Organisms continuously change position by moving or dispersing their propagules. This ubiquitous feature of life generates a wide range of ecological and evolutionary patterns at population margins, including increased dispersal rates, the spread of invasive species, and mismatched geographical and niche limits. My research aims to elucidate how dispersal generates these biogeographical patterns across scales in unison with other biological processes.
My research work combines both theoretical and statistical approaches. I use theory to generate empirically testable insights that unify concepts across seemingly disparate systems. Naturally, my research relies on long walks and pen and paper. Although my research has a strong theoretical bent, I collaborate with empiricists to test theoretical predictions.
Climate Adaptation
As the climate changes, many species are forced to move poleward. However, this poses a risk to species with limited dispersal capacity that are slow to track the climate. Alternatively, a species may adapt to the local climate, which can buffer against species extinction. Therefore, to understand species’ response to climate change, we are building process-based hierarchical Bayesian models to identify the genetic basis of local adaptation. Our statistical method offers two advantages over traditional phenomenological statistical models. First, we provide a rigorous framework for probabilistically estimating genetic variation from noisy, incomplete genetic data (e.g., RAD-seq, pool-seq, and low-coverage genome sequencing). Second, we use a demographic evolutionary model to partition the genetic variation into adaptive and non-adaptive components.
For more, see:
Goel, Nikunj, Christen M. Bossu, Justin J. Van Ee, Erika Zavaleta, Kristen C. Ruegg, and Mevin B. Hooten. “Identifying genomic adaptation to local climate using a mechanistic evolutionary model.” Methods in Ecology and Evolution 16, no. 10 (2025): 2448-2460.
Goel, Nikunj, Christen M. Bossu, Seorim Yi, Timothy M. Brown, Erica CN Robertson, Peri E. Bolton, Ben J. Vernasco et al. “Identifying adaptive variation in spatially structured populations using low-coverage whole-genome sequencing data.” Molecular Biology and Evolution (2026): msag255.
Biological invasions
We face an invasion crisis. Rapid globalization of trade and commerce has pushed many species beyond their native ranges, causing massive economic and biodiversity losses. Therefore, understanding the drivers of the establishment and spread of invasive species is critical to maintaining ecosystem health.
To this end, I am exploring the interplay between population demography and human transportation networks to study two broad questions: how species spread via human dispersal pathways, and why some species become more invasive than others. Answering these questions will advance ecological theory and provide insights for controlling invader populations and mitigating their adverse effects.
For more, see:
Goel, Nikunj, Andrew M. Liebhold, Cleo Bertelsmeier, Mevin B. Hooten, Kirill S. Korolev, and Timothy H. Keitt. “A mechanistic statistical approach to infer invasion characteristics of human‐dispersed species with complex life cycle.” Ecological Monographs 95, no. 1 (2025): e70003.
Spatial sorting
Heritable variation in traits that confer differential lifetime reproductive success can fuel evolutionary change by natural selection. However, at the margins, populations may face another kind of evolutionary pressure: traits that confer dispersal advantage may be overrepresented in newly occupied patches even if those traits do not confer a fitness advantage. This mechanism of directional evolutionary change is called spatial sorting.
Starting from first principles, I am developing the theory of spatial sorting to answer: What drives evolution at population margins? How can we design experiments to measure and interpret trait changes at margins in the broader context of evolutionary theory?
For more, see:
Goel, Nikunj. “Evolution in a moving frame of reference.” bioRxiv (2021): 2021-09.
Goel, Nikunj, Mattheau S. Comerford, Anastasia Bernat, Scott P. Egan, Thomas E. Juenger, and Timothy H. Keitt. “Measuring the Strength of Spatial Sorting.” bioRxiv (2025).
Determinants of range limits
Understanding the mechanisms that limit species’ geographical ranges is a central challenge in biogeography theory. Historically, biogeographers have argued that, at large spatial scales, climate is the primary determinant of species distributions, constraining the broad outlines of populations through niche requirements. As such, source-sink dynamics can be ignored, since they typically operate at species-movement length scales.
Using a reaction-diffusion model that combines local growth and dispersal, we show that species may use sink patches near the bioclimatic limit as stepping stones to occupy faraway sink patches, extending species distributions far beyond the climatic envelope. These stepping-stone dynamics may matter for species with high dispersal and low growth sensitivity—possibly even over large spatial scales.
For more, see my ESA (2020) talk and
Goel, Nikunj, and Timothy H. Keitt. “The mismatch between range and niche limits due to source-sink dynamics can be greater than species mean dispersal distance.” The American Naturalist 200:3, 448-455 (2022).
Distribution and resilience of savanna and forest
Climate change is expected to result in large-scale biome shifts. However, we lack a predictive understanding of which ecological processes govern biome distributions and whether biomes are resilient to global change.
We explore the interplay between fire-vegetation feedback and dispersal at the savanna-forest boundary using reaction-diffusion models, paleoecological data, and remote sensing products. We find that climate, continental-scale source-sink dynamics, and dispersal barriers determine biome limits. Moreover, dispersal can generally allow biomes to recover after perturbations.
For more, see -
Goel, Nikunj, Vishwesha Guttal, Simon A. Levin, and A. Carla Staver. “Dispersal increases the resilience of tropical savanna and forest distributions.” The American Naturalist 195, no. 5 (2020) - 833-850.
Goel, Nikunj, Erik Scott Van Vleck, Julie C. Aleman, and A. Carla Staver. “Dispersal limitation and fire feedbacks maintain mesic savannas in Madagascar.” Ecology, 101(12):e03177 (2020).
Goel, Nikunj, Julie C. Aleman, and A. Carla Staver. “Dispersal limitation and fire feedback maintain mesic savannas in Madagascar: Reply.” Ecology 107, no. 4 (2026): e70332.