Ecological communities are composed of species spanning orders of magnitude in abundance. A natural and widespread assumption is that the rarest species are the most vulnerable to extinction. But is abundance alone sufficient to assess vulnerability? In this talk, I present a series of interconnected results showing that a species' vulnerability depends critically on the diversity of its dispersal strategies, the structure of its competitive interactions, and the heterogeneity of the landscape it inhabits.
Starting from microscopic individual-level dynamics, macroscopic metapopulation and metacommunity models are derived that naturally incorporate dispersal network structure and environmental heterogeneity. Spatially varying environments can support multispecies coexistence in competitive metacommunities through the spontaneous emergence of spatial niches, even among species that would exclude each other locally. Building on this, a single quantity, the competitive balance, integrates dispersal diversity and interspecific interactions to assess a focal species' vulnerability to extinction. This metric reveals that greater heterogeneity in dispersal strategies can reduce vulnerability for a rare species in unfavorable competitive contexts. These predictions are tested against datasets from two tropical and one temperate forests, where effective per-species dispersal parameters are estimated directly from data, yielding strong agreement with theoretical expectations. Together, these results show that vulnerability is not a single-species property but an emergent community-level quantity, and this requires understanding the ecological context in which a species is embedded.