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21.
Bruce A. Forster 《Journal of Environmental Economics and Management》1977,4(4):305-312
This paper examines the problem of pollution control is an economy which produces two commodities which have different polluting characteristics. The model sheds light on the change is the optimal combination of commodities such as public transportation as opposed to private transportation, detergents and soap, returnable and nonreturnable bottles, and so on. 相似文献
22.
23.
Bruce A Forster 《Journal of Environmental Economics and Management》1981,8(2):118-133
The purpose of this paper is to provide a theoretical bridge between the many-commodity general equilibrium models and the simpler one good-one pollutant models used in environmental economics. The interest is in determining the conditions that will permit a vector of pollutants (or goods) to be treated as if it were only one quantity, the amount of environmental pollution (or consumption). A general equilibrium model is constructed and the concepts of separability and functional structure are applied to examine the requirements for consistent aggregation. It is shown that this aggregation process may in general produce two entirely different sets of aggregate measures of pollution and consumption. This result is of theoretical and empirical significance. Alternative criteria for aggregation suggest that the aggregation depends upon very stringent features of the economy concerned. 相似文献
24.
25.
Apostolos Kapranas P. Pacheco L. D. Forster J. G. Morse R. F. Luck 《Behavioral ecology and sociobiology》2008,62(6):901-912
We examined whether several facultatively gregarious encyrtid (Hymenoptera: Encyrtidae) endoparasitoids of brown soft scale,
Coccus hesperidum L., manifest precise sex allocation under field conditions. Metaphycus luteolus (Timberlake), Metaphycus angustifrons (Compere), Metaphycus stanleyi (Compere), and Microterys nietneri (Motshulsky) evince brood sex ratios that are female-biased and extremely precise (low variance in the number of sons per
host). Typically, this sex allocation pattern is attributed to extreme local mate competition (LMC) in which only one foundress
exploits a patch of hosts and mating occurs mostly between her offspring. However, such a pattern of sex allocation was not
detected for Metaphycus helvolus (Compere). Also, a large proportion of the broods in all five species contained only daughters; thus, an excess of male-only
broods was expected if unmated females (i.e., females that can produce only sons) contribute offspring before mating. All-male
broods were rare in our samples. This finding coupled with the life history characteristics of these wasps, such as the exploitation
of aggregated hosts and the long life span and mobility of males, suggest that nonlocal mating is frequent. Our empirical
work suggests that it is advantageous to allocate precise sex ratios in cases in which mating opportunities for males are
not restricted to their natal host and/or when multiple foundresses exploit large patches of hosts. Limited theoretical work
also supports this prediction but more detailed studies of this taxon’s mating structure and other life history characteristics
are necessary to understand their sex allocation decisions. 相似文献
26.
Paolo Lo Bue Stefano Colazza Lisa D. Forster Jocelyn G. Millar Robert F. Luck 《Chemoecology》2004,14(3-4):151-156
Summary. Metaphycus sp. nr.
flavus (Encyrtidae: Hymenoptera)
is a parasitoid species collected from the Mediterranean
region which lays its eggs in the immature stages of several
economically important soft scale insects (Hemiptera:
Coccidae), including brown soft scale, Coccus hesperidum
L. (= host insect). Preliminary tests suggested that the parasitoid
is most successful in producing offspring when it
oviposits in the younger stages of brown soft scale. In
Y-olfactometer bioassays measuring wasp choices and residence
times, naïve parasitoids were significantly more
attracted to yucca leaves infested with 26, 27, or 28 d-old
scale than to uninfested leaves, whereas leaves with older
(29-30 d-old) scale were no more attractive than uninfested
leaves. Parasitoids also spent significantly more time in the
arm with yucca leaves infested with 26 d-old scale than in
the arm with uninfested leaves. These results are consistent
with observations of the parasitoids reproductive success on
scale of different ages, whereby older scale are more likely
to encapsulate the developing eggs of M.
sp. nr. flavusfemales than are younger scale. Further bioassays determined
that yucca leaves that had been infested with 26 d-old
scale but from which the scale had been removed were as
attractive as infested leaves. In contrast, infested yucca
leaves from which scale had been removed and the leaves
subsequently washed with distilled water were less attractive
than infested leaves. Furthermore, the wash water
containing scale residues was attractive to female wasps. In
total, these results suggest that Metaphycussp. nr. flavus
females utilize volatile, water soluble compounds produced
by brown soft scale as cues to locate suitable hosts. 相似文献
27.
In their analyses of the impact of pollution taxation on the location of polluting decisions, U. K. Mathur (J. Environ. Econom. Management 3, 16–28 (1976)) and S. S. Gokturk (J. Reg. Sci. 19, 461–467 (1979)) obtained the result that a tax increase on urban pollution concentration may not succeed in pushing the polluting firm away from the urban center. In this paper is shown that the sufficient condition for success in this case depends upon the specification of the production and pollution emissions technology and may be the opposite to the one posited by Mathur and has more intuitive appeal. 相似文献
28.
29.
F. Rossi R. M. Forster F. Montserrat M. Ponti A. Terlizzi T. Ysebaert J. J. Middelburg 《Marine Biology》2007,151(6):2077-2090
The effect of physical disturbance in the form of trampling on the benthic environment of an intertidal mudflat was investigated.
Intense trampling was created as unintended side-effect by benthic ecologists during field experiments in spring and summer
2005, when a mid-shore area of 25 × 25 m was visited twice per month by on average five researchers for a period of 8 months.
At the putatively-impacted location (I) (25 × 25 m) and two nearby control locations (Cs) (25 × 25 m each), three sites (4 × 4 m) were randomly selected and at each site, three plots (50 × 50 cm) were sampled after
18 and 40 days from the end of the disturbance. Multivariate and univariate asymmetrical analyses tested for changes in the
macrofaunal assemblage, biomass of microphytobenthos and various sediment properties (grain-size, water content, NH4 and NO3 concentrations in the pore water) between the two control locations (Cs) and the putatively-impacted location (I). There were no detectable changes in the sediment properties and microphytobenthos biomass, but variability at small scale
was observed. Microphytobenthos and NH4 were correlated at I to the number of footprints, as estimated by the percentage cover of physical depressions. This indicated that trampling
could have an impact at small scales, but more investigation is needed. Trampling, instead, clearly modified the abundance
and population dynamics of the clam Macoma balthica (L.) and the cockle Cerastoderma edule (L.). There was a negative impact on adults of both species, probably because footsteps directly killed or buried the animals,
provoking asphyxia. Conversely, trampling indirectly enhanced recruitment rate of M. balthica, while small-sized C. edule did not react to the trampling. It was likely that small animals could recover more quickly because trampling occurred during
the growing season and there was a continuous supply of larvae and juveniles. In addition, trampling might have weakened negative
adult-juvenile interactions between adult cockles and juvenile M. balthica, thus facilitating the recruitment. Our findings indicated that human trampling is a relevant source of disturbance for the
conservation and management of mudflats. During the growing season recovery can be fast, but in the long-term it might lead
towards the dominance of M. balthica to the cost of C. edule, thereby affecting ecosystem functioning. 相似文献
30.
Forster DL 《Journal of environmental quality》2002,31(1):32-37
This paper summarizes research that investigates the effects of alternative farming practices on the performance of Lake Erie basin farms. First, data from a representative panel of about 100 farmers is analyzed to determine how conservation tillage, rotations, and other factors affected farms' economic returns during 1987-1992. Statistical analysis of these data is unable to demonstrate that there is any significant relationship between farming system (i.e., tillage and rotation) variables and farm profitability. Next, a farm-level bioeconomic simulation model is used to analyze the effects of conservation tillage adoption on farm profitability, farm size, and pollutant emissions. Findings are that tillage system, farm size, and crop selection are determined jointly and may substantially improve economic performance of farms. Conservation tillage enables farms to be larger and more specialized, and as a result, farm profitability improves. Statistical analysis of farm panel data is unable to show the effect of tillage on profitability because it neglects to account for endogeneity of variables (or joint effects of tillage, size, crop selection, and performance) in production decisions. 相似文献