Global biodiversity is currently declining at an unusually high rate. National and international initiatives to counteract this decline bring about a pressing demand to quantify current and future human impacts on biodiversity.
A major opportunity
A major opportunity to improve biodiversity modelling lies in the increasing availability of large-scale, multi-species data sets and the ongoing advances in modelling techniques and software. This allows for a species-by-species approach to biodiversity modelling based on so-called species distribution models (SDMs). SDMs are quantitative (regression-based) relationships between the abundance or occurrence of a species on the one hand and a set of environmental factors on the other. Clear advantages of an SDM approach to biodiversity modelling include its great flexibility and the complementary information it provides to aggregated biodiversity measures like overall species richness. On the contrary, the SDM approach to biodiversity modelling has been criticised because it typically ignores biotic interactions, which may significantly modify species distributions. However, a consistent approach to systematically include biotic interactions in SDMs has not yet been developed.
A procedure to account for biotic interactions in species distribution models
In this path-finding project, we aim to establish and test a procedure to account for biotic interactions in species distribution models. To that end, we propose to establish an interacting species distribution modelling (iSDM) approach consisting of multiple simultaneous algorithms that combine species occurrence data with data on environmental conditions and prior knowledge on species habitat preferences and species interactions (e.g., predator-prey relationships, competition, facilitation). We focus on climate and land use as these are two main determinants of species distributions.
We will test the approach for a restricted set of species with high-quality data available on occurrence and potential interactions, such as birds, mammals and vascular plants, in well-studied ‘simple’ ecosystems with relatively few interacting species, like the Arctic.
Validation
The approach will be validated in two ways: i) based on cross-validation and ii) by stacking the iSDM predictions over the different species and comparing the species richness estimates thus obtained with location-specific species richness observations.
A significant stepping stone
In a later stage, we intend to apply the iSDM approach developed in this path-finding project to a larger set of species and regions in order to systematically quantify the importance of biotic interactions for various taxonomic groups and at different spatial scales. Thus, we will shed light on the yet unresolved issue regarding the scale dependency of biotic interactions. In addition, this path-finding project provides a significant stepping stone towards a global-scale species-by-species biodiversity assessment model, which is to be developed within the IMAGE-GLOBIO modelling framework of PBL Netherlands Environmental Assessment Agency. This aspect is further explained in section.
