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51.
Claire W. Varian-Ramos Jordan Karubian Vanessa Talbott Irma Tapia Michael S. Webster 《Behavioral ecology and sociobiology》2010,64(6):967-977
The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because
these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However,
many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical
work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence
of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should
lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females
and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit
to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the
dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased
broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common
in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing
sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring. 相似文献
52.
J. Andrew Grant Dianne Balraj Georgia Mavropoulos‐Vagelis 《Natural resources forum》2013,37(4):269-279
International forestry governance is an integral part of the global policy debates on how to prevent deforestation, illicit extraction, and unsustainable timber practices. Africa is an important producer of timber, yet the region is beset by a lack of capacity and other governance challenges in the management of its forestry sector. We employ a network governance analysis to examine the extent to which the evolution and operation of the Forest Stewardship Council (FSC) and la Commission des Forêts d'Afrique Centrale (COMIFAC) have addressed governance challenges. We assess the strengths and weaknesses of these two leading examples of international forestry governance by introducing recent evidence and insights from Africa. We conclude with a policy‐relevant discussion of how the FSC and COMIFAC might enhance authority, legitimacy, and effectiveness and improve forestry governance in Africa and other parts of the world. 相似文献
53.
Efforts to draw inferences about species occurrence frequently account for false negatives, the common situation when individuals of a species are not detected even when a site is occupied. However, recent studies suggest the need to also deal with false positives, which occur when species are misidentified so that a species is recorded as detected when a site is unoccupied. Bias in estimators of occupancy, colonization, and extinction can be severe when false positives occur. Accordingly, we propose models that simultaneously account for both types of error. Our approach can be used to improve estimates of occupancy for study designs where a subset of detections is of a type or method for which false positives can be assumed to not occur. We illustrate properties of the estimators with simulations and data for three species of frogs. We show that models that account for possible misidentification have greater support (lower AIC for two species) and can yield substantially different occupancy estimates than those that do not. When the potential for misidentification exists, researchers should consider analytical techniques that can account for this source of error, such as those presented here. 相似文献
54.
Grant D. Jacobsen 《Journal of Environmental Economics and Management》2011,61(1):67-78
This paper examines the relationship between climate change awareness and household behavior by testing whether Al Gore's documentary An Inconvenient Truth caused an increase in the purchase of voluntary carbon offsets. I find that in the two months following the film's release, zip codes within a 10-mile radius of a zip code where the film was shown experienced a 50 percent relative increase in the purchase of voluntary carbon offsets. During other times, offset purchasing patterns for zip codes inside the 10-mile radius were similar to the patterns of zip codes outside the 10-mile radius. There is, however, little evidence that individuals who purchased an offset due to the film purchased them again a year later. 相似文献
55.
Anthony J. Gaston Paul A. Smith Laura McFarlane Tranquilla William A. Montevecchi David A. Fifield H. Grant Gilchrist April Hedd Mark L. Mallory Gregory J. Robertson Richard A. Phillips 《Marine Biology》2011,158(9):1929-1941
The non-breeding movements of marine birds were poorly known until recently, but this information is essential to understanding
the risk to different geographical populations from events on the wintering grounds. We tracked the migration routes and wintering
areas of Thick-billed Murre Uria lomvia from two breeding colonies in eastern Canada: Coats Island in northern Hudson Bay and The Minarets, Baffin Island, during
the period August 2007–May 2008 using geolocation loggers. Birds from The Minarets moved south rapidly post-breeding and wintered
principally off Newfoundland and southern Labrador, or between Newfoundland and southern Greenland, remaining south of 55°N
until at least the spring equinox. Those from Coats Island remained in Hudson Bay until at least mid-November, after which
they moved rapidly through Hudson Strait to winter in southern Davis Strait and the northern Labrador Sea, mostly north of
55°N. Many individuals stayed throughout the winter in areas of heavy ice cover. Adults from the two colonies appear to be
completely segregated in winter and those from Coats Island probably did not enter the area of the winter hunt in Newfoundland.
Unexpectedly, some birds from The Minarets wintered in waters beyond the continental slope and outside the distribution of
pack ice, demonstrating that particular individuals can be wholly pelagic throughout the winter. Coats Island birds returned
through Hudson Strait as soon as open water areas became available in spring. Their sojourn in Hudson Bay coincided very closely
with the occurrence of areas with <90% ice cover. In spite of the relatively large error in positions obtained from geolocation
loggers, our results demonstrated the value of these devices by uncovering a number of previously unknown aspects of Thick-billed
Murre non-breeding ecology in the Northwest Atlantic. Comparison of the non-breeding ecology based on SST experienced in winter
show that the winter niche is broader than hitherto assumed, demonstrating that separate populations may experience different
selection in the face of climate change. 相似文献
56.
Metachronal swimming, in which adjacent appendages stroke in sequence, is widespread among crustaceans inhabiting the transitional
flow realm in which both viscosity and inertia effects are important. However, the design and operation of this propulsion
system in response to various hydrodynamic, energetic, and behavioral needs have not been well investigated. We examine free-swimming
Antarctic krill (Euphausia superba) as a model species and identify three distinct behavioral swimming gaits. The pleopod kinematics of these gaits, hovering,
fast-forward swimming, and upside-down swimming, are quantified via image analysis of high-speed video. Pleopod stroke amplitude
and frequency were found to vary significantly among these swimming modes. In order to increase swimming speed, krill were
found first to increase stroke amplitude and secondarily to increase beat frequency. The kinematics of these distinct swimming
modes provide insight as we consider multi-appendage metachronal swimming from a design standpoint. The ratio of the distance
between adjacent appendage bases and appendage length is identified as a key parameter in metachrony, the value of which is
constrained to a narrow range for a wide variety of species. 相似文献
57.
Within populations of many species, individuals that are otherwise similar to one another in age, size or sex can differ markedly
in behaviours such as resource use, risk taking and competitive ability. There has been much research into the implications
of such variation for intraspecific interactions, yet little investigation into its role in influencing interspecific interactions
outside of a predator–prey context. In this study, we investigated the role of individual-level behavioural variation in determining
the outcomes of interactions between two ecologically similar fishes, the threespine and ninespine sticklebacks (Gasterosteus aculeatus and Pungitius pungitius). Experiment 1 asked whether individuals of both species were consistent in their expression of two behaviours: activity
in novel surroundings and latency to attack prey. For each behaviour, focal individuals were assayed twice, 10 days apart.
Performances were positively correlated between exposures, suggesting behavioural consistency within individuals, at least
over this timescale. Experiment 2 revealed not only differences in habitat use described both by species-level variation,
with ninespines spending more time in vegetated areas, but also by individual differences, with more active individuals of
both species spending more time in open water than in vegetation. Experiment 3 revealed that when heterospecific pairs competed
for prey, bolder individuals consumed a greater share, irrespective of species. These findings suggest that individual-level
variation can facilitate overlap in habitat use between heterospecifics and also determine the outcomes of resource contests
when they meet. We discuss how this might vary between populations as a function of prevailing selection pressures and suggest
approaches for testing our predictions. 相似文献
58.
Brooke E. Buckley Walter W. Piegorsch R. Webster West 《Environmental and Ecological Statistics》2009,16(1):53-62
In modern environmental risk analysis, inferences are often desired on those low dose levels at which a fixed benchmark risk
is achieved. In this paper, we study the use of confidence limits on parameters from a simple one-stage model of risk historically
popular in benchmark analysis with quantal data. Based on these confidence bounds, we present methods for deriving upper confidence
limits on extra risk and lower bounds on the benchmark dose. The methods are seen to extend automatically to the case where
simultaneous inferences are desired at multiple doses. Monte Carlo evaluations explore characteristics of the parameter estimates
and the confidence limits under this setting.
相似文献
R. Webster WestEmail: |
59.
R. Webster West Daniela K. Nitcheva Walter W. Piegorsch 《Environmental and Ecological Statistics》2009,16(1):63-73
A primary objective in quantitative risk assessment is the characterization of risk which is defined to be the likelihood
of an adverse effect caused by an environmental toxin or chemcial agent. In modern risk-benchmark analysis, attention centers
on the “benchmark dose” at which a fixed benchmark level of risk is achieved, with a lower confidence limits on this dose
being of primary interest. In practice, a range of benchmark risks may be under study, so that the individual lower confidence
limits on benchmark dose must be corrected for simultaneity in order to maintain a specified overall level of confidence.
For the case of quantal data, simultaneous methods have been constructed that appeal to the large sample normality of parameter
estimates. The suitability of these methods for use with small sample sizes will be considered. A new bootstrap technique
is proposed as an alternative to the large sample methodology. This technique is evaluated via a simulation study and examples
from environmental toxicology.
相似文献
R. Webster WestEmail: |
60.
We performed batch sorption experiments for 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) on selected soils collected from dairy farming regions of New Zealand. Isotherms were constructed by measuring the liquid phase concentration and extracting the solid phase with dichloromethane, followed by an exchange step, and analysis by HPLC and UV detection. The corresponding metabolite estrone, (E1) formed during equilibration of E2 with soil was taken into account to estimate the total percentage recoveries for the compounds, which ranged from 47-105% (E2 and E1) and 83-102% (EE2). Measured isotherms were linear, although some deviation from linearity was observed in a few soils, which was attributed to the finer textured particles and/or the allophanic nature of the soils having high surface area. There was a marked difference in K(d)(eff) (effective distribution coefficient) values for E2 and EE2 among the soils, consistent with the soils organic carbon content and ranged from 14-170 L kg(-1) (E2), and 12-40 L kg(-1) (EE2) in the soils common for both compounds. The sorption affinity of hormones in the soils followed an order: EE2相似文献