Decades of biogeographic theory suggests that a species geographic range is limited by abiotic conditions towards its high elevation limit and antagonistic biotic interactions towards its low elevation range limit. While many studies have supported the high-elevation range limit prediction, rigorous tests of the low-elevation and antagonistic interaction prediction have been limited. With this work, we tested if three alpine grass species are restricted to the top of the West Elk Mountains, Colorado, USA, in part by higher mammal herbivory rates towards and beyond their low-elevation range limit.
We transplanted individuals of our focal species (Elymus scribneri, Festuca brachyphylla, and Poa alpina) in the core of their range, at their range limit, and in a novel-beyond range limit site that reflected ~2 °C warming. At each site, we factorially excluded above and belowground mammal herbivore access to plants using fencing. Additionally, we collected demographic data from natural populations of the focal species and applied experimental treatment effect sizes to vital rates models (i.e., growth, survival, and reproduction) to project experimental effects on population growth. We found, generally, that herbivory increases from the core of the species’ range towards the limit and novel sites and that restricting above and belowground mammal access to plants increased their growth and reproduction more in limit and novel habitats than in their core range. Additionally, mammal exclusion increased population growth over controls most in limit and novel sites.
Our study suggested that higher herbivory below a species’ elevation range limit contributes to the plant’s exclusion from lower elevations. Importantly, the abiotic environment in novel habitats was hospitable for the individuals, but mammalian herbivory in range limit and novel habitats may drive focal species population growth rates below replacement. Results suggest that as mammals shift their foraging range upslope with further climate change, increased herbivory may drive the local extinction of these alpine restricted grass species.
You can read the full article here: https://onlinelibrary.wiley.com/doi/epdf/10.1111/ele.13829
Reference: Lynn, J.S., Miller, T.E.X. and Rudgers, J.A. (2021) Mammalian herbivores restrict the altitudinal range limits of alpine plants. Ecology Letters.
Text by Joshua S. Lynn, University of New Mexico.
Picture: View of an elevation transect used for the experiment in the West Elk Mountains, Colorado, USA. (Photo credit: Joshua S. Lynn).