  The search for extraterrestrial life hinges on identifying biosignatures,
often focusing on gaseous metabolic byproducts as indicators. However, most
such biosignatures require assuming specific metabolic processes. It is widely
recognized that life on other planets may not resemble that of Earth, but
identifying biosignatures ``agnostic'' to such assumptions has remained a
challenge. Here, we propose a novel approach by considering the generic outcome
of life: the formation of competing ecosystems. We use a minimal model to argue
that the presence of ecosystem-level dynamics, characterized by ecological
interactions and resource competition, may yield biosignatures independent of
specific metabolic activities. Specifically, we propose the emergent
stratification of chemical resources in order of decreasing energy content as a
candidate new biosignature. While likely inaccessible to remote sensing, this
signature could be relevant for sample return missions, or for detection of
ancient signatures of life on Earth itself.
