Spatial Dynamics and Spread of Ecosystem Engineers: Two Patch Analysis.

Ecosystem engineers are organisms characterized by interacting with other organisms thorough physical modifications or modifying their habitat. Examples of ecosystem engineers include Spartina alterniflora cordgrass or the zebra mussel Dreissena polymorpha. For both of these, the effect of modifying the environment can be nonlocal, affecting other regions farther away from the region populated by the ecosystem engineer. This shows the importance of understanding the population dynamics of ecosystem engineers in a spatial context. To do this, we have developed an extension of the ecosystem engineer population model of Cuddington et al. (Am Natur, 2009. https://doi.org/10.1086/597216 ) to the simplest spatial model, incorporating two local populations. We use this model to understand the relationship between dispersal and engineering effects, both at local and regional scales. Our main result is that the delayed Allee effect induced in the nonspatial model is extended to the spatial model, so the spread dynamics of an ecosystem engineer can be similar to the Allee case. However, there are more complex possibilities due to the two components of the dynamics. We also find quantitative guidelines that explain the interaction between spread of the environment modification and organism spread.