Last week I participated in the 23rd year of the Ant Survey at Jasper Ridge Biological Preserve (JRBP). This survey, which began as a graduate student project in Deborah Gordon’s lab at Stanford, has evolved into a community citizen science project and to our knowledge is the longest continuous survey of an invasive insect. Twice a year, dozens of volunteers of all ages, collectively called the “Ant Squad” come together to walk the 1,200-acre preserve and look for ants.

The long-term monitoring being conducted by the Ant Squad at Jasper Ridge Biological Preserve is helping us to better understand nature's systems and how they're changing over time.
The Ant Squad navigates to standard survey locations to understand the impacts of invasive ants on natural ecosystems.

The rationale for the project starting in 1993 was to assess the rate of invasion of the non-native Argentine ant into the Preserve and the impacts on native ant fauna. The Argentine ant, native to Argentina as you may have guessed, is the little brown ant most of us have in our houses here in the Bay Area. It was introduced by accident probably with citrus plants around 1900, and has become dominant in urban and agricultural areas, where there is irrigation, throughout the State.

When they escape into wildlands, the impacts can be really bad. They displace native ants, which has negative impacts on wildlife and plants. In California, the loss of Messor Andrei (pictured above), our local harvester ant is particularly significant. Messor is an important seed disperser in grasslands, and food source to the locally rare Coast horned lizard. Argentine ants replace Messor, and they don’t provide any of the same benefits.  

Personally, I have been walking the same trails at JRBP hunting for ants since 1999.  We have learned so many amazing things by repeating this study over and over, year after year. First, we have seen an expansion of the Argentine ants over time. However, to our surprise they reached their maximum distribution in 1998 following the last big El Niño event. Since then they have actually decreased in distribution, and amazingly we are seeing an increase in the abundance of some native ants. The native North American ant, Prenolepis imparis (the winter ant) is slowly but surely returning to more and more of Jasper Ridge and successfully co-existing with the Argentine ant. You may be noticing this black ant with a pointed abdomen in your backyard too.   

Recently, KQED did a video story about our work at JRBP, and an exciting research finding made by Stanford students, which may help explain how the winter ant is managing to co-exist with the Argentine ant.

Our discoveries demonstrate the value of long-term ecological monitoring. If we had only watched this invasion for 3-years, a typical research project length, we would have concluded that Argentine ants were going to take over the entire preserve and that coexistence was impossible. By watching for 20+ years we have a different picture.  We have learned that weather and climate dictates their distribution, and that impact changes over time. It may be that the native ants will continue to recover!

Ecosystems are dynamic and long-term monitoring is one of the most valuable tools we have to understand these complex systems. Please get in touch if you want to join the Ant Squad or learn more about citizen science and ecosystem monitoring in our region.

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Peninsula Open Space Trust (POST) protects open space on the Peninsula and in the South Bay for the benefit of all. Since its founding in 1977, POST has been responsible for saving more than 87,000 acres as permanently protected land in San Mateo, Santa Clara and Santa Cruz counties. Learn more

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