Biotic interactions and range limits

What limits species’ distributions? Historically, we’ve largely thought about this question in terms of climate. However, most species are likely to be distributed over complex environmental gradients comprising changes in multiple abiotic and biotic variables. Transplant experiments, ideally combined with manipulations of putatively important environmental variables, are the most powerful method to test the relative influence of these variables on the location of the species’ range limit. In my dissertation, I used a variety of greenhouse and field experiments with the California native plant Clarkia xantiana ssp. xantiana (Onagraceae) to untangle complex environmental gradients and quantify the relative influence of both biotic and abiotic factors on plant lifetime fitness inside and outside the subspecies’ geographic range limit.

Relevant papers:

  • Benning, JW, Eckhart VM, Geber MA, and Moeller DA. 2019. Biotic interactions contribute to the geographic range of an annual plant: herbivory and phenology mediate fitness beyond a range margin. American Naturalist, 193:786-797. pdf
  • Benning, JW and Moeller DA. 2019. Maladaptation beyond a geographic range limit driven by antagonistic and mutualistic biotic interactions across an abiotic gradient. Evolution, 73:2044-2059. pdf
  • Benning, JW and Moeller DA. 2021. Microbes, mutualism, and range margins: testing the fitness consequences of soil microbial communities across and beyond a native plant’s range. New Phytologist, 229:2886-2900. pdf
  • Benning, JW and Moeller DA. 2021. Plant-soil interactions limit lifetime fitness outside a native plant’s geographic range margin. Ecology, 102:e03254. pdf

Testing and developing range limit theory

Range limits theory has highlighted that the shape of environmental gradients and the magnitude of dispersal play key roles in the probability of range expansion and the formation of stable range limits. However, we lack empirical tests of recent, and even foundational range limit theory. Furthermore, existing models do not account for temporal environmental variation, a ubiquitous feature of natural environments. Under the mentorship of Dr. Christopher Weiss-Lehman (Univ. of Wyoming) and Dr. Ruth Hufbauer (Colorado State Univ.), I’m using experimental evolution, genomic analyses, and novel models to test key predictions of range limit theory, further our understanding of the genetic basis of range dynamics, and build a comprehensive conceptual model of how spatio-temporal environmental variation interacts with dispersal to influence species range boundaries. This work is supported by an NSF Postdoctoral Fellowship.

Relevant papers:

  • Benning, JW, Hufbauer, RA, and Weiss-Lehman, C. 2021. Increasing temporal variance leads to stable species range limits. Proceedings of the Royal Society B. 289:20220202. pdf

Tempo and mode of adaptation

What factors promote versus limit adaptation? General answers to this question are hard to come by — even for a well-studied process like gene flow, it is still difficult to predict when migration of alleles will encourage versus constrain adaptive evolution. Questions like this are not only of fundamental interest, but also have wide ranging implications for conservation and management of natural populations. I’m exploring themes related to the pace, pattern, and mechanisms of adaptation in several ongoing projects, including:

  • Why do populations vary in their evolutionary responses to the same environmental perturbation? We used a resurrection approach, paired with quantitative genetic and long-term demographic data, to address this question in natural populations of Clarkia xantiana that recently experienced an extreme drought. You can see some teaser results in the figure at right. Collab with Dave Moeller and stellar UMN undergrad Lex Faulkner.
  • How does spatial and temporal environmental heterogeneity influence adaptation to novel environments? Along with modeling approaches, we’re using experiments to document adaptation in real time among flour beetle populations experiencing different patterns of spatio-temporal environmental variation. Collab with Topher Weiss-Lehman and awesome UW undergrads Alex Kissonergis and Annaliese Bronner.

Relevant papers:

  • Benning JW, Faulkner A^, and Moeller DA. 2022. Rapid evolution in response to climate-change-induced drought and its demographic and genetic controls. In revision. preprint. ^ undergraduate mentee
  • Gorton AJ*, Benning JW*, Tiffin PL, and Moeller DA. 2022. The spatial scale of adaptation in a native annual plant and its implications for responses to climate change. Evolution, in press. preprint. * equal contribution

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