Warm, wet regions favor novel invaders, while cold or dry regions favor look‑alikes

What is it about?

Why do some introduced plants become invasive while others fail? Since Darwin, invasion biology has wrestled with a puzzle known as “Darwin’s Naturalization Conundrum”: invaders sometimes succeed by resembling native species (which presumably makes them pre-adapted to local conditions), yet other times by being different (which may enable them to avoid competition or exploit underused niches). We tested whether climate predicts which pathway dominates. Using millions of observations from herbarium specimens and community science records, we modeled the geographic distribution, flowering time (phenology), and evolutionary relatedness (phylogeny) of 2,810 plant species across the conterminous United States, comparing invasive plants to the native communities they co-occur with. We asked: do invaders tend to match native timing and ancestry, or diverge from them, and do these patterns vary along climate gradients?

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Photo by Allan Sharp on Unsplash

Photo by Allan Sharp on Unsplash

Why is it important?

Invasions are a major driver of biodiversity loss, but “what makes an invader successful” varies widely across places. Our results show that this variation is systematic and strongly aligned with climate. In warm, humid regions, invaders are typically more distinct: they often flower earlier, overlap less in flowering with natives, and are more distantly related to the native flora, consistent with success via reduced competition or use of open seasonal niches. In cold or dry regions, invaders are typically more similar: flowering schedules align more closely with natives, and invaders are more closely related, consistent with stronger climatic filtering favoring preadapted strategies.Across nearly all climates, invaders also show longer flowering durations, suggesting extended reproduction is a broadly effective invasion strategy. Overall, our results indicate Darwin’s Naturalization Conundrum is not a paradox but a predictable continuum, highlighting climate as a key axis for anticipating invasion dynamics.

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