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Investigating the role of gorillas in forest maintenance and regeneration.

The role of primates as seed dispersers is widely recognized by ecologists and that of the western lowland gorilla in particular is of relevance, as this species seems to fulfil important criteria for effective dispersal, both quantitatively and qualitatively. One trait that makes it potentially unique as a seed disperser is its regular deposition of seeds in open canopy environments (which it prefers for nesting) where light will not be a limiting factor for subsequent seedling growth and survival. This may infer implications for population dynamics of dispersed plants and is relevant to timber exploiters as many timber species require a high light regime at seedling stage. Despite this importance, seed dispersal by the western lowland gorilla has not been thoroughly investigated. The present research aims to improve the knowledge of the ecological and economic functions fulfilled by the critically endangered western lowland gorilla in a logging concession at the northern periphery of the DBR. Through faecal content analysis, germination trials and monitoring of seedling emergence and growth, this study is designed to describe the diversity of species dispersed, elucidate whether or not other tight relationship exists between gorillas and plant species, and evaluate the effectiveness of dispersal directed towards nesting sites. We believe that providing an economic interest of western lowland gorilla conservation in logging concessions, ie, quantifying the recruitment of seedlings of this timber species by gorillas, and describing how they contribute to forest regeneration and biodiversity maintenance, could be an effective strategy given that logging concessions harbour most remaining gorilla populations.
Results to date demonstrate that seeds of 57 species are consumed and passed undamaged by gorillas and one faecal clump contains, on average, 2.4 seed species and 51.8 seeds; a value which exceeds those previously reported for gorillas and confirms the unique quantitative contribution to seed dispersal of this primate species. Seeds remain in the gut on average for 54.7 hours (measured in captive gorillas), which enables their dispersal over long distances. Moreover, gut passage does not reduce the germination performances of seeds; on the contrary, half of all species tested experienced an enhanced germination success, possibly as a result of separation from the fruit pulp or abrasion of the seed coat. Furthermore, because of the preference of gorillas for nesting in open canopy areas and the fact that half of all defaecation occurs at nest sites, most seeds are dispersed in habitats of early successional stages (62.7%), namely light gaps (23.8%) and young secondary forests (38.9%), with higher light regimes than other habitat types. The theory that gorilla-mediated seed dispersal directed at nest sites may be particularly suitable for post-dispersal seed fate has obtained support from ongoing pairwise comparison of seeds marked at nest site with seeds marked in control sites, where seedlings experience a higher survival and growth rate at nest sites. Furthermore, camera trap data demonstrate a potential; relationship between gorillas and one large-seeded commercial timber species, Chrysophyllum lacourtianum (Sapotaceae), whereby gorillas may play a particularly important dispersal-related role as alternative dispersers may be rare or non-existent.
Time line: PhD 2009-2015
Supervision: Nikki Tagg | Zjef Pereboom | Jean-Louis Doucet (Université de Liège, Gembloux Agro-Bio Tech) | Roseline Beudels-Jamar (Royal Belgian Institute for Natural Sciences) Funding: CRC (KMDA Dehousse) / BelSPo (SSTC)
Datum:1 jan 2009  →  1 dec 2015