Warming and shifting phenology accelerate an invasive plant life cycle

Numerous studies have documented changes in the seasonal timing of organisms’ growth and reproduction in response to climate warming. These changes correlate with documented changes in species’ abundance, but mechanisms linking these trends remain elusive. We investigated the joint demographic effects of advanced reproductive phenology and warming on a globally invasive plant (Carduus nutans) in a field experiment, documenting a substantial shift toward completion of the life cycle at younger ages. Demographic modeling projected 71% of warmed individuals flower as annuals, compared to 61% under current conditions. As this species only reproduces once, this represents a major acceleration of the life cycle. We project a 15% increase in this invader’s population growth rate. We show that rising temperatures accelerate this invasive species’ population growth by increasing the average size of reproducing individuals; increasing the proportion of individuals that survive to reproduce; and increasing the fraction that reproduce as annuals. Major increases in population growth in this, and potentially many other, invasive species will threaten food security and require careful planning to avoid significant environmental and economic impacts.