Evidence for Seed Dispersal by Rodents in Tropical Montane Forest in Africa

The interaction between granivorous scatterhoarding mammals and plants is a conditional mutualism: scatterhoarders consume seeds (acting as predators), but the movement of seed by scatterhoarders may contribute to dispersal (acting as mutualists). Understanding the ecological factors that shape this relationship is highly relevant in anthropogenically disturbed tropical forests where large‐bodied frugivores are extirpated. In such forests, large‐seeded trees that once depended on these frugivores for dispersal may now only have scatterhoarders as prospective dispersers. We studied Carapa oreophila (Meliaceae) in an Afromontane forest, to test the hypotheses that the proportion of seeds immediately consumed or hoarded (dispersed) would vary over a disturbance gradient. Temporal replication also afforded exploration of how habitat effects might vary with food availability. Using a Bayesian framework, we demonstrate that seeds were more likely to be hoarded in less disturbed forest, irrespective of temporal variation in food abundance. In contrast, forest disturbance only appeared to increase seed predation in temporal replicates that coincided with sustained food availability. These results highlight the potential variability in the dynamics between plants and scatterhoarders over fine temporal scales, elucidating possible ecological scenarios where scatterhoarders might act as mutualists (contributing positively to plant recruitment). Our study also fills important knowledge gaps about the importance of scatterhoarders as dispersers in tropical forests depleted of large‐bodied frugivores, particularly in Africa where scatterhoarding mutualisms have not been extensively studied.

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“…While some recent studies have emerged from African forests (Nyiramana et al . , Aliyu et al . , Moupela et al .…”

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Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

et al. 2018

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“…En los bosques tropicales, la estructura espacial de las especies de árboles está altamente determinada por los síndromes de dispersión de semillas y por la aparición de micrositios favorables para el desarrollo de los individuos (Seidler y Plotkin 2006), por lo que las poblaciones con frutos dispersos de forma zoocoria y barocoria tienden a presentar patrones espaciales agregados (Nyiramana et al 2011), conforme lo observado para la población y los individuos reproductivamente maduros. Peres y Baider (1997), Wadt et al (2005) y Salomão (2009) encontraron a través del índice con base en unidades muestreadas, patrones predominantemente agregados en los individuos de B. excelsa.…”

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Patrón espacial y métodos de muestreo para Bertholletia excelsa (castaña de Pará) en la Mesorregión del Bajo Amazonas, estado de Pará, Brasil

et al. 2017

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SUMMARYThe aim of this study was to analyze the spatial pattern and sampling methods for Bertholletia excelsa. The inventory of exploration, by mapping Cartesian coordinates of all trees with dbh ≥ 20 cm, was carried out in an area of 1,000.31 ha. For the definition of the diametric structure, multivariate techniques were used: cluster and discriminant analysis. To analyze the spatial patterns, individuals were grouped into three levels: population, young individuals and adults; being the random deviation defined by the Ripley's K function. The forest inventories were simulated with a simple random sampling, systematic and adaptive, taking into account plots of 2,500 m², with a sampling intensity of 15 % and an error range of 10 %. Comparisons between sampling methods were performed for the accuracy and precision. Four hundred and forty six trees were registered, of which 59 were young individuals and 387 were adults. A low number of trees in the early stages and a high number of individuals in the intermediate classes characterize the diametric structure. The spatial pattern of the adult population was aggregated, while the young individuals were randomly distributed. Systematic sampling is the best procedure to estimate the total number of individuals of B. excelsa; however, there is a need to investigate the effect of aggregation and size of the largest plots of 0.25 hectares on the estimates of adaptive cluster sampling.

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“…Nyiramana et al . () studied the fate of threaded Carapa grandiflora seeds in a montane forest in Rwanda, recovering several cached seeds and finding seedling cotyledon evidence that indicated scatterhoarding by seed‐dispersing rodents. Aliyu et al .…”

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confidence: 99%

“…For African forests as a whole, only a few studies have examined seed fate and the role of rodents in seed dispersal (Doucet , Nyiramana et al . , Moupela et al . , Aliyu et al .…”

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Telemetric tracking of scatterhoarding and seed fate in a Central African forest

Rosin

Poulsen

2016

Biotropica

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In seed predation studies, removal of a seed is only the first step of a dynamic process that may result in dispersal rather than seed death. This process, termed seed fate, has received little attention in African forests, particularly in Central Africa. We experimentally assessed the initial steps of seed fate for two tree species-the large-seeded Pentaclethra macrophylla and the relatively small-seeded Gambeya lacourtiana-in northeastern Gabon. Specifically, we evaluated whether seed size and seed consumer identity are important determinants of seed fate. We established experimental stations under conspecific fruiting trees, each comprising three seeds fitted with telemetric thread tags to facilitate their recovery, and a motion-sensitive camera to identify visiting mammals. In total, animals removed 76 tagged seeds from experimental stations. Small Murid rats and mice primarily removed small Gambeya seeds, whereas large-bodied rodents and mandrills primarily removed large Pentaclethra seeds. Gambeya seeds were carried shorter distances than Pentaclethra seeds and were less likely to be cached. The two large-bodied rodents handled seeds differently: Cricetomys emini larderhoarded nearly all (N = 15 of 16) encountered Pentaclethra seeds deep in burrows, while Atherurus africanus cached all (N = 5 of 5) encountered Pentaclethra seeds singly under 1-3 cm of leaf litter and soil, at an average distance of 24.2 m and a maximum distance of 46.3 m from experimental stations. This study supports the hypothesis that seed fate varies based on seed size and seed consumer identity, and represents the first telemetric experimental evidence of larderhoarding and scatterhoarding in the region.Abstract in French is available with online material.

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Evidence for Seed Dispersal by Rodents in Tropical Montane Forest in Africa

Cited by 38 publications

References 24 publications

Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

Patrón espacial y métodos de muestreo para Bertholletia excelsa (castaña de Pará) en la Mesorregión del Bajo Amazonas, estado de Pará, Brasil

Telemetric tracking of scatterhoarding and seed fate in a Central African forest

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