251 research outputs found
Chains, Antichains, and Complements in Infinite Partition Lattices
We consider the partition lattice on any set of transfinite
cardinality and properties of whose analogues do not hold
for finite cardinalities. Assuming the Axiom of Choice we prove: (I) the
cardinality of any maximal well-ordered chain is always exactly ; (II)
there are maximal chains in of cardinality ; (III) if,
for every cardinal , we have , there
exists a maximal chain of cardinality (but ) in
; (IV) every non-trivial maximal antichain in has
cardinality between and , and these bounds are realized.
Moreover we can construct maximal antichains of cardinality for any ; (V) all cardinals of the form
with occur as the number of
complements to some partition , and only these
cardinalities appear. Moreover, we give a direct formula for the number of
complements to a given partition; (VI) Under the Generalized Continuum
Hypothesis, the cardinalities of maximal chains, maximal antichains, and
numbers of complements are fully determined, and we provide a complete
characterization.Comment: 24 pages, 2 figures. Submitted to Algebra Universalis on 27/11/201
Constructing end-to-end models using ECOPATH data
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Marine Systems 87 (2011): 227-238, doi:10.1016/j.jmarsys.2011.04.005.The wide availability of ECOPATH data sets provides a valuable resource for the comparative analysis of marine ecosystems. We show how to derive a bottom-up transform from the top-down ECOPATH; couple this to a simple NPZD web with physical forcing; and use the end-to-end model (E2E) for scenario construction. This steady state format also provides a framework and initial conditions for different dynamic simulations. This model can be applied to shelf ecosystems with a wide range of physical forcing, coupled benthic/pelagic food webs, and nutrient recycling.
We illustrate the general application and the specific problems by transforming an ECOPATH model for the Northern Californian Current (NCC). We adapt results on the upwelling regime to provide estimates of physical fluxes and use these to show the consequences of different upwelling rates combined with variable retention mechanism for plankton, for the productivity of fish and other top predators; and for the resilience of the ecosystem. Finally we show how the effects of inter-annual to decadal variations in upwelling on fishery yields can be studied using dynamic simulations with different prey-predator relations.
The general conclusion is that the nature of the physical regimes for shelf ecosystems cannot be ignored in comparing end-to-end representations of these food webs.This work was supported by the US-GLOBEC Pan-regional Synthesis progra
Integrating bioenergetics and foraging behavior : the physiological ecology of larval cod (Gadus morhua)
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2004How do larval cod, Gadus morhua, balance foraging effort against the high cost of
swimming in a viscous hydrodynamic regime? A respirometry system was developed to
measure the activity metabolism of individual larvae. The cost of swimming was
modeled as a power-performance relationship (energy expenditure as a function of
swimming speed) and as the cost of transport (the cost to travel a given distance). The
cost of transport was high relative to juvenile and adult fish, but larvae swam more
efficiently as they grew and became better able to overcome viscous drag.
A large-volume observation system was developed to record foraging behavior in
three dimensions. There are two phases of the saltatory search cycle used by larval cod:
the burst which serves to position larvae within a new search volume and the pause when
larvae search for prey Burst characteristics did not change under different prey
treatments, but pause duration increased while foraging capacity and swimming activity
decreased when prey were absent. Longer pause durations could reflect greater effort to
visually process each search volume when prey were difficult to find. Reduced
swimming activity could also be an energy conservation strategy under unfavorable
foraging conditions.
By applying the cost of swimming model to the observed swimming intensity of
freely foraging larvae, foraging activity was estimated to account for up to 80% of
routine metabolism. A trophodynamic model was developed incorporating observed
foraging behavior and swimming costs to estimate the prey density required to cover all
metabolic demands. Small larvae (5mm) can survive on typical mean Georges Bank prey
densities in mildly turbulent conditions. Larger larvae (>6mm) can survive even at high
turbulence levels.
Simulated alternative foraging strategies predict that when predator-prey contact rates
are high, the greatest net energy gain is realized with short pause durations. When
predator-prey contact rates are low, larvae should achieve greater net energy gains by
remaining at rest for extended periods. Larvae observed foraging in the absence of prey
do not change behavior as much as the simulation model predicts, suggesting that they
use a prey encounter maximization strategy rather than an energy conservation strategy.This research was funded by grants from the Ocean Life Institute, the Coastal Ocean
Institute, the Rinehart Coastal Research Center, and the Cecil H. and Ida M. Green
Technology and Innovation Program. Funding was also provided by ONR project
N000149610684 and NSF award OCE-9632606 to Scott Gallager
The Role of Organizational and Interorganizational Factors on Planned Adoption of Electronic Commerce
Internet technologies, especially the World Wide Web, are predicted to lead to changes in the transfer of information between trading partners. This paper focuses on identifying organizational and interorganizational factors which will impact the planned adoption of electronic commerce. The interorganizational system will become successfulonly if those factors which are found to have an impact on the adoption of the innovation are handled effectively by the system. Prior to the planned adoption these factors need to be evaluated and managed to ensure a successful adoptio
Analysis of Energy Flow in US GLOBEC Ecosystems Using End-to-End Models
End-to-end models were constructed to examine and compare the trophic structure and energy flow in coastal shelf ecosystems of four US Global Ocean Ecosystem Dynamics (GLOBEC) study regions: the Northern California Current, the Central Gulf of Alaska, Georges Bank, and the Southwestern Antarctic Peninsula. High-quality data collected on system components and processes over the life of the program were used as input to the models. Although the US GLOBEC program was species-centric, focused on the study of a selected set of target species of ecological or economic importance, we took a broader community-level approach to describe end-to-end energy flow, from nutrient input to fishery production. We built four end-to-end models that were structured similarly in terms of functional group composition and time scale. The models were used to identify the mid-trophic level groups that place the greatest demand on lower trophic level production while providing the greatest support to higher trophic level production. In general, euphausiids and planktivorous forage fishes were the critical energy-transfer nodes; however, some differences between ecosystems are apparent. For example, squid provide an important alternative energy pathway to forage fish, moderating the effects of changes to forage fish abundance in scenario analyses in the Central Gulf of Alaska. In the Northern California Current, large scyphozoan jellyfish are important consumers of plankton production, but can divert energy from the rest of the food web when abundant
Unclear associations between small pelagic fish and jellyfish in several major marine ecosystems
During the last 20 years, a series of studies has suggested trends of increasing jellyfish (Cnidaria and Ctenophora) biomass in several major ecosystems worldwide. Some of these systems have been heavily fished, causing a decline among their historically dominant small pelagic fish stocks, or have experienced environmental shifts favouring jellyfish proliferation. Apparent reduction in fish abundance alongside increasing jellyfish abundance has led to hypotheses suggesting that jellyfish in these areas could be replacing small planktivorous fish through resource competition and/or through predation on early life stages of fish. In this study, we test these hypotheses using extended and published data of jellyfish, small pelagic fish and crustacean zooplankton biomass from four major ecosystems within the period of 1960 to 2014: the Southeastern Bering Sea, the Black Sea, the Northern California Current and the Northern Benguela. Except for a negative association between jellyfish and crustacean zooplankton in the Black Sea, we found no evidence of jellyfish biomass being related to the biomass of small pelagic fish nor to a common crustacean zooplankton resource. Calculations of the energy requirements of small pelagic fish and jellyfish stocks in the most recent years suggest that fish predation on crustacean zooplankton is 2â30 times higher than jellyfish predation, depending on ecosystem. However, compared with available historical data in the Southeastern Bering Sea and the Black Sea, it is evident that jellyfish have increased their share of the common resource, and that jellyfish can account for up to 30% of the combined fish-jellyfish energy consumption. We conclude that the best available time-series data do not suggest that jellyfish are outcompeting, or have replaced, small pelagic fish on a regional scale in any of the four investigated ecosystems. However, further clarification of the role of jellyfish requires higher-resolution spatial, temporal and taxonomic sampling of the pelagic community.publishedVersio
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Evidence that summer jellyfish blooms impact Pacific Northwest salmon production
Interannual variability in salmon (Oncorhynchus spp.) production in the northeast Pacific is understood to be driven by oceanographic variability and bottom-up processes affecting prey availability to juvenile salmon. Scyphozoan jellyfish have an important role in shaping the pathways of energy flow through pelagic food webs. While jellyfish obtain high production rates and biomasses as major consumers of zooplankton production, they have few predators and may divert plankton production away from higher trophic levels. Although jellyfish are planktivorous and juvenile coho (O. kisutch) and Chinook (O. tshawytscha) salmon are mainly piscivorous, they may be indirect competitors for plankton production. Ecosystem model simulations suggested that among all trophic interactions within the Pacific Northwest coastal food web, juvenile salmon are particularly sensitive to jellyfish blooms, and that salmon production will be suppressed in years of high summer jellyfish biomass. Pelagic surveys off Oregon and Washington (1999â2012) were used to examine the interannual relationship between salmon production and the dominant jellyfish species, the sea nettle Chrysaora fuscescens, off the Pacific Northwest coast. There was a significant, negative correlation between sea nettle biomass and the strength of adult coho and Chinook salmon returns to the Columbia River. Examination of spatial distributions across years showed a positive association between sea nettles and salmon. Within individual years, significant differences between the distribution of sea nettles and yearling coho and Chinook salmon generally occurred during cooler ocean summers, perhaps due to the greater expanse of optimal salmon habitat resulting from more upwelling. Whether the association is behavioral or a product of oceanographic processes, association enhances the opportunity for indirect competition. Examination of feeding incidence in September showed that salmon stomachs were less full at locations with higher sea nettle biomass
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Seasonal food web models for the Oregon inner-shelf ecosystem : investigating the role of large jellyfish
Previously published in California Cooperative Oceanic Fisheries Investigations Progress Report, 2007, Vol.48; access courtesy of publisher and authors.We developed two seasonal food-web models, spring
and summer, within the Ecopath framework for the
Oregon upwelling ecosystem to investigate the role of
large jellyfish as competitors for zooplankton prey. We
used information about fish and jellyfish biomass, distribution,
and diet derived from pelagic trawl survey
data. Information about lower trophic-level production
was acquired from zooplankton survey data. The models
indicate that in spring, jellyfish are a modest consumer
of zooplankton, and forage fishes dominate the
system in terms of biomass and consumption. By late
summer, jellyfish become the major zooplankton consumers,
and they consume 17% of the summer zooplankton
production while forage fish consume 9%.
Jellyfish appear to divert zooplankton production away
from upper trophic levels. Only 2% of the energy consumed
by jellyfish is passed to higher trophic levels.
However, the role of jellyfish as competitors may be
moderate; a large proportion of zooplankton production
(40%â44%) is not consumed but lost to detritus.Keywords: food-web models, Jellyfis
Jellyfish, Forage Fish, and the World\u27s Major Fisheries
A majority of the worldâs largest net-based fisheries target planktivorous forage fish that serve as a critical trophic link between the plankton and upper-level consumers such as large predatory fishes, seabirds, and marine mammals. Because the plankton production that drives forage fish also drives jellyfish production, these taxa often overlap in space, time, and diet in coastal ecosystems. This overlap likely leads to predatory and competitive interactions, as jellyfish are effective predators of fish early life stages and zooplankton. The trophic interplay between these groups is made more complex by the harvest of forage fish, which presumably releases jellyfish from competition and is hypothesized to lead to an increase in their production. To understand the role forage fish and jellyfish play as alternate energy transfer pathways in coastal ecosystems, we explore how functional group productivity is altered in three oceanographically distinct ecosystems when jellyfish are abundant and when fish harvest rates are reduced using ecosystem modeling. We propose that ecosystem-based fishery management approaches to forage fish stocks include the use of jellyfish as an independent, empirical âecosystem healthâ indicator
Jellyfish, Forage Fish, and the World\u27s Major Fisheries
A majority of the worldâs largest net-based fisheries target planktivorous forage fish that serve as a critical trophic link between the plankton and upper-level consumers such as large predatory fishes, seabirds, and marine mammals. Because the plankton production that drives forage fish also drives jellyfish production, these taxa often overlap in space, time, and diet in coastal ecosystems. This overlap likely leads to predatory and competitive interactions, as jellyfish are effective predators of fish early life stages and zooplankton. The trophic interplay between these groups is made more complex by the harvest of forage fish, which presumably releases jellyfish from competition and is hypothesized to lead to an increase in their production. To understand the role forage fish and jellyfish play as alternate energy transfer pathways in coastal ecosystems, we explore how functional group productivity is altered in three oceanographically distinct ecosystems when jellyfish are abundant and when fish harvest rates are reduced using ecosystem modeling. We propose that ecosystem-based fishery management approaches to forage fish stocks include the use of jellyfish as an independent, empirical âecosystem healthâ indicator
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