Amy Lauren Angert

Determining the best seed sources for restoration can be a challenge for practitioners, especially under climate change. The number of variables and the spectrum of potential solutions can be daunting. No singular seed sourcing strategy, “local‐is‐best” or otherwise, is appropriate for all species and restoration efforts. Here we argue that the choice of strategy must be context‐dependent. Species variation in life history, demographics, and genetics influences the extent and drivers of local adaptation, as well as the capacity to adapt to rapid change. Proposed alternative strategies to traditional local sourcing offer a broader range of options to better fit the diversity of species and restoration goals. Although evidence is still somewhat lacking for these new strategies due to the relatively recent impacts of climate change, restoration programs offer an opportunity as experiments to evaluate the risks and benefits of different sourcing strategies. The most proactive response in the face of unprecedented change is to move away from a “one‐size‐fits‐all” approach toward a considered and informed choice of seed source strategy.

Most predictions of whether populations will adapt to warming range edges ignore species interactions. We experimentally tested whether range-edge populations can adapt to warming within a competitive, model plant community ( Lemna spp. and Spirodela polyrhiza duckweeds). Notably, we found that adaptation to warming range edges was possible only when populations evolved with interspecific competitors. Moreover, competitors enabled the evolution of both high-temperature tolerance and increased thermal performance breadth at the range edge, but not at the cooler range core. Our results reveal that competitors accelerate thermal adaptation when there is a shared evolutionary response to both competition and warming. Overall, we highlight the urgency of including community context in predicting future range shifts, showing that antagonistic interactions do not necessarily hinder adaptation to climate deterioration.

Despite the prevailing view that ecological divergence drives speciation, we know little about when or how nascent lineages evolve the ecological differences needed to coexist upon secondary contact. Here, we apply ecological coexistence theory to quantify the potential for coexistence among 126 allopatric lineages of the globally distributed duckweed Spirodela polyrhiza . Using competition experiments simulating secondary contact, we found that rapid accumulation of niche differences stabilized coexistence to permit sympatry among potentially interbreeding lineages. Competition against sister-species Spirodela intermedia further showed that niche differences accumulate more slowly post-speciation, revealing that niche differences enabling coexistence evolve well before timescales at which speciation is complete. Our findings suggest that rapid coexistence may thus contribute to time-lags in speciation, shaping both the origin and maintenance of biodiversity.

Populations that are declining as a result of climate change may need to evolve to persist. Although evolutionary rescue has been demonstrated in theory and in the laboratory, its relevance to natural populations facing climate change remains unknown. Here we link rapid evolution and population dynamics in scarlet monkeyflower, Mimulus cardinalis , during exceptional drought. We leverage whole-genome sequencing across 55 populations to identify climate-associated loci. Simultaneously we track demography and allele frequency change throughout the drought. We establish range-wide population decline during the drought, geographically variable rapid evolution, and variable population recovery that is predictable by standing genetic variation in, and rapid evolution at, climate-associated loci. These findings demonstrate the possibility of evolutionary rescue in the wild, showing that genetic variation at adaptive, but not neutral, loci predicts population recovery.

Premise: While range expansion is hypothesized to be a mechanism for species persistence under climate change, many eco‐evolutionary models describe demographic and genetic processes during expansion that may increase genetic drift, decrease genetic variation, and ultimately decrease relative fitness at the leading edge. These predictions assume dispersal occurs from the low‐density leading edge during colonization, common in post‐glacial expansion at the continental scale (~20,000 years ago), but relatively understudied on contemporary timescales, like alpine glacier recession since the end of the Little Ice Age (~150 years ago). Methods: We use the native alpine plant Erythranthe ( Mimulus ) lewisii to quantify neutral genetic diversity (single nucleotide polymorphisms) and infer signatures of genetic drift across two contemporary instances of range expansion on alpine glacier forelands in Garibaldi Provincial Park, BC, Canada, by testing for the presence of signatures of increased genetic differentiation and decreased genetic variation toward the contemporary range edge relative to the historical range core over space and time. Results: We find weak support for the prediction of increasing genetic differentiation toward the range edge, and no support for decreasing genetic diversity toward the range edge. This suggests dispersal occurring primarily from the leading edge is not characterizing colonization, with the implication that potential relative reductions in range‐edge fitness due to range expansion as predicted by theory are likely not applicable in nature at this spatiotemporal scale. Conclusions: Together, our results suggest that demographic dynamics of colonization following alpine glacier retreat do not result in the loss of genetic diversity over space and time.

Transgenerational plasticity (TGP) could contribute to phenotypic differences as much as allelic variation and within-generation plasticity. Here we use northern and southern populations of Mimulus cardinalis collected prior to and following a severe drought and grew plants in a multi- factorial experiment across three generations to tease apart allelic, TGP, parental effects, and plasticity. Where grand-offspring are likely to experience similar stressors as grandparents, TGP is often considered advantageous; our results show no such advantage. Instead, we find a TGP pattern analogous to local adaptation. Regardless of current environment, grand-offspring exhibit increased fitness when grandparents were exposed to environments that matched historical conditions and reduced fitness when exposed to foreign environments. We also find the evolutionary loss of TGP; prior to drought, northern flowering time and southern pollen viability were significantly affected by grandparent treatment but following four years of drought, grandparent treatment no longer affected these reproductive traits. Lastly, we find that TGP can have a greater effect on fitness than allelic change, parental environment, and within-generation plasticity. Our results indicate an additional way that phenotypes arise, sheds light on the potential for how rapid evolution might occur, and has significant implications for how we design evolutionary ecology experiments.

Summary: Herbaceous plant species have been the focus of extensive, long‐term research into climate change responses, but there has been little effort to synthesize results and predicted outlooks. This primer summarizes research on climate change responses for eight intensively studied herbaceous plant species. We establish generalities across species, examine limitations, and propose a path forward. Climate change has reduced fitness, caused maladaptation, and/or led to population declines in at least part of the range of all six forb species. Plasticity alone is likely not sufficient to allow adjustment to shifting climates. Most model species also have spatially restricted dispersal that may limit genetic and evolutionary rescue. These results are surprising, given that these species are generally widespread, span large elevation ranges, and have substantial genetic and phenotypic variation. The focal species have diverse life histories, reproductive strategies, and habitats, and most are native to North America. Thus, species that are rare, habitat specialists, or endemic to other parts of the world are poorly represented in this review. We encourage researchers to design demographic and field experiments that evaluate plant traits and fitness in contemporary and potential future conditions across the full life cycle, and that consider biotic interactions in climate change responses.

Organisms have evolved diverse adaptive strategies to cope with environmental fluctuations. Slow‐growing long‐lived species tend to exhibit low temporal variability in population growth (strongly buffered demographically), whereas fast‐growing short‐lived species optimize growth in favorable years (weakly buffered). These patterns set up the expectation that differentiation in demographic buffering may reduce disparities in long‐term fitness among species, enhancing the potential for coexistence in variable environments. Yet, this expectation has never been empirically tested for trees. Here, we quantified differences in long‐term population growth among 204 co‐occurring tropical trees spanning a life‐history spectrum from strongly to weakly buffered. We found that interspecific differences in demographic buffering reduced disparities in long‐term population fitness at low densities, highlighting demographic differentiation as a key mechanism promoting coexistence in fluctuating environments. However, simulated increases in temperature, precipitation, and drought variability produced divergent fitness responses among species and exacerbated interspecific fitness disparities. Together, these findings provide a novel perspective on the mechanisms that underpin the astounding tree diversity in tropical forests.

Populations declining due to climate change may need to evolve to persist. While evolutionary rescue has been demonstrated in theory and the lab, its relevance to natural populations facing climate change remains unknown. Here we link rapid evolution and population dynamics in scarlet monkeyflower, Mimulus cardinalis , during an exceptional drought. We leverage whole-genome sequencing across 55 populations to identify climate-associated loci. Simultaneously we track demography and allele frequency change throughout the drought. We establish range-wide population decline during the drought, geographically variable rapid evolution, and variable population recovery that is predictable by standing genetic variation in and rapid evolution at climate-associated loci. These findings demonstrate evolutionary rescue in the wild, showing that genetic variation at adaptive, but not neutral loci, predicts population recovery.