Conclusion

I hope you have enjoyed reading my blog, for I have enjoyed where the idea of invasive alien species (IAS) has taken me. From the research carried out for this blog, it is possible to see that invasive alien species are a major threat to endemic, specialised species. This is due to the pathways by which invasive species invade and become established having changed and been manipulated over time, where natural spread has been replaced as the dominant pathway by accidental and deliberate introductions. The reasons for this including scientific experiments and techniques employed to enhance agriculture, or because colonisers of new lands felt homesick and wanted to bring a part of home to the new land. Therefore, the threat posed by IAS has moved from a naturally occurring phenomenon to one that is highly influenced by anthropogenic activities, with increasing impact as trade routes have increased and connectivity between countries and areas has developed.

It is through the characteristics of invasive alien species that make them such a threat to biodiversity and pose the threat of extinction to endemic species, particularly those found on islands. Their generalised requirements enable them to outcompete local species, as is the case with the Signal and the European Crayfish, replacing the original species in their ecological niche.

Through my research I have also tried to discuss the role of humans as invasive species, and how over history, we have posed a threat to ourselves, particularly with respect to the spread of disease. It is also important to consider ourselves as part of nature, and not necessarily a steward of it, although at present we may be assuming this role due to our knowledge, and perhaps guilt, of our impact on the environment. What is crucial is that through our activities, consider ourselves as invasive species, we have had a direct impact on species extinctions throughout history, but this has never been more prevalent than it has currently. Our increased industrialisation and the global coverage of our species is having detrimental effects on global populations of other species, be they aquatic or terrestrial. It is therefore important to mitigate our impacts and, with respect to invasive species, this can be done by increased monitoring of pathways, implement rules and regulations to reduce the likelihood of invasions, learn from our mistakes to put in place better strategies in the future to protect against them and at the same time, further our knowledge on potential impacts of scientific experiments, so we do not have another case such as myxomatosis.

What role do IAS play in the future? This cannot be predicted for the impact of climate change and global warming on regions is not entirely clear and therefore predicting which species will become invasive, which is already difficult to determine currently, is a near impossible task.

It is therefore important to understand that anthropogenic activities have been and are directly influencing the ecology of the planet, of which our role with invasive species plays but a contributory role, leading to increased extinctions of species, which is why it is considered we are in the 6^th mass extinction event in the planet’s history (Barnowski, 2011).

http://moodle.ucl.ac.uk/file.php/10643/Lectures/Barnowsky_et_al_nature_2011.pdf

A Threat to Ourselves

With this post I am considering disease and its transmission a type of invasive alien species, such as Crowl et al. (2008).

It would seem that humans pose a particularly great threat to themselves in the form of disease prevalence and transmission. When mankind made the transition from hunter-gatherers to farming communities, technological advances in farming provided increased food supply, therefore allowing populations to start expanding (Gupta, 2004). This domestication of plants and animals paved the way for social development and settlement expansion. As Gupta (2004) describes, the domestication period of plants and animals took place between 10,000-7,000 cal years BP, leading to the increase in density of human populations within settlements. This process did everything to aid the existence of infectious diseases, particularly with respect to infectious disease that require individuals to come into close contact with the disease source. It is when populations became large enough that infectious disease, such as smallpox and measles, were able to become self-sustaining. Harrison et al. (1998) stating populations sizes needing to be in the order of hundreds of thousands.

Usually when such disease in introduced into a new population, the effect can be disastrous, often leading to large-scale mortality. This is particularly the case when the disease has never been present in a population before. This was the case with the bubonic plague, aptly named the Black Death. Between 1346 and 1351 the disease killed around 25 million people across Europe, Northern Africa and the Near East (McEvely, 1988). This disease is spread through droplet infection and is carried by fleas that live on rats. The spread across the world at that time can be attributed to trade routes between countries, where rats were present on-board ships, then being released into the harbours of trade countries and spreading from there (Mitchell, 2003). Another example is the spread of disease through colonisation of new lands. When Europeans settled new lands, such as the Americas, Pacific Islands and Australia, the success of the conquerors has been greatly attributed to the spread o disease that were brought with them.

The domestication of animals has also allowed infectious pathogens to jump the species gap and infect humans, examples including influenza from pigs and geese, faecal contamination of water by livestock and salmonella to name a few. One of the most virulent diseases to have occurred in societies is the presence of malaria. This disease is transmitted via mosquitos and anthropogenic forest clearance increased the area in which mosquitos are able to habit (Mitchell, 2003).  It is our development as a species that has enabled these pathogens to develop, exist and survive, acting as invasive species when introduced into a new population or host. Epidemics are therefore a marker of human civilisation and can be considered when investigation anthropogenic impacts on the world around us. Disease has been widely discussed in historic literature in early civilisations (Mitchell, 2003). However, examining the presence of disease past historic records through investigation of skeletal remains becomes a different and much more difficult process, infectious disease identification, let alone identification of species may never be possible (Roberts and Manchester, 1995).

Disease is therefore very much consequence of human development and our ancestors’ progression from hunter-gatherer communities to larger settled civilisations. As skeletal remains often do not provide insights into cause of death, knowledge of how civilisations dealt with infected bodies could provide general insight into infectious disease in the past, prior to historic accounts of disease occurrence and transmission. This threat to ourselves has come about inherently due to our species advancing into civilisation and provides insight into the idea that humans are ourselves a part of nature, and that we too should be considered as invasive threat to one another through our exploitation of the world's resources. This is highlighted by mankind's colonial history and the historic spread of disease from community to community as a result of increasing globalisation and our dominance as a species within the world around us.

http://www.esajournals.org/doi/abs/10.1890/070151

http://www.tandfonline.com/doi/pdf/10.1080/0043824032000111353

http://ukpmc.ac.uk/abstract/MED/3055286/reload=0;jsessionid=r5KoRCYr0JOIeTkOXOkq.0

http://repository.ias.ac.in/21961/

Increased anthropogenic influence on marine extinctions

Jean Baptiste de Lamarck and Thomas Huxley believed that humanity could not cause the extinction of marine species (Roberts and Hawkins, 1999). This idea, based on the abundance of marine fisheries at the time, led them to believe that the sea was an inexhaustible source of food and wealth for societies that have access to them and that anthropogenic activities would have a minimal impact on populations (Pauly et al., 2002). This idea is still carried forward to the present day despite there being a drastic and, in some cases, irreversible changes to marine populations. This therefore means that, at present, marine species are at a far greater risk to extinction than we have so far assumed (Pauly et al., 2002).

Global catches by fisherman have been declining since the 1980. Figure 1 shows fish catches between 1950-2002, and clearly show that the total number of fish caught has ben declining since the mid 1980s, or plateaued if china is included. This decline in catches indicates a decline in fish stocks globally and that action needs to be taken to reduce the anthropogenic impact on global fish stocks.

                              Figure 1: Graph to show global fish catches between 1950 and 2002.

What this graph does not indicate is that there have been vast technological advances within the fishing industry and that these may in fact be masking the true decline in fish stocks as fisherman are able to travel further to fish and target fish in a lower trophic level (Thurstan et al., 2010). These advances in technology and changes in the type of fish caught poses a greater threat to marine animals, one that was less prevalent throughout the history of the human interactions with marine life. As of 2003, there had been 133 reported cases of extinction within marine populations (Dulvy et al., 2003). These extinctions are entirely due to anthropogenic activities, be it through exploitation through the fishing industry, habitat loss through coastal developments, introduction of invasive species, climate change, pollution and disease. However, the association between invasive species and species extinctions are in most cases speculative, anecdotal or based upon limited field observations (Gurevitch and Padilla, 2004). This does not mean that human facilitated invasive species are solely contributing to the extinction of species however it has been seen that their presence comes hand in hand with threats such as habitat change and exploitation.  According to Clavero and Garcia-Berthou (2005) 91 of the 680 extinct species identified by the IUCN are directly attributed to the presence of invasive species. This again shows that the threat of invasive species is significant, however when considered in combination with other threats, as discussed with respect to marine species above, their presence becomes a very serious issue. Thousands of years ago this issue would not have been so prevalent. Since the expansion of global population and the globalisation of the world, our impact on such threats has enhanced the vulnerability of certain species to extinction. Our role as facilitator has clearly had a dramatic impact on aquatic, combined with our increasing demands for fish in our fiscally driven global economy.

http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=271938&_user=7237960&_pii=S0169534705000042&_check=y&_origin=article&_zone=relatedPdfPopup&_coverDate=2005-03-31&piiSuggestedFrom=S0169534704002022&wchp=dGLzVlt-zSkWz&md5=4d45f9ec568cd0343b8e641711c45bd7/1-s2.0-S0169534705000042-main.pdf

http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=271938&_user=7237960&_pii=S0169534704002022&_check=y&_origin=article&_zone=toolbar&_coverDate=30-Sep-2004&view=c&originContentFamily=serial&wchp=dGLbVlk-zSkzV&md5=220ec95f1e36e1b45127b1481e248fc4/1-s2.0-S0169534704002022-main.pdf

http://www.nature.com/ncomms/journal/v1/n2/abs/ncomms1013.html

http://onlinelibrary.wiley.com/doi/10.1046/j.1467-2979.2003.00105.x/full

http://www.sciencedirect.com/science/article/pii/S0169534798015845

http://www.nature.com/nature/journal/v418/n6898/full/nature01017.html

Climate change and IAS

From the readings for a previous post, Diamond’s comment (2002) about unpredictable climate inspired me to investigate further the influence of climate change on extinctions and the part it plays in contributing to the movement of invasive species. This next post will look at evidence to suggest the role of climate change in contributing to extinction events as well as how it will influence invasive alien species in the future.

There are arguments that humans have only had a significant impact on climate since 1800 AD (Crutzen and Stoermer, 2000) as this has been identified as when atmospheric concentrations of atmospheric CO₂ and CH₄ have started to increase above previous longer-term levels. However there is also evidence to back up arguments that anthropogenic activities, in fact, have had significant impacts on climate many thousands of years before (Ruddiman, 2003). Ruddiman (2003) compiles evidence to show that changes in atmospheric concentrations of greenhouses gases cannot be explained by natural events, such as orbital forcing and that the Holocene CO₂ concentration trend does not match any other trend seen in previous interglacial periods. These ‘anomalies’ have been attributed to agricultural techniques such as rice farming in Asia from 7500 BP and natural loses in terrestrial biomass associated with deforestation (Ruddiman, 2003). Putting the direct impact deforestation has on species and the landscape aside, these actions have indirectly influenced species composition and ecological interactions, by creating/expanding existing environmental conditions and decreasing others.

McLaughlin et al., (2002) do however state there have been few extinctions directly linked ‘mechanistically’ to climate change, it is usually a combination of habitat fragmentation as well as climate change that induces extinction. This therefore shows that climate change is a contributory factor and is not a direct cause of extinction in its own right, it will push species to the edge of their ecological limits, but it requires a combination of factors for the species to then become extinct. These factors could include increased predation, hunting or removal by humans, landscape changes through activities such as farming or settlement. Decline in possible habitats through anthropogenic activities is therefore a more important factor as it reduces the range in which the species can exist if the one it is currently present in becomes uninhabitable.  McLaughlin et al., (2002) discuss this with respect to two different populations of checkerspot butterfly where climate change caused variability in precipitation. When modelled with butterfly populations, this effect was seen to amplify population fluctuations, leading to rapid extinctions. However with global warming predicted to dramatically increase over the next 40-50 years, if mitigation actions are not implemented, then future predictions of the effect of climate change on extinction rates need to be considered. Thomas et al., (2004) predicted that, from sample regions that cover about 20% of the world, between 15-37% of species within those regions would be extinct, or committed to extinction, without any possibility of recovery if action is not taken. These calculations were made on the basis of a mid-range climate-climate warming scenario for 2050 (Thomas et al., 2004).

It is therefore important to think about the impact climate change could potentially have on invasive species. They have been broken down into five categories (change in pathways, change in environmental constraints, change in distributions, change in impacts and change in management effectiveness) (Hellmann et al., 2008), shown in figure 1.  

                             

               Figure 1: the 5 responses by invasive species to climate change  (Hellmann et al., 2008)

The predominant issue in relation to invasive species and climate change is that changes are subtler and take place over a longer period of time, compared to the current issues surrounding invasive species. This means that resource managers have a difficult time knowing when to start addressing the issue. However, using the five categories described in Figure 1 as a platform, these changes to invasive species would then lead to a totally different approach to how to manage them. These would require research that integrates invasions and climate-change biology (Hellmann et al., 2008). It will take more time to observe and understand, through wider research, how invasive species will respond to climate change as well as understanding which new species will become invasive.

http://www.pnas.org/content/99/9/6070.short

http://www.nature.com/nature/journal/v427/n6970/abs/nature02121.html

http://onlinelibrary.wiley.com.libproxy.ucl.ac.uk/doi/10.1111/j.1523-1739.2008.00951.x/pdf

http://www.nature.com/nature/journal/v418/n6898/full/nature01019.html?lang=en

The potential risk of introduction of non-native species to humans

I thought I would add a little light-heartedness to this blog with this clip from the second Jurassic Park movie. Jokes aside, it does highlight some of the issues already spoken about previously, the introduction of species through scientific experiments, and how they can go horribly wrong. Although this case is extreme and unrealistic, it shows that a lack of knowledge and understanding can have disastrous effects, albeit in a Hollywood movie.

The domestication of animals: the emergence, ethos and contribution to species loss; an entirely anthropogenic factor

Humans made the transition from a hunter-gatherer species to a farming based one over the course of a few thousand years, between 13,000 -8500 (Diamond, 2002). This process brought about the domestication of both plants and animals to provide human populations with the food required to survive. The domestication of species quite obviously involving a relationship between humans and the target species, where humans play the dominant role in its reproduction and its food supply (Diamond, 2002).  However, it has been argued that the domestication of species is simply another representation of a mutualistic relationship, such as those that occur naturally outside from human influence (Zeder, 2006). However, this is an over-simplification and I do not feel is entirely true, as the species is manipulated purely for anthropogenic purposes. However, this could be seen as the species taking advantage of the willingness of humans to promote and develop them as an evolutionary pathway (Zeder, 2006).

The domestication of species is considered and important facet of biodiversity (Dirzo and Raven, 2003), this statement however is not intended to portray them in a good light. We depend on so few species to provide us with all of our dietary requirements, which our exploitation and capitalist economy has let to the decimation of original landscapes and through that, an overall loss in biodiversity through species extinctions. With our agricultural expansions, coupled with our explosive increase in global populations, the threat of further species extinctions is greater. The consequences of our exploitation within this industry, we are fragmenting landscapes, reducing original areas of species and creating isolated pockets of elevated levels of biodiversity, simply as they have yet to be exploited.  It is within these isolated pockets where some of our last remaining species exist naturally in the wild. Examples include the Gorilla and the Orang-utan. However, as the theory of island biogeography states, as the size of the area in which species reside, population numbers decline due to increased competition for less resources (Whittaker and Fernandez-Palacios, 2007). A study of 173 mammalian species showed that historic range of species has declined by more than 50% )Dirzo and Raven, 2003). This therefore leads to the conclusion that increasing domestication, i.e. the spread of agricultural techniques, advancing hand in hand with increasing populations and urbanisation, will inevitably lead to a decline in biodiversity and add more species to the extinction list.

The domestication of species could potentially be labelled as a mistake. The first farmers did not set out with a goal for the domestication of species to be so prevalent; it was simply about surviving in conditions that did not allow hunter-gatherer techniques to be successful (Diamond, 2002). Perhaps if they had foreseen this then maybe the original settlers, at the very beginning of the Holocene, would have never allowed it to happen, had they been conscious of the world around them and their impacts on it. It is this factor, which has inadvertently contributed to the loss of many species.

http://onlinelibrary.wiley.com/doi/10.1002/evan.20101/pdf

http://www.annualreviews.org.libproxy.ucl.ac.uk/doi/pdf/10.1146/annurev.energy.28.050302.105532

http://www.nature.com/nature/journal/v418/n6898/full/nature01019.html?lang=en