Disentangling the ecological impact of tourism and urban land use on island ecosystems: changes in biodiversity, habitat structure, and trophic position

Sebastian Steibl and Christian Laforsch, Animal Ecology, University of Bayreuth, Bayreuth, Germany, Jonas Franke, Remote Sensing Solutions (RSS) GmbH, Munich, Germany, Gerhard Gebauer, Laboratory of Isotope Biogeochemistry, University of Bayreuth, Bayreuth, Germany

Background/Question/Methods
Among the most prevalent threats to terrestrial biodiversity worldwide is human land use. The increasing land demands for agriculture, urban development, tourism, or infrastructure, just to name a few, have caused declines in species abundance and richness worldwide. Particularly vulnerable to this accelerating species loss are islands, as they bear an exceptionally high number of endemic and range-restricted species. Especially on islands in the tropics, tourism is becoming an increasingly important form of land use that is converting former pristine islands into island-wide tourist establishments. Yet, there is still little scientific data about the ecological consequences of this relatively new and increasingly important form of land use on insular ecosystems, and direct comparisons of its severity relative to other land uses are virtually absent.
Here, we analyzed how tourism land use impacts the overall ground-associated invertebrate diversity and habitat structure of small tropical insular ecosystems and explored its effects on the trophic niche of impacted insular invertebrate taxa. Disentangling and comparing the impacts between tourism and urban land use was realized by investigating islands that were either used solely for tourism, or used as permanent settling by the local population, or remained uninhabited.
Results/Conclusions
Tourism land use is linked to a drastic decline in ground-associated invertebrate diversity on tropical insular ecosystems that even exceeds the impact of urban development, compared to uninhabited islands. Remote sensing data indicated that the drivers for this observed loss differ between the two land uses. Habitat fragmentation and a reduction in vegetation density were the predominant drivers for the observed diversity loss on islands with urban land use, but land use/ cover changes could not model the observed loss on tourist islands, suggesting that factors like pesticide application are driving the invertebrate decline on tourist islands.
Stable isotope analysis of different invertebrate taxa demonstrated that tourism and urban land use are linked to significant shifts in the trophic position of different invertebrate taxa compared to uninhabited islands, likely due to altered resource availability. However, these shifts towards anthropogenic resources might allow certain invertebrates to persist in the anthropogenic environment.
This presentation demonstrates the far-reaching impact of tourism land use on islands and shows that its adverse effects exceed those of urban development. It further suggests that two land uses impact local biodiversity via different mechanisms, making it necessary to tailor conservation actions specifically to the type of land use.