Article

Rarity as a life-history correlate in Dudleya (Crassulaceae).

The nine Dudleya species that occur around the Santa Monica Mountains were studied. Five are 6 rare narrow endemics, one is rare with an intermediate range, and three are common with broader ranges. 7 Life-history traits were measured in wild populations and in plants grown from wild collected seeds in 8 common gardens. Rare species grew to a smaller size and reproduced earlier than common species. The 9 small body size of the rare species was correlated with smaller reproductive outputs compared to the larger10 bodied common species. The rare species also tended to have lower seedling survival. Reproductive output 11 and survival affect population size, persistence, and dispersal, all of which affect species distributions. The 12 habitat requirements of the study species varied in terms of geology, mesoclimate, and co-occurring 13 vegetation, with the rare species being more restricted than the common species. To further understand how 14 habitat plays a role in limiting species distributions, the nine species were grown in an inland garden and in 15 a coastal garden. In the inland garden, plants of all species were smaller in size than in the coastal garden. 16 Moreover, the growth disparity between plants in the two gardens was greatest for the rare species. The rare 17 species have a lower tolerance for hot dry conditions compared to the common species. In the Santa 18 Monica Mountains region, the habitat conditions required by the rare species are not as prevalent as those 19 of the common species. Differences in life-histories constrained by tradeoffs affect the prevalence of the 20 species, as well as specialization on rare habitats. Such differences in rarity become grist for species 21 selection at the scale of macroevolution.

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