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Wild herbivores enhance resistance to invasion by exotic cacti in an African savanna

Wells, Harry B.M.; Crego, Ramiro D.; Alston, Jesse M.; Ndung'u, S. Kimani; Khasoha, Leo M.; Reed, Courtney G.; Hassan, Abdikadir A.; Kurukura, Samson; Ekadeli, Jackson; Namoni, Mathew; Stewart, Peter S.; Kimuyu, Duncan M.; Wolf, Amelia A.; Young, Truman P.; Kartzinel, Tyler R.; Palmer, Todd M.; Goheen, Jacob R.; Pringle, Robert M.

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Authors

Harry B.M. Wells

Ramiro D. Crego

Jesse M. Alston

S. Kimani Ndung'u

Leo M. Khasoha

Courtney G. Reed

Abdikadir A. Hassan

Samson Kurukura

Jackson Ekadeli

Mathew Namoni

Peter Stewart peter.s.stewart@durham.ac.uk
PGR Student Doctor of Philosophy

Duncan M. Kimuyu

Amelia A. Wolf

Truman P. Young

Tyler R. Kartzinel

Todd M. Palmer

Jacob R. Goheen

Robert M. Pringle



Abstract

Whether wild herbivores confer biotic resistance to invasion by exotic plants remains a key question in ecology. There is evidence that wild herbivores can impede invasion by exotic plants, but it is unclear whether and how this generalises across ecosystems with varying wild herbivore diversity and functional groups of plants, particularly over long-term (decadal) time frames. Using data from three long-term (13- to 26-year) exclosure experiments in central Kenya, we tested the effects of wild herbivores on the density of exotic invasive cacti, Opuntia stricta and O. ficus-indica (collectively, Opuntia), which are among the worst invasive species globally. We also examined relationships between wild herbivore richness and elephant occurrence probability with the probability of O. stricta presence at the landscape level (6150 km2). Opuntia densities were 74% to 99% lower in almost all plots accessible to wild herbivores compared to exclosure plots. Opuntia densities also increased more rapidly across time in plots excluding wild herbivores. These effects were largely driven by megaherbivores (≥1000 kg), particularly elephants. At the landscape level, modelled Opuntia stricta occurrence probability was negatively correlated with estimated species richness of wild herbivores and elephant occurrence probability. On average, O. stricta occurrence probability fell from ~0.56 to ~0.45 as wild herbivore richness increased from 6 to 10 species and fell from ~0.57 to ~0.40 as elephant occurrence probability increased from ~0.41 to ~0.84. These multi-scale results suggest that any facilitative effects of Opuntia by wild herbivores (e.g. seed/vegetative dispersal) are overridden by suppression (e.g. consumption, uprooting, trampling). Synthesis. Our experimental and observational findings that wild herbivores confer resistance to invasion by exotic cacti add to evidence that conserving and restoring native herbivore assemblages (particularly megaherbivores) can increase community resistance to plant invasions.

Citation

Wells, H. B., Crego, R. D., Alston, J. M., Ndung'u, S. K., Khasoha, L. M., Reed, C. G., …Pringle, R. M. (2023). Wild herbivores enhance resistance to invasion by exotic cacti in an African savanna. Journal of Ecology, 111(1), https://doi.org/10.1111/1365-2745.14010

Journal Article Type Article
Acceptance Date Sep 22, 2022
Online Publication Date Oct 27, 2022
Publication Date 2023
Deposit Date Mar 20, 2023
Publicly Available Date Mar 29, 2024
Journal Journal of Ecology
Print ISSN 0022-0477
Electronic ISSN 1365-2745
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 111
Issue 1
DOI https://doi.org/10.1111/1365-2745.14010

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.




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