Research
Every species eventually reaches limits to its geographic range, leading to the question of what prevents a species from expanding its range via niche evolution. We examine the effects of quantitative genetic variation, individual fitness, and demographic processes on the dynamics of adaptation to novel conditions such as those beyond range edges or those that have arisen due to climatic changes. Further, we investigate why some species can evolve broad climatic niches and large geographic ranges, while other species are narrowly restricted to a limited range of environments and places. At the community level, we study the effects of changing climate on community composition and climatic niche affinities. Cumulatively, our research provides a comprehensive understanding of constraints to niche evolution within and among populations, species, and communities.
Every species eventually reaches limits to its geographic range, leading to the question of what prevents a species from expanding its range via niche evolution. We examine the effects of quantitative genetic variation, individual fitness, and demographic processes on the dynamics of adaptation to novel conditions such as those beyond range edges or those that have arisen due to climatic changes. Further, we investigate why some species can evolve broad climatic niches and large geographic ranges, while other species are narrowly restricted to a limited range of environments and places. At the community level, we study the effects of changing climate on community composition and climatic niche affinities. Cumulatively, our research provides a comprehensive understanding of constraints to niche evolution within and among populations, species, and communities.
PERSIST: Predicting Evolutionary Rescue of a Species In Space and Time
Adaptive evolution is a key means for populations to persist under environmental change. Yet, whether populations can adapt quickly enough to keep up with the rapid pace of changing climate remains largely unknown, and range limit theory suggests that the probability of evolutionary rescue varies across species’ ranges. To predict evolutionary change, we can 1) estimate the evolutionary response in phenotypes from one generation to the next via the breeder’s equation, or 2) directly predict the rate of adaptation via the fundamental theorem of natural selection.
As part of an NSF-funded Bridging Ecology and Evolution project with co-PIs Chris Muir (U of Hawaiʻi), Lluvia Flores-Rentería (San Diego State U), Jeff Diez (U of Oregon), and Jay Sexton (UC Merced), we will integrate these two evolutionary approaches with population ecology models by investigating whether evolution can rescue populations from decline when they encounter rapid environmental change. We will address the following aims about how the probability of evolutionary rescue varies across a species’ range:
To address these objectives, we will perform a resurrection study comparing ancestors and descendants derived from seed collected before and after a period of severe drought and heat in western North America. We will transplant seedlings from leading-edge, central, and trailing-edge populations of the perennial herb, Mimulus cardinalis, into three common gardens at differing range positions and quantify natural selection on traits, additive genetic variances for traits and fitness, and differences in population growth rates and traits between ancestors and descendants.
Related publications
Adaptive evolution is a key means for populations to persist under environmental change. Yet, whether populations can adapt quickly enough to keep up with the rapid pace of changing climate remains largely unknown, and range limit theory suggests that the probability of evolutionary rescue varies across species’ ranges. To predict evolutionary change, we can 1) estimate the evolutionary response in phenotypes from one generation to the next via the breeder’s equation, or 2) directly predict the rate of adaptation via the fundamental theorem of natural selection.
As part of an NSF-funded Bridging Ecology and Evolution project with co-PIs Chris Muir (U of Hawaiʻi), Lluvia Flores-Rentería (San Diego State U), Jeff Diez (U of Oregon), and Jay Sexton (UC Merced), we will integrate these two evolutionary approaches with population ecology models by investigating whether evolution can rescue populations from decline when they encounter rapid environmental change. We will address the following aims about how the probability of evolutionary rescue varies across a species’ range:
- Quantify natural selection in contrasting environments by linking traits, fitness components, and population growth,
- Assess the extent to which the breeder’s equation predicts realized rates of trait evolution across the species’ range, and
- Determine where in the species’ range evolutionary rescue is most likely based on standing genetic variation for fitness.
To address these objectives, we will perform a resurrection study comparing ancestors and descendants derived from seed collected before and after a period of severe drought and heat in western North America. We will transplant seedlings from leading-edge, central, and trailing-edge populations of the perennial herb, Mimulus cardinalis, into three common gardens at differing range positions and quantify natural selection on traits, additive genetic variances for traits and fitness, and differences in population growth rates and traits between ancestors and descendants.
Related publications
Population persistence in a variable world
Evaluating how climate alters demographic rates is crucial for understanding current population dynamics and predicting population trajectories and species distributions in response to climate change. We are collaborating with Amy Angert (UBC) on an NSF LTREB project with the goal of advancing our understanding of how spatiotemporal variation in climatic drivers affects population stability and persistence. We have the following aims over the next ten years:
To address these objectives, we will build a demographic data set of unparalleled scope using the scarlet monkeyflower (Mimulus cardinalis), a widespread perennial herb that spans a broad latitudinal and climatic gradient in western North America. This species is an ideal model for understanding population persistence and adaptation in a rapidly changing climate because we can uniquely synthesize extensive observational and experimental datasets. Our combination of large-scale and long-term demographic observations (21 populations over 10-21 years), experimental work in greenhouse and field common gardens (from the PERSIST project above), and genomic studies makes this a particularly powerful system for dissecting how historical and contemporary climate adaptation shape distribution and abundance.
Evaluating how climate alters demographic rates is crucial for understanding current population dynamics and predicting population trajectories and species distributions in response to climate change. We are collaborating with Amy Angert (UBC) on an NSF LTREB project with the goal of advancing our understanding of how spatiotemporal variation in climatic drivers affects population stability and persistence. We have the following aims over the next ten years:
- Test when responses of vital rates (e.g., survival, growth, fecundity) to temporal environmental variation promote climate buffering or tracking, and assess how these mechanisms vary across spatial gradients in life history and climate.
- Evaluate how local adaptation of life history and other traits modifies range-wide inferences of population dynamics
- Assess the contributions of phenotypic plasticity and genetic adaptation to demographic stability following extreme events.
To address these objectives, we will build a demographic data set of unparalleled scope using the scarlet monkeyflower (Mimulus cardinalis), a widespread perennial herb that spans a broad latitudinal and climatic gradient in western North America. This species is an ideal model for understanding population persistence and adaptation in a rapidly changing climate because we can uniquely synthesize extensive observational and experimental datasets. Our combination of large-scale and long-term demographic observations (21 populations over 10-21 years), experimental work in greenhouse and field common gardens (from the PERSIST project above), and genomic studies makes this a particularly powerful system for dissecting how historical and contemporary climate adaptation shape distribution and abundance.
Integrating evolutionary and migratory potential of Chamaecrista fasciculata into forecasts of range-wide population dynamics under climate change
Populations across species' ranges likely vary in their migratory and adaptive potential under climate change, yet we lack a comprehensive understanding of which populations are most vulnerable to climate change because forecasts of range shifts often fail to account for population-level variation in plasticity and genetic variation. We ask: to what extent can we improve mechanistic predictions of range dynamics under climate change by modelling genomic variation, gene flow rates, plasticity, and additive genetic variances in traits and fitness?
This NSF-funded Organismal Response to Climate Change project involves a highly collaborative team of researchers, including Jill Anderson, Megan DeMarche, (University of Georgia), Susana Wadgymar (Davidson College), Emily Josephs (Michigan State University), and Jenny Cruse-Sanders (State Botanical Garden of Georgia). We are combining approaches from evolutionary biology, field ecology, and population genomics to forecast range-wide dynamics under climate change in a native legume (Chamaecrista fasciculata) that is broadly distributed across central and eastern North America to address the following aims:
Our work will provide a robust framework for predictions of range-wide responses to climate change in systems that are less amenable to manipulation. We will collaborate with conservation practitioners in the Georgia Plant Conservation Alliance and Southeastern Grasslands Initiative to produce risk assessment tools that project range dynamics under climate change for endangered plant species.
Related publications
Populations across species' ranges likely vary in their migratory and adaptive potential under climate change, yet we lack a comprehensive understanding of which populations are most vulnerable to climate change because forecasts of range shifts often fail to account for population-level variation in plasticity and genetic variation. We ask: to what extent can we improve mechanistic predictions of range dynamics under climate change by modelling genomic variation, gene flow rates, plasticity, and additive genetic variances in traits and fitness?
This NSF-funded Organismal Response to Climate Change project involves a highly collaborative team of researchers, including Jill Anderson, Megan DeMarche, (University of Georgia), Susana Wadgymar (Davidson College), Emily Josephs (Michigan State University), and Jenny Cruse-Sanders (State Botanical Garden of Georgia). We are combining approaches from evolutionary biology, field ecology, and population genomics to forecast range-wide dynamics under climate change in a native legume (Chamaecrista fasciculata) that is broadly distributed across central and eastern North America to address the following aims:
- Examine the migratory potential of populations under climate change using population genomic estimators of historical gene flow.
- Evaluate adaptive potential by exposing paternal half-sib families from 12 populations to contemporary climates and simulated climate change in common gardens across the range (including a garden near Raleigh, NC!).
- Forecast eco-evolutionary dynamics under climate change using models that differ in the degree to which they incorporate data on species occurrence, additive genetic variance in fitness in response to climate, trait expression, sequence variation, and gene flow.
Our work will provide a robust framework for predictions of range-wide responses to climate change in systems that are less amenable to manipulation. We will collaborate with conservation practitioners in the Georgia Plant Conservation Alliance and Southeastern Grasslands Initiative to produce risk assessment tools that project range dynamics under climate change for endangered plant species.
Related publications
Effects of changing climate on community assembly
If climate is important in structuring plant communities on mountaintops, then climate change should result in losses of cool-adapted species and increases of warm-adapted species in these communities. Through collaborating with the non-profit organization GLORIA (Global Observation Research Initiative in Alpine Environments) Great Basin, we contribute to long-term monitoring of 29 peaks in 8 target regions in California and Nevada. Our goal is to examine the effects of climate change on alpine plant communities as part of a broader international effort using the same protocol on mountain peaks across the globe. As a first step to understanding how climate structures alpine plant communities in this region, we studied how communities are distributed across multiple scales of climatic complexity ranging from a single elevation of one peak to an elevation gradient encompassing the entire range of the White Mountains in California. We found that the presence and abundance of cool, wet-adapted species increased strongly with elevation across the entire mountain range, but these relationships were weaker within any given peak (Smithers & Oldfather et al. 2020). These findings suggest that climate was important in structuring communities at broad spatial scales, but that micro-climatic and non-climatic factors were more likely to shape community assembly at finer scales. While species might move upslope in response to climate change at broad spatial scales, pockets of suitable habitat at finer spatial scales may buffer plants under changing climate.
Related publications
If climate is important in structuring plant communities on mountaintops, then climate change should result in losses of cool-adapted species and increases of warm-adapted species in these communities. Through collaborating with the non-profit organization GLORIA (Global Observation Research Initiative in Alpine Environments) Great Basin, we contribute to long-term monitoring of 29 peaks in 8 target regions in California and Nevada. Our goal is to examine the effects of climate change on alpine plant communities as part of a broader international effort using the same protocol on mountain peaks across the globe. As a first step to understanding how climate structures alpine plant communities in this region, we studied how communities are distributed across multiple scales of climatic complexity ranging from a single elevation of one peak to an elevation gradient encompassing the entire range of the White Mountains in California. We found that the presence and abundance of cool, wet-adapted species increased strongly with elevation across the entire mountain range, but these relationships were weaker within any given peak (Smithers & Oldfather et al. 2020). These findings suggest that climate was important in structuring communities at broad spatial scales, but that micro-climatic and non-climatic factors were more likely to shape community assembly at finer scales. While species might move upslope in response to climate change at broad spatial scales, pockets of suitable habitat at finer spatial scales may buffer plants under changing climate.
Related publications
Climatic niche width and geographic range size
Closely related species often differ dramatically in their geographic range sizes, with implications for extinction risk. One key hypothesis about variation in geographic range size among species is that species with larger geographic ranges have evolved broader environmental tolerances than those with small ranges, perhaps due to reduced adaptive potential in narrowly distributed species. Previously, we experimentally showed that geographically widespread species have broader thermal tolerances than narrowly distributed species. Moreover, species with broader thermal tolerance experience greater variation in temperature across their ranges and have higher genetic variation for thermal tolerance, illustrating how both extrinsic and intrinsic factors shape variation in environmental tolerance among species (Sheth & Angert 2014). In a study using ecological niche models of all western North American monkeyflower species, climatic niche width was a strong predictor of geographic range size (Sheth et al. 2014), suggesting that species with narrow niches and small geographic ranges may be doubly at risk of extinction. In collaboration with Amy Angert and Naia Morueta-Holme, we recently conducted a meta-analysis highlighting the paucity of plant studies that test the relative importance of multiple hypotheses in explaining variation in geographic range size (Sheth et al. 2020). We are excited to develop studies that fill this knowledge gap, and tackle questions about how niche breadth is partitioned among individuals, populations, and species.
Related publications
Closely related species often differ dramatically in their geographic range sizes, with implications for extinction risk. One key hypothesis about variation in geographic range size among species is that species with larger geographic ranges have evolved broader environmental tolerances than those with small ranges, perhaps due to reduced adaptive potential in narrowly distributed species. Previously, we experimentally showed that geographically widespread species have broader thermal tolerances than narrowly distributed species. Moreover, species with broader thermal tolerance experience greater variation in temperature across their ranges and have higher genetic variation for thermal tolerance, illustrating how both extrinsic and intrinsic factors shape variation in environmental tolerance among species (Sheth & Angert 2014). In a study using ecological niche models of all western North American monkeyflower species, climatic niche width was a strong predictor of geographic range size (Sheth et al. 2014), suggesting that species with narrow niches and small geographic ranges may be doubly at risk of extinction. In collaboration with Amy Angert and Naia Morueta-Holme, we recently conducted a meta-analysis highlighting the paucity of plant studies that test the relative importance of multiple hypotheses in explaining variation in geographic range size (Sheth et al. 2020). We are excited to develop studies that fill this knowledge gap, and tackle questions about how niche breadth is partitioned among individuals, populations, and species.
Related publications