NSF ARTICLE ON THE SPREAD OF FIRE ANTS

FROM:  NATIONAL SCIENCE FOUNDATION 

Border crossing: 10 things to know about invasive fire ants on the march

Are fire ants using natural corridors to advance the front?

Heading for a summer picnic or hike, or just out to mow your lawn? In the U.S. Southeast and beyond, you might want to watch where you walk.

Fire ants. Crossing the border from South America, they're on the march northward. How does habitat--in particular, corridors that connect one place with another--help the ants spread?

To find out, the National Science Foundation (NSF) talked with ecologist and program director Doug Levey of its Division of Environmental Biology, and researcher Julian Resasco, now of the University of Colorado, Boulder (formerly at the University of Florida, Gainesville).

This week Resasco, Levey and colleagues published a paper in the journal Ecology reporting new findings on habitat corridors and fire ants. They conducted their NSF-funded study in an experimental forest in South Carolina, at the USDA Forest Service - Savannah River site.

1. Where did fire ants come from, and where are they found now?

(Resasco) Fire ants are native to South America, where they're found from Western Amazonia to northeastern Argentina. Fire ants were accidentally introduced by humans to the southeastern U.S. almost a century ago. Now they're established in parts of the Caribbean, China, Southeast Asia, Australia, and New Zealand.

2. Why are fire ants a problem?

(Resasco) Fire ants are very aggressive, have painful stings, and can occur at high densities. They can displace native ants and other kinds of small animals, including reptiles, birds, and mammals. Because they have a broad diet that includes plants, they're a major economic problem in agriculture. The USDA estimates that fire ant control, property damage from the ants, and medical treatment from stings cost several billion dollars each year.

3. How do fire ants disperse?

(Resasco) Fire ants disperse during mating flights, also called nuptial flights, when winged, unmated queens and males emerge from nests to find mates. (Mated queens dig a small hole to lay their eggs, in the hope of establishing new colonies.)

There are two social forms of fire ants, and they disperse very differently. In the monogyne social form (named for having a single egg-laying queen), mated queens fly high in the air and establish new colonies--often miles away from their original colonies. In the polygyne social form (named for multiple egg-laying queens), mated queens disperse poorly, establishing new nests near their original colonies. Fire ants can also be accidentally transported over long distances by human commerce and travel.

4. Why are some types of fire ants worse than others?

(Resasco) Because polygyne fire ants establish new colonies near existing ones and are non-territorial, their densities are much higher than the densities of monogyne fire ants, which are spaced more widely apart because their colonies are territorial. The higher densities of polygyne fire ants make their effects greater.

5. What is a habitat corridor and why is it useful in conservation?

(Levey) Corridors are strips of habitat that join otherwise isolated patches of the same habitat type. They're important because they facilitate movement of plants and animals from one patch to another. By linking small populations to each other, corridors create larger populations that are more resistant to extinction.

6. Do habitat corridors help fire ants colonize new areas?

(Resasco) Yes, but in one situation. In areas already dominated by the polygyne form, we found that patches of habitat connected by corridors had higher fire ant densities than did unconnected patches. In areas dominated by the monogyne form, however, corridors had no effect on fire ant densities. This difference is likely because monogyne queens can easily colonize isolated patches. Polygyne queens, having more limited dispersal, appear to benefit from the connectivity that corridors provide.

7. Could habitat corridors help other invasive species disperse?

(Resasco) There is no evidence that habitat corridors assist in the spread of other invasive species. We think this is because invasive species are usually already good dispersers--the best example is the monogyne form of fire ants.

8. Can we figure out in advance when corridors will help species invade?

(Levey) We think the best way to predict which species will benefit from corridors is by considering their natural ability to disperse. Species that regularly disperse long distances, or are easily able to travel through or above hostile habitats, are unlikely to respond to the presence of corridors. Species that are poor dispersers and tightly linked to a particular type of habitat are most likely to depend on corridors when traveling from one patch to another.

9. Overall, are corridors beneficial or detrimental?

(Resasco) The balance of evidence strongly suggests that corridors are beneficial for conservation. Many studies have shown positive effects of corridors on dispersal and species diversity. The evidence of negative effects is much weaker. The more we understand about how corridors work, the better we can make informed decisions to maximize positive effects and minimize negative ones.

10. What surprised you the most in this study?

(Resasco) The age of habitat patches seemed to be important in determining whether corridors facilitated dispersal by polygyne fire ants. We only saw a corridor effect in the most recently created patches. We hope to determine whether this effect is transient, or if higher densities of polygyne fire ants and lower diversity of native ants persist in patches connected by corridors.

-- Cheryl Dybas, NSF

STUDY LOOKS AT POSITIVE AFFECTS OF INVASIVE SPECIES ON THE ENDANGERED

FROM:  NATIONAL SCIENCE FOUNDATION 

Eradicating invasive species sometimes threatens endangered ones

Study of California Clapper Rail and salt marsh cordgrass Spartina offers new insights

What should resource managers do when the eradication of an invasive species threatens an endangered one?

In results of a study published this week in the journal Science, researchers at the University of California, Davis, examine one such conundrum now taking place in San Francisco Bay.

The study was led by UC Davis researcher Adam Lampert.

"This work advances a framework for cost-effective management solutions to the conflict between removing invasive species and conserving biodiversity," said Alan Tessier, acting deputy division director in the National Science Foundation's (NSF) Directorate for Biological Sciences, which supported the research through NSF's Dynamics of Coupled Natural and Human Systems (CNH) Program.

CNH is also co-funded by NSF's Directorates for Geosciences and Social, Behavioral & Economic Sciences.

"The project exemplifies the goals of the CNH program," says Tessier, "which are to advance the understanding of complex systems involving humans and nature."

The California Clapper Rail--a bird found only in San Francisco Bay--depends on an invasive salt marsh cordgrass, hybrid Spartina, as nesting habitat.

Its native habitat has slowly vanished over recent decades, largely due to urban development and invasion by Spartina.

Study results show that, rather than moving as fast as possible with eradication and restoration plans, the best approach is to slow down the eradication of the invasive species until restoration or natural recovery of the system provides appropriate habitat for the endangered species.

"Just thinking from a single-species standpoint doesn't work," said paper co-author and UC-Davis environmental scientist Alan Hastings.

"The whole management system needs to take longer, and you need to have much more flexibility in the timing of budget expenditures over a longer time-frame."

The scientists combined biological and economic data on Spartina and on the Clapper Rail to develop a modeling framework to balance conflicting management goals, including endangered species recovery and invasive species restoration, given fiscal limitations.

While more threatened and endangered species are becoming dependent on invasive species for habitat and food, examples of the study's specific conflict are relatively rare--for now.

Another case where the eradication of an invasive species threatened to compromise the recovery of an endangered plant or animal is in the southwestern United States, where an effort to eradicate Tamarisk was cancelled because the invasive tree provides nesting habitat for the endangered Southwestern Willow Flycatcher.

"As eradication programs increase in number, we expect this will be a more common conflict in the future," said paper co-author and UC Davis scientist Ted Grosholz.

Other co-authors include scientists James Sanchirico of UC Davis and Sunny Jardine of the University of Delaware.

-NSF-

Media Contacts
Cheryl Dybas, NSF

EPA ISSUES FINAL VESSEL GENERAL PERMIT REGULATING COMMERCIAL VESSEL DISCHARGES

FROM: ENVIRONMENTAL PROTECTION AGENCY
EPA Finalizes Vessel General Permit
Action will help protect U.S. water quality and reduce risk of invasive species

WASHINGTON – The U.S. Environmental Protection Agency (EPA) today issued a final vessel general permit regulating discharges from commercial vessels, including ballast water, to protect the nation’s waters from ship-borne pollutants and reduce invasive species in U.S. waters.

The final vessel general permit covers commercial vessels greater than 79 feet in length, excluding military and recreational vessels, and will replace the 2008 vessel general permit due to expire on Dec. 19, 2013.

This permit regulates 27 specific discharge categories, and will also provide improvements to the efficiency of the permit process, and clarify discharge requirements by the following:

- Reduce the risks of introduction of invasive species. The permit includes a more stringent numeric discharge standard limiting the release of non-indigenous invasive species in ballast water. The permit also contains additional environmental protection for the Great Lakes, which have suffered disproportionate impacts from invasive species, aligning federal standards with many Great Lakes states by requiring certain vessels to take additional precautions to reduce the risk of introducing new invasive species to U.S. waters.

- Reduce administrative burden for vessel owners and operators. The permit will eliminate duplicative reporting requirements, expand electronic recordkeeping opportunities, and reduce self-inspection frequency for vessels that are out of service for extended periods.

The new discharge standards are supported by independent studies by EPA’s science advisory board and the National Research Council, and are consistent with those contained in the International Maritime Organization’s 2004 Ballast Water Convention. EPA is issuing the permit in advance of the current permit's expiration to provide the regulated community time and flexibility to come into compliance with the new requirements.

PLANTS VS ZOMBIE PLANTS

FROM: U.S. NATIONAL SCIENCE FOUNDATION

Global Plant Diversity Hinges on Local Battles Against Invasive Species
January 17, 2013
In Missouri forests, dense thickets of invasive honeysuckle decrease the light available to other plants, hog the attention of pollinators and offer nutrient-stingy berries to migrating birds.

They also release toxins that decrease the germination of nearby native plants.

Why, then, do studies of invasive species come to different conclusions about their effects and lead some organizations to suggest we accept their presence?

Biologists Kristin Powell, Tiffany Knight and Jon Chase of Washington University in St. Louis have found an answer.

Most studies of the effects of invasive plants are done at a single scale, report the scientists in this week's issue of the journal Science. Some studies scrutinize biodiversity in meter-square quadrats, while others scan biodiversity in entire islands or regions.

Meanwhile, invasives decrease biodiversity at small--but not at large--scales, the researchers discovered, leading them to conclude that how invasive species research is conducted can produce conflicting results.

"Perhaps not surprisingly, the big picture perspective is fundamentally different than the small-scale perspective," says Doug Levey, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

Probing for scale dependence

The biologists had long suspected that studies of invasive species came to different conclusions because of scale dependence.

To test this notion, they analyzed 57 previous studies and confirmed a pattern: Invasive plants cause a large loss in species richness at small scales, but this effect diminishes at larger scales.

To test for scale dependence in the field, they chose three study sites in different ecosystems across the United States, each straddling an invasion front: a hammock forest in central Florida; an oak-hickory forest in eastern Missouri; and a tropical forest on the Big Island of Hawaii.

The hammock forest, a mix of live oak, cabbage palm, sweet gum and pignut hickory, is being invaded by the flax lily (Dianella ensifolia). Native to Africa and Asia, the lily forms dense mats on the forest floor.

Amur honeysuckle (Lonicera maackii), a mid-story shrub introduced from East Asia as an ornamental to provide bird habitat, is the issue in the oak-hickory forests.

The fire tree (Morella faya), a canopy tree that boosts nitrogen levels in the soil, making it inhospitable to native species and more suitable for invasives, is the troublemaker in the Hawaiian forest.

Invasives don't just sweep the board

"We counted the number of species per unit area in plots that varied in size from one meter square to 500 meters square--a quarter the size of a football field--on either side of the invasion front and then plotted the number of species against the size of the plot," Powell says.

"At small scales, invaded plots had many fewer species than uninvaded plots, but they picked up species more rapidly. At broad scales the invasives' effect on diversity virtually disappeared."

The reason for this "scale effect" is probability, says Powell.

"Invasives reduce the number of individual plants in a plot, and if there are fewer plants, there are fewer species," she says.

The invaded sites can catch up with uninvaded ones, Knight says, because the number of species does not increase indefinitely.

"At any site, if you sample larger and larger areas, the number of species will eventually plateau," Knight says.

At an invaded site, she says, "you reach that plateau later, but you do reach it eventually."

What it means for gardeners

The research helps to explain seemingly contradictory findings in the scientific literature, but what does it mean for people who've been hacking down honeysuckle in their backyards, and brushing their boots before entering conservation areas to avoid bringing in invasives?

Is it worth it or not?

"Emphatically yes," Knight says.

"Invasive species are a serious threat. If we're going to deal with them, we need the cooperation of the public."

Invasive plants have negative effects on plant communities at smaller scales--the scales that are crucial for ecosystem services like water management and nutrient cycling.

Take the bush honeysuckle choking Missouri's natural areas, for example.

It was seeded by birds carrying honeysuckle berries from backyards. To prevent it from turning nature preserves into shrub monocultures, people must remove it from their yards or choose not to plant it in the first place.

While the small scale justifies the fight, the large scale offers hope.

"Invasive plant species are reducing the abundance of native plant species, but most species are still present when we search for them at broad scales," says Knight.

"They haven't gone extinct yet."

Which means that it's not too late to restore habitat and increase abundances of native species, says Knight, "so they can contribute to critical ecosystem services and are less vulnerable to extinction."