VisSim v9 Saves Hawaii from Invasive Species

VisSim is helping to solve problems in far-flung places, including the Hawaiian islands. Francis Benevides, an electronics engineer and affiliate faculty member with the University of Hawaii at Hilo, has been using VisSim for a number of years to help monitor and contain a frog species that has invaded Hawaii and is threatening to alter two of the islands’ vulnerable ecosystems.

The frog in question

The frog in question is the coqui frog (Eleutherodactylus coqui). It arrived in Hawaii around 1988, probably on imported nursery plants. The frog is native to and beloved in Puerto Rico, but in Hawaii it is an invasive species. Without natural predators to keep its population in check in Hawaii, the frog has quickly proliferated, especially on The Big Island (the Island of Hawaii), and achieves population densities three times those in its native Puerto Rico habitats. It preys on a large variety of insects and other invertebrates at a fearsome rate, and creates a hospitable environment, and dense food source, for other potential invasive species, such as frog-eating snakes--all of great concern to biologists.

A Public Nuisance

What’s more, the male coqui is a public-noise nuisance in Hawaii. From sunset to sunrise, this one-inch frog’s two-part call (“co-KEE”) reaches a mean sound level of about 80 decibels (dB) from a meter away; the state health standard is 70dB (around the loudness of a handheld mixer). Residents are now required to disclose whether their property is home to coqui frogs when readying to sell; real-estate values have been hurt. Hotels deal with disgruntled, sleep-deprived guests, and nurseries with fewer sales. At first, efforts to locate and analyze the frog populations on the islands—in order to remove them and to study them—focused on capturing, marking and re-capturing them. Using a model he created with VisSim that lets him measure and analyze coqui acoustics, Benevides has been able to enhance biologists’ and government authorities’ containment efforts. His findings help identify where coqui have settled--and are apt to settle--based on factors like temperature and elevation. He and his team have been able to shed light on coqui behavior, including its peak calling time. As a co-founder of the Coqui Frog Working Group, Benevides finds this gratifying.

VisSim v9 vector operations key to estimating Coqui populations

His VisSim model provides an estimate of the density of calling male coqui frogs from average measurements of sound-pressure levels (SPL) taken in the field, Benevides explains. “The simple model consists of ‘coqui sound sources’ configured in a rectilinear grid equally spaced from each other. The model varies the spacing between the ‘coqui sound sources’ until reaching the average SPL value obtained from the field measurements.”
Benevides and his team establish 20 x 20 meter plots in the field, take digital recordings of the coqui chorus within the plot, and use VisSim to process the data. They filter out non-coqui sound using band pass filters at the two distinctive “co-KEE” frequencies to get the average SPL. “Finally, we count the number of calling coqui within the plot to obtain plot density and compare the empirical plot density data with that predicted by the VisSim model.”

"Creating a model in v9 is almost too easy"

Benevides notes that “VisSim’s vast repertoire of block and mathematical functions make creating a model almost too easy. As an early Beta tester of VisSim version 9, he found it a quantum leap in facilitating ease of design and reducing turn-around time for model development.” VisSim’s graphics and design capabilities are, he adds, “formidable and powerful, and I really like its improved matrix capability in version 9.”

But It's Tough to Contain an Invasive Species

Efforts to contain or reduce the coqui population have succeeded on some Hawaiian islands, like Oahu, to a point where the frogs are no longer a threat. The Big Island and Maui are now the only ones that have a sustainable population of the frogs, says Benevides. (The frogs are on the Big Island are here to stay, because there are just too many of them.)

VisSim Helps Evaluate Treatment Efficacy

Funds to eradicate and control the coqui population need to be used efficiently, and VisSim helps with that, too, by making it possible to compare the density of the frogs pre- and post-treatment, Benevides notes. “When treating and spraying coqui-habitated areas with citric acid, for example, we need to determine its efficacy. Has it been useful, has it reduced frog numbers or activity?”

The Viewer Makes it Easy To Share Results

Benevides also appreciates how user-friendly VisSim has proven to be for his colleagues. “VisSim is icon-based, which makes it very easy to teach others. I am especially fond of VisSim’s free viewer, which allows my associates, clients, students, etc, the opportunity to run my simulations without having to purchase VisSim software. I can’t say the same for other platforms.”