Data from: Drought resistance drives population temporal stability of annuals in drylands

Understanding the mechanisms determining population temporal stability is
key to explaining species diversity and coexistence, and to maintaining
multiple ecosystem functions over time. Functional traits should offer
mechanistic insights into the drivers of stability, but the generalization
of a trait–stability relationship is lacking. Our overarching hypothesis
is that traits predicted by bet-hedging theory to reduce variability in
population size, i.e., delayed germination and/or bigger seeds and/or
traits associated with higher drought resistance (high intrinsic water-use
efficiency, high turgor loss point, slow relative growth rate, high leaf
dry matter content, low SLA), lead to higher population temporal
stability. We linked these traits to the year-to-year variation in winter
annuals’ abundance of 178 populations (66 species) over 13 years. We
tested the generality of these relationships in a biodiversity hotspot
along a gradient of rainfall mean, variability, and unpredictability,
defining three climates (Mediterranean, semi-arid, arid), considering also
the spatial micro-heterogeneity defined by perennial shrubs. Away from
shrubs, higher drought resistance was consistently associated with higher
population stability in all climates. Under the shrubs, however, this
relationship disappeared or was reversed. Delayed germination predicted
higher stability in the arid open habitat only. Our results unveiled
diverse drought resistance strategies within annuals in drylands, and
elucidated their influence on population temporal stability. Our results
challenge the long-standing assumption that delayed germination is the
most important bet-hedging trait for annuals in drylands. Finally, we
highlight the crucial need of including local microhabitat conditions in
the assessment of population stability. Synthesis: The detection
of drought resistance as a key driver of population temporal stability
represents a significant advancement in evolutionary theory, trait-based
ecology, and our understanding of community stability.