Bush pig (Potamochoerus porcus) seed predation of bush mango (Irvingia gabonensis) and other plant species in Democratic Republic of Congo

Abstract

Bush pigs, otherwise known as red river hogs, (Potamochoerus porcus) are known seed predators in Afrotropical forests (Ghiglieri et al., 1982; Whitesides, 1985; Blake & Fay, 1997; White & Abernethy, 1997). Seed predators are key species affecting plant population demographics by influencing the survival of early successional stages, such as seeds and seedlings, thereby playing a pivotal role in the regeneration, colonisation ability and spatial distribution of plants (Hulme, 1998). While largely omnivorous (Kingdon, 1997) bush pigs are also the largest member of the granivore guild in the Democratic Republic of Congo (DRC), their relative impact on structuring plant communities could be significant. To assess the nature of bush pig seed predation, we firstly recorded all plant species predated by bush pigs at the long-term LuiKotale field site, in the DRC, over a period of eighteen months. This new list was used to estimate how many tree species (species richness) and how many trees (abundance) within the tree community are affected by bush pig predation, based on a plot census of heterogeneous primary forest (12-ha plots). We also assessed the role of bush pigs on seed fate in the fruit-fall zone, focusing on the bush mango (Irvingia gabonensis), an Afrotropical tree of local and Western World economic value (White & Abernethy, 1997). We estimated seed predation and pathogen infection on seeds in the fruit-fall area and tested the density-dependent hypothesis: the density-dependent hypothesis suggests that predation and pathogen levels will be elevated in the vicinity of the parent plant (Janzen, 1998; Connell, Boer & Gradwell, 1971; Schupp, 1992), becoming less prevalent the further one moves away from the parent plant as seeds escape such pressure (Hubbell, 1980; Howe & Smallwood, 1982). We consequently tested for potential distance effects within 100 m of parent plants to assess the relative impact of bush pigs.