Understanding the role of consumers in density-dependent plant population dynamics is a long-standing goal in ecology. However, the generality of herbivory effects across heterogeneous landscapes is poorly understood due to the pervasive influence of context-dependence. We tested effects of native insect herbivory on the population dynamics of an exotic thistle, Cirsium vulgare, in a field experiment replicated across eight sites in eastern Nebraska. Using hierarchical Bayesian analysis and density-dependent population models, we found potential for explosive low-density population growth (λ > 5) and complex density fluctuations under herbivore exclusion. However, herbivore access drove population decline (λ < 1), suppressing complex fluctuations. While plant–herbivore interaction outcomes are famously context-dependent, we demonstrated that herbivores suppress potentially invasive populations throughout our study region, and this qualitative outcome is insensitive to environmental context. Our novel use of Bayesian demographic modelling shows that native insect herbivores consistently prevent hard-to-predict fluctuations of weeds in environments otherwise susceptible to invasion.
Bibliographical noteFunding Information:
Research sites were provided by Johannes Knops and Walter Bagley (University of Nebraska), Arnold Mendenhall and Marian Langan (Audubon Society Nebraska), Jay Woltemath and Rob Ruskamp (Pawnee State Recreational Area), and Gene Hanlon and Terry Genrich (City of Lincoln). We thank Brigitte Tenhumberg for providing helpful advice that improved the experiment and manuscript. We thank Elizabeth Bockman Eckberg, Daniel Basso, Danielle Spengler, Andrea Slothe and Michelle Angelroth for assistance with data collection. We thank Aldo Compagnoni for helpful discussion on the modelling and help with coding. JOE was funded by University of Nebraska-Lincoln Life Sciences Interdisciplinary Graduate Fellowships and a William Sampson Rangeland Fellowship, as well as grants from the School of Biological Sciences Special Funds, Initiative for Evolutionary and Ecological Analysis, and Center for Great Plains Studies. ELS was supported by the National Science Foundation Graduate Research Fellowship (NSF grant DGE#1450681).
© 2017 John Wiley & Sons Ltd/CNRS
- Cirsium vulgare
- environmental context
- hierarchical Bayesian model
- insect herbivory
- integral projection models
- invasive species
- population dynamics