The wildland-urban interface introduces a suite of factors that complicate plant species recovery including pollinator declines from reduced habitat quality. Despite that most angiosperms depend on invertebrate visitors for reproduction, plant-pollinator interactions are rarely considered in conservation management strategies. Pollinators promote genetic diversity via sexual reproduction and outcrossing, thereby improving plant fitness, a goal for stabilizing rare populations. National Key Deer Refuge, in the Lower Florida Keys, is a heterogeneous landscape that contains many endemic flowering plants and invertebrate pollinators. The refuge is intermittently dispersed between urban developments that spray insecticides year-round for mosquito control. Extensive studies show that broad spectrum insecticides negatively affect non-target invertebrates, including pollinators; however, indirect effects on plant reproduction have not been documented in conservation areas. We chose three imperiled species of native plants throughout three islands in the Lower Florida Keys to investigate direct and indirect effects of mosquito insecticide on flower visitor activity and plant reproduction (fruit set). For species whose reproductive biology was unknown, we set up pollinator exclusion trials to determine dependence on visitors for reproduction. We hypothesize that flowers open following an insecticide application would have lower visitation rates and fruit set than flowers open at unsprayed sites.
Results/Conclusions
Open flowers at treatments sites had a decreased visitor rate, but only obligately entomophilous species had significantly reduced fruit set. Automatic self-pollination is a common fail-safe mechanism in short-lived herbaceous plants when efficient pollinators are sparse, and this mechanism is apparently operating in one of the species, Linum arenicola. For rare plants, however, reliance on selfing can constrain genetic diversity, and this mechanism may mask ecological instability, such that populations may be apparently viable but declining. Conservation management for rare flowering plants should therefore consider habitat quality for pollinators by including buffer zones from insecticide drift and restricting spray routes to dense residential neighborhoods. Green house and field pollination trials for L. arenicola is necessary to determine seed viability and seedling vigor from cross pollen, self-pollen, and pollen supplement treatments; these results will provide more insight for population viability of this rare species and if decreased pollinator activity from insecticides negatively effects the species.