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Enemy Release Hypothesis (enemy + release_hypothesis)
Selected AbstractsResistance to Plant Invasion?BIOTROPICA, Issue 2 2010A Native Specialist Herbivore Shows Preference for, Higher Fitness on an Introduced Host ABSTRACT The response of native herbivores to the introduction of a new plant to the community has important implications for plant invasion. Under the Enemy Release Hypothesis introduced species become invasive because of reduced enemy control in the new range, while under the New Association Hypothesis introduced species lack effective defenses against native enemies because they do not share an evolutionary history. I tested the response of a native South-American specialist herbivore Utetheisa ornatrix (Lepidoptera: Arctiidae) to a native (Crotalaria incana) and an introduced host (Crotalaria pallida) (Fabaceae: Papilionoideae). I compared seed predation rates between the two hosts in the field, and I tested preference and performance traits with common garden experiments. Utetheisa ornatrix caused much higher seed predation rates on the introduced host than on the native host. Females also preferred to oviposit on the introduced over the native host. Additionally, larvae feeding on the introduced host had higher fitness (higher pupal weight) than larvae feeding on the native host. I discuss how the response of this specialist herbivore to this introduced host plant contradicts the predictions of the Enemy Release Hypothesis and support the New Association Hypothesis. This study shows that the New Association Hypothesis can also be true for specialist herbivores. Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp [source] Effect of generalist insect herbivores on introduced Lepidium draba (Brassicaceae): implications for the enemy release hypothesisJOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2008K. P. Puliafico Abstract The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem-mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple-species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH. [source] Plant,soil feedback induces shifts in biomass allocation in the invasive plant Chromolaena odorataJOURNAL OF ECOLOGY, Issue 6 2009Mariska Te Beest Summary 1. ,Soil communities and their interactions with plants may play a major role in determining the success of invasive species. However, rigorous investigations of this idea using cross-continental comparisons, including native and invasive plant populations, are still scarce. 2. ,We investigated if interactions with the soil community affect the growth and biomass allocation of the (sub)tropical invasive shrub Chromolaena odorata. We performed a cross-continental comparison with both native and non-native-range soil and native and non-native-range plant populations in two glasshouse experiments. 3. ,Results are interpreted in the light of three prominent hypotheses that explain the dominance of invasive plants in the non-native range: the enemy release hypothesis, the evolution of increased competitive ability hypothesis and the accumulation of local pathogens hypothesis. 4. ,Our results show that C. odorata performed significantly better when grown in soil pre-cultured by a plant species other than C. odorata. Soil communities from the native and non-native ranges did not differ in their effect on C. odorata performance. However, soil origin had a significant effect on plant allocation responses. 5. ,Non-native C. odorata plants increased relative allocation to stem biomass and height growth when confronted with soil communities from the non-native range. This is a plastic response that may allow species to be more successful when competing for light. This response differed between native and non-native-range populations, suggesting that selection may have taken place during the process of invasion. Whether this plastic response to soil organisms will indeed select for increased competitive ability needs further study. 6. ,The native grass Panicum maximum did not perform worse when grown in soil pre-cultured by C. odorata. Therefore, our results did not support the accumulation of local pathogens hypothesis. 7. ,Synthesis. Non-native C. odorata did not show release from soil-borne enemies compared to its native range. However, non-native plants responded to soil biota from the non-native range by enhanced allocation in stem biomass and height growth. This response can affect the competitive balance between native and invasive species. The evolutionary potential of this soil biota-induced change in plant biomass allocation needs further study. [source] Barley yellow dwarf viruses (BYDVs) preserved in herbarium specimens illuminate historical disease ecology of invasive and native grassesJOURNAL OF ECOLOGY, Issue 6 2007CAROLYN M. MALMSTROM Summary 1In plant invasion ecology, viruses and other pathogens are often considered in terms of the enemy release hypothesis, which predicts that plants become invasive in new ranges if they escape pathogens from their home range. However, pathogens may sometimes facilitate host spread rather than hinder it. 2Previously, we hypothesized that apparent competition mediated by barley and cereal yellow dwarf viruses (Luteoviridae: BYDVs, CYDVs) may have facilitated historical grassland invasion in California, USA, where Eurasian grasses displaced native grasses in the 18th and 19th centuries (the disease facilitation hypotheses). However, this could have happened only if the viruses were present during the invasion, which is unknown. 3To investigate the historical ecology of BYDVs in California grasses, we analysed preserved virus infections in herbarium specimens and used the historical virus sequences to determine rough time estimates of relevant phylogenetic events. 4The historical viral RNA sequences we identified in invasive and native grasses date from 1917 and are among the oldest recovered from plants thus far and the oldest from North America. 5Herbarium evidence and phylogenetic analysis suggest that BYDVs were likely to have been present in wild grasses during the California grassland invasion and to have shared some functional characteristics with present-day isolates, supporting the disease facilitation hypothesis. 6We found evidence of virus spread from California to Australia (or, less likely, from Australia to California) in the late 19th century, when much horticultural exchange occurred, as well as potential correspondence in the timing of virus diversification events and the beginning of extensive human exchange between the Old and New Worlds. 7Synthesis. Increasing evidence indicates that viruses are important in the ecology of grasslands and may, in some cases, mediate apparent competition among species. Historical data provide essential insight into plant virus ecology and suggest the need to examine human influence on plant virus diversification and spread within natural ecosystems. [source] Herbivores, but not other insects, are scarce on alien plantsAUSTRAL ECOLOGY, Issue 5 2008ERBAN PROCHE Abstract Understanding how the landscape-scale replacement of indigenous plants with alien plants influences ecosystem structure and functioning is critical in a world characterized by increasing biotic homogenization. An important step in this process is to assess the impact on invertebrate communities. Here we analyse insect species richness and abundance in sweep collections from indigenous and alien (Australasian) woody plant species in South Africa's Western Cape. We use phylogenetically relevant comparisons and compare one indigenous with three Australasian alien trees within each of Fabaceae: Mimosoideae, Myrtaceae, and Proteaceae: Grevilleoideae. Although some of the alien species analysed had remarkably high abundances of herbivores, even when intentionally introduced biological control agents are discounted, overall, herbivorous insect assemblages from alien plants were slightly less abundant and less diverse compared with those from indigenous plants , in accordance with predictions from the enemy release hypothesis. However, there were no clear differences in other insect feeding guilds. We conclude that insect assemblages from alien plants are generally quite diverse, and significant differences between these and assemblages from indigenous plants are only evident for herbivorous insects. [source] Test of the enemy release hypothesis: The native magpie moth prefers a native fireweed (Senecio pinnatifolius) to its introduced congener (S. madagascariensis)AUSTRAL ECOLOGY, Issue 1 2008EVE M. WHITE Abstract The enemy release hypothesis predicts that native herbivores will either prefer or cause more damage to native than introduced plant species. We tested this using preference and performance experiments in the laboratory and surveys of leaf damage caused by the magpie moth Nyctemera amica on a co-occuring native and introduced species of fireweed (Senecio) in eastern Australia. In the laboratory, ovipositing females and feeding larvae preferred the native S. pinnatifolius over the introduced S. madagascariensis. Larvae performed equally well on foliage of S. pinnatifolius and S. madagascariensis: pupal weights did not differ between insects reared on the two species, but growth rates were significantly faster on S. pinnatifolius. In the field, foliage damage was significantly greater on native S. pinnatifolius than introduced S. madagascariensis. These results support the enemy release hypothesis, and suggest that the failure of native consumers to switch to introduced species contributes to their invasive success. Both plant species experienced reduced, rather than increased, levels of herbivory when growing in mixed populations, as opposed to pure stands in the field; thus, there was no evidence that apparent competition occurred. [source] | ||||||||||