Blog Archive:
Beneath Our Feet
Earthworms in the National Parks
By: Mac Callaham, USDA Forest Service Southern Research Station, Georgia, USA
Photo from George Washington Memorial Parkway.
I plop down into my seat as I board the flight. I give a brief nod of greeting to my neighbor, and notice that he is (like me) of an age which might indicate that he could expect to pass the flight time in conversation, rather than totally absorbed in a liquid crystal display.
I start with a standard question, “Are you headed out, or headed home?” And we’re off!
When it’s my turn, I tell him that I’m headed out to a conference where I’ll give a presentation on my research on earthworms. I know this is a topic that will keep the conversation rolling all the way from Atlanta to New York… fortunately, we have refreshments!
It’s generally true that people are interested in earthworms, and even more so when I tell them that I study invasive earthworms. People are also quite interested – and protective – of their National Parks, so I find that I usually have an attentive audience when I talk about my work on earthworms in the Parks.
“Invasive earthworms?!?” they exclaim. “There’s more than one kind?” they gasp. Then in rapid succession: “Where do they come from? What do they do? How do you know they’re invasive?” and more. I do my best to answer them, and eventually get around to describing the work that my colleagues and I have been doing at the Great Smoky Mountains National Park (GSMNP) in Tennessee, and the George Washington Memorial Parkway (GWMP) in Virginia and Washington, DC.
In the GSMNP it’s an introduced Asian worm that’s moving into the Park from the edges. This worm is one that’s sold as bait, and goes by the trade name of “Alabama Jumper.” It’s aptly named, because (although not technically from Alabama) they definitely jump. When molested these worms can flip and twist and throw themselves up off the ground, sometimes catching several inches of air in the process. This species is a cause for concern because where it becomes established, it can reach very high densities, and it consumes much of the fallen leaves on the forest floor. These leaves are habitat for lots of other invertebrates, as well as some larger animals like salamanders. It’s no surprise that the GSMNP is considered a hotspot of biodiversity for forest floor creatures like millipedes and salamanders considering the rugged, inaccessible terrain, the lush vegetation, and the warm and wet conditions that predominate. On the other hand, it is a bit surprising, and alarming that one introduced earthworm species can outcompete these other forest floor dwellers, and impact their numbers and diversity, but this is exactly what our team has documented in recent years.
At the George Washington Memorial Parkway (GWMP) in Washington DC, we sampled earthworms and other soil invertebrates to help catalog the existing biodiversity of the Parkway and its constituent Parks (including Great Falls NP). We were also interested in whether the past history of human uses of the land could be detected in the soil animal community. There’s evidence that major disturbances can contribute to the establishment of non-native earthworm species, and the GWMP provided a great opportunity to examine this relationship with well documented history of soil disturbances ranging from the canal-building activities at Great Falls Park in the 1780s, through the Civil War entrenchments, and on into contemporary disturbances. We’ve uncovered good news and bad news with this work. On the one hand we’ve found what we believe to be an undescribed native species of millipede at one of the GWMP network parks (Turkey Run Park), but on the other hand, we found several individuals of a European earthworm species that has never been reported in North America before our sampling.
Alabama Jumper.
Photo © Susan Day / UW Madison Arboretum
All this brings up a couple of important points. First, we still don’t seem to have a good handle on the species diversity that we have native to the soils of North America, and second, there are new species introductions happening all the time, and we don’t have a good handle on what these introductions will mean for the native species. Will this latest introduced species become invasive? Will it choke out some native species, or otherwise decrease our native biodiversity? Is there any way to control these invasive species?
Out the window, our flight from Atlanta to New York has skirted the eastern slope of the Smoky Mountains, and passed within sight of the National Mall in DC. My new friend leans over and looks down on these landscapes. He is reflective.
“Wow, there’s a lot going on down there that I never thought about before…”
I nod knowingly. I tell him that few people ever really think about what’s going on right under their feet, but I tell him that now he’s one of the lucky ones.
Earthworm invasions in northern forests
By Erin Cameron, Postdoctoral Researcher, Helsinki University, Finland
Lumbricus terrestris. Image by E. Cameron
Finishing my paper route always took longer on rainy days when I was a kid – I had to walk slowly to avoid stepping on earthworms and occasionally I stopped to move them off the sidewalk. I would never have believed that earthworms were invasive in much of Canada and the northern United States! In those previously glaciated areas, there are no native earthworms, but instead only European earthworms that were introduced to North America with the arrival of European settlers.
Earthworm populations can only expand about 5 to 15 meters per year on their own, and consequently people play a key role in their spread. For my master’s thesis with Dr. Erin Bayne at the University of Alberta, I tried to determine how earthworms were spreading in Alberta’s boreal forest. I was sold on the research question once I realized that I’d need to canoe or kayak across lakes to test whether earthworms were most common near boat launches where anglers might dump their earthworm bait. After a couple near misses but only one capsizing incident, we found that earthworms were present at approximately 70% of the boat launches and roads sampled, but only 35% of far shores and less than 15% of forest interiors. They were also more likely to occur at older roads than more recently built roads, suggesting that earthworms were introduced by vehicle traffic (their eggs can become stuck in tire treads) not during construction of the roads.
After examining how earthworms were being introduced, we started to investigate their effects in the boreal forest. Surprisingly to most people, earthworms do not always improve soil health or benefit other organisms. When exotic earthworms invade forests where there are no native earthworms, they consume leaf litter layers, mix organic and mineral soil horizons, and affect nutrient cycling. These impacts on soil structure and ecosystem functioning can then lead to cascading effects on other organisms. In northern Alberta, we found that earthworms decreased the thickness of the leaf litter layer, reduced the abundance and diversity of microarthropods, and decreased plant biomass, depending on the species. Not all species were negatively affected though – one of the key predators of earthworms, the American robin, was more likely to occur in areas where earthworms were present.
Sampling for earthworms in the boreal forest. Image by R. Rocha
Earthworm invasions are at an earlier stage in northern boreal forests than temperate hardwood forests, where the deep burrowing and mineral soil dwelling species that cause the largest changes are more widespread. At our study sites, the most common species is a litter dwelling species called Dendrobaena octaedra. But because most people are not aware that earthworms are invasive, they continue to introduce earthworms by dumping their bait, moving soil, or not cleaning their tires when travelling to remote areas. We started a citizen science project to collect data on earthworm distributions across Alberta, which at the same time serves to increase public awareness about earthworm invasions: http://worms.educ.ualberta.ca
However, earthworm invasions are occurring globally, rather than only in North America. We also lack data on distributions of native and exotic species of earthworms at broad scales, making it difficult to determine the key factors driving their distributions. To address this issue, we started a working group (sWORM; https://www.idiv.de/?id=429) at the German Centre for Integrative Biodiversity Research (iDiv) to synthesize data on earthworm distributions. Let us know if you have earthworm data and want to participate!
Further reading:
Cameron EK, Bayne EM, Clapperton MJ. 2007. Human-facilitated invasion of exotic earthworms into northern boreal forests. Ecoscience 14: 482-490.
Cameron EK, Bayne EM. 2012. Invasion by a non-native ecosystem engineer alters distribution of a native predator. Diversity and Distributions 18: 1190-1198.
Craven D et al. 2016. The unseen invaders: introduced earthworms as drivers of change in plant communities in North American forests (a meta-analysis). Global Change Biology 23: 1065-1074.
What lies beneath: South Africa’s megadiversity of soil biota Part III
By Dr. Charlene Janion-Scheepers & SERG members
This is the final in a three-part blog series highlighting the rich soil biodiversity found in South Africa.
In our previous blog we discussed some key findings of our review on the rich soil biodiversity of South Africa. In this last blog we want to highlight some key conservation priorities, threats to soil biota and some future directions we think are necessary for the advancement of soil biota research in South Africa.
Threats to soil biota in South Africa
Global drivers, such as land degradation, exploitation, pollution, climate change and
biological invasions, are serious threats to South African biodiversity. For many understudied groups even the identification of invasive species are problematic, while the impact of these invasives on the indigenous species are also unknown. Climate change will probably directly and indirectly favour invasive species in all South African ecosystems, thus the identification and assessment of distributions of invasive species should become a research priority for all soil biota groups.
Other threats to soil biota include intensified land-use. The livelihoods of people in South Africa depend in many ways on the continued functioning of the soil ecosystem, thus there is an urgent need for basic biodiversity knowledge in order to facilitate the soil ecosystem research required to assess sustainability.
Conservation
Soil dwelling species are usually classified as Data Deficient in the IUCN red list criteria. This appears to be related to the limited number of soil biota researchers, difficulties in identification, and inherent logistic difficulties in surveying and sampling. Even the most basic IUCN Red List criteria require a reasonable understanding of the taxonomy and distribution of individual species. The results from our review agree with previous findings, that many taxonomic groups of soil biota could not be assessed for conservation status due to a lack of baseline data. However, exceptions do exist, and the recent First Atlas of the Spiders of South Africa provides an excellent model of what is possible. In addition, the inclusion of endemic soil biota in conservation planning should be the next step to ensure soil habitat conservation.
Future research directions
The major issues that need to be addressed were clear: funding needs to be put in place to:
Train taxonomists
Consolidate and curate existing collections for improvement of data storage and management
Capture existing data
Fill gaps identified in this paper, especially focusing on the functional roles of soil biota
Use our existing and growing expertise as a base to tackle a continental deficiency in our understanding of soil ecosystems
Use current taxonomic expertise to facilitate the development of DNA barcode libraries
Sampling areas that have been poorly studied should be a priority for future work, which includes the Nama-Karoo, Northern Cape and Eastern Cape
Fig. 1: A schematic example of an integrative sampling approach.
In South Africa, funding and expertise is required in a coordinated research framework. Successful examples of this approach have been demonstrated for Europe, such as BISQ and EcoFINDERS. The development of an integrative sampling approach to sampling soil communities (Fig. 1) should be initiated in South Africa to place taxonomic knowledge in an ecological context and develop monitoring tools to provide valuable advice for soil health management. Such an overall strategy for South African soil biota research is needed, which recognises that although different research priorities exist for each group, sharing and contrasting experiences will help advance our knowledge across the board. We see the formation of SERG as the first of many steps towards the goal of an integrative approach to soil ecosystem research in South Africa.
What lies beneath: South Africa’s megadiversity of soil biota Part I
By Dr. Charlene Janion-Scheepers, Postdoctoral Research Fellow, Monash University, Australia
This is the first in a three-part blog series highlighting the rich soil biodiversity found in South Africa.
Soils are integral to agricultural productivity, biodiversity and the maintenance of ecosystem services. However, soil ecosystem research depends on foundational biological knowledge that is often missing. In a recent review published in Pedobiologia, we review the current knowledge on the soil biota of South Africa. The paper outlines the literature and sampling methods used to assess soil biota, the available taxonomic expertise and depository of main collections within South Africa, the availability of identification guides and online resources, and the status and distribution of described species.
This review was the result of two workshops held by the Soil Ecosystem Research Group in South Africa (SERG). We are a soil biodiversity research group that provides a platform for linking and promoting research on soil organisms. One of the first priorities identified by SERG was the need to collate and mobilise data and collections such that we can consolidate and compare the state of knowledge of each group. We also identified that foundational work on soil organisms is needed to facilitate research on soil health, as was outlined in our paper The unknown world: Understanding soil health in South Africa.
The first Soil Health Workshop held at the XVII Entomological Society of Southern Africa Congress in Bloemfontein, 6 July 2011.
Second workshop of the Soil Ecosystem Research Group held at the XVIII Entomological Society of Southern Africa Congress, 2 July 2013, North West University, Potchefstroom.
In our next blog What lies beneath: South Africa’s megadiversity of soil biota (part II) we will discuss the rich soil biodiversity found in South Africa.
The Many Roles of Protists in the Soil
By Dr. Enrique Lara, University of Neuchâtel, Switzerland
This is part two in four part soil protist series! Part 1 can be read here.
Figure 1: This unidentified amoeba is one of the members of the extremely diverse protist community inhabiting the soil of a common indoor flower pot; new species can be found even in the least exotic environments! This species feeds on yeasts and bacteria.
Protists are extremely diverse in soils, often reaching thousands of species of protists and fungi per gram. If we bring these numbers to our scale of perception, this means that a little piece of soil the size of a fingernail hosts a number of species comparable to the diversity of insects in a hectare of tropical rainforest! Like in the jungle, the different organisms play various roles in the soil ecosystem. Globally, these roles can be divided in three great categories: osmotrophs, phototrophs and phagotrophs.
Osmotrophs absorb their food from the environment; they are unable to engulf preys. They play a fundamental role in the decomposition of dead organic matter produced by plants. Mostly fungi take this role, but they are not alone! Another very common group of soil osmotrophs is the oomycetes, which closely resemble fungi but are now classified within the stramenopiles- a group very distant to fungi together with many algae such as the marine kelps! Some organisms evolved from photosynthetic ancestors to live in the absence of light and became secondarily osmotrophs, like the green alga Polytomella. Osmotrophic organisms often tend to become parasites during evolution; they start the evolutionary process as mostly free-living organisms that infect occasionally any potentially weakened host. Then, they become gradually more and more specialized and virulent. Many species of fungi and oomycetes are well known plant parasites, and are responsible for huge economic losses every year. Others infect animals (including humans) and even other fungi! Other groups are entirely parasitic such as the Phytomyxea (plant parasites) and the Apicomplexans (animal parasites, including amongst others the agent of malaria Plasmodium falciparum), which can be extremely abundant and diverse in soils. However, osmotrophs can also become Mr. Niceguy and collaborate with plants: mycorrhiza are the most widespread and famous example.
Being a phototroph, obtaining energy from the sun like a plant, in soils may seem contradictory; however, phototrophic organisms are numerous and diverse as well. Logically, they are limited to the upper part of the soil that is reached by light; they are responsible (together with mosses and cyanobacteria) for the formation of so-called cryptogamic crusts, which are common in deserts and high altitude soils. Some of these groups are well known in lakes and rivers (like diatoms, green algae, xanthophytes), but most often species are specific to soils as they went through specific adaptations to be able to colonize these environments.
Many protists in soils are phagotrophic, which means that they prey on other organisms through phagocytosis (just like the macrophages of our immune system). Bacteria are a common food source for them, and it has been shown that predation by protists is the main source of mortality for soil bacteria. By eating these preys, nutrients are released and taken up by plants; it has been shown that this phenomenon, coined the soil microbial loop, is key in driving plant productivity. However, all bacteria are not equally preyed upon by protists, and food preferences vary drastically even between closely related protist species. On the other hand, bacteria are by no means defenceless and produce secondary metabolites that can kill protist predators. This make trophic interactions between protists and bacteria extremely complex. But bacteria are by no means the only prey of protists. Fungi are also consumed, and some species of ciliates possess a cytostome (=cell mouth) that prevents them from eating anything else; they are simply unable to consume bacteria! Others are top predators and will feed only on other protists. Some, like the tiny shelled amoeba Cryptodifflugia, are able to kill even nematodes, and practice a kind of pack hunting to slay their victims which weigh about hundred times more than them!
Figure 2: A testate amoeba, Centropyxis aerophila, hunting for small protists and fungi in its favourite environments, forest litter. It uses its pseudopod to move forward and capture preys by immobilizing them before engulfing.
The situation is complicated even more as some organisms may belong to two functional categories at the same time. Many soil flagellates and amoebae are capable of both actively hunting for preys and absorbing nutrients from the environment, thus combining phagotrophy and osmotrophy. Phototrophy and phagotrophy are also often combined, especially in wet soils like in peatlands (where it is largely practised by golden alga like Ochromonas, Synura and Mallomonas). Altogether, functional diversity of eukaryotes in soils is immense. Our knowledge on their diversity is now at a turning point where it starts to be evaluated, but still remains an open field for new, exciting discoveries.
Marvelous soil present, another adventure in Brussels
By Gerlinde De Deyn
Wageningen University, Dept. Soil Quality
September 2015. Regular readers of this blog will not be surprised that I was in Brussels for the European Union Researchers’ night, this year was very special: the 10th anniversary of researchers’ the night! Not only in Brussels of course, lots to see and do across Europe at this major science outreach event which runs simultaneously in all main cities of the EU http://ec.europa.eu/research/researchersnight/index_en.htm.
For this occasion I was not asked to bring a living soil micro-zoo, just myself and my reflections on what makes science so wonderful for me. The setting: a predominantly French interview by the public from Brussels, with Christophe Deborsu as moderator and Stefaan Vaes (University of Leuven, Dept. of Mathemathics) and me (Flemish soil ecologist who hardly spoke French since leaving Belgium fifteen years ago) as the researchers.
How and at which age did we get inspired to become a scientist? What do we earn and how many hours a week do we work? Why did you move to another country? What impact does your science have on society? What is the current status of biodiversity? How come there are so few female professors? These were just a few of the questions that came a long during the interview. Not always easy to answer, but luckily not due to language - thanks to an eager public and multi-lingual moderator.
Was there any soil ecology involved? Sure there was in this International Year of Soils! We gave a copy of the European Soil Biodiversity Atlas (French or English version) to each person posing a question. Perhaps some of them will get the spark of wonder and turn into soil ecologists… Given the enthusiasm I also promised that a Global Atlas of Soil Biodiversity will come out later this year, something we are all looking forward to of course J.
PS: As with previous events also now great meet scientists you would otherwise never meet, a tip from Stefaan Vaes if you like math and visualizations of it check out this site: http://imaginary.org/
Taming the wilds of Central Park
Last week we successfully collected 595 samples from across Central Park in New York City. I described this huge undertaking in my previous post, so you can find out a bit more here about collaborators and sampling scheme.
Briefly, we collected soil samples, from 15 points across each of the 51 blocks running west to east in Central Park. For those of you not familiar with CP, the park is ½ mile wide and 3 miles long (51 blocks)! The park is not continuous however. There is quite a bit of rugged terrain- rock outcroppings, sports fields with 7 foot tall fences, the Met, ponds, children, fountains, dogs, cars, bikes, yoga stroller classes, Shakespeare in the park, bridges, waterfalls, music stages, merry-go-rounds… you get the idea. Check out our photos here for shots of us sampling in the wild.
We had 10 participants split between four groups, each sampling a roughly equivalent section of the park. Beginning on the steps of the Museum, we split up into groups of two and three, double checked the GPS units, measured out 5cm on our corers with sharpies and tape, and gathered cell phone numbers mostly to facilitate friendly competition throughout the day.
The first hour was slow, as each group found a sampling routine and adjusted to the rugged terrain. Then the pace started to pick up and sampling was flurried in the next 4-5 hours. By 1 p.m. the groups across the park were slowing. High humidity accompanied by 90° temperature, will do that. My group was motivated by a stop at an ice cream stand, others were not as lucky to find refreshments and were tempted instead by fountains. Still, we finished the last of the sampling by 6:30 p.m. and had all the samples safely stored in the museum by 7 p.m.! 12 hours of sweating, a few minor scrapes and bruises, a bit of heat exhaustion, but success! Really this is a huge accomplishment for one day- 600 samples... I still am in awe that we actually finished!
Wednesday after the sampling, we met again at the Museum. This time to sieve all the samples! Sieving is a monotonous process at best- take soil out of bag, sieve, separate, repeat. During the craziness of sieving we entered GPS points and a few volunteers collected water samples from all the major bodies of water in the park. Check out this sweet google map. All the samples are now ready to be processed! We will soon begin analyzing soil characteristics- pH, nutrients, moisture and microbial biomass and this fall we will sequence all soils and water samples.
This was really a fantastic sampling effort, and without the cooperation and determination of everyone involved we could not have pulled it off. Thanks again to Susan Perkins, our linchpin at the museum and Liz Johnson.
Stay tuned for more on this project and if you have questions on this project please contact me at Kelly.Ramirez@colostate.edu.