Barriers or corridors? The overlooked role of unpaved roads in endozoochorous seed dispersal

Abstract

Summary1. 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. 2. 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. 3. 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. 4. The role of SLD as seed attractors was species-dependent. We found from 2Á7 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. 5. 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.

Road avoidance responses determine the impact of heterogeneous road networks at a regional scale

“…The effect produced by the nearest road has been previously observed for red deer (Rost & Bailey ; Meisingset et al . ; also in our study area: Suárez‐Esteban, Delibes & Fedriani ), although the authors did not discuss the subjacent mechanisms potentially responsible for it. In our case, the results indicate that this effect may be mediated by gap avoidance.…”

Unpaved roads disrupt the effect of herbivores and pollinators on the reproduction of a dominant shrub

“…SLD verges have the potential to host shrubby hedgerows (Suárez-Esteban et al 2013b) that can act as wind and dust screens, as well as provide pollinators with habitat for both foraging or nesting (Mwangi et al 2012;Morandin & Kremen 2013). Natural hedgerows along roadsides can be achieved by conserving endozoochorous seed dispersal vectors that positively select SLD verges for defecation (Suárez-Esteban et al 2013a) and by promoting shrub establishment along SLD verges (Karim & Mallik 2008;Suárez-Esteban et al 2013b).…”

“…Large ungulates such as red deer and caribou (Rangifer tarandus) usually avoid linear structures such as SLD (James & Stuart-Smith 2000;Suárez-Esteban et al 2013a). Accordingly, we only found a negative effect of ungulates on H. halimifolium fruit set in the scrubland (Fig.…”

“…Interestingly, SLD can also modify the behavior of large herbivores such as ungulates. Wild ungulates usually avoid SLD and other similar habitat edges (Cadenasso & Pickett 2000;Suárez-Esteban et al 2013a). Therefore, SLD could buffer herbivore damage on plant reproduction (e.g.…”

Modelagem multi-hierárquica de distribuição potencial e seleção de filtros ambientais de espécies invasoras no Estado de São Paulo

“…Rodovias estão intimamente relacionadas com a frequência de distúrbios (Fyumagwa et al, 2013;Parendes & Jones, 2000) e com a dispersão de espécies exóticas formando corredores que interligam áreas anteriormente não conectadas Suárez-Esteban, Delibes, & Fedriani, 2013;Veldman & Putz, 2010). Portanto, estes resultados são lógicos e esperados em se tratando de espécies invasoras, segundo nossas análises referentes à coleta dos pontos de ocorrência, tanto P. elliottii quanto M. maximus aparecem frequentemente associados a rodovias ou margem de rodovias (respectivamente 24,13% e 43,5% do total de pontos).…”