Seed-dispersal distributions by trumpeter hornbills in fragmented landscapes

Abstract

Frugivorous birds provide important ecosystem services by transporting seeds of fleshy fruited plants. It has been assumed that seed-dispersal kernels generated by these animals are generally leptokurtic, resulting in little dispersal among habitat fragments. However, little is known about the seed-dispersal distribution generated by large frugivorous birds in fragmented landscapes. We investigated movement and seed-dispersal patterns of trumpeter hornbills (Bycanistes bucinator) in a fragmented landscape in South Africa. Novel GPS loggers provide high-quality location data without bias against recording long-distance movements. We found a very weakly bimodal seed-dispersal distribution with potential dispersal distances up to 14.5 km. Within forest, the seed-dispersal distribution was unimodal with an expected dispersal distance of 86 m. In the fragmented agricultural landscape, the distribution was strongly bimodal with peaks at 18 and 512 m. Our results demonstrate that seed-dispersal distributions differed when birds moved in different habitat types. Seed-dispersal distances in fragmented landscapes show that transport among habitat patches is more frequent than previously assumed, allowing plants to disperse among habitat patches and to track the changing climatic conditions.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…The ability to fly long distances allows large-bodied frugivores to connect habitat patches (Lees and Peres, 2009;Spiegel and Nathan, 2007). Habitat fragmentation can cause changes in the movement patterns of frugivores, with consequences for seed dispersal (Lenz et al, 2011), especially for plants with large, big-seeded fruits because their dispersal often only depends on one or a few large frugivores (Corlett, 1998;Guimarães et al, 2008). Seed dispersal effectiveness of plants with smaller fruit largely depends on the range of frugivore body sizes in the network, with smaller frugivores allowing for within-patch dispersal and larger frugivores for between-patch dispersal (Spiegel and Nathan, 2007).…”

“…Large frugivores (e.g. the trumpeter hornbill Bycanistes bucinator) may change their movement patterns, with unimodal seed-dispersal distribution within forests but bimodal distribution in fragmented agricultural landscapes (Lenz et al, 2011). Individual fruiting trees, even exotic ones, in farmland may be important food sources for the frugivore community and thus represent foci for seed dispersal and forest regeneration, even in highly degraded landscapes (Berens et al, 2008;Fisher et al, 2010).…”

Space use by foragers consuming renewable resources

“…Often these animals play an important ecological role as part of mutualistic interactions, as they pollinate or disperse the seeds of the plants they visit. For seed dispersal in particular, empirical and theoretical studies show that the spatial distribution of plants contributes to the seed deposition patterns through its effect on animal movement [7,8,9,10,11,12,13,14,15]. Understanding the emergence of space use of animals foraging for renewable resources, besides being an interesting theoretical topic, can allow us to build better studies of animal-plant interactions.…”

Spatial and Temporal Variation in Hornbill Densities in Namdapha Tiger Reserve, Arunachal Pradesh, North-East India

“…Protected Areas like the Namdapha Tiger Reserve that harbour hornbill populations at relatively high densities, can potentially serve as a source for adjoining unprotected areas, which experience logging and higher hunting pressures and have low hornbill densities. Given that most hornbill species are highly mobile and range widely, greater abundances of hornbills inside Protected Areas would also result in greater probability of movement of hornbills between forest areas, resulting in greater rates of seed dispersal and potentially enhanced regeneration of degraded nonprotected forests [33].…”