Abstract
Plant species migrations, or range shifts, in response to changing climate are one of many interacting factors influencing plant population and community dynamics in an era of global change. Range shifts may cause novel assemblages of competing species because species may respond to changing climate at different rates. Range-expanding species may directly influence resident species through resource competition or indirectly by modifying the local environment both aboveground and belowground. Further, range-expanding plant species can create novel plant-soil feedbacks (PSFs) by altering soil microbial community structure and function and the interactions of resident plant species with microbial symbionts. These changes can have important implications for resident plant population dynamics and their ability to coexist with novel competitors. Here we test the impacts of competitive interactions and plant-soil feedbacks (PSFs) of a range-expanding sagebrush species (Artemisia. rothrockii) on the demography and population growth rates of two resident alpine plant species (Koeleria macrantha and Eriogonum ovalifolium). We use an experimental, multi-year field approach combined with integral projection modeling to determine how PSFs and competition influence species coexistence in both the historic and range expansion zone of A. rothrockii. We find that sagebrush has an overall net negative effect on herbaceous plant demography, primarily due to negative PSFs for plants growing in sagebrush-conditioned soil. However, these negative soil effects are partially buffered via facilitation effects for herbs growing under or nearby sagebrush canopies. In general, population growth rates were more sensitive to survival than other demographic rates, furthermore this sensitivity to survival was higher for herbaceous species in sagebrush soils. Identifying the major drivers of plant population dynamics and species interactions remains an important and unresolved question in ecology. PSFs are a central mechanism influencing plant species interactions, yet the majority of PSF research has made little direct connection between plant population dynamics and PSFs in situ. We believe that utilizing a field-based approach, focusing on multiple components of plant demography, is an important next step in understanding the role of PSFs and species interactions in a rapidly changing world.
Highlights
Changes in climate and land use are creating novel communities of organisms around the globe (Tylianakis et al, 2008; Lurgi et al, 2012)
Inducing negative plant-soil feedbacks (PSFs) is a common mechanism by which non-native invasive plants gain a competitive advantage over resident species (Suding et al, 2013), and we extend this line of reasoning to a native rangeexpanding species
Pairwise contrasts for all demographic rates among plot treatments within each elevation and the probabilities that each treatment is greater than another treatment are listed in Tables S1 and S2
Summary
Changes in climate and land use are creating novel communities of organisms around the globe (Tylianakis et al, 2008; Lurgi et al, 2012). Range shifts are limited by both environmental and biotic filters as well as species dispersal abilities (HilleRisLambers et al, 2012) and many species are unable to migrate (Zhu et al, 2012). Together, these changes in species distributions are “reshuffling” the composition of plant communities, and often have significant community and ecosystem consequences, such as altered nutrient cycling and net primary production (Wardle et al, 2011; Alexander et al, 2016; Manrubia et al, 2019). Assessing the influence of range-expanding competitors on the demography and population dynamics of resident plant species will be critical to predicting whether resident and range-expanding species will successfully coexist
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