November 16, 2011
Kivu giant pouched rat caught on camera trap eating a seed of Carapa grandiflora. Photo by: Aisha Nyiramana.
For those in temperate countries familiar with squirrels, the fact that rodents play a big role in dispersing seeds is not surprise. However, it was long thought that tropical rodents behaved in such a way as to leave seeds no chance to sprout.
Kivu giant pouched rat at Nyungwe National Park, Rwanda with researcher Kate McFadden. Photo: (c) Kate McFadden, Columbia University, USA.
Using camera traps, Forget and PhD student Aisha Nyiramana with Butare University documented Kivu giant pouched rats feeding on the fruits of the Carapa grandiflora and scatter-hoarding a proportion of its seeds. Forget says that this means it's highly likely other giant rats in Africa play a similar ecological role. Although, none of the rats are listed as threatened by the IUCN Red List, they are still imperiled by the same forces driving a general decline in African wildlife: habitat loss and bushmeat hunting.
"In the Afromontane forest, cattle ranching and agriculture are destroying the last natural forest habitat that occur at high altitudes," Forget says, adding that in fragmented forests the giant rats may actually be hurting overall tree diversity, since they prey on some seeds and not others.
"Thus, when forest is disturbed, so are the giant rats," Forget adds.
But it's more than just forest loss and fragmentation that is threatening the continent's giant rats. Bushmeat hunting has also become a problem and soon may worsen according to Forget.
Giant rat for bushmeat in Cameroon. Photo by: Pierre-Michel Forget.
However these species are not seen as just food on the continent: an NGO known as APOPO has been teaching African giant rats to detect land mines in post-conflict countries. Trained to smell TNT, the rats are able to locate mines without setting them off (due to their relatively small size). The organization also works with giant rats to detect tuberculosis in human mucus. These are hero rats indeed, and they may not be the only rodents that deserve such a title. Forget says that a number of other rodents in Africa likely play a role in dispersing seeds, but much more research is needed to determine their efficacy.
"The question remains of how many of them behave as efficient dispersers, e.g. that they do not consume all their hoards as in time of food crisis, but save some of them that can be later used for seedling recruitment. It is often a very small fraction of the total seed crop produced by the plants, but such small percentage are crucial for their survival, and that of the rodents too in the end. If a rodents eats all his stored seeds, then he will starve in the lean season, and the plant won’t recruit. If the same phenomenon repeats over time due to a lack of resources, or that rodent goes extinct, then no doubt many tree species will also fail to reproduce and will disappear," explains Forget, adding that, "As in Ice Age, one seed and one giant rat can make a big difference to save the forest."
CITATION: Aisha Nyiramana, Irene Mendoza, Beth A. Kaplin, and Pierre-Michel Forget. Evidence for Seed Dispersal by Rodents in Tropical Montane Forest in Africa. Biotropica vol 43 (6) page 654-657. doi: 10.1111/j.1744-7429.2011.00810.x
Bushmeat in Cameroon. The bushmeat trade targets rodents (top two), primates (second from the bottom), and pangolins (bottom) among many other species. Photo by: Pierre-Michel Forget.
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