José Hernán Sarasola, CONICET associate researcher at the Instituto de las Ciencias de la Tierra y Ambientales de la Pampa (INCITAP, CONICET-UNLPam) [Institute of Earth and Environmental Sciences of La Pampa], and his research team recently revealed that large felid predators with an exclusively carnivorous diet can contribute to their ecosystems as secondary seeds dispersers. The study was published in Scientific Reports.
“So far, the only hypothesis was that these top predators could act on the basal levels of the food web, that is to say the plants, via the control -or relaxation- of the population of herbivorous. So what was known was that the increase or suppression of a predator within a certain ecosystem can lead to its transformation through an interrelated effects chain. This is known as trophic cascade”, José Hernán Sarasola, CONICET associate researcher, explains.
The team found that without the need of an herbivorous mediator, the cougar, in this particular case, can also work as long distance seed dispersers. This function is very important to maintain biodiversity and plant communities because it allows them to interact genetically among each other and make certain species colonize new areas or colonize again others.
Cougars (puma concolor) make contact with the seeds to be dispersed by capturing eared doves (zenaida auriculata). These birds, whose populations grew markedly in semi-arid areas of the country, can accumulate in their craw a large amount of seeds before finally digesting them. At first, these birds are not seed dispersers because the seeds are destroyed completely when they are ingested, except when the bird dies carrying the seeds in its craw, what allows them to germinate. Another possibility would be that they were preyed on by a cougar or another predator that after doing that becomes another secondary disperser agent.
“The cougar feeds on eared doves and ingests the seeds that remain in the bird’s craw. When the seeds are defecated by the feline, they do not lose their germinative properties”, Sarasola comments.
The study was conducted by the INCITAP team at the Reserva Natural [Nature Reserve] Parque Luro in La Pampa. The researchers took seed samples from faeces to find if after passing through the digestive tract of the cougar the seeds’ viability was affected.
“We caught eared doves to find the seeds in their craws and we examined the cougars’ faeces with the same objective. We proved that after passing through the cougars’ digestive tracts the seeds did not lose their germinative capacity”, the researcher describes.
When considering the importance of this phenomenon, it is important to note that the sum of the distances that eared doves can fly and that cougars can cover in a short period of time can disperse those seed in areas remote from the places where they were originally taken, thus colonizing new territories or communicating populations.
“These processes are rare or difficult to research, but we should take into consideration that the eared doves can fly up to 100 kilometers from their nests to their feeding ground. The cougar is also an animal with a great capacity to move. In just a few hours, one seed can travel hundreds of kilometers, thus ensuring the connectivity between plant communities”, Sarasola explains.
It is also important to highlight that this interaction between eared doves and cougars at the Luro Reserve, reported by the team, can happen in any other ecosystem that includes large felid predators and a significant bird population.
“What we are showing now for the first time can be a much more widespread phenomenon. The cougar, for instance, is present practically in almost all American territory. Wherever this feline coexists with large amounts of seed-eating birds, it is possible to have a phenomenon of predation and seed dispersal”, the researcher concludes.
By Miguel Faigón.
About the research:
José Sarasola. Associate researcher. INCITAP and CECARA.
Juan Ignacio Zanón-Martínez. Post-doctoral fellow. INCITAP and CECARA.
Andrea Silvia Costán. Doctoral fellow. INCITAP and CECARA.
William J. Ripple, Oregon State University, USA.