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Title: Native ecotypic variation and the role of host identity in the spread of an invasive herbivore Cactoblastis cactorum (Berg)

item BROOKS, CHRISTOPHER - Mississippi State University
item ERVIN, GARY - Mississippi State University
item VARONE, LAURA - South American Biological Control Lab(SABCL)
item LOGARZO, GUILLERMO - South American Biological Control Lab(SABCL)

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2011
Publication Date: 2/1/2012
Citation: Brooks, C.P., Ervin, G.N., Varone, L., Logarzo, G. 2012. Native ecotypic variation and the role of host identity in the spread of an invasive herbivore Cactoblastis cactorum (Berg). Ecology. 93(2):402-410.

Interpretive Summary: Many of the theories that guide the study of invasive species are based on the concept of ecological niche. The niche of a species represents the physiological boundaries and the conditions under which a species persists, considering biological constraints, predation, parasitism and competition. Environmental niche models (ENMs) are tolls that can be use to predict invasive species distribution and dispersion to new environments. These types of theoretical models need to be tested with real cases of species invasion. Cactoblastis cactorum is an escaped biological control species and was used in this work to determine the role of environmental variables in contrast with the interaction of the insect with its host plants. We utilized data from the distribution in the native range (Argentina). We found that the interactions with new host plants that were not present in the native range played an important role in the invasion process and dispersion of C. cactorum in North America. This information could be used in future management strategies for the control of this new pest.

Technical Abstract: Environmental niche models (ENMs) have gained enormous popularity as tools to investigate potential changes in species distributions resulting from climate change and species introductions. Despite recognition that species interactions can influence the dynamics of invasion spread, most implementations of ENMs focus on abiotic factors as the sole predictors of potential range limits. Implicit in this approach is the assumption that biotic interactions are relatively unimportant, either because of scaling issues, or because fundamental and realized niches are equivalent in a species’ native range. When species are introduced into exotic landscapes, changes in biotic interactions relative to the native range can lead to occupation of different regions of niche space and apparent shifts in physiological tolerances. We use an escaped biological control organism, Cactoblastis cactorum (Berg.), to assess the role of the environmental envelope as compared with patterns of host-herbivore associations based on collections made in the native range. Because all non-native populations are derived from a single C. cactorum ecotype, we hypothesize that biotic interactions associated with this ecotype are driving the species’ invasion dynamics. Environmental niche models constructed from known native populations perform poorly in predicting non-native distributions of this species, except where there is an overlap in niche space. In contrast, genetic isolation in the native range is concordant with the observed pattern of host use, and strong host association has been noted in non-native landscapes. Our results support the hypothesis that the apparent shift in niche space from the native to the exotic ranges results from a shift in biotic interactions, and demonstrate the importance of considering biotic interactions in assessing the risk of future spread for species whose native range is highly constrained by biotic interactions.