USGS Invasive Species Science: From Guam's Brown Treesnake to Florida's Pythons

A USGS scientist with an Argentine tegu, one of the large reptiles now established in southern Florida. USGS.

The problem

Invasive, nonnative plants, animals and diseases damage the ecosystems they enter. Like "biological wildfires," they spread fast and can affect almost every land and water ecosystem.

• They are among the greatest environmental challenges of the century, costing the United States an estimated more than $120 billion a year.
• Managers of Interior Department and other lands often rank them their top resource problem.
• They are considered second only to habitat degradation in harm to the world's ecosystems.

The branch

The Invasive Species Science Branch of the USGS Fort Collins Science Center helps managers by studying:

• how invaders arrive, which areas are vulnerable, and where invasions will go next;
• methods to control them;
• models of where species are and may be, and ways to share data with partners and the public.

It also holds a large share of the world's expertise on invasive reptiles — combining field herpetology with advanced statistics to estimate detection rates, population sizes and the odds of eradication, from the western Pacific to the U.S. mainland and Puerto Rico.

Mapping where species are — and will be

Managing any species — common, rare or invasive — starts with knowing where it lives and what drives that. Branch scientists model species from tamarisk, Russian olive, Africanized honey bees and nutria to the threatened lesser prairie-chicken, at scales from a single park or refuge to the globe. Models draw on current and future climate, satellite data (such as MODIS plant-growth timing), land cover, topography and human features.

• Resource for Advanced Modeling (RAM): a shared facility where remote-sensing and climate experts, habitat modelers, field ecologists and land managers work together.
• Software for Assisted Habitat Modeling (SAHM): a tool the branch helped build that runs five habitat models — Maxent, boosted regression trees, logistic regression, multivariate adaptive regression splines and random forest — consistently and repeatably, combining environmental layers with field observations to map suitable habitat and help predict and manage spread.

A modeling workshop at the Resource for Advanced Modeling. USGS.

Nutria

Nutria (coypu, Myocastor coypus), South American rodents that degrade wetlands, are established in the Southeast and Pacific Northwest. With the USGS National Wetlands Research Center, the branch built a physiological model based on cold limits and a statistical model based on where nutria have been found — the base for a global and national model of suitable habitat that can be run under future climates to guide early detection.

Model maps displayed at the modeling facility. USGS.

Buffelgrass

African buffelgrass (Pennisetum ciliare) is spreading fast across the desert Southwest. Unchecked, it takes over and fuels frequent, fast wildfires that threaten natural areas and neighboring cities, spoil views, close attractions, cut essential services, and could hurt tourism, property values and the economy — as well as imperiled species. With the National Park Service and other land managers, the branch built a decision-support model — a state-and-transition model simulating spread and treatment even with incomplete data — to help target limited funds through adaptive management.

Brown treesnakes on Guam

The brown treesnake has wiped out many of Guam's native birds, bats and lizards. For more than two decades the branch's Invasive Reptile Project has developed and tested ways to control it at every scale.

• Improving tools: rodent-baited traps, toxicants delivered from the air and in bait tubes, and visual searches.
• Juveniles: island-wide road surveys found many young snakes, which evade control tools — and many snakes that escape Guam on cargo, ships and planes are juveniles. Surveys of forest edges and interiors aim to learn where they live.
• Landscape suppression: aerial toxicant bait, developed by the U.S. Department of Agriculture and partners; the branch helps validate it and model the best timing of repeat drops.

Rapid Response Team. Since 2002, a multi-agency team led by the USGS has helped find and capture snakes that reach other islands. It trains responders on Guam in visual searching, trapping and interviewing witnesses, leads responses to sightings, and does outreach across the Pacific — with partners from the Interior and Defense departments, USDA, Guam, the Northern Mariana Islands, Hawaii, the Federated States of Micronesia, the Marshall Islands and Palau.

Bringing back birds. The endangered Mariana swiftlet survives in only three caves on Naval Base Guam, and other native birds, such as the Guam rail, are extinct in the wild or awaiting reintroduction. USDA trapping rings the swiftlet caves, but snakes still get through — and a few resident snakes could do outsized harm. The Guam National Wildlife Refuge has fenced out snakes and begun trapping to make room for reintroductions. The branch studies how to deploy control tools to catch the most snakes, and how few snakes must remain for native birds to persist.

A Guam rail. Photograph by Leá Bonewell, USGS.

Pythons and tegus in Florida

The Everglades — the only U.S. place that is a World Heritage Site, an International Biosphere Reserve and a Wetland of International Significance — is the focus of a restoration worth billions of dollars. Invasive reptiles threaten it.

• The Burmese python appears to have contributed to steep declines of several mid-sized mammals.
• The Argentine tegu and the northern African python are also established, with impacts not yet well understood.
• The branch is developing and testing environmental DNA sampling, traps and visual-search methods, and studying the invaders' ecology to find weak points control can exploit.

Sources

Based on Robert N. Reed and Katie Walters, "Invasive Species Science Branch: research and management tools for controlling invasive species," U.S. Geological Survey Fact Sheet 2014–3076 (2015), Fort Collins Science Center; a work of the United States government in the public domain. The USGS photographs are taken from the fact sheet's PDF; photographs credited to Colorado State University, ApexRMS and Denison University, and the staff directory, are not reproduced. More: the Fort Collins Science Center.