Patterns and processes of soil faunal biodiversity in urban ecosystems
Soil biodiversity provides important ecosystem services for human survival and well-being but little is known about its patterns and processes in urban ecosystems.
A critical examination of the recent literature reveals that neither biotic homogenization nor urban convergence hypotheses hold true for urban soil faunal biodiversity. A new conceptual framework is proposed for examining the emergence of belowground biodiversity patterns in urban ecosystems following the initial massive disturbance associated with urban development and under subsequent multiple, interacting processes including urban land use, land management, human population density, and urban age. This model posits that a new time zero is set by the drastic changes to the site during initial urban development from which ecological succession proceeds under the influence of anthropogenic factors. Studies on nematode biodiversity have proven especially useful for determining the structure and function of soil food webs in highly fragmented urban landscapes. Nematode soil biodiversity in urban ecosystems is characterized by the general reduction in species richness, predominance of stress tolerant r-strategists, and the overall trophic downgrading of the food webs compared to the nearby less disturbed forest ecosystems. Nematode communities tend to be less diverse in intensively-managed urban lawns, compared to urban vacant lots that receive infrequent mowing and no pesticides or fertilizers. High inputs of N fertilizers negatively affect nematode biodiversity and food web structural complexity in urban lawns, whereas pesticides seem to have little effect over the long-term. Nematode communities tend to be less diverse at the urban fringe compared to the urban core, likely due to extensive physical disturbance associated with ongoing urban development at the urban fringe. Nematode abundance and species richness increase with urban age and correlate positively with soil C, organic matter, and pH, which also increase with urban age. Nematode abundance and species richness however do not correlate positively with soil C, organic matter and pH along the distance to road gradient, suggesting decoupling of soil processes due to potential contaminants from the roads. Relationship between heavy metal contamination and nematodes and other soil fauna is complex and it depends upon organism’s taxonomic and trophic group, and on soil factors that influence the bioavailability of the metals. Further research is needed on urban soil biodiversity and its ecosystem services to foster the development of sustainable urban ecosystems.