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An invasion of insects? The potential future dispersal of the Asian tiger mosquito Aedes albopictus in Bavaria

by Franziska Niemitz (27.11.2009)

My Master Thesis is concerned with the present worldwide distribution and potential future dispersal in Bavaria of the Asian tiger mosquito Aedes albopictus. During the last couple of decades the species has rapidly dispersed around the globe with the aid of global trade. From its native Asian range it has spread to North and South America as well as to Africa and Europe. By now it has established in several European countries, of which some are geographically very close to Germany. The dispersal of the species brings with it a serious health concern as the species is capable of transmitting 23 arboviruses dangerous to humans. With respect to its high mobility and recent global dispersal, it is postulated that Ae. albopictus colonises climatically suitable habitats around the world with the help of global trade. Considering the projections of the regional climate model REMO (Jacob, 2001), climate change is believed capable of altering the climatic conditions in Bavaria in favour of Ae. albopictus. It is therefore further postulated that future climatic conditions will evolve such that they will allow Ae. albopictus upon arrival to establish in Bavaria in a diffuse manner.

The probability of presence of Ae. albopictus conditional on suitable climatic conditions predicted by the Global model with regards to the current climatic conditions.[Bildunterschrift / Subline]: The probability of presence of Ae. albopictus conditional on suitable climatic conditions predicted by the Global model with regards to the current climatic conditions.

In order to investigate the above postulates, the climatic envelope of the species is modelled. The maximum entropy modelling programme Maxent (Phillips, 2008) was chosen to model the species geographic distribution and potential future dispersal. The climatic niche model predicts the geographic distribution of a given species as a function of occurrence locations and particular climatic conditions prevailing at occurrence locations. The data on species occurrence consisted of a data set with presence points from the native as well as the alien range, kindly provided by Benedict et al. (2007). The climatic information for the present climate was taken from the freely available WorldClim data base (Hijmans, 2008) and the projected future climate for Bavaria originated from the regional climate model REMO (Jacob, 2001). Employing all available data, a global present distribution map of Ae. albopictus was modelled with Maxent. The map identified regions that have suitable climate for the establishment and survival of the species, representing the risk which is derived from climatic suitability. As invasion is also partially a function of proximity between infested countries and those which are not yet infested, the map also indirectly denotes the risk due to geographic proximity. The risk of future dispersal of Ae. albopictus was examined more regionally for the case of Bavaria. Two models were run with global occurrence data and climate projections for the time periods 2011 - 2040, 2041 - 2070 and 2071 - 2100.

The resulting global distribution and risk map produced by Maxent successfully identified regions worldwide that are facing risk of establishment of Ae. albopictus as they fall into the climatic envelope of the species. The presence of the species is verified with the help of literature for many of those countries that are predicted to be at risk by Maxent. Furthermore does the map deliver valuable information on countries that are also facing risk, either due to suitable climatic conditions or their proximity to infested countries. It is shown that Ae. albopictus successfully colonises climatically suitable habitat around the world.

In a consecutive step, the future risk of invasion is investigated for Bavaria. Model results indicate that future climate evolution in Bavaria will be able to facilitate an extensive and diffuse dispersal of Ae. albopictus upon arrival from the middle of this century onwards. The results of this study demonstrate that Ae. albopictus has succeeded to disperse around the world and to establish in regions that have suitable climatic conditions. Its high mobility makes it likely, that it will also be able to establish and survive in Bavaria from the middle of this century onwards. By then climatic conditions are predicted to be suitable to support the survival of Ae. albopictus. However, this will only be the case if the species manages to enter Bavaria. Maxent only predicts the probability of suitable climatic conditions in geographic space and not the actual probability of invasion or dispersal of the species. It does not take into account any vectors that would facilitate the dispersal nor does it incorporate any barriers that might hinder the dispersal.

However, the model predictions are helpful for identifying regions where there is a high risk due to suitable climatic conditions. For such cases, information on vectors such as international transport of goods or barriers in the form of human induced pest control, should be evaluated additionally. A comprehensive assessment of risk of invasion can then be issued.

Quellennachweis:

1. Jacob D. (2001): A note on the simulation of the annual and inter-annual variability of the water budget over the Baltic Sea drainage basin. Meteorology and Atmospheric Physics 77, 61-73.

2. Phillips S. (2008): A brief tutorial on the use of Maxent written by the software developers: accessed 23.10.2008, www.cs.princeton.edu/.

3. Benedict M., Levine R., Hawley W.A., Lounibos L.P. (2007): Spread of the tiger: Global risk of invasion by the mosquito Aedes albopictus. Vector Borne and Zoonotic Diseases 7, 76-85.

4. Hijmans R.J. (2008): Worldclim data set and data description, accessed: 13.11.2008, http://www.worldclim.org/format.htm.


Franziska Niemitz
Franziska Niemitz
* 1984, Göttingen

Stationen
  • 2006-2008
  • Universität Bayreuth, "Global Change Ecology" (Masterstudiengang)
  • Masterarbeit
  • "Global Present Distribution and Future Dispersal Potential of Aedes albopictus", Betreuer: Prof. Dr. Carl Beierkuhnlein
  • 2003-2006
  • Lancaster University, Physics Studies (Bachelorstudiengang)
  • Bachelorarbeit
  • "Unravelling Neutrino Physics", Betreuerin: Dr. Laura Kormos

Praktika
  • 01/2009 – 04/2009
  • Praktikum bei der Münchener Rück im Bereich Geo Risk
  • 04/2008 – 05/2008
  • Praktikum am Helmholtz Zentrum für Umweltforschung
  • 07/2005 – 08/2005
  • Praktikum im European Space Operations Centre, Darmstadt