Insects and the city: what island biogeography tells us about insect conservation in urban areas

S Fattorini

doi:10.5194/we-16-41-2016

Abstract

Abstract. Habitat fragmentation caused by urbanization is considered a prominent threat to biodiversity. Urban development creates a mosaic of natural fragments which can be occupied by organisms able to survive in small spaces. These fragments are a set of habitat islands separated by less suitable non-native habitats. Because of their isolation, communities of urban green spaces can be investigated using hypotheses developed in island biogeography. The "equilibrium theory of island biogeography" (ETIB) allows the formulation of some predictions about how various characteristics of green spaces (such as their area, shape, level of isolation, environmental heterogeneity, age) should influence species richness. Many studies found support for ETIB predictions, but results varied considerably according to the species' sensitivity to patch size, matrix characteristics, and history of the city. In some cases ETIB predictions were falsified. These contrasting results warn against making generalizations on conservation strategies only based on ETIB models. On the other hand, the ETIB may represent a useful framework for urban conservation, especially for small animals like insects, if the roles of other factors, such as the surrounding landscape, the specific needs of the species under study, and the history of the urbanization process, are taken into account.

Highlights

From the perspective of the organisms that live in urban green spaces, the urban environment can look like a set of habitat islands, which form the green infrastructure, separated by inhospitable or less suitable environments
Biodiversity studies in urban areas have been inspired by the theory of island biogeography (e.g. Faeth and Kane, 1978)
The “equilibrium theory of island biogeography” (ETIB), developed by MacArthur and Wilson in the 1960s, was at the base of the principles of reserve design initially proposed by Diamond in the 1970s and can be applied to urban green spaces

Summary

Introduction

From the perspective of the organisms that live in urban green spaces (e.g. parks, wetlands, gardens, backyards, green roofs, green gardens), the urban environment can look like a set of habitat islands, which form the green infrastructure, separated by inhospitable or less suitable environments (e.g. builtup areas, industrial sites, parking lots, streets). Biotic communities of urban green spaces should have population dynamics similar to those of islands. Since their inception, biodiversity studies in urban areas have been inspired by the theory of island biogeography The “equilibrium theory of island biogeography” (ETIB), developed by MacArthur and Wilson in the 1960s, was at the base of the principles of reserve design initially proposed by Diamond in the 1970s (see Triantis and Bhagwat, 2011, for a review) and can be applied to urban green spaces. The ETIB allows the formulation of some explicit predictions about the influence of area, shape, environmental diversity, level of isolation, and other characteristics of urban green spaces on species richness and extinction levels

Predictions about species richness

Predictions about species extinction

Empirical evidence

Conclusions and future work