This functions creates a MizerParams object describing a community-type model.

newCommunityParams(
  max_w = 1e+06,
  min_w = 0.001,
  no_w = 100,
  min_w_pp = 1e-10,
  z0 = 0.1,
  alpha = 0.2,
  f0 = 0.7,
  h = 10,
  gamma = NA,
  beta = 100,
  sigma = 2,
  n = 2/3,
  kappa = 1000,
  lambda = 2.05,
  r_pp = 10,
  knife_edge_size = 1000,
  reproduction
)

Arguments

max_w

The maximum size of the community. The w_inf of the species used to represent the community is set to this value.

min_w

The minimum size of the community.

no_w

The number of size bins in the consumer spectrum.

min_w_pp

The smallest size of the resource spectrum. By default this is set to the smallest value at which any of the consumers can feed.

z0

The background mortality of the community.

alpha

The assimilation efficiency of the community.

f0

The average feeding level of individuals who feed on a power-law spectrum. This value is used to calculate the search rate parameter gamma.

h

The coefficient of the maximum food intake rate.

gamma

Volumetric search rate. Estimated using h, f0 and kappa if not supplied.

beta

The preferred predator prey mass ratio.

sigma

The width of the prey preference.

n

The allometric growth exponent. Used as allometric exponent for the maximum intake rate of the community as well as the intrinsic growth rate of the resource.

kappa

Coefficient of the intrinsic resource carrying capacity

lambda

Scaling exponent of the intrinsic resource carrying capacity

r_pp

Coefficient of the intrinsic resource birth rate

knife_edge_size

The size at the edge of the knife-edge-selectivity function.

reproduction

The constant reproduction in the smallest size class of the community spectrum. By default this is set so that the community spectrum is continuous with the resource spectrum.

Value

An object of type MizerParams

Details

A community model has several features that distinguish it from a multi-species model:

  • Species identities of individuals are ignored. All are aggregated into a single community.

  • The resource spectrum only extends to the start of the community spectrum.

  • Reproductive rate is constant, independent of the energy invested in reproduction, which is set to 0.

  • Standard metabolism is turned off (the parameter ks is set to 0). Consequently, the growth rate is now determined solely by the assimilated food

The function has many arguments, all of which have default values.

Fishing selectivity is modelled as a knife-edge function with one parameter, knife_edge_size, which determines the size at which species are selected.

The resulting MizerParams object can be projected forward using project() like any other MizerParams object. When projecting the community model it may be necessary to keep a small time step size dt of around 0.1 to avoid any instabilities with the solver. You can check for these numerical instabilities by plotting the biomass or abundance through time after the projection.

References

K. H. Andersen,J. E. Beyer and P. Lundberg, 2009, Trophic and individual efficiencies of size-structured communities, Proceedings of the Royal Society, 276, 109-114

See also

Other functions for setting up models: newMultispeciesParams(), newTraitParams()

Examples

if (FALSE) { params <- newCommunityParams(f0=0.7, z0=0.2, reproduction=3e7) sim <- project(params, effort = 0, t_max = 100, dt=0.1) plotBiomass(sim) plotSpectra(sim) }