What drives germination and seedling survival in an Afrotropical forest?

Hunting in otherwise intact tropical forests removes organisms from some trophic levels, which can change population and community dynamics at other levels. The preferred game species can be dispersers of seeds (e.g. primates, large birds), predators of seeds (e.g. rodents), browsers of juvenile plants (e.g. ungulates) or disturbers of the forest floor (e.g. pigs or peccaries). Hunting one or more of these groups will change animal abundances and this may change seed dispersal patterns and seed or seedling survival in the forest. Previous studies have shown that seedling communities in an Afrotropical rainforest in southeastern Nigeria are strongly affected by the loss of important seed-dispersing primates, including Cross River gorillas (Gorilla gorilla diehli), chimpanzee (Pan troglodytes elioti) and drill (Mandrillus leucophaeus). The dynamics of the seedling community in the forest understory play a central role in directing plant recruitment and the future composition and structure of the forest.

Sampling in the current study
(a) Edu Effiom and Dan Out tagging seedlings; and (b) a male drill (Mandrillus leucophaeus) in a captive breeding enclosure in the study area, run by Pandrillus. Image credits: (a) E. Effiom; (b) O. Olsson.

A recent study by Olsson et al. and published in AoBP investigated how germination and survival of tree seedlings are affected by competition and reduced seed dispersal in three neighbouring forest reserves in south-eastern Nigeria. The authors used a total of sixty 5 × 5 m plots of three types: plots cleared of all seedlings, plots selectively cleared of all primate-dispersed seedlings and control plots. The authors conclude that inter-seedling competition may be irrelevant to seedling recruitment in hunted sites, where dispersal limitation appears to be a much stronger force shaping the seedling plant community, and thus hunting indirectly reverses the importance of competition and dispersal limitation in structuring seedling communities. Thus, the loss of large mammals, such as apes and monkeys, is likely to change the future of the forests.

Further reading

Olsson, O., Nuñez-Iturri, G., Smith, H. G., Ottosson, U., & Effiom, E. O. (2019). Competition, seed dispersal and hunting: what drives germination and seedling survival in an Afrotropical forest? AoB PLANTS, 11(2). https://doi.org/10.1093/aobpla/plz018