Local and landscape scale variables shape insect diversity in an urban biodiversity hotspot.

Local community structure is shaped by processes acting at local and
landscape scales.  The relative importance of drivers operating
across different spatial scales are difficult to test without observations
across regional or latitudinal gradients.  Cities exhibit strong
but predictable environmental gradients overlaying a mosaic of highly
variable but repeated habitat types within a constrained area.
 Thus, cities present a unique opportunity to explore how both
local and landscape factors influence local biotic communities.
 We used insect communities to examine the interactions among
local environmental variables (such as temperature and relative humidity),
local habitat characteristics (such as plant community composition), and
broad-scale patterns of urbanization (including biophysical, human-built,
and socio-economic variables) on local insect abundance, species richness,
and species composition in Los Angeles, a hot, dry, near-desert
city.  After accounting for seasonal trends, insect species
richness and abundance were highest in drier and hotter sites, but the
magnitude of local environmental effects varied with the degree of
urbanization.  In contrast, insect species composition was best
predicted by broad-scale urbanization trends, with the more native
communities occurring in less urbanized sites and more cosmopolitan
insects occurring in highly urbanized sites.  However, insect
species richness and abundance were >30% higher and insect
composition was similar across sites that hosted either native or
drought-tolerant plants, regardless of the degree of
urbanization.  These results demonstrate that urban insect
biodiversity is a product of interacting mechanisms working at both local
and landscape scales.  However, local scale changes to urban
habitats, such as cultivating plants that are adapted to the natural
environment nearest the city, can positively impact urban biodiversity
regardless of location.