Patterns of biotic community organization and reorganization: A conceptual framework and a case study

摘要

Reorganization is an important concept for confronting complex adaptive systems (CAS) theory with ecological reality. However, little work has been done to translate the reorganization idea into a practical conceptual framework. This paper focuses on community-level reorganization, the process of re-forming patterns in relation to the distribution of species density (abundance) and their frequency of occurrence in space (incidence). We assert that changes in species positions in the incidence-abundance (IA) phase plane depict community reorganization in response to environmental changes. This is because species positions in the IA plane represent the most prominent organizational features of a biotic community. We identified four sequential levels of species reorganization in the IA phase plane: reshuffling of species, species appearance, species disappearance and whole-assemblage shift. We propose that the sequential levels represent an increase in reorganization intensity depending on the extent of environmental change. We formulate the Environmental Change and Re-Organization (ECRO) hypothesis specifying that ecosystems respond predictably in terms of community reorganization in the IA phase plane to external drivers. The predictable reorganization follows the four sequential levels of organization in response to intensity of environmental change. We suggest that the response of a species assemblage to external drivers in sequential levels of reorganization is independent of ecosystem properties, type of environmental variables, taxa, and spatio-temporal scales. We tested the predictability of reorganization according to the ECRO hypothesis, using annual plant assemblages of a semiarid shrubland. These assemblages exhibit CAS properties as suggested by Levin: high species diversity, high numbers of individuals, local interactions among individuals in relation to water consumption, and annually selected species subsets for replication. We investigated annual plant assemblage organization and reorganization for 12 years in response to disturbance and resource input, using the IA phase plane. The field study supports our assertion that reorganization of species assemblages in response to environmental change can be represented by species repositioning in the IA phase plane, and that community reorganization follows the four sequential levels of reorganization in response to the intensity of environmental change. Our conceptual framework and experimental studies demonstrate that hypotheses related to core CAS concepts of organization and reorganization can be tested by linking them with community ecology concepts of species patterns in the IA phase plane. We also discuss the relationship between reorganization in the IA phase plane and resilience, regime shift and ecosystem functioning as affected by species response and effects traits.