Apex predators can structure ecosystems through trophic cascades: linking the frugivorous behaviour and seed-dispersal patterns of mesocarnivores

Current global change scenarios demand knowledge on how anthropogenic
impacts affect ecosystem functioning through changes in food web
structure. Frugivorous mesocarnivores are a key link in trophic cascades
because, while their abundance and behaviour are usually controlled by
apex predators, they can provide high-quality seed-dispersal services to
plant communities. Thus, the recent rewilding of large carnivores
worldwide can trigger cascading effects for plants. We
investigated the top-down effects of an apex predator (Iberian
lynx Lynx pardinus) on seed-dispersal services mediated by two
mesocarnivore species (red fox Vulpes vulpes and stone marten Martes
foina) at the plant community level by comparing areas with and without
lynx in a Mediterranean mountain range in Southern Spain. We
collected scats of mesocarnivores (n = 1575) to assess frugivory and seed
dispersal of 15 plant species over two consecutive fruiting seasons and
two habitat types (open and forest). Specifically, we assessed the effect
of lynx presence on (i) seed occurrence and fleshy-fruit biomass per scat,
(ii) the number of scats containing seeds, and (iii) the diversity of
dispersed seeds. The quantity and diversity of dispersed seeds drastically
decreased under predation risk for both mesocarnivore species. Seed
dispersal by stone martens was negatively affected by the presence of
lynx, with a marked reduction in the number of scats with seeds (93%) and
the diversity of dispersed seeds (46%). Foxes dispersed 68% fewer seeds in
open habitats when coexisting with lynx, probably leading to differential
contributions to seed-dispersal effectiveness among habitats. Our
study reveals a novel trophic cascade from apex predators to plant
communities. The behavioural responses of frugivorous mesocarnivores to
predation risk and the reduction in the intensity of their faecal
deposition pattern are probably related to their lower abundance when
co-occurring with apex predators. While rewilding apex predators is a
successful conservation tool, attention should be paid to cascading
effects across food webs, particularly where frugivore megafauna are
missing and mesocarnivores provide unique services to plant communities.