On the island nation of Madagascar, the long-limbed local primates, lemurs, are for some trees, essential helpers. It is advantageous for a tree to scatter its progeny not just to the wind and widely, but where they will find fertile ground and clement conditions for growth. Some trees recruit animals for this task by tempting them with delicious and nutritious fruits – inside which hide seeds sealed in hard, indigestible coats for passage through the hazards of teeth, stomach, and alimentary canal.. In the tropics, up to 90 percent of trees make use of animals to spread their seeds out from under the branches of the parent tree. In some cases, the fruits are adapted to specific animal partners, without which the trees have difficulty thriving. The fruit-eating lemurs are disappearing from Madagascar, and that may spell trouble for the trees.
Researchers at Rice University wondered if the lemurs deposited seeds in better-than-average growing spots, and how the attentions of multiple species of lemurs synergized. Graduate student Onja Razafindratsima and colleagues observed the relationship of the long-lived rainforest tree, Cryptocarya crassifolia, and three lemur species, Eulemur rubriventer (red- bellied lemur), Eulemur rufifrons (red-fronted brown lemur), and Varecia variegata editorum (southern black-and-white ruffed lemur). The tree C. crassifolia makes large brown fleshy fruits about the size of an apricot. Lemurs are the largest animals that eat them. The three lemur species all poop seeds while resting, feeding, or moving about the forest canopy, but each species has its own travel patterns.
Razafindratsima, a Madagascar native, recruited and trained a team of about ten people living near the Centre ValBio research station near Ranomafana Nation Park to observe lemur toiletry and categorize the density of the forest canopy where the lemurs deposit C. crassifoliaI seeds. The team members used their experience and knowledge of the forest to follow 24 groups of lemurs without the assistance of radio collars. The set out to test three hypotheses:
- lemurs deposit seeds in non-random rainforest “microhabitats’ defined by how much sunlight pierces the canopy cover
- these lemur-ferried seeds fare better, on average, than brethren fallen beneath the branches of the parent trees or dropped in random spots
- lemur species are not equally helpful to the tree. Some lemurs leave seeds in better locations, on average, than others.
Razafindratsima and colleagues found that, on balance, the lemurs were not depositing seeds in particularly advantageous rainforest locations (they didn’t do better than seeds the team planted at random), through seeds moved out from under the parent trees were four times as likely to sprout than seeds that fell straight to ground. Their report is available ahead of print in ESA’s journal Ecology.
Onja Harinala Razafindratsima and Amy Elizabeth Dunham (In press). Assessing the impacts of nonrandom seed dispersal by multiple frugivore partners on plant recruitment. Ecology. http://dx.doi.org/10.1890/14-0684.1
Rice University news: “Gardeners of Madagascar Rainforest at Risk.”