Long-distance dispersal (LDD) includes events in which propagules arrive, but do not necessarily establish, at a site far removed from their origin. Although important in a variety of ecological contexts, the system-specific nature of LDD makes ''far removed'' difficult to quantify, partly, but not exclusively, because of inherent uncertainty typically involved with the highly stochastic LDD processes. We critically review the main methods employed in studies of dispersal, in order to facilitate the evaluation of their pertinence to specific aspects of LDD research. Using a novel classification framework, we identify six main methodological groups: biogeographical; Eulerian and Lagrangian movement/redistributional; short-term and long-term genetic analyses; and modeling. We briefly discuss the strengths and weaknesses of the most promising methods available for estimation of LDD, illustrating them with examples from current studies.The rarity of LDD events will continue to make collecting, analyzing, and interpreting the necessary data difficult, and a simple and comprehensive definition of LDD will remain elusive. However, considerable advances have been made in some methodological areas, such as miniaturization of tracking devices, elaboration of stable isotope and genetic analyses, and refinement of mechanistic models. Combinations of methods are increasingly used to provide improved insight on LDD from multiple angles. However, human activities substantially increase the variety of long-distance transport avenues, making the estimation of LDD even more challenging.

Theory predicts that native plant species should exhibit latitudinal gradients in the strength of their interactions with herbivores. We hypothesize that if an invasive plant species exhibits a different latitudinal gradient in response to herbivores (e.g., a nonparallel gradient), it can create large-scale heterogeneities in community resistance/susceptibility to the invasive species. We conducted a study of latitudinal variation in the strength of herbivory and defenses of native genotypes of Phragmites australis in North America (NA) and Europe (EU) and European invasive genotypes in NA. Within NA, we tested whether (1) invasive genotypes are better defended and suffer less herbivory than co-occurring native genotypes, (2) herbivory and defenses of native P. australis decreases with increasing latitude; and (3) invasive genotypes exhibit either no latitudinal gradient, or a nonparallel latitudinal gradient in herbivory and defenses compared to native genotypes. For the European genotypes, we tested two additional hypotheses: (4) defenses, nutritional condition, and herbivory would differ between the native (EU) and invasive ranges (NA) and (5) latitudinal gradients in defenses and herbivory would be similar between ranges. Within NA, chewing damage, internal stem-feeding incidence, and aphid abundance were 650%, 300%, and 70% lower, respectively, on invasive than native P. australis genotypes. Genotypes in NA also differed in nutritional condition (percent N, C:N ratio), but there was little support for invasive genotypes being better defended than native genotypes. For the European genotypes, herbivory was significantly lower in the invaded than native range, supporting the enemy-release hypothesis. Defense levels (leaf toughness and total phenolics) and tissue percent C and percent N were higher in the invaded than native range for European genotypes. Overall, latitudinal gradients in P. australis nutritional condition, defenses, and herbivory were common. Interestingly, chewing damage and stem-feeder incidence decreased with latitude for native P. australis genotypes in NA and EU, but no latitudinal gradients in response to herbivores were evident for invasive genotypes in NA. Nonparallel latitudinal gradients in herbivory between invasive and native P. australis suggest that the community may be more susceptible to invasion at lower than at higher latitudes. Our study points to the need for invasion biology to include a biogeographic perspective.

Invasive plants can disrupt a range of trophic interactions in native communities. As a novel resource they can affect the performance of native insect herbivores and their natural enemies such as parasitoids and predators, and this can lead to host shifts of these herbivores and natural enemies. Through the release of volatile compounds, and by changing the chemical complexity of the habitat, invasive plants can also affect the behavior of native insects such as herbivores, parasitoids, and pollinators. Studies that compare insects on related native and invasive plants in invaded habitats show that the abundance of insect herbivores is often lower on invasive plants, but that damage levels are similar. The impact of invasive plants on the population dynamics of resident insect species has been rarely examined, but invasive plants can influence the spatial and temporal dynamics of native insect (meta)populations and communities, ultimately leading to changes at the landscape level.

Conservation strategies often call for the utilization of corridors and/or stepping stones to promote dispersal among fragmented populations. However, the extent to which these strategies increase connectivity for an organism may depend not only on the corridors and stepping stones themselves, but also on the composition of the surrounding matrix. Using an herbivore–host‐plant system consisting of the planthopper Prokelisia crocea and its sole host plant, prairie cordgrass (Spartina pectinata), we show that the effectiveness of corridors and stepping stones for promoting planthopper dispersal among patches depended strongly on the intervening matrix habitat. In a low‐resistance matrix (one that facilitates high rates of interpatch dispersal), both stepping stones and corridors promoted high connectivity, increasing the number of colonists by threefold relative to patches separated by matrix habitat only. The effectiveness of stepping stones and corridors was significantly lower in a high‐resistance matrix (one that promotes low rates of interpatch dispersal), with stepping stones failing to improve connectivity for the planthoppers relative to controls. Thus, we conclude that the matrix is an integral component of landscapes and should be considered together with corridors and stepping stones in strategies designed to increase dispersal among fragmented populations.

The transfer of organisms among patches is a key process influencing the spatial structure and regional dynamics of a population; yet, detailed experimental studies of animal movement among patches are uncommon. I performed a series of mark-recapture studies to quantify the movement of a planthopper, Prokelisia crocea (Hemiptera: Delphacidae), among discrete patches of its host plant, prairie cordgrass (Spartina pectinata). Results from these dispersal studies were used to predict the natural distributions and to characterize the spatial population structure of P. crocea. Planthopper emigration loss per patch increased linearly with the density of female conspecifics and was nonlinearly related to patch size (small Ͼ large Ͼ intermediate sized patches). Planthopper spatial spread was diffusive and 2.7 times faster among cordgrass patches in a heterogeneous habitat (patches embedded in nonhost vegetation) than within a homogeneous habitat (pure cordgrass). Immigration by planthoppers was an increasing function of patch size but was independent of patch isolation (at the scale of this study). The natural distribution of planthoppers in a prairie fragment, obtained from a survey of 146 cordgrass patches over five generations, was well predicted from the dispersal experiments. Planthopper densities and patch occupancy rates were positively correlated with patch size (cordgrass patches Ն0.8 ha were continually occupied), but uncorrelated with patch isolation. Based on this survey, the rate of patch extinction was 21% per generation, highest in small and moderately isolated patches, and approximately equal to the recolonization rate per generation. Finally, the dynamics of local patch populations were asynchronous, even for patch pairs Ͻ10 m apart. I conclude that P. crocea exhibits a population structure most closely resembling a mainland-island metapopulation, but with high patch connectivity. Under these circumstances, processes operating within the few mainland patches are probably more important than regional processes (patch extinctions/recolonizations) in influencing population persistence.