Compact cities or sprawling suburbs? Optimising the distribution of people in cities to maximise species diversity

Abstract

Conservation of biodiversity in urban environments depends on species’ responses to the intensity of urban development. “Land sharing” and “land sparing” represent alternate ends of a gradient that conceptualises a trade‐off between the human population and biodiversity. We used a linear optimisation procedure to (a) identify the optimal allocation of land for people and nature, (b) assess whether the optimal allocation is closer to land sparing or land sharing and (c) examine how this might change under scenarios of human population growth. We surveyed birds in 28 landscapes, each 25 ha in size, along a gradient of human population density (zero to c. 1,600 persons/25 ha) in the Greater Melbourne region, Australia. Species’ responses to population density were estimated using generalised additive models (GAMs). These relationships were then used to determine the optimal allocation of land among different categories of population density based on maximising a community index, the geometric mean of relative abundance (G) of bird species. Human population density was an important driver of the reporting rate for 28 species. Response curves differed among “urban avoider,” “urban adapter” and “urban exploiter” species. For the current human population in the study area, the optimal allocation of land included elements of both land sharing and land sparing. However, for scenarios of increased population size, optimal allocation converged upon a land sparing design. Synthesis and applications. Urban areas represent a mosaic of land uses that offer habitats of differing quality. Land sharing, based on sustaining biota among residential areas, performed poorly under all scenarios due to its inability to support species that depend on natural or seminatural habitat. To sustain more than a homogenised avifauna in urban regions, large tracts of natural vegetation are needed within, or adjacent to, the urban environment. Protecting natural areas on urban fringes will be critical to the safeguarding of nature in the future as urban populations and land‐use inevitably expand.

Bird conservation and the land sharing‐sparing continuum in farmland‐dominated landscapes of lowland England

“…Whilst we arbitrarily set the area of the third compartment to match that of spared habitat, other optimisation‐based approaches are possible (e.g., Geschke et al. ) and may further reconcile the trade‐off between the conservation of winners and losers.…”

“…Although 3-compartment sparing could be described as a both-and strategy, it still depends on high-yield farming to deliver the majority of the food production target. Whilst we arbitrarily set the area of the third compartment to match that of spared habitat, other optimisation-based approaches are possible (e.g., Geschke et al 2018) and may further reconcile the tradeoff between the conservation of winners and losers.…”

The relationship between wealth and biodiversity: A test of the Luxury Effect on bird species richness in the developing world

“…Geschke, James, Bennet, & Nimmo, 2018), as well as social aspects that can benefit local communities and hence further address additional key development goals for Sustainable Cities and Communities. Geschke, James, Bennet, & Nimmo, 2018), as well as social aspects that can benefit local communities and hence further address additional key development goals for Sustainable Cities and Communities.…”

Generalists are the most urban‐tolerant of birds: a phylogenetically controlled analysis of ecological and life history traits using a novel continuous measure of bird responses to urbanization

“…Terminology (i.e. differentiating among avoiders, adapters, or exploiters) also varies among studies (Kark et al , Croci et al , Geschke et al ), affecting interpretation (Fischer et al , McDonnell and Hahs ). There is clearly a need for continuous measures of urbanization (Evans et al ), where a species is assessed over its entire distribution in response to urban environments.…”