21 | | |
22 | | 2. The concentration parameters are relative values that the user needs to set by trying alternatives (generally in the range 0.5 to 4.0) to see what values give general distribution patterns similar to those observed in the field. Low values (<1.0) lead to weak distortion of movement toward preferred cells and hence to more widely spread distributions, while high values (e.g. 3.0) give distributions strongly concentrated near the preferred cells. |
23 | | |
24 | | 3. Mean annual movement distances ([wiki:EwEugDispersal Ecospace Dispersal] form) have to be set large enough for migrating species to be able to "track" movements in preferred locations. As a general rule, set the base dispersal rate for migratory species to at least 100L km/yr., where L is mean body length in cm. |
25 | | |
26 | | 4. Setting high concentration parameter values (>2.0) and/or moving animals through a very complex map with many coastal blocking features can result in numerical instability in the Ecospace solution algorithm. The best way to correct this is to reduce the simulation time step; it may also be necessary to reduce the SOR w relaxation weight ([wiki:EwEugEcospaceParameters Ecospace parameters] form) used in solving the linear equations involved in the numerical scheme for integrating the spatial rate equations (an alternating implicit method). |
27 | | |
28 | | 5. Setting high concentration parameter values can also result in "overfishing": Ecospace allocates total fishing effort over the map proportional to the total number of cells initially used by each fishing fleet, so when the model generates a concentrated distribution of some favoured species, the total effort will concentrate accordingly and can sometimes generate very high fishing rates near the centre of the migrating stock distribution. Remedies include reducing total effort ([wiki:EwEugEcospaceFishery Ecospace fishery] form, total effort multiplier) and distributing effort more widely (Ecospace fishery form, reduce value of "effective power"). |
29 | | |
30 | | 6. Concentrating a migratory predator can cause local depletion of food organisms and/or reduced per-predator feeding rates due to prey vulnerability limits. If these effects cause simulated total predator biomass to incorrectly decline over time (and if the user determines that the declines are not due to an artifactual overfishing effect), then it may be necessary to either increase total prey abundances (in Ecopath) or vulnerability of prey to the predator (Ecosim [wiki:EwEugVulnerabilitiesFlowControl Vulnerabilities] form). |
31 | | |
32 | | 7. Multi-stanza population dynamics may behave strangely or incorrectly when one or more life history stages are migratory while other(s) are not. Ecospace does not keep track of the full population age/size distribution for each spatial cell (prohibitive memory and computing time requirement), and instead uses a running equilibrium approximation to the population composition. This approximation tends to "dampen" abundance fluctuations in the early life history stanzas that might be created by, for example, seasonal movement of the adults to spawning locations near preferred juvenile habitats. |
| 21 | 1. The concentration parameters are relative values that the user needs to set by trying alternatives (generally in the range 0.5 to 4.0) to see what values give general distribution patterns similar to those observed in the field. Low values (<1.0) lead to weak distortion of movement toward preferred cells and hence to more widely spread distributions, while high values (e.g. 3.0) give distributions strongly concentrated near the preferred cells. |
| 22 | 1. Mean annual movement distances ([wiki:EwEugDispersal Ecospace Dispersal] form) have to be set large enough for migrating species to be able to "track" movements in preferred locations. As a general rule, set the base dispersal rate for migratory species to at least 100L km/yr., where L is mean body length in cm. |
| 23 | 1. Setting high concentration parameter values (>2.0) and/or moving animals through a very complex map with many coastal blocking features can result in numerical instability in the Ecospace solution algorithm. The best way to correct this is to reduce the simulation time step; it may also be necessary to reduce the SOR w relaxation weight ([wiki:EwEugEcospaceParameters Ecospace parameters] form) used in solving the linear equations involved in the numerical scheme for integrating the spatial rate equations (an alternating implicit method). |
| 24 | 1. Setting high concentration parameter values can also result in "overfishing": Ecospace allocates total fishing effort over the map proportional to the total number of cells initially used by each fishing fleet, so when the model generates a concentrated distribution of some favoured species, the total effort will concentrate accordingly and can sometimes generate very high fishing rates near the centre of the migrating stock distribution. Remedies include reducing total effort ([wiki:EwEugEcospaceFishery Ecospace fishery] form, total effort multiplier) and distributing effort more widely (Ecospace fishery form, reduce value of "effective power"). |
| 25 | 1. Concentrating a migratory predator can cause local depletion of food organisms and/or reduced per-predator feeding rates due to prey vulnerability limits. If these effects cause simulated total predator biomass to incorrectly decline over time (and if the user determines that the declines are not due to an artifactual overfishing effect), then it may be necessary to either increase total prey abundances (in Ecopath) or vulnerability of prey to the predator (Ecosim [wiki:EwEugVulnerabilitiesFlowControl Vulnerabilities] form). |
| 26 | 1. Multi-stanza population dynamics may behave strangely or incorrectly when one or more life history stages are migratory while other(s) are not. Ecospace does not keep track of the full population age/size distribution for each spatial cell (prohibitive memory and computing time requirement), and instead uses a running equilibrium approximation to the population composition. This approximation tends to "dampen" abundance fluctuations in the early life history stanzas that might be created by, for example, seasonal movement of the adults to spawning locations near preferred juvenile habitats. |