THE EFFECT OF HABITAT HETEROGENEITY ON SPECIES-DIVERSITY PATTERNS - ACOMMUNITY-LEVEL APPROACH USING AN OBJECT-ORIENTED LANDSCAPE SIMULATION-MODEL (SHALOM)

Major progress has been made recently in our understanding of large-sc ale ecological processes and patterns. Here, a spatially explicit, mul ti-species, process-based, object-oriented landscape simulation model (SHALOM) is described that is built upon major lessons from fields suc h as metapopulation dynamics and landscape ecology. Consistent with th e current landscape ecology terminology, SHALOM has physical classes ( landscape, habitat, cell, patch) and biological classes (population, s pecies, community). Each class has functions and characteristics that are strongly based on ecological realism. Processes of SHALOM are mode lled on local and global scales. At the local scale, populations grow continuously, and are affected by: (I) a community-level saturation ef fect (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 species' niche space and the patch's habitat space); and (3) demographic stochasticity (inverse population-size dependent residual s from deterministic birth and death rates). The global-scale processe s of the model include fitness-optimizing migration and catastrophic s tochasticity (disturbance) that can be controlled for its probability, intensity, and spatial range. The processes of the model use allometr ic relationships and energy as a common currency to bridge differences between species of different body sizes located in habitats of differ ent 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 functio ns 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 o f interspecific competition, demographic stochasticity and dispersal r evealed different predictions when different combinations of these pro cesses were used. One novel prediction was that the complex relationsh ip between dispersal and demographic stochasticity caused the global e xtinction of the largest species. This, in turn, might have further im plications for conservation. Overall, the model represents a synthetic approach that provides ways to explore high-level ecological complexi ty and suggests predictions for future studies of macroecological ques tions. (C) 1998 Elsevier Science B.V. All rights reserved.