TY - JOUR
T1 - Enemy release and plant invasion
T2 - Patterns of defensive traits and leaf damage in Hawaii
AU - Funk, Jennifer L.
AU - Throop, Heather L.
N1 - Funding Information:
Acknowledgments We thank Curt Daehler, Dan Gruner and Peter Vitousek for comments on a previous version of this manuscript and Heraldo Farrington, Linda Pratt, Randi Schneider and Doug Turner for Weld and laboratory support. We also thank the Hawaii Department of Fish and Wildlife for access to Weld sites. J. L. F. was funded by the National Parks Ecological Research Fellowship Program, a partnership between the National Park Service, the Ecological Society of America and the National Park Foundation. It is funded by a generous grant from the Andrew W. Mellon Foundation.
Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2010
Y1 - 2010
N2 - Invasive species may be released from consumption by their native herbivores in novel habitats and thereby experience higher fitness relative to native species. However, few studies have examined release from herbivory as a mechanism of invasion in oceanic island systems, which have experienced particularly high loss of native species due to the invasion of non-native animal and plant species. We surveyed putative defensive traits and leaf damage rates in 19 pairs of taxonomically related invasive and native species in Hawaii, representing a broad taxonomic diversity. Leaf damage by insects and pathogens was monitored in both wet and dry seasons. We found that native species had higher leaf damage rates than invasive species, but only during the dry season. However, damage rates across native and invasive species averaged only 2% of leaf area. Native species generally displayed high levels of structural defense (leaf toughness and leaf thickness, but not leaf trichome density) while native and invasive species displayed similar levels of chemical defenses (total phenolics). A defense index, which integrated all putative defense traits, was significantly higher for native species, suggesting that native species may allocate fewer resources to growth and reproduction than do invasive species. Thus, our data support the idea that invasive species allocate fewer resources to defense traits, allowing them to outperform native species through increased growth and reproduction. While strong impacts of herbivores on invasion are not supported by the low damage rates we observed on mature plants, population-level studies that monitor how herbivores influence recruitment, mortality, and competitive outcomes are needed to accurately address how herbivores influence invasion in Hawaii.
AB - Invasive species may be released from consumption by their native herbivores in novel habitats and thereby experience higher fitness relative to native species. However, few studies have examined release from herbivory as a mechanism of invasion in oceanic island systems, which have experienced particularly high loss of native species due to the invasion of non-native animal and plant species. We surveyed putative defensive traits and leaf damage rates in 19 pairs of taxonomically related invasive and native species in Hawaii, representing a broad taxonomic diversity. Leaf damage by insects and pathogens was monitored in both wet and dry seasons. We found that native species had higher leaf damage rates than invasive species, but only during the dry season. However, damage rates across native and invasive species averaged only 2% of leaf area. Native species generally displayed high levels of structural defense (leaf toughness and leaf thickness, but not leaf trichome density) while native and invasive species displayed similar levels of chemical defenses (total phenolics). A defense index, which integrated all putative defense traits, was significantly higher for native species, suggesting that native species may allocate fewer resources to growth and reproduction than do invasive species. Thus, our data support the idea that invasive species allocate fewer resources to defense traits, allowing them to outperform native species through increased growth and reproduction. While strong impacts of herbivores on invasion are not supported by the low damage rates we observed on mature plants, population-level studies that monitor how herbivores influence recruitment, mortality, and competitive outcomes are needed to accurately address how herbivores influence invasion in Hawaii.
KW - Defense allocation
KW - Herbivory
KW - Invasive species
KW - Pathogen
KW - Phenolics
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U2 - 10.1007/s00442-009-1497-4
DO - 10.1007/s00442-009-1497-4
M3 - Article
C2 - 19916065
AN - SCOPUS:77949773037
SN - 0029-8549
VL - 162
SP - 815
EP - 823
JO - Oecologia
JF - Oecologia
IS - 4
ER -