Frugivorous largely increases the germination success of caucho, a large Amazon tree species.
3 Jun 2021 | Duration of reading: 6 min
By Raíssa Sepulvida Alves
Frugivorous are animals that feed on fruits with no damage to the seeds. This behaviour is known, for example, for many species of primates (see here) and birds (see here). Frugivory is a mutualistic interaction between angiosperm plants (plants with fruit) and frugivorous vertebrate animals. This interaction benefits plant species in several stages. In a study that is being finalized, we carried out a field experiment in Cotriguaçu, Mato Grosso, comparing two important processes of frugivory: seed cleaning and removal of seeds away from the cospecific tree (tree of the same species).
In the first process, the animal removes the fruit pulp, which is fleshy in many cases, to feed on, which cleans the seeds. We, humans, do the same, for example, with the avocado and mango: we eat the pulp, and we discard the large seeds. The seed cleaning decreases the pathogen and predators attack, which are attracted by the fleshy pulp, rich in sugar. The same happens in our house when the ripe fruits rot quickly. Besides the enemy’s avoidance, the seed cleaning also removes germination inhibitors, triggering the embryo development.
In a second moment, the animal may ingest the whole fruit keeping the seeds intact. Then, the animal defecates the cleaned seeds over the area it uses to move around. We do the same with fruits that have small seeds, hard to remove manually, like grapes and guavas: we swallow the whole fruit (pulp and seeds). If we still lived in the forest as our ancestors, we would also spread the seeds when we defecated on the soil. I know that is weird to imagine such a scene, but it is exactly what happens with wild animals. When the frugivores clean and disperse the seeds, they act as forest gardeners, increasing the germination success of trees that will become reproductive adults that produce new fruits.
Figure 1. Woolly monkey (Lagothrix cana) (a) feeding, (b) curious, (c) eating caterpillars, (d) jumping, (e) vocalizing and (f) female with a baby on the back.
The caucho (Castilla ulei) is commonly present in the diet of large primates in the Amazon forest as the spider monkey (Ateles sp.) and the woolly monkey (Lagothrix sp.). These animals feed on the pulp of the fruit, discarding the clean seeds under the cospecific or dispersing them far away.
We carried out a germination experiment in the field to test the importance of seed cleaning and removal away from the cospecific, thus simulating the action of a frugivorous primate (but also other frugivorous animals), cleaning the seed manually. Clean seeds germinated 9.5 times more and produced 9 times more seedlings than seeds that were not cleaned, regardless of where they were deposited. These results tell us that seed cleaning by frugivores is a crucial process for caucho germination.
In our study site, Cotriguaçu, Mato Grosso, we observed woolly monkeys (L. cana) feeding on caucho’s tree and other 25 species at least of fruits from August 2018 and December 2019.
Figure 2. Adult female of gray woolly monkey (Lagothrix cana) with a baby on the back feeding on the caucho (Castilla ulei) fruits. Illustration: Paula Paz.
Caucho in Spanish means rubber. This species was the pioneer in rubber harvest, even before the rubber tree (Hevea brasiliensis). The Caucho is a species with a long life cycle, that is, individuals take a long time to become reproductive adults and, therefore, are more susceptible to early mortality due to unpredictable events (such as changes in climate and the fall of other adult trees). In our study, for example, even with pulp removal, only 1% of the 800 monitored individuals remained alive after 300 days. Therefore, the large increase in the germination rate after the manipulation of the fruit by frugivores is important to compensate for the high mortality rate of seedlings and maintain the renewal of their populations.
Figure 3. Different stages of caucho: (a) fleshy infructescence; (b) cleaned seeds; (c) germinated seeds; seedlings with (d) 10 days and (e) five months. Figure from Sepulvida (2020)
Figure 4. Scheme showing pulpy seeds attracting various predators and pathogenic fungi under the fruiting tree, where there is a high density of fruit. When cleaned by frugivores such as the woolly monkey, the seeds escape these agents of mortality and are more likely to germinate and become seedlings regardless of where they are deposited. Authorship of Sepulvida (2020)
The woolly monkeys are the most sighted frugivores in Cotriguaçu (1.8 individuals/10 km). These animals can feed on a great quantity of caucho’s fruits. Conversely, species such as caucho, which are hardly dependent on large frugivores to maintain their reproductive cycle, face two big threats: the loss of forest area per si and the loss of large seed dispersers. Large-sized vertebrates are the first to disappear either by hunting or habitat degradation. Even if small forest fragments remain standing, the extinction of large vertebrates such as woolly monkeys threaten the permanence of species highly dependent on frugivory.
Figure 5. Mean number of (a) germinated seeds, (b) seedlings and (c) death in up to 297 days under the treatments: cleaned seeds or seeds with pulp (with no frugivore manipulation) under a conspecific or heterospecific tree. Each sample size had 10 seeds. Figure from Sepulvida (2020)
As we see happening in the Amazon, large areas of forests are being converted into pastures and monocultures or even suffering irregular logging. Such threats result in a ripple effect of loss of animals and the plant species they disperse. This loss of interactions is already critically advanced in the Atlantic Forest, which is explored from colony Brazil. And if we don't stop deforestation in the north of the country, we will see a similar process happening in the Amazon. Thus, studies like ours, which assess the benefits and complexity of ecological relationships in this megadiverse and balanced Amazonian system, albeit under constant threat of threat, are extremely important.
Science is done collaboratively
This project was developed as part of the master's dissertation biologist Raíssa Sepulvida in the Post-Graduation Program in Ecology and Biodiversity at UNESP - Rio Claro, with supervisor of the Professor PhD. Laurence Culot of the Laboratory of Primatology and co-supervisor PhD Carlos Peres, Professor at the School of Environmental Sciences, University of East Anglia, UK. The field activities were carried out at Fazenda São Nicolau/ONF-Brasil in partnership with the ecotourism company SouthWild and were sponsored by FAPESP and Rufford Foundation.
Want to know more? Access the links below!
Comita, L. S. et al. (2014) Testing predictions of the Janzen-Connell hypothesis: A meta-analysis of
experimental evidence for distance- and density-dependent seed and seedling survival. Journal of Ecology, 102(4), 845-856. (Link)
Fuzessy, L. F. et al. (2016). How do primates affect seed germination? A meta-analysis of gut passage effects on neotropical plants. Oikos, 125(8), 1069-1080. (Link)
Levi, T., Peres, C. A. (2013). Dispersal vacuum in the seedling recruitment of a primate-dispersed Amazonian tree. Biological Conservation, 163, 99-106. (Link)
Sepulvida, R. (2020). Effect of fruit handling by frugivores on seed dispersal effectiveness. Dissertação de mestrado, Pós-graduação em Ecologia e Biodiversidade, Universidade Estadual Paulista (UNESP – Rio Claro). (Link)