Priority resource access mediates competitive intensity between an invasive weevil and native floral herbivores |
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Authors: | S M Louda T A Rand A A R Kula A E Arnett N M West B Tenhumberg |
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Institution: | (1) School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA;(2) Department of Mathematics, University of Nebraska, Lincoln, NE 68588, USA;(3) USDA, Agricultural Research Service, Northern Plains Agricultural Research Laboratory, 1500 North Central Ave., Sidney, MT 59270, USA;(4) Program in Behavior, Ecology, Evolution and Systematics, University of Maryland, College Park, MD 20742, USA;(5) Center for Biodiversity, Unity College, Unity, ME 04915, USA; |
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Abstract: | Mechanisms underlying invasive species impacts remain incompletely understood. We tested the hypothesis that priority resource
access by an invasive biocontrol weevil, Rhinocyllus conicus, intensifies and alters the outcome of competition with native floral herbivores over flower head resources of the non-target,
native host plant Cirsium canescens, specifically with the predominant, synchronous tephritid fly Paracantha culta. Four main results emerged. First, we documented strong, asymmetric competition, with R. conicus out-competing P. culta. Second, weevil priority access to floral resources accelerated competitive suppression of P. culta. Evidence for competitive suppression with increased weevil priority included decreases in both the numbers and the total
biomass of native flies, plus decreases in individual P. culta fly mass and, so, potential fitness. Third, we found evidence for three concurrent mechanisms underlying the competitive
suppression of P. culta by R. conicus. Prior use of a flower head by R. conicus interfered with P. culta pre-oviposition behavior. Once oviposition occurred, the weevil also reduced fly post-oviposition performance. Preemptive
resource exploitation occurred, shown by the significant effect of flower head size on the total number of insects developing
and in the magnitude of R. conicus effects on P. culta. Interference also occurred, shown by a spatial shift of surviving P. culta individuals away from the preferred receptacle resources as R. conicus priority increased. Finally, fourth, using an individual-based model (IBM), we found that the competitive interactions documented have the potential
for imposing demographic consequences, causing a reduction in P. culta population sizes. Thus, priority resource access by an invasive insect increased competitive impact on the predominant native insect in the
invaded floral guild. This study also provides the first experimental evidence for non-target effects of a weed biological
control agent on an associated native insect herbivore. |
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