# Add dispersal constraint to an existing `scenario`

Source: `R/add_constraint.R`

`add_constraint_dispersal.Rd`

Add dispersal constraint to an existing `scenario`

## Usage

```
add_constraint_dispersal(mod, method, value = NULL, type = NULL, ...)
# S4 method for BiodiversityScenario
add_constraint_dispersal(mod, method, value = NULL, type = NULL, ...)
```

## Arguments

- mod
A

`BiodiversityScenario`

object with specified predictors.- method
A

`character`

indicating the type of constraints to be added to the scenario. See details for more information.- value
For many dispersal

`"constrain"`

this is set as`numeric`

value specifying a fixed constrain or constant in units`"m"`

(Default:`NULL`

). For kissmig the value needs to give the number of iteration steps (or within year migration steps). For adaptability constraints this parameter specifies the extent (in units of standard deviation) to which extrapolations should be performed.- type
A

`character`

indicating the type used in the method. See for instance``kissmig``

.- ...
passed on parameters. See also the specific methods for adding constraints.

## Details

**Dispersal**:
Parameters for `'method'`

:

`sdd_fixed`

- Applies a fixed uniform dispersal distance per modelling timestep.`sdd_nexpkernel`

- Applies a dispersal distance using a negative exponential kernel from its origin. #' The negative exponential kernel is defined as: $$f(x) = \frac{1}{2 \pi a^2} e^{-\frac{x}{a}}$$ where \(a\) is the mean dispersal distance (in m) divided by 2.`kissmig`

- Applies the kissmig stochastic dispersal model. Requires``kissmig``

package. Applied at each modelling time step.`migclim`

- Applies the dispersal algorithm MigClim to the modelled objects. Requires`"MigClim"`

package.

A comprehensive overview of the benefits of including dispersal constrains in species distribution models can be found in Bateman et al. (2013).

The following additional parameters can bet set:

## Note

Unless otherwise stated, the default unit of supplied distance values (e.g. average dispersal
distance) should be in `"m"`

.

## References

Bateman, B. L., Murphy, H. T., Reside, A. E., Mokany, K., & VanDerWal, J. (2013). Appropriateness of full‐, partial‐and no‐dispersal scenarios in climate change impact modelling. Diversity and Distributions, 19(10), 1224-1234.

## See also

Other constraint:
`add_constraint()`

,
`add_constraint_MigClim()`

,
`add_constraint_adaptability()`

,
`add_constraint_boundary()`

,
`add_constraint_connectivity()`

,
`add_constraint_minsize()`

,
`add_constraint_threshold()`

,
`simulate_population_steps()`