Climate change poses a threat to biodiversity, and it is unclear whether species can adapt to or tolerate new conditions, or migrate to areas with suitable habitats. Reconstructions of range shifts that occurred in response to environmental changes since the last glacial maximum (LGM) from species distribution models (SDMs) can provide useful data to inform conservation efforts. However, different SDM algorithms and climate reconstructions often produce contrasting patterns, and validation methods typically focus on accuracy in recreating current distributions, limiting their relevance for assessing predictions to the past or future. We modeled historically suitable habitat for the threatened North American tree green ash
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Fraxinus pennsylvanica using 24 SDMs built using two climate models, three calibration regions, and four modeling algorithms. We evaluated the SDMs using contemporary data with spatial block cross‐validation and compared the relative support for alternative models using a novel integrative method based on coupled demographic‐genetic simulations. We simulated genomic datasets using habitat suitability of each of the 24 SDMs in a spatially‐explicit model. Approximate Bayesian computation (ABC) was then used to evaluate the support for alternative SDMs through comparisons to an empirical population genomic dataset. Models had very similar performance when assessed with contemporary occurrences using spatial cross‐validation, but ABC model selection analyses consistently supported SDMs based on the CCSM climate model, an intermediate calibration extent, and the generalized linear modeling algorithm. Finally, we projected the future range of green ash under four climate change scenarios. Future projections using the SDMs selected via ABC suggest only minor shifts in suitable habitat for this species, while some of those that were rejected predicted dramatic changes. Our results highlight the different inferences that may result from the application of alternative distribution modeling algorithms and provide a novel approach for selecting among a set of competing SDMs with independent data.Free, publicly-accessible full text available July 2, 2025 -
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Abstract Local adaptation is a fundamental phenomenon in evolutionary biology, with relevance to formation of ecotypes, and ultimately new species, and application to restoration and species’ response to climate change. Reciprocal transplant gardens, a common garden in which ecotypes are planted among home and away habitats, are the gold standard to detect local adaptation in populations.
This review focuses on reciprocal transplant gardens to detect local adaptation, especially in grassland species beginning with early seminal studies of grass ecotypes. Fast forward more than half a century, reciprocal gardens have moved into the genomic era, in which the genetic underpinnings of ecotypic variation can now be uncovered. Opportunities to combine genomic and reciprocal garden approaches offer great potential to shed light on genetic and environmental control of phenotypic variation. Our decadal study of adaptation in a dominant grass across the precipitation gradient of the US Great Plains combined genomic approaches and realistic community settings to shed light on controls over phenotype.
Common gardens are not without limitations and challenges. A survey of recent studies indicated the modal study uses a tree species, three source sites and one growing site, focuses on one species growing in a monoculture, lasts 3 years, and does not use other experimental manipulations and rarely employs population genetic tools. Reciprocal transplant gardens are even more uncommon, accounting for only 39% of the studies in the literature survey with the rest occurring at a single common site. Reciprocal transplant gardens offer powerful windows into local adaptation when (a) placed across wide environmental gradients to encompass the species’ range; (b) conducted across timespans adequate for detecting responses; (c) employing selection studies among competing ecotypes in community settings and (d) combined with measurements of form and function which ultimately determine success in home and away environments.
Synthesis . Reciprocal transplant gardens have been one of the foundations in evolutionary biology for the study of adaptation for the last century, and even longer in Europe. Moving forward, reciprocal gardens of foundational non‐model species, combined with genomic analyses and incorporation of biotic factors, have the potential to further revolutionize evolutionary biology. These field experiments will help to predict and model response to climate change and inform restoration practices. -
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PREMISE A disjunct distribution, where a species’ geographic range is discontinuous, can occur through vicariance or long‐distance dispersal. Approximately 75 North American plant species exhibit a ~650 km disjunction between the Ozark and Appalachian regions. This disjunction is attributed to biogeographic forces including: (1) Eocene–Oligocene vicariance by the formation of the Mississippi embayment; (2) Pleistocene vicariance from interglacial flooding; (3) post‐Pleistocene northward colonization from separate glacial refugia; (4) Hypsithermal vicariance due to climate fluctuations; and (5) recent long‐distance dispersal. We investigated which of these pathways most likely gave rise to the Appalachian‐Ozark disjunction in
Delphinium exaltatum .METHODS We genotyped populations of
D. exaltatum from five Ozark and seven Appalachian localities, analyzed genetic structure, tested the order and timing of divergences usingDIYABC , and conducted niche reconstructions up to 21,000 years before present (YBP).RESULTS Populations fell into five main genetic clusters, i.e., a group in the central Appalachians, and four “lowland” groups. DIYABC analyses showed the central Appalachian and lowland lineages diverging 11,300 to17,000 YBP, and the lowland groups diverging 6800 to 10,900 YBP. Niche reconstructions showed that suitable climate for the central Appalachian lineage experienced large spatial discontinuity starting 14,000 YBP, such that divergence and persistence before this period is less plausible than divergence thereafter.
CONCLUSIONS Our results did not fully support any of the original hypotheses. Rather, the oldest divergence likely occurred after 13,500 YBP through expansion into newly opened habitat in the Appalachians. The Appalachian‐Ozark disjunction likely resulted from northward dispersal of the lowland lineage as climate warmed during the Holocene.
