Climate change and invasive species refer to the process of the environmental destabilization caused by climate change. These environmental changes facilitate the spread of invasive species — species that are not historically found in a certain region, and often have a negative impact to that region's native species. This relationship is notable because climate change and invasive species are also considered by the USDA to be two of the top four causes of global biodiversity loss.
The interaction between climate change and invasive species is complex and is difficult to assess. Climate change is likely to favour some invasive species and harm others, but few studies have identified specific consequences of climate change for invasive species. Consequences of climate change for invasive species are distinct from consequences for native species due to different characteristics (traits and qualities associated with invasions), management and abundance and can be direct, through the species survival, or indirect, through other factors such as pest or prey species.
Human-caused climate change and the rise in invasive species are directly linked to changing of ecosystems. The destabilization of climate factors in these ecosystems can lead to the creation of a more hospitable habitat for invasive species, thus allowing them to spread beyond their native ranges. Climate change broadens the invasion pathway that enables the spread of species. Not all invasive species benefit from climate change, but most observations show an acceleration of invasive populations. Examples of invasive species that have benefited from climate change include insects (such as the Western corn rootworm and other crop pests), pathogens (such as cinnamon fungus), freshwater and marine species (such as the brook trout), and plants (such as the umbrella tree).
Measurably warmer or colder conditions create opportunities for non-native terrestrial and marine organisms to migrate to new zones and compete with established native species in the same habitat. Due to their adaptability, non-native plants may invade and dominate newly suitable ecosystems.
So far, there have been more observations of climate change having a positive or accelerating effect on biological invasions than a negative one. However, most literature focuses on temperature only and due to the complex nature of both climate change and invasive species, outcomes are difficult to predict.
There are many ways to manage the impact of invasive species. Prevention, early detection, climate forecasting and genetic control are some ways communities can mitigate the risks of invasive species and climate change. Although the accuracy of models that study the complex patterns of species populations are difficult to assess, many predict range shifts for species as climates change.
Definitions
Invasive species According to the International Union for Conservation of Nature (2017), IUCN, invasive species are "animals, plants or other organisms that are introduced into places outside their natural range, negatively impacting native biodiversity, ecosystem services or human well-being."
Climate change will also redefine which species are considered as invasive species. Some taxa formerly considered as invasive may become less influential in an ecosystem changing with time, while other species formerly considered as non-invasive may become invasive. At the same time, a considerable amount of native species will undergo a range shift and migrate to new areas.
Shifting ranges, and changing impacts of invasive species, make the definition of the term "invasive species" difficult – it has become an example of a shifting baseline. Considering the changing dynamics mentioned above, Hellmann et al. (2008), concludes that invasive species should be defined as "those taxa that have been introduced recently" and exert a "substantial negative impact on native biota, economic values, or human health." Consequently, a native species gaining a larger range with a changing climate is not considered to be invasive, as long as it does not cause considerable damage.
The taxa that have been introduced by humans throughout history have changed from century to century and decade to decade, and so has the rate of introductions. Studies of global rates of first records of alien species (counted as the amount of first records of established alien species per time unit) show that during the period 1500–1800 the rates stayed at a low level, whereas the rates have been increasing constantly since the year 1800. 37% of all the first records of alien species have been registered as recently as during the period 1970–2014.
The invasion of alien species is one of the major drivers of biodiversity loss in general, and the second most common threat being related to complete species extinctions since the 16th century. Invasive alien species are also capable of reducing the resilience of natural habitats, and agricultural as well as urban areas, to climate change. Climate change, in turn, also reduces the resilience of habitats to species invasions.
Biological invasions and climate change are both two of the key processes affecting global diversity. Yet, their effects are often looked at separately, as multiple drivers interact in complex and non-additive ways. Some consequences of climate change have been widely acknowledged to accelerate the expansion of alien species, however, among which increasing temperatures is one.
Invasion pathway The process of biological invasion occurs in a series of discrete steps, collectively known as the invasion pathway. It is commonly divided into four main stages: the introduction or transport stage, the colonization (or casual) stage, the establishment or naturalization stage, and the landscape spread or invasion stage. The invasion pathway describes the successive environmental filters that a species must overcome at each stage in order to become invasive. A variety of mechanisms influence the outcome of these steps, including climate change. In the initial transport stage, the filter is primarily geographic. In the second, colonization stage, the relevant filter consists of abiotic conditions. During the third, establishment stage, biotic interactions—such as competition, predation, and mutualisms—serve as the main filter. In the final landscape spread stage, landscape features and spatial heterogeneity determine which species successfully pass through this filter.
Due to climate change and melting arctic ice, the shipping industry will make start to be a significant play in the introduction and transport stage. Increasing temperatures are leading to formations of shorter travel routes, and in turn, easier ways for invasive species to spread. Organisms that hitch along the hulls of the ships are less likely to die in transit since the routes are shorter and their metabolism is slowed due to cold temperatures.
Interactions
The interaction between climate change and invasive species is complex and not easy to assess. Climate change is likely to favour some invasive species and harm others, but few authors have identified specific consequences of climate change for invasive species.
As early as 1993, a climate/invasive species interaction was speculated for the alien tree species Maesopsis eminii that spread in the East Usambara mountain forests, Tanzania. Temperature changes, extremes of precipitation and decreased mist were cited as potential factors promoting its invasion.
Consequences of climate change for invasive species are distinct from consequences for native species due to different characteristics (traits and qualities associated with invasions), management and abundance and can be direct, through the species survival, or indirect, through other factors such as pest or prey species.
So far, there have been more observations of climate change having a positive or accelerating effect on biological invasions than a negative one. However, most literature focuses on temperature only and due to the complex nature of both climate change and invasive species, outcomes are difficult to predict.
Favorable conditions for the introduction of invasive species Effects on invasion pathway stages Climate change will interact with many existing stressors that affect the distribution, spread, abundance and impact of invasive species. Hence, in relevant literature, the impacts of climate change on invasive species are often considered separately per stage of the invasion pathway: (1) introduction/transport, (2) colonization/casual stage, (3) establishment/naturalization, (4) spread/invasion stage. According to those invasion stages there are 5 nonexclusive consequences of climate change for invasive species according to Hellmann:
Altered transport and introduction mechanisms Altered climatic constraints on invasive species Altered distribution of existing invasive species Altered impact of existing invasive species Altered effectiveness of management strategies
The first consequence of climate change, altered mechanisms for transport and introduction mechanisms, is given as invasions are often purposefully (e.g. biocontrol, sport fishing, agriculture) or accidentally introduced with the help of humans and climate change could alter the patterns of human transport. Changed recreational and commercial activities will change human transport and increase the propagule pressure of some non-native species from zero, e.g., connecting new regions or above a certain threshold that allows for establishment. Longer shipping seasons can increase the number of transports of non-native species and increase propagule pressure supporting potential invaders as the monkey goby. Additionally, introductions for recreation and conservation purposes could increase.
Changing climatic conditions can reduce native species' ability to compete with non-native species and some currently unsuccessful, non-native species will be able to colonize new areas if conditions change towards their original range. Multiple factors can increase the success of colonization, as described in more detail below in 2.2.
There is a wide range of climatic factors that affect the distribution of existing invasive species. Range limits due to cold or warm temperature constraints will change as a result of global warming, so that cold-temperature constrained species will be less restricted in their upper-elevation and higher-latitude range limits and warm-temperature constrained species will be less restricted in their lower-elevation and lower-latitude range limits. Changing precipitation patterns, the frequency of stream flow and changes in salinity can also affect hydrologic constraints of invasive species. As many invasive species have been selected for traits that facilitate long-distance dispersal it is likely that shifts in suitable climatic zones favour invasive species.
The impact on native species can be altered through population densities of invasive species. Competition interactions and abundance of native species or resources take part in the relative impact of invasive species.
The effectiveness of different management strategies is dependent on climate. For instance, mechanical control of invasive species by cold, hard freezes or ice cover can become less effective with increasing temperatures. Changes in the fate and behaviour of pesticides and their effectiveness in controlling invasive species can also occur. Decoupling of the relationship between some biocontrol agents and their targets can support invasions. On the other hand, the effectiveness of other biocontrol agents could increase due to species range overlaps.
Effects on climatic conditions