Alien Species in Urban Environments

Abstract

In general, invasive or ‘alien’ species are regarded as one of the two most important global drivers of biodiversity loss, the other being direct habitat despoliation. Urban environments are amongst the most accessible to many such species that are introduced and spread by human activity, and also amongst those in which these two paramount causes of conservation concern are forcibly associated. The most commonly cited roles of alien species, of both plants and animals, are as threats to native taxa and environments, but the wider ecological roles they may play in urban environments are acknowledged increasingly. Many alien plants in urban environments are vital resources, predominantly as food, for native insects: several examples noted below illustrate this. Alien species can thus be critical supplementary or replacement resources, and some can provide ecological ‘services’ naturally diminished by urban disturbances. The variety of these possible roles is enormous (Schlaepfer et al. 2011), as is the variety of taxa involved. Discussion of animals is here restricted to insects as the most pervasive faunal adventives in many urban areas. However, the arrivals of many predatory or scavenging rodents, mustelids, birds and others far beyond their natural ranges have been direct results from industrialisation and urbanisation, and almost any such insectivore may be cause for concern. The major involvements of such vertebrates until now has been in more natural environments, where severe impacts to native insects in forests (such as weta in New Zealand) or island ecosystems (such as Hawaii) continue to command suppression: their urban impacts are, by contrast, generally far less significant or obscured by major habitat transformations.