By Will DeBerry
We all know that a plant or animal does not have to be large to make a huge impact within an ecosystem. The sea star, for example, is technically a keystone species. When they are removed from ecosystem mussels reproduce so quickly that it negatively affects the rest of the environment. Yet a recent study, which used Peru’s Manu Biosphere Reserve in its computer model, noted that larger bird species are just as important as their smaller counterparts in terms of ‘size matching’ seed size to bird size. It also noted that larger species (both birds and mammals) are frequently more affected by deforestation than other animals.
“It has been suggested that big frugivores (fruit-eating birds) are important, but why?” team leader Isabel Donoso said in an interview. The answer lies largely in the fact that only large birds can consume and transport larger seeds. When a plant has a seed so large only certain frugivores can travel with it, the risk becomes higher, but the reward sweetens as well. Large frugivores have the potential to spread seeds much further away from their starting location than do their smaller counterparts. Since producing a large seeds requires tons of energy from the plant, larger seeds are rare just like large frugivores. Both need to exist for the other to thrive.
However, this gamble does not account for deforestation and human impact. “Big birds or big mammals are usually the ones that are more impacted by humans because of deforestation,” Donoso said. This phenomenon of human-induced animal loss is known as ‘defaunation’ and can have a terrible impact through “…diversity decays in plant communities, trophic cascades in food webs, and the collapse of entire ecological communities (i.e. ecological meltdown).”
As the team removed the number of large frugivores from their model, they saw a drastic drop in the spreading of larger seeds. As the number of large frugivores continued to trend downward in the model, the number of large seeds in the ecosystem dwindled rapidly as well, which points toward large frugivores as a prerequisite to spreading larger seeds and maintaining forest biodiversity. The original journal article concludes with “In particular, the subtle interplay between size matching and size trade-offs in plants highlights that defaunation will have severe and unforeseen consequences for coupled plant and animal communities, and their pivotal ecosystem functions.”
Rainforest Partnership is always looking for the most efficient method to make the strongest impact. Along with our other projects in the Colibri area (ecotourism, beekeeping, and a butterfly sanctuary), Rainforest Partnership is conducting a biodiversity study of montane mammals adjacent to the Pui Pui Protected Forest–the first of its kind for this area! The study will inform us of the biodiversity of this part of the Colibri Cloudforest, giving us a greater understanding of these mammals and their role in their environment. Studies such as this one become increasingly significant as human-caused deforestation continues–we need to know the most efficient way to preserve our biodiversity. “If we seek to avoid – and halt – the decay of ecosystem functions, especially in the tropics, we urgently need conservation measures that target large animal species,” Donoso said in a statement. “Otherwise the lush diversity of tropical forests, as we know it, could soon be a shadow from the past.”
Donoso, I., Schleuning, M., García, D., & Fründ, J. (2017, May). Defaunation effects on plant recruitment depend on size matching and size trade-offs in seed-dispersal networks. Proc. R. Soc. B (Vol. 284, No. 1855, p. 20162664). The Royal Society.
John C. Cannon. (2017, June). Why losing big animals causes big problems in tropical forests. Mongabay article: