ecol Monographs 62:277–314, 1992; Legendre et al. in Ecography 25:601–615, 2002; Overmars
et al. in Ecol Model 164:257–270, 2003; Brown and Spector in J Appl Ecol 45:1639–1648, 2008; Koniak and Noy-Meir in Ecol Model
220:1148–1158, 2008). These problems are inherently multivariate, though researchers commonly rely on univariate methods,
such as spatial regression models, to address them. In this paper, we introduce a multivariate method—graphical spatial models—that
extends path analysis to incorporate spatial autocorrelation in one or more variables in a directed graph. We show how both
exogenous and endogenous ecological processes as defined by Legendre et al. (Ecography 25:601–615, 2002) and Lichstein et al.
(Ecol Monographs 72:445–463, 2002) can be represented in a graph. Most importantly, we show how to translate graphs representing
these ecological processes into statistically estimable models. We motivate our theoretical results using an example of stream
health data from the Willamette Valley, Oregon. For these data we are interested in the spatial pattern within both riparian
land use and an index of stream health, and whether there is an association between land use and stream health, after accounting
for these spatial patterns. We use a graphical spatial model to address these ecological questions simultaneously. We find
that the health of a stream decreases as the percent of developed land within a 120-m riparian buffer increases; interestingly,
there is only evidence of spatial pattern within land use. 相似文献
19.
Virtually all animal conflicts occur over access to mates or resources that affect survival, the two key components of fitness.
In this paper, we report that predation risk and mate defense jointly affect the outcomes of contests between male sand crabs
(Scopimera globosa) for burrows in which crabs mate and take shelter from predators. We observed the contests under three different conditions:
(1) the natural condition of low predation risk and without the presence of a female; (2) the first experiment in which we
imposed upon only intruding males the perception of predation risk—by digging them from their burrows, capturing and handling
them, and placing them into other males’ burrows—to increase the value of the burrows for the intruders as shelter, and (3)
the second experiment in which we repeated this treatment but increased the resource value of the burrow to the resident by
placing a female in his burrow. The difference in body size between contestants was the main determinant of victory in all
analyses. However, perceived predation risk also partly affected the outcomes of the fights: The motivated intruders were
likely to win even when they were a little smaller than the residents. In addition, defense of a female had a significant
effect on the outcomes of fights: The motivated residents won more fights than the motivated intruders, indicating that these
two treatments caused asymmetric increases of the resource value. This is the first report of two external factors simultaneously
raising resource value, affecting motivation of contestants, and altering the outcome of fights. 相似文献
20.
Stefan Van Dongen 《Environmental and Ecological Statistics》2006,13(2):213-228
Plant–herbivore interactions are complex and affect herbivore fitness components and life history traits in many different
ways. In this paper, we present results from an experiment studying the effects of leaf quality on pupal survival and duration
of pupation (as measured by time-to-emergence) in the winter moth. Because only surviving pupae are at risk of emerging, analysis
of time-to-emergence should exclude the dead pupae. However, due to right censoring, the survival status could not be determined
for each individual. This failure to determine the group of moths at risk of emerging a priori motivated the development of
a joint model of both survival probability and time-to-emergence. We formulate the model in a Bayesian framework and apply
Monte Carlo Markov Chain (MCMC) to obtain posterior distributions. Time-to-emergence is modeled by a Cox Proportional Hazards
(CPH) model where only the surviving pupae are at risk of emergence. Probability of pupal survival was modeled by a Generalized
Linear Mixed Model (GLMM). The censored individuals were included in the analysis as a missing value in the GLMM. The GLMM
then generated prior distributions of survival probabilties—and thus of the probability of being at risk of emergence—for
these 19 individuals, conditional on the model parameters. The CPH model was formulated as a count process and the binary
frailty was incorporated as a zero-inflated Poisson model. Zeros in this model represent the non-survivors. Leaf quality did
not appear to influence time-to-emergence. Pupal survival was affected in a complex and unexpected way showing opposite effects
in males and females. We also explored the robustness of our model against increased levels of censoring. While the degree
of censoring was low in our study (< 1%), we artificially increased it to 67%. Although further study is required to study
the generality of these results in a theoretical framework, our explorations suggest that the newly proposed technique may
be widely applicable in a variety of situations where the identification of the at risk population cannot be done in a straightforward
way.
Received: January 2005 / Revised: June 2005 相似文献