Abstract
Compositional changes in natural communities associated with anthropogenic influence often lead to localised extinctions and biodiversity loss. Soil invertebrates are also threatened by urbanisation due to habitat fragmentation, vegetation changes and management, soil alteration, degradation, and disappearing shelter sites. The aim was to assess terrestrial isopod (Oniscidea) assemblages in differently degraded urban forest patches of a metropolitan area (Budapest, Hungary). Study sites were compared by their species richness, composition and the relevant background factors (soil properties, dead wood, litter characteristics, and canopy closure). The degree of urban disturbance was expressed using an urbanisation index (UI) based on built-up density and vegetation cover. The isopods were identified to species level, and were qualified by their habitat preference and naturalness index (TINI). Average Rarity Index (ARI), derived from TINIs provided information on the degree of naturalness/disturbance of each habitat. Altogether 14 isopod species were collected from 23 sample sites. Urbanisation indirectly affected on the composition of isopod assemblages through the quantity of dead wood and soil plasticity. ARIs and UIs of sample sites were negatively correlated. Urban patches harboured habitat generalist, synanthropic and established introduced species with low naturalness value of assemblages. Areas with no or low anthropogenic disturbance maintained stable native, autochthonous assemblages that were characteristic of rural sites in the region. Transitional zones between rural and urban habitats usually maintained a mixed isopod fauna consisting of both urban and rural elements.
Highlights
Increasing number of studies explore the effects of urbanisation on biological communities at a global level (Niemelä et al 2000, McKinney 2008, Richter and Weiland 2012, Wang et al 2012a)
Intensity of anthropogenic disturbance was expressed in urbanisation indices (UI)
According to the results of principal component analysis (PCA), sample sites were arranged along a gradient that reflects the intensity of urbanisation (Fig. 2)
Summary
Increasing number of studies explore the effects of urbanisation on biological communities at a global level (Niemelä et al 2000, McKinney 2008, Richter and Weiland 2012, Wang et al 2012a). The alteration and fragmentation of natural habitats generally leads to a shift in species composition, resulting in biotic homogenisation and changes in ecosystem services as well (McPherson 1998, Whitford et al 2001, McKinney 2006, Tratalos et al 2007) Human activity, such as construction industry, air pollution and pollutant emissions of vehicles and the use of chemicals, contributes to urban soil degradation (Pouyat et al 2008). The majority of soil invertebrates are highly sensitive to disturbances (Barbercheck et al 2009) and environmental changes (Santorufo et al 2012) This includes the macrodetritivore fauna, which has an important role in the ecosystems’ nutrient cycling. Woodlice (Isopoda: Oniscidea) are one of the major invertebrate group contributing to these processes (Anderson 1988, Paoletti and Hassall 1999)
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