Disentangling the drivers of reduced long-distance seed dispersal by birds in an experimentally fragmented landscape

Abstract

Seed dispersal is a crucial component of plant population dynamics. Human landscape modifications, such as habitat destruction and fragmentation, can alter the abundance of fruiting plants and animal dispersers, foraging rates, vector movement, and the composition of the disperser community, all of which can singly or in concert affect seed dispersal. Here, we quantify and tease apart the effects of landscape configuration, namely, fragmentation of primary forest and the composition of the surrounding forest matrix, on individual components of seed dispersal of Heliconia acuminata, an Amazonian understory herb. First we identified the effects of landscape configuration on the abundance of fruiting plants and six bird disperser species. Although highly variable in space and time, densities of fruiting plants were similar in continuous forest and fragments. However, the two largest-bodied avian dispersers were less common or absent in small fragments. Second, we determined whether fragmentation affected foraging rates. Fruit removal rates were similar and very high across the landscape, suggesting that Heliconia fruits are a key resource for small frugivores in this landscape. Third, we used radiotelemetry and statistical models to quantify how landscape configuration influences vector movement patterns. Bird dispersers flew farther and faster, and perched longer in primary relative to secondary forests. One species also altered its movement direction in response to habitat boundaries between primary and secondary forests. Finally, we parameterized a simulation model linking data on fruit density and disperser abundance and behavior with empirical estimates of seed retention times to generate seed dispersal patterns in two hypothetical landscapes. Despite clear changes in bird movement in response to landscape configuration, our simulations demonstrate that these differences had negligible effects on dispersal distances. However, small fragments had reduced densities of Turdus albicollis, the largest-bodied disperser and the only one to both regurgitate and defecate seeds. This change in Turdus abundance acted together with lower numbers of fruiting plants in small fragments to decrease the probability of long-distance dispersal events from small patches. These findings emphasize the importance of foraging style for seed dispersal and highlight the primacy of habitat size relative to spatial configuration in preserving biotic interactions.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…Due to their requirements for extensive home ranges, large frugivorous birds are especially extinction prone in small fragments (Renjifo, 1999;Uriarte et al, 2011). The ability to fly long distances allows large-bodied frugivores to connect habitat patches (Lees and Peres, 2009;Spiegel and Nathan, 2007).…”

“…Sub-Andeans: Renjifo, 1999; Amazonia: Uriarte et al, 2011). The proportion of fruit in primate diets is positively correlated with home range size (Milton and May, 1976) and species persistence in forest fragments (Boyle and Smith, 2010).…”

“…The proportion of fruit in primate diets is positively correlated with home range size (Milton and May, 1976) and species persistence in forest fragments (Boyle and Smith, 2010). The disappearance of large frugivores thus decreases the probability of long-distance dispersal of fleshy-fruited plants from small patches and fragments (Fragoso, 1997;Fragoso et al, 2003;Spiegel and Nathan, 2007;Uriarte et al, 2011). The response of small-to-medium-sized frugivores to fragmentation is probably driven by species' habitat specialisation and matrix tolerance, and their ability of gap-crossing (Table 1).…”

Chuva de sementes em remanescentes florestais de Campo Verde, MT

“…Resultados similares foram obtidos por Stefanello et al (2009) em trecho de vegetação ciliar (Floresta Estacional Semidecidual), no meio e na foz do rio Pindaíba, em Mato Grosso, onde 85,7 e 77,5% das espécies desses ambientes não utilizam o vento como forma de propagação (zoocórica). Altas proporções de espécies zoocóricas presentes na chuva de sementes são indícios de ambientes conservados (TABARELLI;PERES, 2002;MELO et al, 2010;URIARTE et al, 2011).…”

Climate change suggests a shift of H5N1 risk in migratory birds

“…The result indicated that the transmission efficiency of HPAI H5N1 among poultry was 1.7 times higher in regions where infected wild birds had been detected compared with regions without infected wild birds (Keawcharoen et al, 2011). In addition, waterfowl may transfer the virus mechanically during long distance migration, and feathers infected with HPAI H5N1 could also be a source of environmental contamination with high viral loads (Uriarte et al, 2011;Yamamoto et al, 2010).…”