Research Highlights the Impact of Invasive Rats on Forest Vegetation

Recent research demonstrates the adverse impacts invasive rats have on forest habitats and native plant species in Luquillo Experimental Forest, Puerto Rico.

Invasive rats are notorious for their adverse effects on island ecosystems. They harm the well-being of a myriad of native plants and animals. Despite this, little is known about their specific impacts on the vegetation of forest habitats in Puerto Rico. Emerging research published in the journal Biotropica aimed to change this.  

The research was carried by Aaron Shiels and fellow researchers within tropical rainforest habitat in the Luquillo Experimental Forest, Puerto Rico. The site was selected partially due to the fact it is on an island as well as for the surrounding urban and suburban landscapes. The study utilized short-term seed removal trials in the hopes of understanding the distribution of invasive rats and how they are impacting native plant health.  

The trials hoped to explore the incidence of native seed removal by invasive rats on the forest floor. Four native tree species were chosen for the study:  Guarea guidonia, Buchenavia capitata, Tetragastris balsamifera, and Prestoea acuminata. Researchers removed seeds of each of these species from the forest floor and assigned them to a total of 26 plots. Some plots enclosed within a metal-mesh cage to prevent vertebrate access, whereas the rest were vertebrate-accessible. Cameras were then set up to monitor the plots and detect rat activity.

Prestoea acuminata one of the species included in the study. Credit: WikiCommons

The results indicated that vertebrates removed 7-48 seeds from the forest floor on a given day within each 10-day trial period. About 65% of the confirmed trail camera sightings at the vertebrate-accessible sites were of invasive black rats. The research highlighted that although the removal of seeds did not always lead to seed predation, it is placing a strain on native plant communities by altering forest composition. It also acknowledged that most of the removed seeds were of Buchenavia, Guarea, and Tetragastris—indicating that invasive black rats do not discriminate when it comes to habitat type.

Bromeliads in the forest within Luquillo. Credit: US Forest Service

There is still further work to be done, but this research provides hope for the future of forest habitats and the plant communities found there. A valuable next step would be creating a vulnerable species list of these and other species highly susceptible to invasive black rat predation. This promising new development will help inform future management techniques and strategies to mitigate the harmful effects of invasive black rats within island ecosystems and all over the world.  

Source: Wiley Biotropica
Featured Photo: Aerial view of Luquillo Experimental Forest, Puerto Rico Credit: NASA’s Marshall Space Flight Center

About Stephanie Dittrich

Stephanie Dittrich is a current senior in Environmental Studies at UC Santa Cruz and a transfer student from De Anza College. She is also currently pursuing a Certificate of Achievement in Geospatial Technologies and a second Associates Degree in Graphic Design from Foothill College. She has worked in multiple marketing and design focused roles at environmental nonprofits as well as the Genomics Institute at UC Santa Cruz. She just finished spending 3 months in Costa Rica conducting field work where she did an independent research project and wrote a scientific paper about flight response time in the Morpho peleides butterfly. In her spare time, Stephanie enjoys working on creative photography and design projects, often centered around wildlife photography, as well as more experimental and contemporary subject matter.

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