Resolving the context-dependency of local heterogeneity-diversity relationships across rocky reefs worldwide

Environmental heterogeneity is widely thought to promote biodiversity, yet
its variable effects limit its predictive power. This variability can be
better understood by considering key mediating factors: different forms of
local heterogeneity, organismal groups and their associated traits, and
the broader environmental context (e.g., latitude, substrate type). To
address these factors, we analysed 144 studies (24,412 data points and
2,815 effects) from rocky reefs worldwide. Heterogeneity was defined as
spatial variability in an area, and heterogeneity metrics were grouped
into facets such as three-dimensional structure (e.g., substrate
rugosity), complexity (e.g., fractal dimension), and feature variability
(e.g., mussel size classes). All facets promoted biodiversity, but effects
were context-dependent, with three-dimensional structures having the
strongest impact, likely due to increased niche provision and substrate
area. Responses also varied across organismal groups, with small-bodied
and mobile species benefiting most. Additionally, heterogeneity reduced
grazing and enhanced recruitment, helping promote biodiversity. Effects
were strongest on biogenic substrates, at lower latitudes, and in more
stressful intertidal zones. Overall, the influence of local heterogeneity
would depend on how it is generated and measured, organisms’ traits, and
prevailing environmental conditions. These insights inform the development
of a conceptual model predicting heterogeneity’s context-dependent effects
on biodiversity across systems.