Relationships Among Invasives and Native Plants and Pollinators

Introduction

Image Details

South Dakota’s Badlands National Park contains a large expanse of mixed grass prairie. This unique ecological mosaic is home to several rare and endemic plants including Visher’s Buckwheat (Eriogonum visheri). The small Visher’s Buckwheat flower requires a very specific set of environmental conditions that can be found within the unique geological formations of the Badlands. Issues related to climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change and human land use change could be devastating for Visher’s Buckwheat. For example, changing seasonal patterns could reduce the number of available pollinators in the area, reducing the reproductive success of Visher’s Buckwheat. 

Badlands National Park is also home to numerous invasive plant species including, but not limited to, Russian Thistle (Salsola tragus), Yellow Sweetclover (Melilotus officinalis), and Canada Thistle (Cirsium arvense). Often, potentially harmful invasive plants are removed to conserve these delicate ecosystems. However, within mixed grass prairies, there exists a complex web of interactions between plants and animals, and it is possible for relationships to exist among the invasive plants targeted for removal and the plants and pollinators that are targeted for conservation. While identifying these relationships may be difficult, it is essential both to understanding how the removal of invasive plants may influence the survival of pollinators and rare and endemic plants, and to determining the conservation practices most suitable to the plant and pollinator community. 

To better understand how pollinators and the plants that depend on them respond to the presence or removal of invasive plant species, the U.S. Geological Survey (USGS) Northern Prairie Wildlife Research Center conducted several research projects in Badlands National Park that identified the roles of, and relationships among, invasive plants, various pollinators, and endemic plants.

Key Issues Addressed

The conservation of the endemic Visher’s Buckwheat in Badlands National Park depends on its ability to efficiently reproduce. Since Visher’s Buckwheat is rare and its populations are restricted to a unique geographic range, it is sensitive to increased reproductive competition caused by the introduction of new species. For example, if the pollen of a different plant species (such as an abundant invasive species invasive species
An invasive species is any plant or animal that has spread or been introduced into a new area where they are, or could, cause harm to the environment, economy, or human, animal, or plant health. Their unwelcome presence can destroy ecosystems and cost millions of dollars.

Learn more about invasive species ) is deposited on Visher’s Buckwheat’s flowers, this pollen may block reproductive organs and prevent the production of a viable seed which is necessary for Visher’s Buckwheat reproduction. 

It should be noted that invasive plants may provide a higher abundance of pollen or nectar than native plants which could attract pollinators away from natives. However, if invasive plants are growing nearby and attracting new pollinators to the area, it is also possible for native plants to have increased pollinator visitation. Without a better understanding of the relationships among Visher’s Buckwheat and the surrounding invasive plants, it is difficult to determine whether or not invasive plant removal is necessary for the conservation of this rare, endemic plant. 

Pollinator conservation practices tend to focus only on bees when many other insect taxa are also important pollinators. To understand how removing invasive plants influences pollinators and the plants they pollinate, land managers must also consider the contributions of non-bee pollinators such as beetles, wasps, and flies.

Pollinators may depend on nectar and pollen from invasive plants. Therefore, it is important to consider whether the removal of invasive plants might harm pollinators who have become dependent on the pollen and nectar they provide before proceeding with removal of invasive species.

Project Goals

• Identify relationships among Visher’s Buckwheat and two nearby invasive plant species, Russian Thistleand Yellow Sweetclover, to better understand the consequences of the presence and removal of invasive plant species on Visher’s Buckwheat. 
• Determine the role of multiple insect taxa in providing pollinator services to better understand which pollinator species contribute to rare and endemic plant pollination.
• Use pollen transport data from Badlands National Park to determine if the removal of invasive plants is harmful to pollinators that use their pollen and nectar resources. 

Project Highlights

Calling All Taxonomists: Gathering plant and pollinator data requires special attention to species identification. Without a skilled taxonomist on the team, data collection can be exceedingly difficult. 

• Innocuous Invasives: Pollen from the invasive plants Russian Thistleand Yellow Sweetclover did not affect Visher’s Buckwheatreproduction as shown by Larson et al. 2021. 
• A Bee or Not a Bee─They All Carry Mixed Pollen: The study done by the USGS Northern Prairie Wildlife Research Center found that, while non-bee pollinators were less likely than bees to carry pollen from multiple species, there was no single pollinator that visited or carried pollen from Visher’s Buckwheat exclusively. Additionally, there were only subtle differences in visitation frequency and pollen load sizes of bees and non-bee pollinators meaning both bees and non-bee pollinators are equally important for the pollination of Visher’s Buckwheat. 
• Pollinator Diversity Improves Resilience: Bees, flies, beetles, and wasps were all important to pollen transfer, but each with varying contributions and at different times during the season. This wide range of pollinator contributions enhances the prairie plant community’s resilience to environmental disturbances and will be increasingly important as climate change increases the likelihood of unfavorable environmental conditions. 
• Native Plants Know That Timing is Everything: The USGS Northern Prairie Wildlife Research Center determined that the native Few-flowered Buckwheat (Eriogonum pauciflorum) had many of the same insect pollinators as the endemic Visher’s Buckwheat. Since Few-flowered Buckwheat is a perennial, it may be a more reliable alternative source of pollen and nectar for pollinators than the invasiveRussian Thistle which is an annual. Therefore, Few-flowered Buckwheat can sustain pollinators during times that Visher's Buckwheat is not abundant. Additionally, a study done in the northern Great Plains wheatgrass prairie communities within Badlands National Park showed that while pollinators were attracted to the invasive Canada Thistle, if it was removed and there were native plant species present, pollinators would switch to native plants.

Lessons Learned

Image Details

Year-to-year variation in the individual roles of, and relationships among, plants and pollinators is common. For example, earlier studies done by the USGS Northern Prairie Wildlife Research Center concluded that Russian Thistle was detrimental to Visher’s Buckwheat reproduction whereas later studies determined it was not. Therefore, management actions based on pollinator data should not be dictated by any single year but instead be based on observations made over several years. 

As the effects of climate change become more evident, there are rising concerns that unfavorable environmental conditions may result in the loss of important pollinators and, in turn, the valuable plants they pollinate. The relationships among these plants and pollinators are directly related to the community’s resilience to environmental disturbance. Research done by the USGS Northern Prairie Wildlife Research Center found that there were significant relationships among non-bee pollinators and native and invasive plant species. Therefore, understanding the impact of invasive plants on pollinator conservation and on community resilience requires attention to a wide range of insect taxa, including flies, beetles, and wasps, not just bees.

Since many invasive plants provide abundant pollen and nectar, they may attract new pollinators to the area, which could be beneficial for nearby native plants. However, it is also possible for invasive plants to outcompete native plants for existing pollinators or other resources, interfering with the reproduction of native plants. These contrasting effects have historically caused uncertainty as to whether the possible benefits of invasive plants outweigh their threats. Ultimately, The USGS Northern Prairie Wildlife Research Center found that higher floral abundance in native plant species would serve as a better resource for pollinators than invasive species regardless of the possibility of invasive plants providing alternative pollen and nectar.  

Next Steps

• Publish analysis of pollen data collected in 2009-2010 during a season long study
• Share current and future research results with land managers to inform best practices 
• Seek out additional taxonomists for in-lab insect species identification

Funding Partners

• Natural Resource Preservation Program (NRPP)
• USGS Invasive Species Program 
• USGS Northern Prairie Wildlife Research Center 
• USGS Patuxent Wildlife Research Center 
• Badlands National Park

Resources

• Larson, D.L., et al. (2014). “Using a network modularity analysis to inform management of a rare endemic plant in the northern Great Plains, USA.” J Appl Ecol 4(51): 1024-1032. 
• Larson D.L., et al. (2016). “Exotic Plant Infestation Is Associated with Decreased Modularity and Increased Numbers of Connectors in Mixed-Grass Prairie Pollination Networks.” PLoS One 11(5): e0155068. 
• Larson, D. L., Larson, J. L., & Buhl, D. A. (2018). “Conserving all the pollinators: Variation in probability of pollen transport among insect taxa.” Natural Areas Journal 38(5), 393-401. 
• Larson, D. L., et al.. (2021). “Coflowering invasive plants and a congener have neutral effects on fitness components of a rare endemic plant.” Ecology and Evolution 11(9), 4750–4762.
• Larson, D. L., et al. (2022). “Variation in foraging patterns as reflected by floral resources used by male vs female bees of selected species at Badlands National Park, SD, USA.” Arthropod-Plant Interactions.

Contact

Diane Larson, USGS Northern Prairie Wildlife Research Center: dlarson@usgs.gov

CART Lead Author

Maddison E Elliott, Student Author, VSFS: elliott.me@outlook.com

Suggested Citation

Elliott, M., E. (2022). Understanding the Relationships Among Invasive Plants, Native Plants and Pollinators in Badlands National Park.” CCAST. Retrieved from https://www.fws.gov/project/relationships-among-invasives-and-native-plants-and-pollinators.