The effect of habitat heterogeneity on species diversity patterns: a community-level approach using an object-oriented landscape simulation model (SHALOM)

Major progress has been made recently in our understanding of large-scale ecological processes and patterns. Here, a spatially explicit, multi-species, process-based, object-oriented landscape simulation model (SHALOM) is described that is built upon major lessons from fields such as metapopulation dynamics and landscape ecology. Consistent with the current landscape ecology terminology, SHALOM has physical classes (landscape, habitat, cell, patch) and biological classes (population, species, community). Each class has functions and characteristics that are strongly based on ecological realism. Processes of SHALOM are modelled on local and global scales. At the local scale, populations grow continuously, and are affected by: (1) a community-level saturation effect (ratio between energy consumed by all populations in a patch and the energy offered by that patch); (2) a species-habitat match (match between a speciesʹ niche space and the patchʹs habitat space); and (3) demographic stochasticity (inverse population-size dependent residuals from deterministic birth and death rates). The global-scale processes of the model include fitness-optimizing migration and catastrophic stochasticity (disturbance) that can be controlled for its probability, intensity, and spatial range. The processes of the model use allometric relationships and energy as a common currency to bridge differences between species of different body sizes located in habitats of different productivities. These processes also allow both intraspecific and interspecific effects to take place simultaneously without assuming a specific relationship between the two. Hence, SHALOM, with its functions and procedures, opens new opportunities to study combined ecosystem, community and population processes. Simulation results given in the paper on species composition and diversity show that the integration of interspecific competition, demographic stochasticity and dispersal revealed different predictions when different combinations of these processes were used. One novel prediction was that the complex relationship between dispersal and demographic stochasticity caused the global extinction of the largest species. This, in turn, might have further implications for conservation. Overall, the model represents a synthetic approach that provides ways to explore high-level ecological complexity and suggests predictions for future studies of macroecological questions.