Abstract:
Ants are recognized for their abilities both to engage in mutualistic interactions with diverse taxa, and to invade and dominate habitats outside their native geographic range. Here, we review the effects of invasive ants on three guilds of mutualists: ant-dispersed plants, ant-tended arthropods, and ant-tended plants. We contrast how those three guilds are affected by invasions, how invasive ants differ from native ants in their interactions with those guilds, and how the seven most invasive ant species differ amongst themselves in those interactions. Ant-dispersed plants typically suffer from interactions with invasive ants, a result we attribute to the small size of those ants relative to native seed-dispersing ants. Effects on the ant-tended arthropods and plants were more frequently positive or non-significant, although it is unclear how often these interactions are reciprocally beneficial. For example, invasive ants frequently attack the natural enemies of these prospective mutualists even in the absence of rewards, and may attack those prospective mutualists. Many studies address whether invasive ants provide some benefit to the partner, but few have asked how invasives rank within a hierarchy of prospective mutualists that includes other ant species. Because ant invasions typically result in the extirpation of native ants, this distinction is highly relevant to predicting and managing the effects of such invasions. Interspecific comparisons suggest that invasive ants are poorer partners of ant-dispersed plants than are most other ants, equally effective partners of ant-tended arthropods, and perhaps better partners of ant-tended plants. Last, we note that the invasive ant taxa differ amongst themselves in how they affect these three mutualist guilds, and in how frequently their interactions with prospective mutualists have been studied. The red imported fire ant, Solenopsis invicta, appears particularly likely to disrupt all three mutualistic interactions, relative to the other six invasive species included in this review.
Abstract:
Plants pollinated by specialists are often thought to receive exceptionally high-quality pollinator service, but in relatively low and unpredictable quantities. We examine and reject this hypothesis for an obligate mutualism between a subtropical New World fig (Ficus aurea) and its species-specific pollinator (Pegoscapus jimenezi). Fig wasps lay eggs within the flowers they pollinate; their offspring destroy a large proportion of fig's seeds. In a 6-year study of this interaction in Florida, U.S.A., we found that pollination intensity was in fact relatively high. Also contrary to expectations, reproductive success of both mutualists (as well as other wasps cohabiting the figs) was extremely variable and generally low, at three different scales of sampling: among figs from a single crop of one tree (thirty-four figs), among crops produced at different times by that tree (126 figs), and across trees over a 1-year period (379 figs). Although variable, fig contents were not completely unpredictable. For example, seed and wasp numbers increased with the number of flowers in a fig, and female and male flower numbers increased together. Little is yet known about the causes either of these relationships or of the massive fig-to-fig variation itself, although there is some evidence that they exist in other fig species as well. Further investigations of these patterns should shed new light on the ecology and evolution of this mutualism.
PMID: 23756587;Abstract:
The foraging decisions of flower-visiting animals are contingent upon the need of an individual to meet both energetic and osmotic demands. Insects can alter their food preferences to prioritize one need over the other, depending on environmental conditions. In this study, preferences in nectar sugar concentrations (0, 12, 24 %) were tested in the hawkmoth Manduca sexta, in response to different levels of ambient humidity (20, 40, 60, and 80 % RH). Moths altered their foraging behavior when placed in low humidity environments by increasing the volume of nectar imbibed and by consuming more dilute nectar. When placed in high humidity environments the total volume imbibed decreased, because moths consumed less from dilute nectars (water and 12 % sucrose). Survivorship was higher with higher humidity. Daily foraging patterns changed with relative humidity (RH): moths maximized their nectar consumption earlier, at lower humidities. Although ambient humidity had an impact on foraging activity, activity levels and nectar preferences, total energy intake was not affected. These results show that foraging decisions made by M. sexta kept under different ambient RH levels allow individuals to meet their osmotic demands while maintaining a constant energy input. © 2013 Springer-Verlag Berlin Heidelberg.
