Abstract
One of the strongest biological impacts of climate change has been the movement of species poleward and upward in elevation. Yet, what is not clear is the extent to which the spatial distribution of locally adapted lineages and ecologically important traits may also shift with continued climate change. Here, we take advantage of a transplant experiment mimicking up‐slope seed dispersal for a suite of ecologically diverse populations of yellow monkeyflower (Mimulus guttatus sensu lato) into a high‐elevation common garden during an extreme drought period in the Sierra Nevada mountains, California, USA. We use a demographic approach to quantify fitness and test for selection on life history traits in local versus lower‐elevation populations and in normal versus drought years to test the potential for up‐slope migration and phenotypic selection to alter the distribution of key life history traits in montane environments. We find that lower‐elevation populations tend to outperform local populations, confirming the potential for up‐slope migration. Although selection generally favored some local montane traits, including larger flowers and larger stem size at flowering, drought conditions tended to select for earlier flowering typical of lower‐elevation genotypes. Taken together, this suggests that monkeyflower lineages moving upward in elevation could experience selection for novel trait combinations, particularly under warmer and drier conditions that are predicted to occur with continued climate change.
Highlights
As climate change progresses, many species are expected to respond by tracking their historical climate envelopes through space
We found that selection generally favored some perennial traits, including larger flowers and larger stem size at flowering, but that drought condi‐ tions selected for earlier flowering in all but the earliest‐flowering fast‐cycling annuals
This suggests that upwardly migrat‐ ing lineages in this system could experience selection for novel trait combinations in the warmer and drier conditions forecasted to occur with continued climate change (Reich et al, 2018)
Summary
Many species are expected to respond by tracking their historical climate envelopes through space. For exam‐ ple, the distribution of vernalization requirements and flowering time in Arabidopsis is predicted to shift with climate change due to differing climatic tolerances among genotypes, with larger propor‐ tions of the species' range predicted to flower earlier and without requiring vernalization (Banta et al, 2012; Marcer, Mendez‐Vigo, Alonso‐Blanco, & Pico, 2016). We experimentally mimic seed dis‐ persal of lower‐elevation populations, as well as local high‐elevation populations, into a high‐elevation montane habitat to compare the pattern of selection on key life history traits among populations and between normal versus drought conditions We considered both di‐ rect effects of trait variation on vital rates, and population growth, and indirect effects through correlated traits. We predicted that selection might be weaker or even in an opposing direction under severe drought conditions
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