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The release of biological control agents has been an important means of controlling invasive species for over 150 years. While these releases have led to the sustainable control of over 250 invasive pest and weed species worldwide, a minority have caused environmental harm. A growing recognition of the risks of biological control led to a focus on risk assessment beginning in the 1990s along with a precipitous decline in releases. While this new focus greatly improved the safety of biological control, it came at the cost of lost opportunities to solve environmental problems associated with invasive species. A framework that incorporates benefits and risks of biological control is thus needed to understand the net environmental effects of biological control releases. We introduce such a framework, using native biodiversity as the common currency for both benefits and risks. The model is based on interactions among four categories of organisms: (1) the biological control agent, (2) the invasive species (pest or weed) targeted by the agent, (3) one or more native species that stand to benefit from the control of the target species, and (4) one or more native species that are at risk of being harmed by the released biological control agent. Conservation values of the potentially benefited and harmed native species are incorporated as well, and they are weighted according to three axes: vulnerability to extinction, the ecosystem services provided, and cultural significance. Further, we incorporate the potential for indirect risks to native species, which we consider will result mainly from the ecological process of agent enrichment that may occur if the agent exploits but does not control the target pest or weed. We illustrate the use of this framework by retrospectively analyzing the release of the vedalia beetle, Novius (= Rodolia) cardinalis, to control the cottony cushion scale, Icerya purchasi, in the Galapagos Islands. While the framework is particularly adaptable to biological control releases in natural areas, it can also be used in managed settings, where biological control protects native species through the reduction of pesticide use. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2005.11.021 Byline: Michal Segoli, Ally R. Harari, Yael Lubin Abstract: The reproductive success of a male is thought to be a function of the number of females he fertilizes. Nevertheless, various naturally occurring male behaviours seem to reduce dramatically the probability of obtaining additional matings. Such behaviours are expected when mating opportunities are limited for males and when males compete strongly for females or fertilizations. In widow spiders, males cohabit in females' webs, engage in long courtship displays, often lose the tip of one or both emboli (copulatory organs) inside the female's genital tract during copulation and are occasionally cannibalized by the female. We investigated conditions that may favour the evolution of a high-investment strategy of mating in white widow, Latrodectus pallidus, males. We followed male movements between females in a patchily distributed population of white widows and estimated the minimum number of males with which field-caught females mated from the number of embolus tips found in their genital tracts. The encounter rate of males with females was low with less than 20% of the searching males reaching a female. Females, in contrast, frequently mated with more than one male (up to six). We suggest that low encounter rates with females, coupled with high intrasexual competition, drives the evolution of a strategy of high investment by males in a single mating, as was observed in the white widow spider. Author Affiliation: (a) Department of Life Sciences, Ben-Gurion University of the Negev, Israel (a ) Department of Entomology, Agricultural Research Organization, The Volcani Center, Israel (a ) Mitrani Department of Desert Ecology, Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Israel Article History: Received 4 August 2005; Revised 28 September 2005; Accepted 12 November 2005 Article Note: (miscellaneous) MS. number: 8644