Integrating biotic interactions in niche analyses unravels patterns of community composition in clownfishes

Mutualistic interactions play a fundamental role in shaping species
distributions, driving niche differentiation, and structuring communities.
Yet their influence on realized niches and patterns of coexistence remains
poorly understood. In clownfishes, mutualism with sea anemones underpins
their biogeography and ecological success, with species classified as
generalists or specialists according to their host specificity. However,
the extent to which host availability constrains or expands clownfish
niches has remained unclear. Here we used ecological niche models (ENMs)
across the Indo-Pacific to examine how host sea anemones shape clownfish
realized niches and community composition. We integrated occurrence data
with climatic and habitat predictors and refined estimates by
incorporating host niches, quantifying changes in niche breadth, position,
and overlap. We further developed a multilayered framework to account for
host use within niche quantification, allowing us to assess patterns of
resource overlap in communities spanning generalist–specialist dynamics.
Our results reveal that mutualistic associations strongly shape clownfish
realized niches, with specialists experiencing greater niche constraints
than generalists due to their reliance on a limited set of hosts. Host
availability emerges as a key driver of community structure, producing
high ecological niche overlap among species that is modulated by host
partitioning. This host-mediated differentiation facilitates coexistence
by reducing resource overlap, with generalist–specialist contrasts playing
a central role in sustaining clownfish biodiversity. Our study highlights
how biotic interactions mediate species ecological niches and shape
community assembly in an iconic mutualistic system. Beyond clownfishes,
our framework offers a transferable approach to incorporate interacting
species into ENMs, improving ecological interpretations and informing
conservation efforts in biodiversity hotspots and other mutualistic
systems.