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Dispersal is considered a vital life history characteristic for insects exploiting temporary habitats, and life history theorists have often hypothesized an inverse relationship between dispersal capability and habitat persistence. Most often, this hypothesis has been tested using interspecific comparisons of dispersal capability and qualitative estimates of habitat persistence. Consequently, most assessments have failed to control for possible phylogenetic nonindependence and they also lack quantitative rigor. We capitalized on existing intraspecific variation in the dispersal capability of Prokelisia planthoppers to examine the relationship between habitat persistence and dispersal, thereby minimizing possible phylogenetic effects. Two congeneric species (Prokelisia marginata and P. dolus) occur in the intertidal marshes of North America, where they feed exclusively on cordgrasses (Spartina). Because these planthoppers exhibit wing dimorphism, flight—capable adults (macropters with fully developed wings) are easily differentiated from flightless adults (brachypters with reduced wings). Thus, dispersal capability can be readily estimated by the percentage of macropters in a population. At a regional spatial scale, we found a highly significant negative relationship between dispersal capability (percent macroptery) and habitat persistence. In this system, habitat persistence is influenced by a combination of marsh elevation, winter severity, and tidal range, which interact to determine the ability of planthoppers to endure through winter in their primary habitat for development. P. marginata develops primarily in low—marsh habitats during summer, habitats that can be subjected to pronounced winter disturbance due to ice scouring and/or extensive tidal inundation. Levels of winter disturbance of the low marsh are extreme along the Atlantic coast, intermediate along the Pacific, and low along the Gulf. Both the failure of P. marginata populations to remain through winter in this habitat, and the dispersal ability of these populations (92%, 29%, and 17% macroptery, respectively), are correlated with levels of disturbance. Thus, in regions where winter disturbance is high, levels of dispersal are correspondingly high to allow for recolonization of extirpated habitats from overwintering sites on the high marsh. Unlike P. marginata, P. dolus develops primarily in high—marsh habitats, which are much less disturbed on all coasts during winter. Consequently, this species remains year—round in its primary habitat for development, and most populations exhibit relatively low levels of macroptery (<10%). When raised under common garden conditions, many more macropters of both species were produced from Atlantic compared to Gulf populations. Thus the proportion of macropters produced from the populations used in this experiment paralleled the incidence of macroptery measured in the field, providing evidence that the geographic variation in dispersal capability in both species has in part a genetic basis. The results of this stu...

We employed a combination of factorial experiments in the field and laboratory to investigate the relative magnitude and degree of interaction of bottom‐up factors (two levels each of host‐plant nutrition and vegetation complexity) and top‐down forces (two levels of wolf‐spider predation) on the population growth of Prokelisia planthoppers (P. dolus and P. marginata), the dominant insect herbivores on Spartina cordgrass throughout the intertidal marshes of North America. Treatments were designed to mimic combinations of plant characteristics and predator densities that occur naturally across habitats in the field. There were complex interactive effects between plant resources and spider predation on the population growth of planthoppers. The degree that spiders suppressed planthoppers depended on both plant nutrition and vegetation complexity, an interaction that was demonstrated both in the field and laboratory. Laboratory results showed that spiders checked planthopper populations most effectively on poor‐quality Spartina with an associated matrix of thatch, all characteristics of high‐marsh meadow habitats. It was also this combination of plant resources in concert with spiders that promoted the smallest populations of planthoppers in our field experiment. Planthopper populations were most likely to escape the suppressing effects of predation on nutritious plants without thatch, a combination of factors associated with observed planthopper outbreaks in low‐marsh habitats in the field. Thus, there is important spatial variation in the relative strength of forces with bottom‐up factors dominating under low‐marsh conditions and top‐down forces increasing in strength at higher elevations on the marsh. Enhancing host‐plant biomass and nutrition did not strengthen top‐down effects on planthoppers, even though nitrogen‐rich plants supported higher densities of wolf spiders and other invertebrate predators in the field. Rather, planthopper populations, particularly those of Prokelisia marginata, escaped predator restraint on high‐quality plants, a result we attribute to its mobile life history, enhanced colonizing ability, and rapid growth rate. Thus, our results for Prokelisia planthoppers suggest that the life history strategy of a species is an important mediator of top‐down and bottom‐up impacts. In laboratory mesocosms, enhancing plant biomass and nutrition resulted in increased spider reproduction, a cascading effect associated with planthopper increases on high‐quality plants. Although the adverse effects of spider predation on planthoppers cascaded down and fostered increased plant biomass in laboratory mesocosms, this result did not occur in the field where top‐down effects attenuated. We attributed this outcome in part to the intraguild predation of other planthopper predators by wolf spiders. Overall, the general paradigm in this system is for bottom‐up forces to dominate, and when predators do exert a significant suppressing effect on planthoppers, their impact is generally legislated by vegetation characte...

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Feeding‐induced plant resistance is a well‐documented phenomenon for leaf‐chewing insects. Furthermore, feeding‐induced resistance provides the mechanistic basis for many cases of delayed interspecific competition, whereby previous feeding by one species diminishes the performance of other herbivores which attack the same plant later in the season. This phenomenon, however, has been very poorly investigated for sap‐feeding insects. The results we present here for salt marsh‐inhabiting planthoppers (Prokelisia dolus and P. marginata) provide one of the few known examples of delayed, plant‐mediated interspecific competition between two sap‐feeding insects. Three lines of experimental evidence from the laboratory, field cages, and open field plots provide support for the detrimental effects of previous feeding by one planthopper species on the subsequent survival and performance of the other. Laboratory experiments showed that prior feeding on cordgrass by one congener resulted in reduced performance of the other in the following generation. However, the effect was asymmetric. Prior feeding by P. dolus resulted in prolonged development and reduced body size (a correlate of fecundity) in P. marginata, whereas only development was protracted in P. dolus when plants were previously exposed to P. marginata. Consequently, P. dolus appears to be the superior competitor in the context of delayed, plant‐mediated interactions. The negative effects of previous feeding by P. dolus on the development time, body size, and survival of P. marginata obtained in the laboratory were confirmed both in cages and on cage‐free islets of cordgrass in the field. Feeding‐induced reductions in host‐plant quality by P. dolus may provide additional impetus for P. marginata to migrate from shared habitats on the high marsh to nutritionally superior plants in the low marsh rarely occupied by P. dolus. The mechanism underlying the delayed competitive effects between Prokelisia planthoppers is most likely diminished plant nutrition, because feeding by P. dolus significantly reduces the concentration of essential amino acids in cordgrass. The asymmetry of plant‐mediated competition between the Prokelisia species may be due to the ability of P. dolus to better tolerate feeding‐depleted levels of plant nitrogen via compensatory feeding. Even though these two planthoppers do not suffer significant fitness reductions during contemporaneous interactions, they compete severely in the context of feeding‐induced plant resistance which is expressed later in the season. This result, coupled with the fact that most studies of interspecific interaction between herbivorous insects are contemporaneous, indicates that interspecific competition may be profoundly underestimated as a structuring force in phytophagous insect communities.