Abstract
AbstractCities currently harbour more than half of the world’s human population and continued urban expansion replaces natural landscapes and increases habitat fragmentation. The impacts of urbanisation on biodiversity have been extensively studied in some parts of the world, but there is limited information from South Asia, despite the rapid expansion of cities in the region. Here, we present the results of monthly surveys of butterflies in three urban parks in Dhaka city, Bangladesh, over a 3-year period (January 2014 to December 2016). We recorded 45% (137 of the 305 species) of the country’s butterfly richness, and 40% of the species detected are listed as nationally threatened. However, butterfly species richness declined rapidly in the three study areas over the 3-year period, and the decline appeared to be more severe among threatened species. We developed linear mixed effect models to assess the relationship between climatic variables and butterfly species richness. Overall, species richness was positively associated with maximum temperature and negatively with mean relative humidity and saturation deficit. Our results demonstrate the importance of urban green spaces for nationally threatened butterflies. With rapidly declining urban green spaces in Dhaka and other South Asian cities, we are likely to lose refuges for threatened fauna. There is an urgent need to understand urban biodiversity dynamics in the region, and for proactive management of urban green spaces to protect butterflies in South Asia.
Highlights
More than half of the world’s human population currently lives in cities, compared to 14% a century ago (Tratalos et al 2007), and the proportion is expected to further increase over the coming decades (Wei and Ewing 2018)
We developed linear mixed effect models to assess the relationship between climatic variables and butterfly species richness
Our results demonstrate the importance of urban green spaces for nationally threatened butterflies
Summary
More than half of the world’s human population currently lives in cities, compared to 14% a century ago (Tratalos et al 2007), and the proportion is expected to further increase over the coming decades (Wei and Ewing 2018) This will exert increased environmental demands on already diminishing surrounding natural habitats (McKinney 2002, 2006; Hahs et al 2009; Elmqvist et al 2013; McDonnell and MacGregor-Fors 2016) through agricultural conversion, intensification and infrastructure development, and loss of natural vegetation to supply the resource demands of a growing urban population (Tratalos et al 2007; Aguilera et al 2019). An increasing intensity of urbanisation often involves loss of green spaces, which leads to a decline in biodiversity (Bergerot, Julliard, and Baguette 2010; Gaston and Evans 2010; Fox 2013) Both positive and negative effects of urbanisation on species richness have been observed, depending on the configuration and spatial scale of the impact (Gaston 2005; Goddard, Dougill, and Benton 2010; Jain, Lim, and Webb 2017; Ramırez-Restrepo and MacGregor-Fors 2017; Iban~ezAlamo et al 2017). Data are lacking from South Asia where urbanisation is progressing rapidly
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