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

Department of Biology, San Francisco State University, San Francisco, California, United States
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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    • "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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    ABSTRACT: Seed dispersal is known to play an important role in the ecology and evolution of plant communities, and there is ample evidence that seed dispersal by primates influences plant population dynamics in tropical forests directly. We used non-parametric statistical methods to estimate the dispersal kernels (i.e. the probability that a seed is moved at a particular distance) generated by woolly monkeys (Lagothrix lagothricha lugens) at a sub-Andean forest in Colombia and test the hypothesis that the time of feeding influences dispersal distances. We collected data on monkey ranging patterns with the aid of GPS units and obtained information on gut retention times from behavioral follows to build a model based on the kernel density estimator. Woolly monkeys drop most seeds hundreds of meters from parent trees and only a small proportion of seeds within close proximity. The time of seed ingestion had a significant effect on dispersal kernels, with seeds from fruits consumed early in the day having a greater chance of landing further away from the tree than seeds swallowed in the late afternoon. The results of this study build on previous findings suggesting that woolly monkeys have a positive effect on the fitness of plants, which may be exacerbated in mountain forests where the diversity of large frugivores is low.
    Full-text · Article · Oct 2014 · International Journal of Primatology
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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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    ABSTRACT: The spatial pattern of endozoochorous seed dispersal depends strongly on the movement patterns of the disperser and the gut transit times of the seeds. In this study, we developed an individual-based simulation model for seed dispersal in the tropical tree Parkia panurensis carried out via two primate species (Saguinus mystax and Saguinus nigrifrons) using data collected at the Estación Biológica Quebrada Blanco in northeastern Peruvian Amazonia. From field data, we identified factors determining the movement patterns of the primates. We assumed that the need for energy (food) is the driving force for movement and that other activities are scheduled accordingly. The final movement pattern is therefore an interplay between directional travel toward fruit trees, semi-directional searching for prey and stationary resting phases. First, we parameterized the model using a genetic algorithm such that simulated and field data converge at very similar target values for the daily path length and home range size. Second, a sensitivity analysis of several parameters in our simulation model revealed the following parameters to be the most important for producing a realistic movement pattern: the number and position of feeding trees and the energy gained from the selected food type. Finally, we introduced the gut transit times of seeds and the defecation habits of the primates, which allowed us to examine the seed shadow generated by a specific troop of primates. The simulated seed shadows of individual P. panurensis trees are similar to those found in nature. We conclude that agent-based modeling using behavioral data has the potential to improve home range estimation and seed shadow prediction, especially for unexplored locations.
    Full-text · Article · Apr 2014 · Ecological Modelling
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    • "The spatio-temporal patterns of animal movement (disperser movement) represent an important component of passive dispersal and are, therefore, a key determinant of seed shadows (the spatial distribution of dispersed seeds and other propagules; Russo et al. 2006). For example, propagule dispersal curves are affected by the movement behaviour of different disperser species (Holbrook and Smith 2000, Westcott et al. 2005), as well as by spatial variation, such as the configuration of landscapes and the patchiness of resources (Morales and Ellner 2002, Carlo and Morales 2008). Despite its importance, the mechanism and effectiveness of LDD events mediated by migratory animals, especially birds, remain almost unexplored. "
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    ABSTRACT: Long distance dispersal (LDD) of propagules is an important determinant of population dynamics, community structuring and biodiversity distribution at landscape, and sometimes continental, scale. Although migratory animals are potential LDD vectors, migratory movement data have never been integrated in estimates of propagule dispersal distances and LDD probability. Here we integrated migratory movement data of two waterbird species (mallard and teal) over two continents (Europe and North America) and gut retention time of different propagules to build a simple mechanistic model of passive dispersal of aquatic plants and zooplankton. Distance and frequency of migratory movements differed both between waterbird species and continents, which in turn resulted in changes in the shapes of propagule dispersal curves. Dispersal distances and the frequency of LDD events (generated by migratory movements) were mainly determined by the disperser species and, to a lesser extent, by the continent. The gut retention time of propagules also exerted a significant effect, which was mediated by the propagule characteristics (e.g. seeds were dispersed farther than Artemia cysts). All estimated dispersal curves were skewed towards local-scale dispersal and, although dispersal distances were lower than previous estimates based only on the vector flight speed, had fat tails produced by LDD events that ranged from 230 to 1209 km. Our results suggest that propagule dispersal curves are determined by the migratory strategy of the disperser species, the region (or flyway) through which the disperser population moves, and the propagule characteristics. Waterbirds in particular may frequently link wetlands separated by hundreds of kilometres, contributing to the maintenance of biodiversity and, given the large geographic scale of the dispersal events, to the readjustment of species distributions in the face of climate change.
    Full-text · Article · Apr 2013 · Ecography
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