Barriers or corridors? The overlooked role of unpaved roads in endozoochorous seed dispersal.
Abstract
Ubiquitous linear developments, such as dirt tracks and firebreaks, termed 'soft' linear developments (SLD), represent weaker landscape modifications than paved roads and highways but still could strongly affect populations and communities. Many animals avoid SLD, but some terrestrial mammals seem to select them for faecal marking. Faeces often contain many viable seeds; therefore, SLD may receive a substantial amount and diversity of seeds, which could have important overlooked consequences for plant recruitment. To evaluate the potential role of SLD as seed attractors, we surveyed transects along SLD verges and along the adjacent scrubland in three patches of Mediterranean scrubland. On each transect, we collected ungulate, carnivore and rabbit faeces during two fruiting seasons (2009 and 2010). We quantified all seeds from fleshy-fruit shrubs within faeces and compared their abundance and diversity at SLD verges vs. adjacent scrubland. The frequency of defecation along SLD varied greatly among dispersers, but ungulates avoided SLD for defecation, and carnivores and rabbits positively selected them. Seed prevalence was higher in faeces of carnivores, and seed damage low compared with faeces of rabbits and especially ungulates. The role of SLD as seed attractors was species-dependent. We found from 2.7 to 124 times more viable seeds of carnivore- and rabbit-dispersed plants along SLD than in the scrubland, while ungulate-dispersed plants were more abundant in the scrubland. Of 13 mammal-dispersed shrubs, 4 species were exclusively found along SLD verges, two were found only in the scrubland, and seven were found in both habitats. Synthesis and applications. By promoting mammal-mediated seed dispersal, soft linear developments (SLD) may act as seed corridors. Given the extremely high density of SLD world-wide, SLD hold a significant overlooked role for management and plant conservation actions. Dispersers selecting SLD can promote roadside restoration, potentially saving financial resources. These feasible benefits must be weighed up against potential spread of alien or undesirable plant species, but we demonstrate the SLD represent a valuable management tool.