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91.
Bailey?C.?McMeansEmail author Michael?T.?Arts Scott?A.?Rush Aaron?T.?Fisk 《Marine Biology》2012,159(5):1095-1105
The marine copepod Calanus hyperboreus accumulates large quantities of lipids and essential fatty acids during summer months in Northern oceans. However, few data
exist regarding their winter fatty acid profiles, which could be informative regarding the use of lipids by C. hyperboreus to successfully survive and reproduce during times of ice-cover and limited food. The present study compared fatty acids
of C. hyperboreus between summer (August 2007 and 2008) and winter (early April 2008 and 2009) in Cumberland Sound, Canada. Summer samples
from both years had significantly higher ∑polyunsaturated fatty acids and unsaturation indices (based on μg fatty acid mg
dry tissue−1) than winter samples and separated on a principal component analysis due to higher 18:2n-6, 18:4n-3, and 20:5n-3, consistent
with phytoplankton consumption. Winter C. hyperboreus had significantly higher ∑monounsaturated fatty acids (MUFA) versus summer samples and separated on the principal component
analysis due to higher proportions of 16:1n-7, 20:1n-9, and 22:1n-9, suggesting they were not actively feeding. Based on the
seasonal fatty acid comparison, C. hyperboreus was catabolizing specific fatty acids (e.g. 20:5n-3), conserving others (e.g. 22:6n-3), and maintaining or increasing biosynthesis
of certain MUFA (e.g. 18:1n-9) during winter. These findings provide insight into the seasonal strategy of acquisition (summer)
and utilization (winter) of specific fatty acids by a key Arctic organism and could become important for monitoring changes
in fatty acids associated with decreased ice-cover duration due to climate warming. 相似文献
92.
Optimal regulation of a polluting natural monopolist must correct for both external damages and market power to achieve a social optimum. Existing non-Bayesian regulatory methods require knowledge of the demand function, while Bayesian schemes require knowledge of the underlying cost distribution. We introduce mechanisms adapted to use less information. Our Price-based Subsidy (PS) mechanisms give the firm a transfer that matches or approximates the incremental surplus generated each period. The regulator need not observe the abatement activity or know the demand, cost, or damage functions of the firm. All of the mechanisms induce the firm to price at marginal social cost, either immediately or asymptotically. 相似文献
93.
Leites LP Robinson AP Rehfeldt GE Marshall JD Crookston NL 《Ecological applications》2012,22(1):154-165
Projected climate change will affect existing forests, as substantial changes are predicted to occur during their life spans. Species that have ample intraspecific genetic differentiation, such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), are expected to display population-specific growth responses to climate change. Using a mixed-effects modeling approach, we describe three-year height (HT) growth response to changes in climate of interior Douglas-fir populations. We incorporate climate information at the population level, yielding a model that is specific to both species and population. We use data from provenance tests from previous studies that comprised 236 populations from Idaho, Montana, and eastern Washington, USA. The most sensitive indicator of climate was the mean temperature of the coldest month. Population maximum HT and HT growth response to changes in climate were dependent on seed source climate. All populations had optimum HT growth when transferred to climates with warmer winters; those originating in sites with the warmest winters were taller across sites and had highest HT growth at transfer distances closest to zero; those from colder climates were shortest and had optimum HT growth when transferred the farthest. Although this differential response damped the height growth differences among populations, cold-climate populations still achieved their maximum growth at lower temperatures than warm-climate populations. The results highlight the relevance of understanding climate change impacts at the population level, particularly in a species with ample genetic variation among populations. 相似文献
94.
Charlie A. R. Hogg Galen C. Egan Nicholas T. Ouellette Jeffrey R. Koseff 《Environmental Fluid Mechanics》2018,18(2):383-394
Gravity currents descending along slopes have typically been studied in quiescent environments, despite the fact that in many geophysical settings there is significant externally driven motion. Here we investigate how the head of a gravity current is influenced by interfacial internal waves at the pycnocline of a two-layer ambient water column. Our experimental measurements show that larger amplitude internal waves, interacting with the gravity current, reduce both the mass transport by the gravity current and its thickness. These results suggest that the ambient internal wave field should be considered when estimating transport by gravity currents in geophysical settings with strong internal waves, such as lakes and the coastal ocean. 相似文献
95.
Sarah Joy Bittick Nicholas D. Bilotti Heather A. Peterson Hannah L. Stewart 《Marine Biology》2010,157(2):317-323
Habitat associations are an integral part of coral reef community structure. Commonly, one organism lives in such close association
within or near another that a spatial refuge occurs, whereby one of the organisms provides protection to the other. This is
often the result of defenses of the host deterring an associate organism’s consumers. In Moorea, French Polynesia, the range
and abundance of the brown macroalga, Turbinaria ornata, have increased drastically since 1980 such that dense aggregations of this macroalga are a dominant component of the backreef
habitat. Turbinaria ornata is both mechanically and chemically defended from herbivores. Other species of macroalgae grow within aggregations of Turbinaria and may benefit from these defenses. This study investigates whether aggregations of Turbinaria create a refuge from herbivory for associate macroalgae. When Turbinaria aggregations were removed experimentally, there was a significant increase in the number of associate algal species. Moreover,
an herbivory assay using the palatable local alga Acanthophora spicifera identified herbivory as the mechanism for lower diversity on bommies lacking Turbinaria aggregations. The local increase in algal richness due to the refuge from herbivory afforded by Turbinaria may be an important contribution to macroalgal and community dynamics on reefs in Moorea, French Polynesia. 相似文献
96.
Previous research on voluntary environmental programs (VEPs) frequently assesses the effectiveness of federal, state, and third party programs and why organizations seek to join such programs. Yet, research has yet to evaluate the effectiveness or firm motivation relative to local VEPs. Recognizing this gap, our paper examines the structure and organization of Fort Collins’ Climate Wise program, a local VEP. Using a variety of sources, we find that the program has successfully met both short- and long-term goals by persistently self-evaluating and seeking outside financial support. Findings from this analysis can aid in understanding and developing local VEPs elsewhere. Specifically, this initial research suggests that local VEPs need to consider local context and available resources when implementing such programs. Furthermore, it is possible for local VEPs to attract a diverse variety of participating firms by avoiding one-size-fits-all participation levels and by establishing a sense of ownership among partners. 相似文献
97.
98.
Ecological communities are structured by both deterministic, niche-based processes and stochastic processes such as dispersal. A pressing issue in ecology is to determine when and for which organisms each of these types of processes is important in community assembly. The roles of deterministic and stochastic processes have been studied for a variety of communities, but very few researchers have addressed their contribution to insect herbivore community structure. Insect herbivore niches are often described as largely shaped by the antagonistic pressures of predation and host plant defenses. However host plants are frequently discrete patches of habitat, and their spatial arrangement can affect herbivore dispersal patterns. We studied the roles of predation, host plant quality, and host spatial proximity for the assembly of a diverse insect herbivore community on Quercus alba (white oak) across two growing seasons. We examined abundances of feeding guilds to determine if ecologically similar species responded similarly to variation in niches. Most guilds responded similarly to leaf quality, preferring high-nitrogen, low-tannin host plants, particularly late in the growing season, while bird predation had little impact on herbivore abundance. The communities on the high-quality plants tended to be larger and, in some cases, have greater species richness. We analyzed community composition by correlating indices of community similarity with predator presence, leaf quality similarity, and host plant proximity. Birds did not affect community composition. Community similarity was significantly associated with distance between host plants and uncorrelated with leaf quality similarity. Thus although leaf quality significantly affected the total abundance of herbivores on a host plant, in some cases leading to increased species richness, dispersal limitation may weaken this relationship. The species composition of these communities may be driven by stochastic processes rather than variation in host plant characteristics or differential predation by insectivorous birds. 相似文献
99.
The concept of evolvability is controversial. To some, it is simply a measure of the standing genetic variation in a population
and can be captured by the narrow-sense heritability (h2). To others, evolvability refers to the capacity to generate heritable phenotypic variation. Many scientists, including Darwin,
have argued that environmental variation can generate heritable phenotypic variation. However, their theories have been difficult
to test. Recent theory on the evolution of sex and recombination provides a much simpler framework for evaluating evolvability.
It shows that modifiers of recombination can increase in prevalence whenever low fitness individuals produce proportionately
more recombinant offspring. Because recombination can generate heritable variation, stress-induced recombination might be
a plausible mechanism of evolvability if populations exhibit a negative relationship between fitness and recombination. Here
we use the fruit fly, Drosophila melanogaster, to test for this relationship. We exposed females to mating stress, heat shock or cold shock and measured the temporary
changes that occurred in reproductive output and the rate of chromosomal recombination. We found that each stress treatment
increased the rate of recombination and that heat shock, but not mating stress or cold shock, generated a negative relationship
between reproductive output and recombination rate. The negative relationship was absent in the low-stress controls, which
suggests that fitness and recombination may only be associated under stressful conditions. Taken together, these findings
suggest that stress-induced recombination might be a mechanism of evolvability. 相似文献
100.
The ascidian Styela clava, native to the north-west Pacific, is an invasive species affecting New Zealand’s marine ecosystems, biodiversity and aquaculture
operations. To provide detailed information on the reproductive biology of S. clava in New Zealand for post-border biosecurity management, long-term seasonal patterns of gametogenesis were determined from
May 2006 to May 2008 in Auckland’s Waitemata Harbour (36°49′20″S, 174°45′85″E). Of particular interest was whether the critical
15°C threshold spawning temperature for reproduction observed in the Northern Hemisphere applied here to the first Southern
Hemisphere study. S. clava gametogenesis followed a regular seasonal cycle with ripe gametes appearing as early as September and persisting to June;
this time frame corresponds to the period when sea surface temperatures in the region first reach 15°C and with spawning occurring
mainly during late summer to early autumn. From photoperiod manipulation, it was determined that spawning occurred at approximately
18:20. The extended reproductive period and a short generation time in the Waitemata Harbour provides a lengthy opportunity
for S. clava to spread. Findings are discussed in relation to S. clava’s post-border management. 相似文献