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.
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