On its own, a bicycle can’t move at all.
Humans are pretty good at moving, with an average jogging speed of 10-12 kilometres per hour.
But when a human gets on a bicycle, they can move across long distances even more quickly and efficiently.
This is an example of synergy. In other words, there is a relationship between a human and a bicycle that allows their combined output to be more than the sum of their individual parts.
Unfortunately, synergy is not always a good thing. Climate change and invasive species are problematic issues on their own, and they also interact to produce synergistic effects that are worse than their independent impacts. Climate change can make ecosystems more vulnerable to invasive species, and invasive species can worsen the impacts of climate change.1,2,3 Together, these two stressors can have diverse social, economic, and environmental impacts.4
Invasive species exacerbating climate change impacts
Invasive species can affect the rate and overall impacts of climate change in various ways. Click on each of the bullets below to learn more.
Ecosystems affected by invasive species are more vulnerable to the impacts of climate change. In habitats that are becoming warmer and drier due to climate change, invasive plants can serve as additional fuel for wildfires, resulting in more frequent and severe fire events.4 For example, a 2013 study in the United States showed that invasive cheatgrass alters regional fire regimes, leading to more frequent and more extensive fires.6 If future climate conditions involve both warmer temperatures and higher water availability, a novel cycle of grass fires could lead to the loss of woody shrubland species.
Plants remove carbon dioxide from the atmosphere, allowing it to be stored in soil. This is known as soil carbon sequestration, and it is an important process for mitigating climate change. Various studies have shown that more carbon is stored in areas with high plant biodiversity, as compared to areas with fewer species.7,8,9 Unfortunately, invasive species are one of the top five drivers of biodiversity loss,10 suggesting that invasive species can reduce carbon sequestration through their impacts on biodiversity. In addition, invasive plants species can alter nutrient availability and have different rates of primary productivity, both of which impact carbon sequestration.11,12 To make matters worse, some evidence suggests that invasive species benefit more than native species from increasing carbon dioxide,13 meaning that carbon release is a vicious cycle favoring invasive species. While this all sounds like bad news, it’s important to remember that every invasive species is different and not all will negatively impact carbon storage, so management should be context specific.11
Climate change exacerbating invasive species impacts
Climate change can intensify each step of the invasion process, while also hindering management options. Click on each of the bullets below to learn more.
Invasion pathways and vectors
Climate change creates new and enhanced pathways for invasion. These pathways do not impact all areas of the world equally. A 2013 study identified future hotspots for invasion based on climatic changes and international trade routes.15 Northwestern North America was one of these hotspots.
As climate change warms the Arctic, new and quicker shipping routes are emerging. These new routes provide two opportunities for invasive species that hitchhike on hulls and in ballast tanks: 1) they can travel to entirely new areas, and 2) their survival rates are improved due to the reduced travel time.3,4,17
Climate change is also altering use of existing shipping routes. For example, climate change is expected to extend the shipping season of the St. Lawrence Seaway, which will allow exotic species to enter the Great Lakes in seasons when they would not previously have had access.3 Warmer temperatures will also increase rates of biofouling (i.e., the accumulation of organisms on ship hulls) and the likelihood of organisms surviving trips in ballast water.
Extreme weather events
Extreme weather events like hurricanes and floods are increasingly frequent due to climate change. During these events, birds, fish, and insects can be moved long distances and across physical barriers like dams.16,17 Not all species will survive these tumultuous journeys, however invasive species may fare better than native ones during and after these extreme weather events. This is because invasive species often have traits that make them highly adaptable, including tolerance of a wide range of environmental conditions and an ability to thrive in disturbed environments.16
Establishment and spread
Many invasive species in temperate regions like Canada originate from tropical regions of the world. Although they have successfully established in their new temperate habitats, their survival and growth has been limited by factors like ice cover or cold temperatures.4,17 As temperatures increase due to climate change, the new habitats of these invasive species begin to feel more like the conditions that they originally evolved in, increasing their chances of survival and growth.17,18,19 At the same time, native species are being shifted out of conditions that they evolved in, weakening their resistance to invaders.
In addition, some of the traits that make exotic species successful invaders also help them deal with climate change.4,20,21 For example, invasive species tend to tolerate a wide range of environmental conditions and they can usually disperse easily, meaning they can easily spread to new areas if conditions in one place become intolerable.
Awakening of sleeper species
Some existing exotic species are currently limited by sub-optimal climate conditions (i.e., they are poorly adapted to the current climate, lacking suitable habitat), but are likely to expand rapidly and become invasive if the climate changes in their favour.17 These species are known as sleeper species. Identifying and controlling sleeper species before they “awaken” is the most cost-effective approach to reducing their impacts under climate change.
In temperate regions like Canada, some invasive species are suppressed by annual dieback due to cold winter temperatures and ice. Under a changing climate, natural controls may need to be replaced with more active management.17 Unfortunately, some forms of active management may be less effective due to climate change. Some invasive species may have an increased tolerance to herbicides as carbon dioxide concentrations increase.17,19 Effectiveness of biocontrol agents (e.g., insects that eat invasive species) may also be altered if the shifting ranges of the biocontrol agent and the target invasive species no longer align, or if climate change affects the amount that a biocontrol agent eats.25 As a result, invasive species that are currently controlled by a predator or herbivore may become problem species once again.17 However, new management options may also emerge as a result of climate change. For example, coastal areas may be able to take advantage of sea level rise to restore tidal flows in coastal wetlands. This type of restoration will help manage species like phragmites and purple loosestrife.17
Climate change impacts on native species
There’s an elephant in the room when it comes to invasive species and climate change: Climate change will cause native species to shift their ranges too.
In the context of climate change, our current ideas about invasive species will be challenged; species that are currently invasive will have a reduced impact, exotic species that are currently harmless will become invasive, and native species will be moving to new areas in search of suitable conditions for their survival.17,26 Native species that adjust their distribution in response to the changing climate are not the same as invasive species. Unlike invasive species, they will be traveling to adjacent areas and will already share some evolutionary history with the species that live there, so they are less likely to cause extensive damage. Native species are also on the move for different reasons: they cannot survive in their native ranges, so shifting ranges is a form of ecological resilience that needs to be facilitated so that these species do not go extinct.
What needs to be done?
As the climate and biodiversity crises heighten, the linkages between invasive species and climate change must be considered in research, policy development, and management.
Three key principles should be followed:
1. Ensure that climate change mitigation does not exacerbate the threat from invasive species.
2. Incorporate climate change projections into management of invasive species.
3. Design climate change adaptations that also contribute to invasive species management.16
This work will require coordination and collaboration by researchers, managers, and practitioners in the fields of climate change and invasive species. CCIS is making this happen by launching a National Invasive Species and Climate Change Symposium. This initiative brings together policymakers, researchers, and practitioners to discuss the synergistic effects of climate change and invasive species. CCIS is also collecting information and feedback on the development of a national invasive species and climate change network.Back to top
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