An invasive plant provides refuge to native plant species in an intensely grazed ecosystem
Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.
KeywordsFacilitation Native–exotic plant interactions Nurse plants Native species diversity Unpalatable exotic plants Nairobi National Park
We thank Mr. Simon Mathenge for help with plant identification during the survey. Permission to conduct the research was granted by National Commission for Science, Technology and Innovation of Kenya (NACOSTI) (Permit Number NCST/RCD/12B/013/24) and Kenya Wildlife Services (KWS). We also thank Rony Adams Onyango and KWS rangers attached to Nairobi National Park for logistical support and providing protection against animals in the park. A.M.O. Oduor received financial support from an International Young Scientist Fellowship of the Chinese Academy of Sciences (No. 2012Y1ZA0011), a Chinese Academy of Sciences (CAS) President’s International Fellowship Initiative (PIFI) (No. 2016PE016) and a research grant from the National Natural Science Foundation of China (No. 312111182). Comments from the editor, two anonymous reviewers, and Dr. Wayne Dawson improved an earlier draft of this manuscript.
- Cronk CB, Fuller JL (1995) Plant invaders. Chapman & Hall, LondonGoogle Scholar
- Githae EW, Nyangito MM (2009) Current status on the occurrence, utilization and management of cactus pear (Opuntia spp.) in Kenya. In: Improved utilization of cactus pear for food, feed, soil and water conservation and other products in Africa, p 220Google Scholar
- Pinheiro J, Bates D, DebRoy S, Sarkar D (2007) nlme: linear and nonlinear mixed effects models. The R Development Core TeamGoogle Scholar
- R Development Core Team (2016) A language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar