Box 1. Spatial concordance – a basis for resolving intra- and
inter-ecosystem patterns
Ecosystems can be distinguished by predicting their component features
(Table S1) and the spatially structured relationships between them.
These complex relationships span biotic and abiotic domains, scales, and
levels of ecological organization. To resolve these complexities, and
how they vary across landscapes, we focus on variations in spatial
concordance within and among assemblages of biotic (B) and abiotic (A)
variables.
Spatial concordance is a condition where two or more ecosystem features
show similar scale-specific responses (e.g., presence, abundance) across
shared segments of a geographic gradient (plots A and B – right panel).
Concordant spatial relationships can arise between individual biotic
(e.g., local species populations – O’Neill 2001) and abiotic (e.g.,
inorganic elements – Austin 2013) ecosystem constituents. Furthermore,
concordances can occur across structural (e.g., vegetation physiognomy
– Yang et al 2017), compositional (e.g.,
community – Pinto-Ledezma and
Cavender-Bares 2021), and functional (e.g., productivity – O’Neill
2001) ecosystem features. Most studies have focused on concordance among
biotic properties (Soranno et al 2019) and particularly how they relate
to community variations (e.g., identity – Austin 2013) or to landscape
heterogeneity (Pickett and Cadenasso 1995). Instead, we emphasize
spatial concordance within and between biotic and abiotic domains (plot
AB – right panel). This integrative approach reflects the reciprocal
roles (Gignoux et al. 2011, Richter and Billings 2015, Halvorsen et al
2020) of biotic-abiotic constituents and processes in ecosystem assembly
(Keith et al 2022). It also provides a means to parse individual and
aggregate (Table S1) sources of ecosystem variation and to identify the
strongest co-varying biotic-abiotic relationships.
Variations in spatial concordance reveal relationships among ecosystem
features and how they scale up to form different ecosystems and the
boundaries separating them. To resolve these relationships and their
roles in shaping intra- and inter-ecosystem patterns, we distinguish
areas where spatial concordance levels are relatively uniform and
continuous, from adjacent areas where these collective properties show
pronounced change. The latter correspond with boundaries – some narrow
and relatively discrete, others wider and more diffuse (Cadenasso et al
2003) – between neighbouring ecosystems. Distinguishing adjacent
ecosystems and their common boundaries requires resolution of joint
distinctions in biotic-abiotic composition and structure.
To illustrate these patterns, random point occurrences of biotic and
abiotic variables were independently simulated across a categorical
landscape. The map (left panel) summarizes how these occurrences relate
to one another, showing landscape areas marked by: (1) high biotic and
abiotic; (2) moderately high abiotic, low biotic; (3) moderately high
biotic, low abiotic; and by; (4) low biotic, low abiotic patterns of
spatial concordance. These geographic areas are depicted in plots
showing individual (plots A and B – right panel) and shared (plot AB –
right panel) biotic and abiotic responses (Y axes) along a spatial
gradient (X axis).