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Rewilding Ants: Conserving Endangered Interactions

Blog by Ruthmery Pillco Huarcaya, Botanical Projects Coordinator
(Translated by Amaris Norwood, DC office intern)  


One of Osa Conservation’s objectives is to support the conservation of at-risk trees through the conservation ex-situ program  (such as the creation of a botanical garden) which is a supplement of the in-situ ecological restoration and rewilding program that we continue to pursue.

About the Cornizuelo

It has been more than a year since we planted the seeds of a Vachellia allenii tree, locally known as a cornizuelo (the tree of the horns).  This tree can be found growing abundantly in both primary and secondary forests and can reach heights of 25 meters. The cornizuelo, characterized by spines that grow in twos, looks like a pair of horns. This species is endemic to Costa Rica and is categorized as endangered (EN) by the International Union for the Conservation of Nature (IUCN). Its greatest risk is the loss of habitat, which is a common consequence of deforestation.  

 Arbol de cornizuelo (Vachellia allenii) creciendo en un bosque protegido (Saladero Ecolodge)

Cornizuelo tree (Vachellia allenii) growing in a protected forest (Saladero Ecolodge)

The Relationship Between The Tree and Ants

The tree coexists with a specific species of ant, the Pseudomyrmex sp., with whom it has established a very special relationship.  In this case, the cornizuelo brings refuge and food to the ants and their offspring. The large, hollow spines grow to become an ideal site for the ants to live, reproduce, and feed. The plant produces small, yellow bodies containing sugar and proteins that serve as abundant and delicious food sources.   

Hoja de un cornizuelo mostrando los cuerpos alimenticios que produce ara alimentar a sus hormigas (foliolulos modificados de color amarillo)

Cornizuelo leaves showing the alimentary bodies that produces ara to feed ants (modified yellow leaflets)


The ant by its part protects its host plant against the attack of herbivores, particularly insects, and further prevents other plants from becoming its competitors for sunlight, space, and nutrients.  When something touches the plant, hundreds of furious ants appear, dispersing to protect the plant from intruders. The
 furious ants produce a free space of vegetation around the cornizuelo by using their jaws to cut vines and eating seeds and seedlings that attempt to grow around them.  Living together has become a matter of survival as much for the plant as for the ants.

Our Rewilding Efforts

Over the course of 9 months, we noticed that our cornizuelos did not develop. They hadn’t been colonized by ants, and possibly, were never colonized. Such was the case with a cornizuelo we planted in the station after throwing away the previous flowers. We then undertook a trip through Saladeros Ecolodge in the National Park of Piedras Blancas, where we found an area with many cornizuelos. As a first attempt, we decided to bring a sample of a seedling with all of its ants.

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Newly colonized cornice seedling. The horn-shaped spines show a hole recently made by an ant (Pseudomyrmex sp.).

 

One time in the nursery, we collected the plant with ants besides our cornizuelos. The ants immediately started to explore and eat from the yellow bodies.  After a few hours, they started to make holes in the thorns, and on the following day, all of the thorns had holes. Our cornizuelos started to grow rapidly, looking vigorous and filled with life.  However, the ants disappeared in a month, probably due to the absence of a queen ant, or because the ants got lost while leaving to explore.

When you destroy a forest, you also destroy the mutualistic interactions between plants and animals that have spent hundreds of years developing. These interactions are very delicate and are difficult to recuperate and restore.  Though our first attempt at rewilding this interaction did not do as well as we hoped, we continue to do more research so that the cornizuelos and their ants stay together.

 

Data Entry Company India

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Ruth monitoring the newly colonized Cornizuelo seedlings