Original Research ArticleThe integration of Artificial Night-Time Lights in landscape ecology: A remote sensing approach
Introduction
In the last centuries, human-induced land-use changes have had detrimental effects on ecological functions of biodiversity rich landscapes (Dale, 1997, Nagendra et al., 2010b, Dale et al., 2011). Several studies on the effectiveness of human embedded protected areas in conserving biodiversity have recommend to look beyond the protected boundaries to develop management framework coupled with the socio-economic dynamics of the surrounding landscapes (Grumbine, 1994, Hansen and DeFries, 2007, Nagendra et al., 2010a, DeFries et al., 2010). As a result, an integrated approach to landscape management where the protected areas are part of a wide regional landscape has been suggested. Subsequently, landscape composition and structure have gradually become key concepts in biodiversity conservation (Saunders et al., 1991, Dauber et al., 2003, Antrop, 2004, Stephens et al., 2004, Geri et al., 2010, Walz, 2011, Tscharntke et al., 2012).
Indeed, in recent years, landscape patterns and the associated socio-economic processes have been integrated into conservation science (Nagendra et al., 2004, Fahrig et al., 2011, Mairota et al., 2013). However, in most cases, landscape is perceived as it is seen during the day (Hölker et al., 2010a, Hölker et al., 2010b, Rich and Longcore, 2006, Lyytimäki, 2013), assuming that landscape patterns and processes remain the same during the night, thereby neglecting the effects of Artificial Night-Time Lights (ANTL) on species, communities and ecosystems. As an example, if a landscape is characterised by high vegetation cover and a low level of fragmentation, it is generally considered to have high suitability for specialist species, capable of fulfilling complex ecological processes (Forman, 1995). Indeed, the night-time configuration of such a landscape is usually ignored when assessing its conservation value. Nevertheless, when perceived from the point of view of a high number of animal species, the situation is rather different (here we do not consider plants, even though there might be some implications due to the effect of ANTL on them too; see Cathey and Campbell, 1975a, Cathey and Campbell, 1975b, Rich and Longcore, 2006). Globally, 30% of all vertebrates and more than 60% of all invertebrates are nocturnal Hölker et al., 2010a, Hölker et al., 2010b which signifies the importance of studying landscape configuration changes during the night due to anthropogenic activities. Indeed, humans, being a diurnal species, use illumination during the night to improve their quality of life and to meet their requirements. Although brighter lights are associated with cities, an increase in artificial lighting is observed in rural landscapes throughout the world (Cinzano et al., 2001). As a result, an “octopus pattern” of illumination that penetrates into formerly dark-at-night landscapes is increasingly observed (Mcdonald et al., 2004).
The last decades saw a marked transformation of the night-time environment over a significant area of the Earth surface due to the rapid increase in the distribution and intensity of ANTL (Longcore and Rich, 2004). As a result, a number of studies addressing the profound consequences of ANTL pollution on the structure of species community and their modified ecological functions have been produced. Some of these studies emphasized the need of integrating night-time patterns of landscape (“nightscapes” hereafter) in the management of protected areas and corridors (Longcore and Rich, 2004, Kronfeld-Schor et al., 2013). A recent review (Gaston, 2013) on the ecological impact of light pollution, highlights the potential influence of ANTL on all levels of biological organisation (cells to ecosystem), concluding that more research is required to find the spatial extent of ANTL pollution on biodiversity-rich landscapes.
On a species level, ANTL is proved to have physiological consequences on humans along with ecological and evolutionary implications on animal and plant populations, to the potential extent of reshaping entire ecosystems (Navara and Nelson, 2007, Hölker et al., 2010a, Hölker et al., 2010b). Natural light regime on every part of the Earth has been invariably consistent for long periods of geological time, playing a key role in shaping ecological and evolutionary processes (Gaston et al., 2013). Many organisms are sensitive to extremely low levels of light at night, well below the upper level of ANTL (Longcore and Rich, 2004, Stone et al., 2009, Gaston et al., 2013). For example, many organisms use nightscapes as cues for migration, directional movement and orientation (Wehner, 1989, Åkesson et al., 2001, Dacke et al., 2003, Dacke et al., 2013, Tuxbury and Salmon, 2005, Ugolini et al., 2005, Warrant and Dacke, 2010, Rodríguez et al., 2012), while some species are sensitive to nightscape patterns for temporal and spatial exploitation of foraging habitats (Buchanan, 1993, Stone et al., 2009, Santos et al., 2010, Polak et al., 2011, Titulaer et al., 2012, Dwyer et al., 2013), inter-specific interactions or predation (Gliwicz, 1986, Longcore and Rich, 2004, Polak et al., 2011), communication (Lloyd, 1994, Bergen and Abs, 1997), moulting, mating and reproduction (Peters and Verhoeven, 1994, Salmon et al., 1995, Rand et al., 1997, Boldogh et al., 2007, Dominoni et al., 2013a). Thus the reorganisation of the nightscape due to ANTL pollution can result in these ecological patterns being affected, altered or even completely disrupted. Examples of such changes have been documented for moths and other insects (Wada et al., 1987, Frank, 2006, McDonnell et al., 2009), invertebrate soil communities (Davies et al., 2012), amphibians (Buchanan, 1993), reptiles (McFarlane, 1963, Rand et al., 1997, Witherington, 1997, Witherington and Martin, 2000, Mazor et al., 2013), birds (Aronoff, 1949, Wiltschko et al., 1993, Le Corre et al., 2002, Jones and Francis, 2003, Gehring et al., 2009, Rodríguez et al., 2012, Dominoni et al., 2013a) and mammals (Bird et al., 2004, Boldogh et al., 2007, Stone et al., 2009, Polak et al., 2011).
Despite strong indications that light-influenced ecosystems suffer from radical changes attributable to ANTL, there is a lack of scientific studies that integrate ANTL into landscape ecology concepts (Rich and Longcore, 2006, Navara and Nelson, 2007, Kyba and Hölker, 2013, Lyytimäki, 2013). This results in a lack of consideration of nightscape configuration in habitat management plans (Stone et al., 2009). The reasons for the general neglect of ANTL in the macroecology realm may be: (i) a lack of legislations which enforce ANTL pollution as a threat to ecosystems (Coatham, 2005); (ii) a lack of scientific knowledge on the impacts of ANTL on ecological systems (Bird et al., 2004) or (iii) unavailability of regional data on ANTL.
In this paper, we used ANTL data derived from remote sensing combined with landscape ecology concepts to investigate the effects of pollution due to direct ANTL. In order to provide a simple and direct methodology to assess ANTL in protected areas, we did not consider pollution caused by (indirect) propagation of light reflected by roads, buildings or landscape features as well as skyglow (Cinzano et al., 2001). We developed a new spectral index named Vegetation Adjusted Night-Time Light Index (VANI) from remotely sensed data to map the nightscapes at different levels of ANTL pollution. The new index was derived by combining Enhanced Vegetation Index (EVI) from Moderate resolution Imaging Spectroradiometer (MODIS, product MOD13Q1) and ANTL data from Day/Night band (DNB) of Visible Infra-red Imaging Radiometer Suite (VIIRS) sensor.
The objectives of this study were the following: (i) to map the extent of ANTL in two protected areas and the surrounding landscape; (ii) to compare the different landscape patterns during day and night; (iii) to investigate the shift in suitable area for high biodiversity (highly vegetated dark areas) when considering direct ANTL; and, (iv) to understand by how much it is necessary to lower light intensity across the landscape in order to preserve highly vegetated dark patches.
Section snippets
Study area
To study the impacts of ANTL on protected areas, we chose two natural reserves, “Colli Euganei” and “Cilento, vallo di Diano e Alburni” (hereafter Cilento). The regional park “Colli Euganei” (SCI IT3260017; 15,096 ha; Fig. 1) is a Site of Community Interest (SCI) located in northern Italy, between latitudes 45.2° and 45.4°. The altitude ranges from sea level to 603 m.a.s.l above sea level. The park is dominated by Quercus spp., Castanea sativa woodlands and Mediterranean scrub. The following
Data processing
Night-time images acquired by the Defence Meteorological Satellite Program Operational Line Scan System (DMSP-OLS) instrument, available since 1992 have been used extensively to study various urban landscape characteristics (Zhang et al., 2013). Many studies using the DMSP-OLS data focus on mapping urban sprawl in last decades, estimating economic indicators such as energy consumption and Gross Domestic Product (GDP) and deriving new population density maps (Elvidge et al., 1997, Sutton et al.,
Results
Both study areas, although being characterized by different environmental conditions, landscape structure, configuration and human pressure, showed a similar pattern of nightscapes. In Fig. 1, latitudinal and longitudinal transects of EVI and VANI are plotted along with park and buffer boundaries. The transect profiles in Fig. 1 showed higher EVI values inside Colli Euganei park than the surrounding landscape. This highlighted the presence of highly vegetated patches inside the park. However,
Discussion
Anthropogenic pressure is one of the main drivers of natural habitat degradation and fragmentation, eroding biodiversity and ecosystem services (Stephens et al., 2004, Gillanders et al., 2008, Marcantonio et al., 2013). ANTL is a major human-induced threat for biodiversity, often overlooked in landscape ecology and ignored in habitat management plans and conservation policies (Bird et al., 2004, Stone et al., 2009, Hölker et al., 2010a, Hölker et al., 2010b). In this study, we demonstrated the
Conclusion
To conclude, the nightscapes of the protected study areas are heavily influenced by the ANTL. Many protected and also unprotected nightscapes worldwide suffer from widespread light pollution (Aubrecht et al., 2010). It is therefore critical to assess the state of nightscapes in the vicinity of ANTL pollution and ensure a vast presence of naturally lit nightscapes worldwide (Hanski, 2005). In this study, we developed a framework to integrate ANTL in landscape ecology using remote sensing data
Acknowledgment
The PhD Scholarship of Matteo Marcantonio and Sajid Pareeth is supported by FIRS>T (FEM International Research School e Trentino). Markus Neteler and Markus Metz were partially funded Fig. 7. VANI classification of Cilento using both original ANTL and simulated ANTL at different exponents (reported in the later strips). Table 3 Gain in VANI-measured suitable area against simulated relative decrease at different power exponents. The relative decrease indicates the percentage decrease in sum of
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Both authors contributed equally to this work.