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

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...

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Bibliographic Details
Published in:	Ecology (Durham) Vol. 92; no. 4; pp. 924 - 937
Main Authors:	Uriarte, Maríía, Anciãães, Marina, da Silva, Mariana T. B, Rubim, Paulo, Johnson, Erik, Bruna, Emilio M
Format:	Journal Article
Language:	English
Published:	Washington, DC Ecological Society of America 01-04-2011
Subjects:	Amazonian rain forest Animal and plant ecology Animal, plant and microbial ecology Animals Aves Biological and medical sciences Birds Birds - physiology Brazil Demography dispersal kernels Effects Forest ecology Forest habitats Forests frugivory Fruit Fruits Fundamental and applied biological sciences. Psychology General aspects Habitat fragmentation Habitats Heliconia acuminata Heliconiaceae - physiology Landscapes manakins Manaus Models, Biological Old growth forests patch size Plant populations Plants Secondary forests Seed dispersal Seeds Seeds - physiology Simulation spatially explicit model thrush Time Factors Trees tropical forest Turdus albicollis Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution South America Brazil America Turdus albicollis Seeds Landscape Long distance patch size Tropical rain forest Tropical forest Manaus Amazonian rain forest thrush Dispersion Fragmentation manakins Vertebrata dispersal kernels fruginory spatially explicit model Brazil Habitat Models Aves Heliconia acuminata habitat fragmentation
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Summary:	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.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0012-9658 1939-9170
DOI:	10.1890/10-0709.1