Seed dispersal by animals: ecological function and ecosystem service

Plant-frugivore mutualism is key to the functioning of ecosystems that guarantee the provision of services for human well-being.

Due to their mobility, toucans are important in the dispersal of seeds between distant sites. Photo: Daniel Luciano
One in four plant species depends on frugivorous animals for seed dispersal. Photo: Giselle Mangini

A tree suggests that a seed once managed to germinate and establish itself in that place. A forest multiplies that idea indefinitely. For many tree species, the arrival of a seed in favourable conditions for germination depends on the intervention of animals that consume the fruits and mobilize the seeds without damaging them. Half of the known species of seed plants require this mutualistic interaction for their dispersal, which in various tropical forests around the world includes more than three-quarters of the tree species. In the subtropical Andean forests of northwest Argentina, this dependence involves more than 250 species of trees, shrubs, epiphytes, lianas and herbs.

As we can see, seed dispersal mediated by frugivores plays a key ecological function for the maintenance and dynamics of forest ecosystems. By spreading seeds, frugivorous animals promote plant survival and ecosystem health. This is because the redistribution of seeds in space allows plants to reach new favourable sites for germination and colonize distant areas, increasing the genetic diversity of populations. This ecological process also reduces the loss of seeds due to the attack of fungi and granivorous animals and reduces competition with other plants of the same species.

Seed dispersal indirectly contributes to numerous other ecological functions. For example, that tree resulting from a successful dispersal is a habitat and source of resources for other species, provides nutrients to the soil and releases oxygen to the air, to list just some of the multiple functions it fulfils. If we extrapolate this idea to a forest, we can become aware of the magnitude of the importance of seed dispersal by animals in the complex network of mechanisms and processes that make to the functioning of an ecosystem.

The ecosystem services that result from seed dispersal by animals are also largely indirect. Through its role in supporting biological diversity and the functioning of ecosystems, it contributes to the maintenance of forest cover, carbon sequestration, regulation of runoff and the provision of resources such as forestry and non-timber products, to mention just a few. The largely indirect relationship between ecological function and the benefit for human well-being, and its consequent difficulty in measuring it in economic terms, means that the importance of seed dispersal as an ecosystem service is usually ignored or minimized. However, the decline in frugivore populations and alterations in natural environments put at risk the integrity of the interactions between plants and seed dispersers, their ecological functions and the ecosystem services they provide. The consequences of these threats are not obvious, since they affect cycles –such as the life of a tree– that are difficult to detect in short-term analysis, which contributes to the difficulty in perceiving them.

At the Instituto de Ecología Regional, several lines of research studied the functioning of plant-animal interactions in natural environments of northwest Argentina. Currently, we are trying to understand the consequences of changes in forests due to human activity on these interactions.


Dr. Pedro G. Blendinger