How bird guts give rare chili peppers a boost

Micronesian starling. (Credit: Peter/Flickr)

New research looks at how a mutually beneficial relationship between birds and chili peppers in the Mariana Islands helps the plants grow in the wild.

The study shows biodiversity can lead to indirect benefits for humans, says study coauthor Haldre Rogers, an assistant professor of ecology, evolution, and organismal biology at Iowa State University.

Organisms depend on each other in intricate and often poorly understood ways, Rogers says, meaning the decline of an animal species may lead to declines in plants with which the animal species shares a mutualistic relationship.

The study, which appears in the journal Ecological Applications, focuses on the donne’ sali chili plant, which grows wild in the forests of the Mariana Islands. Birds eat the plant’s peppers and ingest the seeds, then disperse the seeds to other locations through their excrement.

chili peppers
The donne’ sali chili plant. (Credit: Monika Egerer/Iowa State)

The researchers conducted a range of experiments to determine that gut passage improves the odds that chili seeds will germinate. Video footage confirmed which bird species primarily dispersed the seeds, and then the researchers conducted feeding trials with captive birds to obtain gut-passed seeds. The seeds then underwent planting trials to determine how they performed compared to seeds that hadn’t passed through birds.

Study coauthor Evan Fricke, an Iowa State postdoctoral research associate, says gut passage separates the seeds from the pulp of the chili plants, which improves the likelihood of germination when the seeds settle on the ground. In addition, the researchers found a statistically significant improvement in seed germination separate from pulp removal in seeds passed through a local species of starling.

The finding suggests passage through starlings provides some other benefit to the performance of the chili seeds, though identifying the cause wasn’t in the scope of the experiments, Fricke says. In fact, the name of the pepper plants includes the word ‘sali,’ which is the local name for the Micronesian starling.

Birds don’t carry seeds far enough to save rainforest

The island of Guam, which lost its native bird population due to the introduction of an invasive predatory snake after World War II, further illustrates the importance of the mutualistic relationship between birds and the chili plants. Without birds to disperse the seeds, the researchers found much lower chili populations on Guam compared to the other Mariana Islands.

The research team chose to focus on the chili plants in question because of the unique social significance the people of the Mariana Islands place on them. Fricke says the harvested chili plants provide a source of income as well as a delicious ingredient for spicy foods. Fricke says many local residents claim that this type of chili plant is difficult to cultivate, and that cultivated plants don’t pack the same spicy punch as wild plants.

Fricke says public awareness of the importance of pollinating insects in growing crops and other important plants has increased in recent years, while appreciation for other mutualistic interactions such as seed dispersal lags behind. He says he hopes studies like this one begin to turn the tide.

“This study teaches us about a mutualism that directly benefits people and should bolster our reasons to care about conserving biodiversity,” he says. “The loss of a bird in Guam, for instance, can cascade into a negative impact for people who like to eat these spicy chilies.”

Kudos to snakes for moving seeds around

Monika Egerer, a graduate student at the University of California at Santa Cruz, led the study.

Source: Iowa State University