Theobroma grandiflora. SterculiaceaeA number of neotropical, fleshy-fruited plants have fruits structurally similar to paleotropical fruits dispersed by megafauna (mammals >103 kg), yet this disperser type was extinct in South America 10-15 Kyr BP. These neotropical fruits show impaired dispersal or are dispersed by a coterie of small vertebrates that despite providing seed dispersal services to maintain populations, may be very distinct in basic aspects of seed dispersal dynamics. We introduce an operational definition of megafaunal fruits and perform a comparative analysis of 103 neotropical fruit species fitting this dispersal mode. Megafaunal fruits are well represented in Sapotaceae, Leguminosae, Solanaceae, Apocynaceae, Sterculiaceae, Caryocaraceae, and Arecaceae and combine an overbuilt design with either a single or few (< 3 seeds) extremely large seeds or many small seeds (usually > 100 seeds). They have larger seed load/fruit than closely related non-megafauna species and usually larger seeds when controlling for variation in seediness. As megafauna were likely to perform long distance seed dispersal, megafaunal fruits allow plants to circumvent the trade-off between seed size and dispersal by relying on frugivores able to disperse enormous seed loads over long-distances. Present-day seed dispersal by scatter-hoarding rodents, runoff, flooding, gravity, and human-mediated dispersal allowed survival of megafauna-dependent fruit species after extinction of the major seed dispersers. However, we hypothesize that megafauna extinction may lead to several potential consequences, such as a scale shift reducing the seed dispersal distances, increasingly clumped spatial patterns, reduced geographic ranges and limited genetic variation and increased among-population structuring. The large-scale, fast-paced extirpation and defaunation of large-bodied frugivores in the tropics represents an important threat for these key elements of the plant-frugivore communities.

Photo: Fruit and two seeds of Theobroma grandiflora, Sterculiaceae, a megafauna-dispersed species from Pará (Brazil). Label is approx. 11 cm in length. Museu Paraense Emílio Goeldi, Belem, Pará, Brazil.
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Last Updated: Miércoles, 5 Marzo, 2008 2:01 PM