Invasion of the Earthworms

Invasion of the Earthworms

Image: San Clemente Island by Shishir Paudel

Many of the species of earthworms in North America are exotic species and their presence alters native ecosystems in profound ways that resonate from the soil up through the vegetation and into the vertebrate communities.  So when word came that the US Navy had found earthworms on San Clemente Island, an island thought to be earthworm free, and was looking for an assessment of their distribution and possibilities for eradication I was interested.

I contacted earthworm (and bird) expert Scott Loss at Oklahoma State and we were able to secure the funding.  He put together a team that included post-doc Shishir Paudel and other colleagues at Oklahoma State and Beau MacDonald (at first UWG contract GIS expert and now USC Spatial Sciences Institute staff GIS Project Specialist) did the GIS work and modeling on our end.  The second of the papers from the study came out this week in Diversity and Distributions and Beau put together this summary graphic.


Source: Beau MacDonald, graphical summary of Paudel, S., G.W.T. Wilson, B. MacDonald, T. Longcore, and S. R. Loss. Predicting spatial extent of invasive earthworms on an oceanic island. Diversity and Distributions (2016).

The bottom line is that the earthworms (several species of them) were found near the main road and in areas that were moist.  All of the best-performing predictive models for the distribution of the earthworm included proximity to the paved road.  This suggests that the invasion is in its early stages and is associated with the road in some way.

We speculate, but do not have proof, that the earthworms were introduced when topsoil was brought from the mainland in 2008-2009 to pave the road.  This explanation is consistent our team not finding any earthworms south of the southernmost extent of the paving (the dashed line in the middle map above).

The paper goes into detail about the vegetation conditions where the earthworms were found; they are associated with exotic grasses and other non-native plants.

Time will tell the full effect of the invasion of earthworms on San Clemente Island.  The island has remarkable archeological resources because it used to be free of burrowing animals that moved soil and artifacts around. Being earthworm free (and free of burrowing mammals) was an advantage for those resources in addition to being the natural ecological condition.  I hope this research provides a warning to those proposing and doing construction on oceanic islands with high biological diversity and natural values to sterilize any building materials being imported for use lest they introduce unexpected species to environments where they can do damage.

Paudel, S., G.W.T. Wilson, B. MacDonald, T. Longcore, and S. R. Loss. Predicting spatial extent of invasive earthworms on an oceanic island. Diversity and Distributions (2016).



Invasions of non-native earthworms into previously earthworm-free regions are a major conservation concern because they alter ecosystems and threaten biological diversity. Little information is available, however, about effects of earthworm invasions outside of temperate and boreal forests, particularly about invasions of islands. For San Clemente Island (SCI), California (USA) – an oceanic island with numerous endemic and endangered plant and vertebrate species – we assessed the spatial extent and drivers of earthworm invasion and examined relationships between earthworms and plant and soil microbial communities.


San Clemente Island, southern California, USA.


Using a stratified random sampling approach, we sampled earthworms, vegetation, soils and microbial communities across SCI. We examined the relationship between the presence of invasive earthworms and soil and landscape variables using logistic regression models and implemented a spatial representation of the best model to represent potential site suitability for earthworms. We evaluated the relationship between invasive earthworms and vegetation and microbial variables using ANOVA.


We found that the likelihood of encountering earthworms increased close to roads and streams and in high moisture conditions, which correspond to higher elevation and a north-eastern aspect on SCI. The presence of earthworms was positively associated with total ground vegetation cover, grass cover and non-native plant cover; however, there was no significant relationship between earthworms and microbial biomass. These results suggest that the earthworm invasion on SCI is at an early stage and closely tied to roads and high moisture conditions.

Main conclusions

Climatic variables and potential sources of earthworm introduction and dispersal (e.g. roads and streams) should be broadly useful for predicting current and future sites of earthworm invasions on both islands and continents. Furthermore, the significant positive relationship between non-native plant cover and invasive earthworm presence raises the possibility of an emerging invasional ‘meltdown’ on SCI. Additional study of earthworm invasions on human-inhabited oceanic islands is necessary to identify additional invasions and their potential for negative impacts on unique insular biota.

Unintentional Media Blitz

As a result of the new atlas of of artificial night sky brightness I ended up doing a lot of interviews for national and international outlets, including Science Magazine,, Christian Science Monitor, Scientific American, and USA Today.

Then the American Medical Association released a statement on LED lighting (for which I had provided some background information) and a few more stories came out in and Christian Science Monitor.

A couple of Los Angeles Times stories also happened to include me:

Rare toads (presumably) love him; off-roaders do not 

The sunset that takes an hour to go from date palms to to redwoods

Predicting Continental-Scale Bird Migration Routes from Landscape Parameters

William Winters, one of my GIST students, successfully filed his MS thesis last fall, in which he created proof-of-concept models for bird migration routes at the continental scale.  We developed the topic as a way to fill in a missing scale in the efforts to reduce mortality of birds at towers and buildings.  At the scale of the building and tower, mitigations are now available, including lights-out during migration, and changing the lighting scheme on towers.  But what locations are most likely to have high levels of birds during migration, outside those already known as migratory hotspots (e.g., Cape May)?

Put another way, what places on the landscape are especially bad for tall towers and buildings because they are likely to kill more birds?  Are there really fewer birds killed at obstructions in the western part of the Great Plains as the records in our 2012 PLoS ONE paper might suggest?

Residuals in tower height-mortality regression at communication towers (Longcore et al. 2012).

Residuals in tower height-mortality regression at communication towers (Longcore et al. 2012). Note that the towers along the Front Range of the Rockies killed fewer birds than expected.

I posed the question of whether one could model probable migratory routes using least-cost path analysis and a simple set of physical parameters for sets of known wintering and breeding grounds for Neotropical migrant birds.  William ran with it.

A least-cost corridor raster for Red-eyed Vireos migrating from the Northern Atlantic forest to South America.

A least-cost corridor raster for Red-eyed Vireos migrating from the Northern Atlantic forest to South America (Winters 2015).

After some careful thinking about resolution and projection, William settled upon topography (slope) as a metric of landscape resistance, along with wind and an additional resistance value for crossing the Gulf of Mexico. Then, using pairs of wintering and breeding grounds for Red-eyed Vireo, Kirtland’s Warbler, and Golden-cheeked Warbler, he developed models to predict northbound and southbound migration routes.

The resulting maps, which were the result of some experimentation and comparison with existing observations compiled for the species in the literature and on eBird provide proof-of-concept that one could develop maps for whole species by linking together known wintering and breeding grounds.

Fall and Spring migration routes predicted for Kirtland's Warbler from Michigan only.

Fall migration route predicted for Kirtland’s Warbler from Michigan only (Winters 2015).

The maps show that the least-cost paths for the spring and fall migrations might be different.  For example, the models for Red-eyed Vireos southbound from New England funnel through the Florida Peninsula in the Fall, and return via the Gulf Coast of Florida in the Spring.

To see the full thesis, including many more maps, visit the USC Library website at this link: Identifying areas of high risk for avian mortality by performing a least accumulated-cost analysis.

Belowground interactions with aboveground consequences: Invasive earthworms and arbuscular mycorrhizal fungi

Shishir Paudel, Travis Longcore, Beau MacDonald, Melissa K. McCormick, Katalin Szlavecz, Gail W. T. Wilson,  and Scott R. Loss


Volume 97, Issue 3, March 2016, Pages 605–614

Abstract.  A mounting body of research suggests that invasive nonnative earthworms substantially alter microbial communities, including arbuscular mycorrhizal fungi (AMF). These changes to AMF can cascade to affect plant communities and vertebrate populations. Despite these research advances, relatively little is known about (1) the mechanisms behind earthworms’ effects on AMF and (2) the factors that determine the outcomes of earthworm–AMF interactions (i.e., whether AMF abundance is increased or decreased and subsequent effects on plants). We predict that AMF-mediated effects of nonnative earthworms on ecosystems are nearly universal because (1) AMF are important components of most terrestrial ecosystems, (2) nonnative earthworms have become established in nearly every type of terrestrial ecosystem, and (3) nonnative earthworms, due to their burrowing and feeding behavior, greatly affect AMF with potentially profound concomitant effects on plant communities. We highlight the multiple direct and indirect effects of nonnative earthworms on plants and review what is currently known about the interaction between earthworms and AMF. We also illustrate how the effects of nonnative earthworms on plant–AMF mutualisms can alter the structure and stability of aboveground plant communities, as well as the vertebrate communities relying on these habitats. Integrative studies that assess the interactive effects of earthworms and AMF can provide new insights into the role that belowground ecosystem engineers play in altering aboveground ecological processes. Understanding these processes may improve our ability to predict the structure of plant and animal communities in earthworm-invaded regions and to develop management strategies that limit the numerous undesired impacts of earthworms.

Heading to New Orleans: Ecologically Sensitive Lighting Design

Landscape architects, mark your calendars.  I’ll be part of a joint presentation on Ecologically Sensitive Lighting Design that was just accepted to the American Society of Landscape Architects annual meeting in New Orleans this fall.  I teamed up with lighting designer Linnaea Tillett and lighting engineer Nancy Clanton, two of the top landscape lighting experts in the country on the session proposal.  We will use a case study format to explore approaches to landscape lighting (and not lighting…) that incorporate the psychology of place-making, consideration for nature, and technical advances in the field.

Boulder City Hall lighting design by Clanton and Associates.

Boulder City Hall lighting design by Clanton and Associates.

Upcoming Event: Illuminating Engineering Society Mission Section

I’ll be speaking at Antioch University in Santa Barbara on February 19th at noon, in an event organized by Trish Odenthal of the Illuminating Engineering Society Mission Section. The hour and a half event includes lunch and is good for continuing education credit for AIA Health and NCQLP.  Registration is $30, or $15 with no lunch. Click through the image to register.


I Stand with Linda Sue Beck: The Attack on Science at Malheur National Wildlife Refuge

Linda Sue Beck. It is at her desk that Ammon Bundy, leader of the group of armed anti-government religious fanatics occupying Malheur National Wildlife Refuge, has set up shop. As a federal biologist, like my father was for decades, she works to steward the resources that are held in common trust for all Americans. My stomach turned as the report came through the radio today — approaching a week into the occupation of the Malheur National Wildlife Refuge — and I heard the descriptions of the Bundys picking through her belongings and ridiculing her work.

“She’s not here working for the people,” Ammon’s brother Ryan is quoted as saying. “She’s not benefiting America. She’s part of what’s destroying America.”

The occupiers of the refuge poke fun at Beck, her research on fish, and the normal trappings of a research station, including a dried bird in a storage area. They incredulously claim that the bird is “what they’re going to kill people over.” Presumably “they” is the federal government, and they mean to convey that Nature — the birds, the fish, the land — has no use or value.

These sentiments run counter to American history of conservation and scientific land management. The wildlife refuge system was started because the visionary Teddy Roosevelt could see that the continent risked losing its iconic wildlife if every species and every place was fair game to be hunted. Malheur was one of the first wildlife refuges, established in 1908, and became part of the growing field of scientific wildlife management that came to fruition in the United States.

Cartoonist Ding Darling illustrated the need for scientific game management in the early decades of the 1900s.

Cartoonist Ding Darling illustrated the need for scientific game management in the early decades of the 1900s. (c) Ding Darling Foundation.

Science and the National Wildlife Refuges are intertwined, with an entire model of species conservation and management emerging from regulated hunting and fishing with wildlife refuges at its core. National Wildlife Refuges are places where pathbreaking scientific research has taken place that has led to the great breakthroughs of wildlife management: research on the impacts of lead shot and its replacement by steel shot, the effects of DDT and its subsequent ban, and of course the impacts of harvest on fish and game populations. I know; refuge names were etched into my adolescent vocabulary as my father’s research sites. Patuxent. Missisquoi. Moosehorn. National Wildlife Refuges are secular shrines to wildlife science and scientific management. Do politics and consensus play a role in their management? Certainly, but the National Wildlife Refuges and the U.S. Fish and Wildlife Service are built on the bulwark of the science of wildlife and fisheries sciences.

The armed takeover of Malheur National Wildlife Refuge is, therefore, not just an attack on a federal property. It cuts deeper than that. It is an attack on the modern science-based approach to land management and it is an attack on the value and worth of science and scientists in the United States. This should not come as a surprise. The armed occupiers are extremist Mormons — one of them identified himself as “Captain Moroni” (a figure from the Book of Mormon) and Ammon Bundy describes his actions as the result of consultation with “the Lord.” The occupiers are photographed kneeling in prayer at the refuge. In Linda Sue Beck’s office. Attacks on science from those with extremist religious views are now an unfortunate part of the American political landscape.

Swirling around the Bundys is a maelstrom of conservative malcontents that trace their roots back to the “wise use” movement of the 1980s with its decidedly anti-intellectual and anti-scientific take on the management of public lands. Set aside the ownership of the land — Bundy and the self-styled “patriot” militias of the West fundamentally question the scientific basis for land management.

Unfortunately, the ill-informed reporters sent to cover the slow-motion catastrophe in Oregon fall into the rhetorical trap of the Bundys and their anti-scientific talk-radio enablers. When the occupiers blithely talk of putting the land “to use” again (as if scientific research, recreation, hunting, fishing, education, and all manner of public access were not “use”), the CNN reporter mindlessly repeats the trope, implying that the occupiers have a legitimate demand in wanting to work the land, as if it were some sort of de Tocquevillian tragedy that one of the most productive migratory bird stopover sites on the Pacific flyway was not being overrun with cattle by the ranchers from Utah. No, Malheur National Wildlife Refuge does not need to be worked, and CNN should have reporters that know better than to take the claim at face value.

So I stand with Linda Sue Beck and all of the federal scientists who serve to research, protect, and manage our federal lands. I stand with the scientists, who are under siege, by anti-intellectual know-nothings in the halls of Congress, by vapid inciters on talk radio, and now by armed religious extremists in their very offices. It is time for America to stand up as well.

Travis Longcore, Ph.D.
January 9, 2016