Box 2. Traditions in ecosystem conceptualization and their influence on research and modelling
A critical factor in ecosystem research is resolution on what an ecosystem is. Many theoretical and practical examinations of the ecosystem concept have been presented since its inception (e.g., O’Neill et al 2001) and although all have improved use and understanding of the term, disparities among the prevailing philosophic and scientific traditions of ecosystem science persist (Loreau 2020). Blew (1996) outlined three major traditions in ecology, each rooted in relatively distinct perceptions of the ecosystem concept and its primary definitional criteria (see Table S1). Similar traditions persist in contemporary ecosystem science (Baveye et al 2018, Zarnetske et al 2019, Alahuhta et al 2020). Modified after Blew (1996), the three major traditions include:
1) Biotic tradition. The biotic approach to ecosystem science is organism focused and typically emphasizes either species or, more often, communities as the most important expression of ecosystem organization. Abiotic constituents are ranked with lesser importance and may be employed to model or describe biotic patterning. Spatial properties may be explicitly, or implicitly, recognized, and functional relationships are inferred (O’Neill 2001). Such units are sometimes called bio-ecosystems, ecological communities, or community-ecosystems (Rowe and Barnes 1994). A prominent example is the IUCN global ecosystem red list, which emphasizes biotically defined units for its operational definition (Keith et al 2013).
2) Functional tradition. Under the tenets of this approach to ecosystem science, the singular representation of holism and complexity are an ecosystem’s functional features (Currie 2011). This approach emphasizes the processes (e.g., respiration, decomposition, material cycling), properties (e.g., energy balance, productivity, trophic structuring), or products (e.g., biomass) resulting from interactions between biotic and abiotic ecosystem components (Gignoux et al 2011). Spatial properties may be explicitly or implicitly recognized (DeAngelis and Yurek 2016), and biotic complexity is often generalized to trophic levels, higher taxonomic ranks, or specific functional groups. Prominent examples of this approach are process-based models of ecosystems at local (e.g., Caron-Lormier et al. 2009) and global extents (e.g., Bonan and Doney 2018); ecosystem simulation models (e.g., Xia et al 2017); and mathematical models of individual ecosystems (e.g., Svirezhev et al 1984) or meta-ecosystems (e.g., Leroux and Loreau 2012).
3) Abiotic tradition. Following principles of the abiotic tradition, which is sometimes called the enduring featuresapproach, ecosystems are interpreted as ecologically homogenous areas of terrestrial or marine geography (e.g., Zhao et al 2020). While biotic variables may be employed to name, map, or describe ecosystems defined through this tradition, biota are usually viewed as ephemeral products of more enduring abiotic drivers, such as climate, landform, soil, hydrology, and geology. These latter physical or marine geodiversity features are considered the building blocks of ecosystems (Sayre et al 2009). This approach deemphasizes ecosystem function and dynamics, focusing on steady-state expressions of ecological variability. Units developed through the abiotic tradition are sometimes called geo-ecosystems (Rowe and Barnes 1994) and they are most applied at broader spatial scales. Biomes, ecoregions, ecozones, ecosites, and landscape ecosystems are prominent examples of units developed, following this tradition, in the contemporary literature (e.g., Yang et al 2017, Keith et al 2022).