What sorts of species become ‘invasive aliens’ in a world of climatic change Essay Example

original site of introduction or parent plant (Richardson et al., 2000). It is crucial to differentiate between climatic change, a continuous natural process observed throughout the history of Earth, and climate change, which encompasses human-induced changes linked to greenhouse gas escalation. This essay shall utilize "climatic change" for the former and "climate change" for the latter.The main objective of this essay is to investigate the subject of invasive aliens with regards to climate change, incorporating knowledge on how plants and animals have reacted to past changes in climate. Two distinct perspectives will be employed to answer the question of which species are likely to become invasive in a world impacted by climate change. Biogeographic theory will assess the features of invasive species and their potential outcomes under various global warming scenarios. The essay argues that multiple factors, such as local effects of climate change, habitat disturbance and life history traits of invasive species, will play a significant role in determining which species are most prone to becoming invasive aliens.To begin with, it is recommended that we reassess our definition of 'invasive alien' in light of climate change and recognize the societal construct behind this term. It's crucial to outline the invasive alien issue, which can be divided into four phases illustrated in Figure 1. The introduction of an alien species can happen through human intervention, intentional or unintentional. It's worth mentioning that several species labeled as nuisances were present or acclimatized for a prolonged period before becoming invasive (Myers ; Bazely, 2004). Richardson et al. have similar thoughts regarding plant species.

According to a 2000 study, invasive species can be defined as those that spread by

100m over 50 years for species that propagate through seeds and other propagules, and 6m over 3 years for species spreading through roots, rhizomes or creeping stems. However, determining the boundary between invasive and non-invasive is somewhat arbitrary, though it is a useful concept for understanding species success. Invasiveness has also been mistakenly linked to a species' ecological or economic impact, despite many harmless invasive species such as Aira praecox, Myosotis strict and Velezia rigida that have undetectable environmental or ecological impact (Richardson et al. 2000; Biotech Resources, 1995-1998; IUCN, 1999).

According to Richardson et al. (2000), it is preferable to use the terms 'pest' or 'weed' when discussing invasive species that are considered harmful, which make up 50-80% of these species. They also recommend using the term 'transformer' for the 10% of invasive species that significantly alter ecosystems within large areas. Williamson and Fritter's (1996) 'tens rule' states that only 10% of UK plants successfully complete the colonization process, including introduction, establishment, and invasion. The number of non-native species present varies greatly among different regions and countries.

According to research, many plant species in different countries are not native. In Canada, approximately 28% of plant species fall into this group, while in New Zealand, almost half of vascular plants are non-native (Heywood, 1989; Green, 2000). The Botanical Society of the British Isles has reported that out of a total of 2,947 plant species in the UK, there has been an introduction of 1402 new ones recently (Preston et al. 2002). Despite these statistics, the proportion of non-native plants is still relatively low.

Research on invasive species has mostly focused on economically impactful ones such as those causing

crop or fisheries damage, as noted by Parker and Reichard (1998). Despite this, Crawley et al. (1996) found that only 1% of introduced species in the UK became pests. Myers and Bazely's (2004) adapted Figure 1 illustrates the stages involved in the introduction, establishment, and spread of non-native species.

In 2001, the United States economy incurred a cost of around $125 billion due to invasive species (Baker, 2001). In the past, studying ecosystems with alien species was avoided because they were deemed 'unnatural' and not capable of providing insights into 'real' ecological processes. This resulted in insufficient data on the prevalence of alien plants and sampling bias against them (Crawley et al., 1996). However, there is now growing recognition that some invasive alien species can negatively impact important conservation priorities such as species richness, genetic variability and regional floral compositions (see Groombridge et al.).

According to IUCN (2004), Wilcove et al. (1992, 1998) discovered that invasive alien species can affect biodiversity through various means such as predation, competition (via shading out), hybridization, and transporting pathogens or parasites.

Human activities, such as habitat destruction, fragmentation, over-exploitation, and the introduction of invasive species are key factors contributing to the 'Biodiversity Crisis' or 'Sixth Extinction'. This has led to cascading effects resulting in a chain reaction of extinction. To combat this issue, various organizations including the Convention on Biodiversity and the UN Global Invasive Species Programme have been established under the umbrella of sustainable development movement initiated by Rio Earth Summit in 1992. The IUCN also has a specialized group dedicated to addressing invasive species. According to Lawton and May (1995), current extinction rates due to human impact are significantly higher

than those seen in past episodes. Introduced species pose a threat to approximately 20% of endangered mammal and bird species (MacDonald, 2003).

As per the 2003 source, different species are not equally susceptible to extinction. Certain habitats such as grassland heaths and scrubs, oceanic islands, and tropical forests are more vulnerable. Some nations have formulated or are formulating strategies and regulations to tackle the problem of introduced species (Myers; Bazely, 2004). The Convention on Biodiversity's Article 8h stipulates a precautionary method that includes prevention, eradication, and containment. Measures for prevention encompass border controls, quarantine measures, and licensing prior to introducing a potentially invasive species.

Controlling invasive species can be achieved through various methods, such as chemical, mechanical, biological, and ecological approaches. It is crucial to comprehend and anticipate which species may become invasive due to political, economic, and social factors. Irrespective of their region or genera, any species has the capability of becoming invasive. For survival purposes in their natural habitats, all species must have the potential for expansion or risk extinction. Despite extensive research on invasion and colonization, it remains difficult to predict invasive species (Mooney; Hobbs 2000).

Life history traits can significantly affect a species' evolution, adaptation, population growth, and dynamics. Consequently, these factors can determine whether a species can outcompete existing populations or fill a vacant ecological niche and become invasive (Myers; Bazeley, 2004). Successful invasive species typically exhibit common features such as short generation times and juvenile periods, high offspring numbers, vegetative propagation, and easily dispersed propagules in plants (MacDonald, 2003). A comparative study of native and non-native vascular plants in the UK by Crawley et al. (1996) found that established alien species were

often taller, had larger seeds and showed prolonged seed dormancy. Additionally, Crawley et al. (1996) identified predictable patterns for the establishment of invasive alien plants- weeds introduced to a climate-matched country are likely to grow into similar weeds as native counterparts; the frequency and intensity of habitat disturbances correspond with alien plant establishment rates; and due to their release from specialist pathogens, invasive alien plants usually grow larger and have greater ecosystem impact compared to native species.

Competitive ability is affected not only by intrinsic factors but also by extrinsic biotic and abiotic variables, such as competing species and environmental conditions. According to the same source from 1996, the proportion of alien species varies significantly depending on the habitat. For instance, UK waste ground communities have 0.8% alien species, whereas grass and heath land communities have less than 0.1%.

Given the local context and associated processes, traits that determine a species' potential invasiveness may vary in different situations. While increased attention has been given towards invasive species, studies relating this issue to global climate change are few and far between. Notable exceptions include Dukes and Mooney (1999) and Mooney and Hobbs (2000). Climatic change predictions due to anthropogenically-induced global warming are contested and complex. Uncertainty exists due to numerous feedback mechanisms which may be induced, leading to both positive and negative changes in temperature and precipitation depending on locality. Additionally, models suggest that increased atmospheric CO2 levels and nitrogen deposition are expected (Dukes & Mooney,1999).

Climate change may affect the interactions between alien species in various ways. One such way is that the severity of the impact of invasive species may change, or previously harmless alien species

may become invasive by developing new competitive traits (ibid. 1999). According to research, invasive species tend to possess traits that enable them to exploit the effects of global change (Dukes & Mooney, 1999:135). For instance, cheatgrass (Bromus tectorum), kudzu (Pueraria lobata), and Japanese honeysuckle (Lonicera japonica), which are invasive species in North America, have been observed to respond favorably to increased CO2 levels when grown alone or in monoculture (Smith et al.).

According to Dukes and Mooney (1999), studies (Sasek, 1988; Strain, 1988, 1991) have shown that local species abundance is influenced by various factors in diverse communities, including local resource availability. The effects of increased precipitation levels in arid and semiarid regions of North America could result in the dominance of invasive alien grasses. This is evident in Californian grassland communities residing upon serpentine soil, which are presently composed of native and endemic species. European annual grasses, such as soft chess, are confined to marginal, more fertile soil types.

Although increased precipitation may provide an advantage to European annuals, it can also facilitate the establishment of alien species. For instance, in the Arizonan Sonora Desert, multiple years of above-average rainfall enabled the introduced perennial buffel-grass (Cenchrus ciliaris) to expand, leading to an accumulation of non-native grass litter that increased fire frequency and promoted grass dominance (Burgess et al., 1991, cited in Dukes ; Mooney, 1999; D'Antonio & Vitousek, 1992, cited in Dukes & Mooney, 1999). Similarly, in northern California, the spread of the Argentine ant (Linepithema humile) may be supported by elevated temperatures, which limit foraging time for native ant species due to their upper daily temperature limits (Human & Gordon, 1996).

Climate change could have

differing impacts on invasive alien species depending on the region. In the UK, even a slight warming trend could cause native trees to be replaced by non-native species like Robinia pseudoacacia, Ailanthus altissimus, and Quercus cerris (Pysek et al. 1995). However, a climate scenario model for South Africa that took into account both climate and soil suitability noted that five of the country's major plant invaders faced decreases in range size under a doubled-CO2 climate scenario, with the prickly pear (Opuntis ficus-indica) experiencing a 37% reduction in area covered (Dukes & Mooney, 1999). Overall, while it is uncertain which specific alien species will benefit from climate change, the advantageous life history characteristics of invasive species are likely to persist in many cases.

According to Dukes and Mooney (1999), rapid climate changes could benefit species that have short generation times and are able to expand their ranges quickly, which is a common trait among invasive species. These invaders are typically considered to be 'generalists' due to their wide environmental tolerance and extensive niche (MacDonald, 2003). This feature may enable non-native invasives to withstand newly introduced climate stresses that native species with more specialized niches cannot, as noted by Dukes and Mooney (1999). Moreover, the prevalence of early successional species may increase due to the decline of late-successional species driven by climate change, which is another characteristic shared by numerous invasive species (Dukes & Mooney, 1999).

The proximity of aliens to human populations may play a significant part in encouraging the propagation of invasive species in a world subjected to climate change. Currently, many non-invasive aliens are artificially sustained in gardens. However, under changing climatic conditions, some of these

aliens could potentially establish flourishing 'wild' populations, particularly as they are fast-growing and require little maintenance. The spread of such species may be facilitated by their proximity to disturbed road habitats and the opportunity to 'hitch-hike' on vehicles. In a world of climate change, the life characteristics of invasive alien species are unlikely to alter significantly, although existing aliens may find conditions decidedly favorable for becoming invasive.

It is probable that climatic change may contribute to the increased competitiveness of known and currently invasive alien species, but the type of species that become invasive aliens in a world of climatic change is determined not only by species-specific characteristics, but also by local conditions and processes other than climatic change. The impact of climatic change is just one of several interacting processes of global change, as illustrated by Box 1 below. The importance of other human impacts, such as habitat destruction and disturbance, on enhancing the success of invasive species should not be underestimated (IUCN, 2004). The concept of an 'invasive alien' has been taken for granted in most discussions, yet Trudgill (2001) has questioned its validity by stating that it stems from "semantics, western values and conceptualizations of nature" (Trudgill, 2001: 684).

The way invasive alien species are portrayed in the media is highly emotional, as seen in the recent coverage of the Red King crab (Paralithodes camtschatica). A prime example of this is the headline: "Millions of giant Pacific crabs... are on a destructive path, devouring all in their way. The monster crabs are even making their way down Norway's coastline.

Due to their impressive resilience, which was demonstrated by a mysterious population surge ten years ago,

scientists are concerned that the crustaceans may migrate as far south as Gibraltar. This has led to heightened activity in numerous colonies of these creatures.

The population of the advancing miles along the roof of Europe has surpassed 10 million, causing overwhelming congestion at northern Norway's ports. The current total distance covered by this population exceeds 400 miles and has been described as leaving an "underwater desert" by an expert.

Trudgill (2001) notes that invasive alien species are typically viewed negatively, whereas species that expand into a new area independently are typically welcomed as "first sightings". BBC News (2002) reported on the warm reception of a critically endangered slender-billed curlew at Druridge Bay in Northumberland in 1998. Certain factors, such as negative economic consequences, unappealing appearance or impact on prized native species, can lead to certain species being labeled as "bad" invasive aliens.

While some species such as Japanese knotweed, the American mink, American grey squirrels, Ruddy ducks, and the Mitten crab are considered "bad" aliens, there are also many less publicized "good" aliens that play a vital role in our agricultural economic system and hold cultural significance. Examples of these "good" aliens are rabbits, poppies, and the Sweet Chestnut (Castenea sativa). The debate surrounding invasive aliens often stems from the notion that humans are separate from nature. However, this idea is flawed as the concept of an invasive alien infers that human introduction of species is unnatural and against the laws of nature. Additionally, when humans settle new areas or alter existing habitats, we do not consider ourselves as invasive aliens. Our discussions about invasive alien species tend to carry a heavy burden of guilt as we

perceive our actions as bringing a species outside of its natural or god-given range, thereby upsetting the pre-given balance or stability of a pristine state (Trudgill, 2001).

Although the discourse surrounding biodiversity suggests that all species have a fundamental right to exist, the concept of invasive species implies that this right is only applicable in certain contexts and for specific population sizes (ibid., 2001). However, when we examine the history of British flora, notions of a permanent and stable ecological composition become problematic. The slow and continual build-up of what is currently defined as 'British' flora can be attributed to the successive periods of ice advance and retreat during the Quaternary (Godwin, 1975).

According to paleoecological evidence, determining a specific date in geological history that defines what should and should not be considered native is impossible. As climate change continues to affect the world, a definition of invasive species that relies on old ecological and political boundaries will become unsustainable. Migration is likely the main survival strategy for species that cannot tolerate changes in their current habitat due to climate change (Huntley, 1995). It is important to re-evaluate our perception of which species will become invasive in a world of changing climate. Henderson (forthcoming) suggests a more adaptable definition of 'alien' based on a species' recent dispersal history.

Considering the rapid climate change, it may be necessary to actively introduce or translocate many potentially invasive alien species with slow migration rates in order to ensure their survival on a global scale. It can be inferred that the types of species likely to become invasive aliens in a changing climate are similar to those that are currently invasive aliens.

Traits like short generation times, which are prevalent in current invasive alien species, will remain significant in the future and provide further advantages for some existing invasive aliens due to climate change. However, it should be noted that the intrinsic and climatic factors alone do not determine which species become invasive. Other factors including local processes such as competition from other species and human interventions like habitat disturbance and fragmentation must also be considered when predicting which species will become invasive.

Considering the potential need for certain species to adjust their range in order to survive in a changing climate, labeling certain species as 'invasive aliens' based on political or outdated ecological boundaries may require reconsideration. It may be more appropriate to evaluate species based on their ecological impact rather than their origin, and to shift our perspective from viewing species as having a predetermined place to instead assessing their potential ecological space.