Changes between Version 1 and Version 2 of EwEugDispersal
- Timestamp:
- 2010-11-23 09:31:27 (14 years ago)
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EwEugDispersal
v1 v2 2 2 '''Introduction''' 3 3 4 The organisms (i) in an Ecopath model have an aggregated biomass (B i), and are not assumed to move within the area covered by that Ecopath model. In Ecospace, a fraction (B’i) of the biomass of each cell is always on the move, wherein4 The organisms (i) in an Ecopath model have an aggregated biomass (B,,i,,), and are not assumed to move within the area covered by that Ecopath model. In Ecospace, a fraction (B',,i,,) of the biomass of each cell is always on the move, wherein 5 5 6 B ’ = ''m'' · Bi6 B' = ''m'' · B,,i,, 7 7 8 with ''m'' having the dimension of length / time (i.e., km / year) i.e., a velocity or ‘speed’.8 with ''m'' having the dimension of length / time (i.e., km / year) i.e., a velocity or 'speed'. 9 9 10 10 However, ''m'' is not a rate of directed migration, as occur seasonally in numerous fish populations. Rather, ''m'' should be regarded as dispersal and seen as the rate (km/year) the organisms of given ecosystem would disperse as a result of random movements. … … 14 14 Given differential food consumption and survival rates in preferred vs. non-preferred habitat, this will soon generate richly patterned distributions, wherein each cell includes different biomass of each of the groups in the system. 15 15 16 Note that the final results of Ecopath simulations tend to be largely independent of the specific values of ''m'' used, and hence long debates on the best choice of these values may not be necessary –at least not until field estimate, based, e.g., on tagging studies have become available.16 Note that the final results of Ecopath simulations tend to be largely independent of the specific values of ''m'' used, and hence long debates on the best choice of these values may not be necessary - at least not until field estimate, based, e.g., on tagging studies have become available. 17 17 18 18 Note, finally that the biomass of a group within a given cell is usually not multiplied by the same value of ''m'' for each of the flows out of the cell (4 in the case of a cell not touching on land). … … 30 30 '''Vulnerability to predation in bad habitats''' 31 31 32 The increased vulnerability to predation (or grazing) of various organisms outside their ‘preferred’habitat can be changed using a multipliers. The default value of the multiplier is 2.0 for all groups, and it can be increased by up to a factor of 100, while entering a value of 1 will make this mechanism inoperative.32 The increased vulnerability to predation (or grazing) of various organisms outside their 'preferred' habitat can be changed using a multipliers. The default value of the multiplier is 2.0 for all groups, and it can be increased by up to a factor of 100, while entering a value of 1 will make this mechanism inoperative. 33 33 34 34 Conceptualizing this mechanism is straightforward: imagine as an extreme case how easy it would be for a pelagic carnivore to grab a typical coral reef fish, e.g. a butterfly fish, blown by a freak wave off its reef, into an open water area. A less extreme case would be a member of a very abundant population, pushed out of its preferred habitat by its competitors of the same species.
