Strong patterns of intraspecific variation and local adaptation in Great Basin plants revealed through a review of 75 years of experiments

Abstract

Variation in natural selection across heterogeneous landscapes often produces (a) among‐population differences in phenotypic traits, (b) trait‐by‐environment associations, and (c) higher fitness of local populations. Using a broad literature review of common garden studies published between 1941 and 2017, we documented the commonness of these three signatures in plants native to North America's Great Basin, an area of extensive restoration and revegetation efforts, and asked which traits and environmental variables were involved. We also asked, independent of geographic distance, whether populations from more similar environments had more similar traits. From 327 experiments testing 121 taxa in 170 studies, we found 95.1% of 305 experiments reported among‐population differences, and 81.4% of 161 experiments reported trait‐by‐environment associations. Locals showed greater survival in 67% of 24 reciprocal experiments that reported survival, and higher fitness in 90% of 10 reciprocal experiments that reported reproductive output. A meta‐analysis on a subset of studies found that variation in eight commonly measured traits was associated with mean annual precipitation and mean annual temperature at the source location, with notably strong relationships for flowering phenology, leaf size, and survival, among others. Although the Great Basin is sometimes perceived as a region of homogeneous ecosystems, our results demonstrate widespread habitat‐related population differentiation and local adaptation. Locally sourced plants likely harbor adaptations at rates and magnitudes that are immediately relevant to restoration success, and our results suggest that certain key traits and environmental variables should be prioritized in future assessments of plants in this region.

Seed source regions drive fitness differences in invasive macrophytes

“…The observed variability of traits between source populations indicates phenotypic differentiation that could be adaptive. Our results are similar to those in a recent meta‐analysis indicating that locally sourced plants present higher survival and reproductive fitness in their home environment, harboring adaptations that facilitate their establishment success in these environmental conditions (Baughman et al., 2019). The species response to environmental conditions that differ from that of their home environment can be explored through the lens of other adaptive and non‐adaptive mechanisms that were not tested in the present study.…”

Mixing source populations increases genetic diversity of restored rare plant populations

“…It is promising that mixing multiple source populations can improve fitness, diversity, and conservation outcomes of reintroduced populations of rare species with no measurable outbreeding effects (Rick et al ). Mixing populations over areas of similar adaptation, such as within an ecoregion (Ward et al ; Miller et al ; Gustafson et al ) or sub‐portion of an ecoregion (Baughman et al ), or a provisional seed zone (Bower et al ), can increase the diversity of the plant materials available for restoration while minimizing risks of maladaptation.…”

Assessment of population genetics and climatic variability can refine climate‐informed seed transfer guidelines

“…reduced gene flow) factors to decrease their effectiveness—these factors would be pronounced in topographically and environmentally heterogeneous landscapes such as the western United States (e.g. Baughman et al ).…”