The red imported fire ant, Solenopsis invicta, was accidentally introduced to North America over 60 years ago and has spread throughout the southeastern United States. We document the biogeographic consequences of this invasion. We censused ground‐foraging ant communities on a 2000 km transect from Florida through New York that passed through invaded and intact biotas. Native ant species density peaks at mid‐latitudes in the eastern United States, and the location of this peak corresponds to the range limit of S. invicta. In uninvaded sites, ant species co‐occur less often than expected by chance. In the presence of S. invicta, community structure converges to a random pattern. Our results suggest that the effects of S. invicta on native ant communities are pervasive: not only does the presence of S. invicta reduce species density at local scales, it alters the co‐occurrence patterns of surviving species at a biogeographic scale.

In eastern North America, body size of the larval ant lion Myrmeleon immaculatus increases from south to north, following Bergmann's rule. We used a common-garden experiment and a reciprocal-transplant experiment to evaluate the effects of food and temperature on ant lion growth, body size, and survivorship. In the laboratory common-garden experiment, first-instar larvae from two southern (Georgia, South Carolina) and two northern (Connecticut, Rhode Island) populations were reared in incubators under high-and low-food and high-and low-temperature regimes. For all populations, high food increased final body mass and growth rate and decreased development time. Growth rates were higher at low temperatures, but temperature did not affect larval or adult body mass. Survivorship was highest in high-food and low-temperature treatments. Across all food and temperature treatments, northern populations exhibited a larger final body mass, shorter development time, faster growth rate, and greater survivorship than did southern populations. Results were similar for a field reciprocal-transplant experiment of third-instar larvae between populations in Connecticut and Oklahoma: Connecticut larvae grew faster than Oklahoma larvae, regardless of transplant site. Conversely, larvae transplanted to Oklahoma grew faster than larvae transplanted to Connecticut, regardless of population source. These results suggest that variation in food availability, not temperature, may account for differences in growth and body size of northern and southern ant lions. Although northern larvae grew faster and reached a larger body size in both experiments, northern environments should suppress growth because of reduced food availability and a limited growing season. This study provides the first example of countergradient selection causing Bergmann's rule in an ectotherm.

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The problem of invasive species has reignited interest in biological control as a management tool. Classical biological control involves deliberate release of exotic natural enemies into new environments in an attempt to limit the density of an invasive species. Persistent, sustained limitation of invasive species by coevolved natural enemies is a seductive concept. Evidence now suggests, however, that biological control through the release of natural enemies can carry unanticipated ecological risks. There have been ecological side effects of distributing a deliberately introduced weevil (Rhinocyllus conicus) and an adventitious weevil (Larinus planus) for the biological control of exotic thistles. Both weevils have had major direct effects on key population-growth parameters of native thistles, and R. conicus has had an indirect effect on the interaction between a thistle and a native insect. These findings led us to review how ecological risk is evaluated, and to ask whether pre-release tests can predict the types of ecological effects documented. We conclude that, when done thoroughly, the tests used can determine host specificity by identifying physiological host range, but the usual tests cannot be relied upon to predict the ecological host range or impact on populations of less-preferred but accepted native species. Our data provide support for suggestions that the behavioral and developmental data now taken need to be supplemented with additional data on population parameters to better predict field-host use, population growth, interaction strengths, and ecological outcomes for native species that are potential hosts. Invasividad de Algunos Insectos de Control Biológico y Adecuación de Su Evaluación de Riesgo Ecológico y RegulaciónResumen El problema de las especies invasoras ha despertado nuevo interés en el control biológico como una herramienta de manejo. El control biológico clásico implica la liberación deliberada de enemigos naturales exóticos en nuevos ambientes con la intención de limitar la densidad de una especie invasora. La limitación persistente, sostenida de especies invasoras por enemigos naturales coevolucionados es un concepto seductor. Sin embargo, la evidencia ahora sugiere que la liberación de enemigos naturales para el control biológico puede acarrear riesgos ecológicos no anticipados. Hubo efectos ecológicos secundarios por la introducción deliberada de un gorgojo (Rhinocyllus conicus) y de un gorgojo adventicio (Larinus planus) para el control biológico de abrojos exóticos. Ambos gorgojos han tenido importantes efectos directos sobre los parámetros clave del crecimiento poblacional de abrojos nativos, y R. conicus ha tenido un efecto indirecto en una interacción abrojo -insecto nativo. Estos hallazgos nos condujeron a revisar como se evalúa el riesgo ecológico y a preguntar si las pruebas previas a la liberación pueden predecir los tipos de efectos ecológicos documentados. Concluimos que las pruebas utilizadas, cuando están bien hechas, pueden determinar la especificidad del...