Holbrook, K. M., and T. B. Smith. Seed dispersal and movement patterns in two species of Ceratogymna hornbills in a West African tropical lowland forest. Oecologia

Center for Population Biology, University of California, Davis, CA 95616 USA
Oecologia (Impact Factor: 3.09). 09/2000; 125(2):249-257. DOI: 10.1007/s004420000445


We studied two species of Ceratogymna hornbills, the black-casqued hornbill, C. atrata, and the white-thighed hornbill, C. cylindricus, in the tropical forests of Cameroon, to understand their movement patterns and evaluate their effectiveness as seed dispersers. To estimate hornbill contribution to a particular tree species' seed shadow we combined data from movements, determined by radio-tracking, with data from seed passage trials. For 13 individuals tracked over 12 months, home range varied between 925 and 4,472 ha, a much larger area than reported for other African avian frugivores. Seed passage times ranged from 51 to 765 min, with C. atrata showing longer passage times than C. cylindricus, and larger seeds having longer gut retention times than smaller seeds. Combining these data, we estimated that seed shadows were extensive for the eight tree species examined, with approximately 80% of seeds moved more than 500 m from the parent plant. Maximum estimated dispersal distances for larger seeds were 6,919 and 3,558 m for C. atrata and C. cylindricus, respectively. The extent of hornbill seed shadows suggests that their influence in determining forest structure will likely increase as other larger mammalian dispersers are exterminated.

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Available from: Kimberly Mae Holbrook, Nov 11, 2014
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    • "Avian seed dispersers can contribute to the spread of invasive species with generalized dispersal mechanisms (Renne et al. 2002). In the Usambara Mountains of Tanzania, silvery-cheeked hornbills (Ceratogymna brevis) are effective long-distance (up to four km) dispersers of the exotic Maesopsis eminii (Rhamnaceae) (Cordeiro et al. 2004), and significantly contribute to the rapid invasion of this West African species , which is also dispersed by Ceratogymna hornbills in its native habitat (Holbrook and Smith 2000). "
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    • "The same assumption has been made implicitly in recent work (Holbrook and Smith 2000; Koike et al. 2011). The right-hand side of Eq. (3) assumes that, at time T 0 , feeding occurred at location P 0 and seed deposition happened T* units of time later at a distance R* from the original location, while the conditional density in the left-hand side, refers, in a more general context, to the situation: At time T 0 the monkey was at P 0 , and T units of time later, it was at a distance R from P 0 . "
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    • "It not only influences the spatial patterns of seed dispersal but also affects the regeneration pattern and the spatial-genetic structure of plant populations (Born et al., 2008; Choo et al., 2012; Fragoso et al., 2003). Animal activities that have been shown to contribute differentially to the primary seed shadow include the movements of vectors through their home ranges (Holbrook and Smith, 2000; Will and Tackenberg, 2008), patterns of resting, sleeping and defecation (Cousens et al., 2010; Julliot, 1994), the distribution of food sources and the matrix in between (Alcantara et al., 2000; Harata et al., 2012), seed size (Alcantara et al., 2000; Stevenson, 2000), gut passage time (Stevenson, 2000; Westcott et al., 2005), social and mating behavior (Karubian et al., 2012; Kesler et al., 2010) and interactions between individuals (Charles-Dominique, 1995; Scofield et al., 2012, 2011; Stevenson, 2000). Hence, predicting the seed shadows of animal-dispersed species is highly challenging because of the many factors affecting animal movement decisions and, thus, the unintentional dispersal of seeds. "
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