Restoration of Ecological Function in Terrestrial Systems Impacted by Invasive Species
Invasive species are responsible for the decline or extirpation of many species around the world. When those lost species provide essential ecological functions, the system may further degrade over time. Restoration ecology aims to restore these systems and associated ecological functions. It is important to first understand the invaders and their direct and indirect impacts to the native ecosystems. This requires a thorough understanding of the system and functions pre-invasion. Once these links and mechanisms are understood, managers must decide on a course of action to control or halt the spread of the invasive species and prevent further ecological degradation. Managers must determine what types of control are most appropriate for their systems as well as to what levels an invader must be controlled before restoration actions lead to improved ecological function. Deciding on specific restoration actions will vary considerably from system to system, but must involve considerations such as topography, landcover, feasibility, scale, social impacts, and timing. Specific details about habitats and species natural history are important to incorporate into planning models. Finally, monitoring and adaptive management throughout the course of the restoration and beyond are crucial to long-term success.
Contributors: Dr. Hugo Thierry, McKayla M. Spencer, Ann Marie Gawel, and Dr. Haldre Rogers
- Intervention Ecology: Applying Ecological Science in the Twenty-first Century
- Effects of An Invasive Predator Cascade to Plants Via Mutualism Disruption
- Where to Rewild? A Conceptual Framework to Spatially Optimize Ecological Function
Introduction- Invasion Biology
Because of the increased ease and frequency of transportation of people and goods across the globe, almost all ecosystems have species introduced by humans that do not share an evolutionary history with the native members of the ecosystem. Only some of these species survive to reproduce, and even fewer cause harm. Invasive species are recognized as having been transported to a novel geographic area, establishing in that area, and then causing ecological or economic harm to the systems in that geographic region. Several attempts have been made by researchers in the field to distinguish “invasive” from “non-native,” “alien” and “exotic”. Invasive species were defined in The President's Executive Order 13112 (1999) as, “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health”. The Global Invasive Species Program of the International Union for the Conservation of Nature accepts a similar definition of “invasive alien species” as “This subset of alien species that become established in a new environment, then proliferate and spread in ways that are destructive to native ecosystems, human health, and ultimately human welfare…”. Invasive species are one of the greatest threats to ecological and economic well-being of the planet. Developing common definitions was essential given the prevalence and urgency of the impacts.
Efforts focused on early detection and rapid response are preferable to trying to control a species once it has established. However, in many cases, it can be difficult to identify potential invasive species until they have started causing obvious detrimental effects.
Once a species has been identified as invasive, there are some key questions that need to be asked and answered to attempt restoration of ecological function within an ecosystem. The return of ecosystems to their original state may not be financially feasible or even technically possible due to extinctions, invasive species, or climate change, but these ecosystems still have tremendous value, and managing them to maximize that value requires an understanding of how these systems function. In places where the cause of species loss and species endangerment are still present and the invasive species removal appears intractable, managers may need to utilize the strategy of “intervention ecology” (Figure 1), restoring function within these novel systems without attempting to restore the original ecosystem.
A well-known example of an invasive species that caused detrimental effects to an entire ecosystem, where the intervention ecology approach is now being applied, is the brown treesnake (Boiga irregularis) on the island of Guam. The snake was introduced to the island at the end of WWII, likely a stowaway aboard U.S. military cargo ships. Within approximately 40 years the snake had spread throughout the entire island and eliminated 9 of the 11 species of native forest birds. While the brown treesnake may be the most infamous, other introduced species also have detrimental effects on Guam’s ecosystems. Rats (Rattus sp.), feral pigs (Sus scrofa), and Philippine deer (Rusa mariannae) are well-established and numerous arthropod pests, including the little fire ant and coconut rhinoceros beetle are taking a noticeable toll on local species.
Identifying the Impacts of Non-native Species on the Ecosystem
When a species has been identified in an ecosystem, it is essential to determine how it has impacted the stability, composition, and diversity of the ecosystem. This may be done by comparing changes over time, if data exist from prior to the invasion, or comparing across space if comparable areas exist nearby. Experiments that compare areas where the invasive is excluded to areas where it is present (aka ‘exclosure experiments’) may also shed light on how the system would operate in the absence of the invader.
Invasive species may cause the decline or extirpation of native species that provide essential ecological functions in the ecosystem. For example, the Hemlock Woolly Adelgid (Adelges tsugae), an invasive insect from Asia, has led to the destruction of up to 80% of the hemlock trees in the Eastern United States, which then impacted overall forest composition. In Florida, the burmese python (Python molurus) became a destructive invasive species in less than 20 years by causing severe declines in mammal populations through predation.
- ^ 1.0 1.1 1.2 Hobbs, R.J., Hallett, L.M., Ehrlich, P.R., and Mooney, H.A., 2011. Intervention Ecology: Applying Ecological Science in The Twenty-first Century. BioScience, 61(6), pp. 442–450. doi: 10.1525/bio.2011.61.6.6 Article pdf
- ^ Rogers, H.S., Buhle, E.R., HilleRisLambers, J., Fricke, E.C., Miller, R.H., and Tewksbury, J.J., 2017. Effects of an invasive predator cascade to plants via mutualism disruption. Nature Communications, 8:14557. doi: 10.1038/ncomms14557 Article pdf
- ^ Thierry, H., and Rogers, H., 2020. Where to rewild? A conceptual framework to spatially optimize ecological function. Proceedings of the Royal Society B: Biological Sciences, 287:20193017. doi: 10.1098/rspb.2019.3017 Article pdf
- ^ Williamson, M., and Fitter, A.,1996. The varying success of invaders. Ecology, 77(6), pp. 1661–1666.| doi:10.2307/2265769
- ^ Blackburn, T.M., Pyšek, P., Bacher, S., Carlton, J.T., Duncan, R.P., Jarošík, V., Wilson, J.R., and Richardson, D.M., 2011. A proposed unified framework for biological invasions. Trends in Ecology & Evolution, 26(7), pp. 333–339. doi: 10.1016/j.tree.2011.03.023
- ^ Kraus, F., 2008. Alien Reptiles and Amphibians: A Scientific Compendium and Analysis. Springer, Dordrecht, Netherlands. ISBN: 978-1-4020-8945-9/eISBN: 978-1-4020-8946-6 doi:10.1007/978-1-4020-8946-6
- ^ Kraus, F., 2015. Impacts from Invasive Reptiles and Amphibians. Annual Review of Ecology, Evolution, and Systematics, 46(1), pp. 75–97. doi:10.1146/annurev-ecolsys-112414-054450
- ^ Colautti, R.I., and MacIsaac, H.J., 2004. A neutral terminology to define ‘invasive’species. Diversity and Distributions, 10(2), pp. 135–141. doi:10.1111/j.1366-9516.2004.00061.x Article pdf
- ^ Richardson, D.M., Pyšek, P., Rejmánek, M., Barbour, M.G., Panetta, F.D., and West, C.J., 2000. Naturalization and invasion of alien plants: concepts and definitions. Diversity and Distributions, 6(2), pp. 93–107. doi: 10.1046/j.1472-4642.2000.00083.x Article pdf
- ^ McNeely, J.A., 2000. The future of alien invasive species: changing social views. In: H.A. Mooney and R.J. Hobbs (eds), Invasive Species in a Changing World. Island Press, Washington, DC, pp. 171–190. ISBN: 978-1559637824.
- ^ Simberloff, D., Martin, J.-L., Genovesi, P., Maris, V., Wardle, D.A., Aronson, J., Courchamp, F., Galil, B., García-Berthou, E., Pascal, M., Pyšek, P., Sousa, R., Tabacchi, E., and Vilà, M., 2013. Impacts of biological invasions: what’s what and the way forward. Trends in Ecology & Evolution, 28(1), pp. 58–66. doi: 10.1016/j.tree.2012.07.013
- ^ Marris, E. (2011). Rambunctious Garden: Saving Nature in a Post-wild World. Bloomsbury, New York. ISBN: 978-1-6081-9454-4/eISBN: 978-1-6081-9455-1
- ^ Savidge, J.A., 1987. Extinction of an Island Forest Avifauna by an Introduced Snake. Ecology 68(3), pp. 660–668. doi: 10.2307/1938471
- ^ Wiles, G.J., Bart, J., Beck, R.E., and Aguon, C.F., 2003. Impacts of the Brown Tree Snake: Patterns of Decline and Species Persistence in Guam’s Avifauna. Conservation Biology, 17(5), pp. 1350–1360. doi: 10.1046/j.1523-1739.2003.01526.x
- ^ Hoyer, I.J., Blosser, E.M., Acevedo, C., Thompson, A.C., Reeves, L.E., and Burkett-Cadena, N.D., 2017. Mammal decline, linked to invasive Burmese python, shifts host use of vector mosquito towards reservoir hosts of a zoonotic disease. Biology Letters, 13(10):20170353.doi: 10.1098/rsbl.2017.0353 Article pdf