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891.
Carl Van Colen J. Lenoir A. De Backer B. Vanelslander M. Vincx S. Degraer T. Ysebaert 《Marine Biology》2009,156(10):2161-2171
The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated
from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of
extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated
burrowing within the first minute after their addition in still water, regardless of treatment, only 48–52% had completely
penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed
into the control sediments and BDF with a low diatom biomass (<3.5 μg Chl a g−1 dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated
with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass
and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities
of 5 and 15 cm s−1 was distinctly lower compared to the still-water assays. Only 4.6–5.8% of the larvae were recovered from BDF and control
sediments after 3 h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae
settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement
of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and,
at low flow velocities (5 cm s−1), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms. 相似文献
892.
Ying Hu Liu De Li Liu Min An Yin Lian Fu Ren Sen Zeng Shi Ming Luo Hanwen Wu Jim Pratley 《Ecological modelling》2009
Many plant species defend themselves against herbivorous insects indirectly by producing and releasing induced volatiles to attract natural enemies of the herbivores. In this paper, we consider the recruitment of natural enemies attracted by plant-induced volatiles and introduce the An–Liu–Johnson–Lovett model into the Lotka–Volterra model in an attempt to add this missing vital link in tritrophic interaction. Increase in attraction strength of plant-induced volatiles to the natural enemy leads to high fluctuation amplitude of plant biomass and herbivore population. When the attack strength of natural enemies reaches a certain level, fluctuation amplitude of plant biomass and herbivore population will decrease and plant biomass will approach to its environmental carrying capacity. The simulation demonstrates that plant volatile compounds induced by insects have led to the introduction of a third tritrophic level, e.g., natural enemies, into the plant–herbivore system, resulting in the coexistence of plants, insects, and natural enemies during the evolution process. 相似文献
893.
894.
Is risk-sharing resource taxation in society's best interests if prices are log-normally distributed? 总被引:1,自引:0,他引:1
This paper contributes to our understanding of the perceived benefits for society of risk-sharing resource taxation. In the particular context of log-normally distributed prices a model is developed which enables comparison of risk-sharing resource taxation with an alternative in determining the overall return to society from auctioning an extraction lease. The main finding of the paper is a potential exception to the general preference for risk-sharing resource taxation if the bidding firms are effectively risk neutral. This exception is illustrated numerically in the context of the impact of increased price uncertainty, but it is shown not to be robust with respect to divergences from risk neutrality in the risk attitudes of firms. Consequently, it is concluded that the choice of risk-sharing resource taxation is likely to be in society's best interests, regardless of the probability distribution of prices. 相似文献
895.
Since the beginning of the 20th century the Belgian coast has undergone important changes of which an overview is presented
here. To determine the view of the Belgian public on the Belgian coast and in order to obtain their opinions and solutions
to the problems along the Belgian coast, a questionnaire survey was conducted with a total of 100 respondents divided into
five groups, all active in the coastal zone. The five groups included (1) politicians on various levels of authority, (2)
coastal entrepreneurs and business people, (3) naturalists and scientists, (4) coastal residents and (5) tourists. Coastal
zone problems, as perceived by the different groups, and their solutions are discussed. Former municipalities, in particular,
were held responsible for the current coastal problems. Most respondents were skeptic about the application of recent juridical
instruments (e.g. the Dune Decree), the structural plans and their power to protect the remaining natural areas. The root
of the problems seems to lie in lack of coordination and communication between different authorities responsible for the coastal
zone. 相似文献
896.
897.
Reliability of Elasticity Analysis: Reply to Mills et al. 总被引:2,自引:0,他引:2
898.
M. D. Moffett A. McLachlan P. E. D. Winter A. M. C. De Ruyck 《Journal of Coastal Conservation》1998,4(1):87-90
The effects of varying intensities of human trampling on sandy beach macrofauna were investigated at an exposed beach on the
Eastern Cape coast. An experimental approach investigated the survival rates of four macrofaunal species which were subjected
to human trampling at different intensities in a holiday-activity simulation. It was found that the clamDonax serra was slightly impacted at all trampling intensities whileDonax sordidus and the isopodEurydice longicomis were affected only at high trampling intensities. Vigorous beach games, such as volleyball, may have a damaging effect onD. serra. In a second experiment, the severe effects of human trampling onD. serra and the benthic mysidGastrosaccus psammodytes were investigated using numbered animals in enclosures. The results indicated that few members of the macrofauna were damaged
at low trampling intensities but substantial damage occurred under intense trampling. 相似文献
899.
An individual-oriented model is constructed which simulates the collective foraging behaviour of a colony of honey-bees,
Apis mellifera. Each bee follows the same set of behavioural rules. Each rule consists of a set of conditions followed by the behavioural
act to be performed if the conditions are fulfilled. The set of conditions comprises the state of external information available
to the bee (e.g. the dancing of other bees) and internal information variables (like memorised location of a food source and
homing motivation). The rules are partly observational (i.e. they capture the observable regularities between the present
external information and the individual bee's behaviour), and partly involve hypothesised internal-state variables (e.g. abandoning
tendency and homing motivation), because no observable (physiological) aspect has as yet been detected in the bee which correlates
with changes in the internal motivation. Our aim is to obtain a set of rules that is necessary and sufficient for the generation
of the collective foraging behaviour observed in real bees. We simulated an experiment performed by Seeley et al. in which
a colony of honey-bees chooses between two nectar sources of different profitabilities which are switched at intervals. A
good fit between observed and simulated collective forager patterns was obtained when the model included rules in which the
bees (1) relied on the information acquired from previous flights to a source (e.g. profitability and time of day when the
source was found), (2) used positional information obtained by attending recruitment dances and (3) did not abandon a (temporarily)
deteriorated source too fast or too slowly. The significance of the following issues is discussed: the role of internal and
external information, source profitability, the spatial precision of the dance communication, the ability to search for a
source after the source position has been transmitted, the tendency to abandon a deteriorated source, and the concepts of
scout, recruit, (un)employed forager, and foraging history.
Received: 26 January 1998 / Accepted after revision: 16 May 1998 相似文献
900.
Perfluorinated compounds (PFCs) are a group of anthropogenic chemicals containing diverse functional groups and chain lengths. They are known to be persistent and bioaccumulative explaining their worldwide environmental presence. The toxicological information on these chemicals is still incomplete and insufficient to assess their environmental impact and structure-activity relationship. In the present study, the developmental effects of PFOS (perfluorooctane sulfonate, C8), PFOA (perfluorooctanoic acid, C8), PFBS (perfluorobutane sulfonate, C4) and PFBA (perfluorobutanoic acid, C4) were evaluated in zebrafish embryos (Danio rerio). The different chain lengths and functional groups of the selected chemicals made it possible to determine the structure-activity relationship of these compounds. PFCs with longer chain lengths (C8) tend to be more toxic than PFCs with shorter chain lengths (C4). Comparison based on the functional groups of compounds with the same chain length indicates that PFCs with a sulfonate group have a larger toxic potential than the ones with a carboxyl group. Furthermore, exposure to the different PFCs resulted in some general effects, such as deformations of the tail and an uninflated swim bladder, as well as in more specific effects which might be related to the structure of the tested chemicals. Oedemas and effects on length could only be detected in 8-carbon PFCs while malformations of the head were a more specific action of the sulfonated PFCs. Effects on hatching rate and success were found in PFOA exposed embryos and heart rates were affected after exposure to PFOS, PFOA and PFBS. 相似文献