Landscape Connectivity for Urban Insects

Abstract

Insects can provide many lessons for urban planners. Although complex, many responses of insects to urban development emphasise the importance of landscape integrity and open spaces – self-evident also in many other contexts related to human welfare and biodiversity conservation – and that maintaining variety is a primary concern. Viewing open spaces as ‘habitat’ for insects in relation to their propensity for dispersal and colonising those spaces emphasises the central relevance of landscape structure, as in other, non-urban, environments. Thus, many of the studies that provide information on insect roadkill (p. 129) were undertaken primarily to assess the roles of roadways as barriers (insects either crossing the roads or turning back at the edge and avoiding doing so) or as corridors for movement. Fahrig (2007) used four broad categories of animal habitats to develop ideas on animal movements in anthropogenic landscapes. They provide very perceptive considerations for urban environments, as (1) continuous habitat; (2) patchy habitat within a high quality matrix; (3) patchy habitat within a low quality matrix; and (4) patchy ephemeral habitat. Fahrig used these categories to imply four ‘movement types’ that could have different consequences for the populations involved, as summarised in Fig. 10.1, with the ‘evolved movement parameters’ and their risks compared. She also emphasised that many landscapes and species do not fit easily into this scheme, but that the extremes in the broad continua represented help to indicate the great influences of landscape change. Habitat extent (area and quality) interact with movement patterns. A part of Fahrig’s discussion, for species in a continuous habitat, illustrates her focus. There, species are likely to encounter boundaries only infrequently, and should readily cross them when met as the risk of leaving is low and crossing is likely to lead rapidly to suitable habitat. Such species, however, are at high risk from habitat loss if that continuity is replaced by a ‘risky movement’ cover, by which patch sizes are reduced, edge lengths increased, and emigration rates increase together with distance between remaining patches, leading to increased mortality during movement and lowered chances of colonisation. Those species are also unlikely to respond to risks within the matrix.