Experimental Invasions Using Biological Control Introductions: The Influence of Release Size on the Chance of Population Establishment |
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Authors: | Fritzi S Grevstad |
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Institution: | (1) Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853, USA;(2) Present address: Department of Entomology Cordley Hall, Oregon State University, Corvallis, OR, 97331-2907, USA, e-mail |
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Abstract: | Introductions of biological control organisms offer a unique opportunity to experimentally study the process of invasion by
exotic species. I used two chrysomelid beetles, Galerucella calmariensis and Galerucella pusilla, which are currently being introduced into North America for the biological control of purple loosestrife (Lythrum salicaria), to determine how the initial size of a release affects the probability that the introduced population grows and persists.
I released both species into stands of their host plant at 36 sites scattered throughout central New York State using four
release sizes: 20, 60, 180, and 540. I returned to these sites over the next 3 years to census the populations. For both species,
the probability of population establishment increased with release size. Population growth rates also depended positively
on release size. The implication from these results is that the demographic factors whose influence depends on population
size or density such as demographic stochasticity, Allee effects, and genetics play important roles in the establishment of
invading populations. A second set of releases was used to determine if it was at all possible for a single gravid female
to found a population. Out of twenty individual females released, one female (a G. calmariensis) founded a population that persisted until the end of the study (3 generations).
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | biological control biological invasions colonization Galerucella calmariensis Galerucella pusilla population establishment release size |
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