Fig. 6

Schematic representation of engineering-strength hypothesis (hypothesis 2). This hypothesis describes how local biodiversity effects of an invasive ecosystem engineer are expected to depend on the strength of the engineering species, with engineering strength defined as the number of habitats that can be invaded and transformed and local defined as the areas invaded by the engineering species. An invading engineer is likely to create a single new habitat type, thereby putting a maximum on the species gain. The stronger the ecosystem engineer, the more existing habitat types with their communities it will displace. As a result, a stronger ecosystem engineer is likely to cause a net decrease of biodiversity when regarded at the local scale. On a larger scale, also accounting for the areas that are not occupied by the invasive ecosystem engineer, diversity effects can be very different and will strongly depend on the chosen scale