The role of dispersal and local environment in urban land snail assemblages: an example of three cities in Central Italy

Abstract

Ecologists increasingly appreciate the central role that urban biodiversity plays in ecosystems, however much urban biodiversity is neglected, especially some very diverse groups of invertebrates. For the first time in southern Europe, land snail communities are analysed in four urban habitats along a geographical gradient of three cities, using quantitative methods and assessing the relative roles of local environmental conditions (“distance from sea”, “distance from city centre”, “vegetation cover”) and spatial effects by principal coordinate analysis of neighbour matrices, redundancy analysis and variation partitioning. A total of 53 species was recorded, a richness similar to that of natural areas. At habitat level, species richness did not show a clear increasing trend from more to less urbanized habitats, but rather a homogeneous pattern. At city level, study areas hosted rather heterogeneous species assemblages and biotic homogenization did not seem to have any impact; indeed, only three species could be considered alien. Variation partitioning showed that land snail communities were mostly structured by environmental factors, even when spatial structures independent of measured environmental variables were included: “vegetation cover” and “distance from city centre” were the environmental variables that explained most of the variation in species composition. The lack of strong spatial structure also unexpectedly suggested that transport by humans aids dispersal of organisms with low mobility, which are usually limited by spatial constraints in natural environments. These results provide ecological and conservation implications for other invertebrate groups, suggesting to set priorities in management strategies that include habitat conservation at local scale

Functional connectivity in replicated urban landscapes in the land snail (Cornu aspersum)

“…However, they tend to be intensively affected by fragmentation (and habitat loss, Öckinger et al., ; Piano et al., ) when they move among distant habitat patches to disperse or move away from disturbances. Despite their low degree of mobility, organisms such as terrestrial Gastropods can persist and are largely spread across urban landscapes (Barbato, Benocci, Caruso, & Manganelli, ). The garden snail Cornu aspersum (Gastropoda, Helicidae, formerly Helix aspersa ) is a widespread, synanthropic species (Ansart, Madec, & Guiller, ; Barbato et al., ; Kerney, Cameron, & Bertrand, ).…”

“…Despite their low degree of mobility, organisms such as terrestrial Gastropods can persist and are largely spread across urban landscapes (Barbato, Benocci, Caruso, & Manganelli, ). The garden snail Cornu aspersum (Gastropoda, Helicidae, formerly Helix aspersa ) is a widespread, synanthropic species (Ansart, Madec, & Guiller, ; Barbato et al., ; Kerney, Cameron, & Bertrand, ). It has poor mobility (a maximum of 10–50 m per month during activity periods, Dahirel et al., ; Dan, ) due to the extremely high cost associated with movement, in energy (foot muscle contraction) and water (mucus production, Denny, ).…”

“…Despite their low degree of mobility, organisms such as terrestrial Gastropods can persist and are largely spread across urban landscapes (Barbato, Benocci, Caruso, & Manganelli, 2017). The garden snail Cornu aspersum (Gastropoda, Helicidae, formerly Helix aspersa)…”

“…is a widespread, synanthropic species (Ansart, Madec, & Guiller, 2009;Barbato et al, 2017;Kerney, Cameron, & Bertrand, 2006). It has poor mobility (a maximum of 10-50 m per month during activity periods, Dahirel et al, 2016b;Dan, 1978) due to the extremely high cost associated with movement, in energy (foot muscle contraction) and water (mucus production, Denny, 1980).…”

Land snail dispersal, abundance and diversity on green roofs

“…Generally, most land snail species in North America are associated with moist forest ecosystems, and the potentially harsh conditions of green roof habitats (e.g., prolonged exposure to direct sunlight, comparatively less shelter habitat) may not support diverse land snail communities. Yet, land snails have been well documented in a variety of urban habitats [9][10][11][12], are common "hitchhiker" species that are often transported on commercial materials such as horticultural plants [13], and may even disperse via translocation on larger vertebrate animals [14][15]. Moreover, land snails are often seen crawling on building walls and could actively colonize green roofs on their own.…”