Can dispersal mode predict corridor effects on plant parasites?

Abstract

Abstract. Habitat corridors, a common management strategy for increasing connectivity in fragmented landscapes, have experimentally validated positive influences on species movement and diversity. However, long-standing concerns that corridors could negatively impact native species by spreading antagonists, such as disease, remain largely untested. Using a large-scale, replicated experiment, we evaluated whether corridors increase the incidence of plant parasites. We found that corridor impacts varied with parasite dispersal mode. Connectivity provided by corridors increased incidence of biotically dispersed parasites (galls on Solidago odora) but not of abiotically dispersed parasites (foliar fungi on S. odora and three Lespedeza spp.). Both biotically and abiotically dispersed parasites responded to edge effects, but the direction of responses varied across species. Although our results require additional tests for generality to other species and landscapes, they suggest that, when establishing conservation corridors, managers should focus on mitigating two potential negative effects: the indirect effects of narrow corridors in creating edges and direct effects of corridors in enhancing connectivity of biotically dispersed parasites.

Edge effects, not connectivity, determine the incidence and development of a foliar fungal plant disease

“…Previous studies have shown that host spatial distribution does affect the occurrence of vectored diseases (Thrall and Antonovics 1995). Studies from our experiment have shown that corridors affect the movement of insect pollinators such as butterflies (Haddad et al 2003), and disease levels of insect-caused galls are higher in patches connected by corridors (Sullivan et al 2011). Yet, no experimental studies have examined the role of corridors in the spread of vectored plant diseases.…”

“…Habitat corridors can alter the interactions between plant diseases and their hosts by affecting patterns of pathogen dispersal (Sullivan et al 2011). Although patterns of disease incidence ultimately depend on a variety of factors, including host susceptibility and environmental conditions, dispersal of disease propagules determines disease spread (McCartney et al 2006).…”

Microevolutionary Effects of Habitat Fragmentation on Plant-Animal Interactions

“…Small fragments are more exposed to herbivores and plant pathogens due to microclimate conditions favorable for their proliferation [9,49]. Despite the fact that herbivory rates often decrease with fragment size [50], small fragments are more exposed to novel antagonists (e.g., fungal diseases, parasitoids, galling, and mining insects) that arrive from the matrix and are strengthened by edge effects [49,51,52]. The spread of antagonists from the matrix could be strengthened by the use of biological corridors as a conservation strategy, since they may act as dispersion routes for diseases [49,52].…”

“…Despite the fact that herbivory rates often decrease with fragment size [50], small fragments are more exposed to novel antagonists (e.g., fungal diseases, parasitoids, galling, and mining insects) that arrive from the matrix and are strengthened by edge effects [49,51,52]. The spread of antagonists from the matrix could be strengthened by the use of biological corridors as a conservation strategy, since they may act as dispersion routes for diseases [49,52]. This situation is of critical importance when remnants of native habitat are surrounded by agricultural matrices, from which large generalist herbivores may act as pathogen vectors [53,54].…”

Landscape corridors can increase invasion by an exotic species and reduce diversity of native species

“…Yet, invasive species are not uniformly strong dispersers and it is possible that corridors may differentially affect their spread, depending on the capacity of each species for movement. Recent work suggests that species traits and behaviors related to movement are important for predicting species responses to altered landscape configuration, including the presence of corridors (Damschen et al 2008, Minor et al 2009, Sullivan et al 2011. We examine how differences in dispersal behavior of two social forms of invasive fire ants influence their use of corridors and their subsequent impacts on native ant diversity.…”