16.11.2017: Forschung international

Schmetterlingspopulationen in der Stadt: Klein und genetisch verarmt

Populations urbaines de papillons : petites et pauvres génétiquement


Estelle Rochat et al.

Je dichter bebaut eine Gegend ist, desto kleiner sind die Schmetterlingsbestände und deren genetischen Vielfalt. Dies zeigen Computersimulationen und genetische Daten des Kleinen Kohlweisslings (Pieris rapae) aus der Region Marseille (F). Der Grund: Mit zunehmender Bebauungsdichte werden ihre Lebensräume seltener und fragmentierter. Um dieser Entwicklung entgegenzuwirken, ist es wichtig, die Grünflächen einer Stadt ökologisch aufzuwerten und sowohl untereinander als auch mit Lebensräumen ausserhalb der Stadt zu vernetzen.

Plus une région est densément bâtie, plus les populations de papillons sont petites et génétiquement pauvres. C’est ce que montrent des simulations informatiques et des données génétiques de la piéride de la rave (Pieris rapae) de la région de Marseille (F). En cause : avec l’augmentation de la densité du bâti, leurs habitats deviennent plus rares et plus fragmentés. Afin de contrecarrer ce développement, il est important de valoriser écologiquement les espaces verts d'une ville et de les mettre en réseau les uns avec les autres ainsi qu'avec les milieux naturels hors de la ville.


In this study, the effect of urbanization on the genetic diversity and population persistence of a particular species of butterfly, the small white (Pieris rapae) was measured in the Marseille region. Computer simulations showed that genetic diversity fell by 60–80% in areas with a high urbanization rate, which means they have over 56% impervious land cover (i.e., land that has been developed with roads, buildings and other structures). In less dense neighborhoods, with between 3% and 13% impervious land cover, the loss in genetic diversity was just 16–24%. Results also indicated that the butterfly population is 70–90% smaller in heavily urbanized areas. What’s more, butterflies that can fly only short distances seem to be more vulnerable to the effects of growing urbanization. To quantify the findings, the results of the computer simulations were combined with empirical data from a database of genetic information at Aix-Marseille University. The DNA of a population of 145 butterflies of the species Pieris rapae (small white) in the Marseille region was examined and compared with simulated genetic data on 1,633 butterflies – spanning around 100 generations – of two species: the small white, which can fly up to four kilometers, and a less motile species that can fly up to two kilometers.
Using genetic data, the scientists focused in this study on species dispersal – the ability of a species to move around within a given area. Resistance maps of Marseille were calculated by giving a resistance score to each part of the city based on its land cover, topography and how difficult it is for butterflies to move around within it. Areas with tall buildings were given a high score, while those that could serve as butterfly habitats such as parks and grasslands were given a low score. Butterfly’s known behaviors were used to identify areas where they would be inclined to fly based on factors like vegetation and sunlight.
The simulation results were compared with genetic data on butterflies that had been sampled and genotyped in 2010 on a 100 km stretch of land extending from downtown Marseille to its outermost suburbs. Simulation results lined up with the genetic data and could be extended to cover the entire city and thereby get a big-picture view. A huge difference in population persistence between downtown and the suburbs was identified. Butterflies in highly urbanized areas had very little potential habitats and space to move around and it was assumed to be harder for them to encounter other butterflies of the same species to reproduce. They showed a substantial reduction in genetic diversity, which potentially reduces their ability to survive and adapt to the environment.
A host of methods already exists for cities to maintain and favor biodiversity in urban areas. In the context of this study, green roofs, urban gardens, grass planted between tram lines and plants grown on balconies can all help prevent the habitats of certain butterfly species from being isolated and disappearing. Indeed, preserving and fostering biodiversity in urban areas in the long-term is only possible if a city’s green spaces are contiguous with each other and with more natural spaces outside the city.

Quelle: EPFL

Keywords:
Dispersal; genetic diversity; habitat fragmentation; population persistence; urbanisation

Art der Publikation:
Fachpublikation

Literatur:
Rochat E. et al. (2017): Persistence of butterfly populations in fragmented habitats along urban density gradients: motility helps. Heredity, advance online publication. doi:10.1038/hdy.2017.40

https://actu.epfl.ch/news/menace-sur-la-survie-des-papillons-en-milieu-urb-2/
http://www.nature.com/hdy/journal/vaop/ncurrent/full/hdy201740a.html



Kontaktadresse:
Dr. Ivo Widmer
Akademie der Naturwissenschaften Schweiz (SCNAT)
Forum Biodiversität Schweiz
Haus der Akademien
Laupenstrasse 7
CH-3001 Bern

ivo.widmer@scnat.ch
Tel: +41 (0)31 306 93 42


Zurück zur Liste