Data from: Compact cities or sprawling suburbs? optimising the distribution of people in cities to maximise species diversity

1. Conservation of biodiversity in urban environments depends on the responses of species 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 1) identify the optimal allocation of land for people and nature, 2) assess whether the optimal allocation is more similar to land sparing or land sharing, and 3) examine how this might change under scenarios of human population growth. 2. We surveyed birds in 28 landscapes, each 25 ha in size, along a gradient of human population density (zero to ~1600 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. 3. 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, 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. 5. Synthesis and applications. Urban areas represent a mosaic of land uses that offer habitats of differing quality. Land sharing, based on sustaining biota amongst residential areas, performed poorly under all scenarios due to its inability to support species that depend on natural or semi-natural 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.

1. 城市环境中的生物多样性保护，有赖于物种对城市开发强度的响应。“土地共享（land sharing）”与“土地 sparing（land sparing）”构成了一个梯度谱系的两端，该梯度刻画了人类人口与生物多样性之间的权衡关系。本研究采用线性优化流程，实现三大目标：1）明确人类与自然的最优土地分配方案；2）评估该最优分配方案更趋近于土地共享还是土地 sparing模式；3）探究在人口增长情景下，该最优分配方案可能发生的变化。
2. 我们在澳大利亚大墨尔本地区，沿人类人口密度梯度（0~约1600人/25公顷），对28处面积均为25 ha的景观开展了鸟类调查。利用广义可加模型（generalised additive models, GAMs）估算了物种对人口密度的响应关系。随后基于最大化鸟类群落相对丰度几何均值（G）这一社区指数，通过上述响应关系确定了不同人口密度等级下的最优土地分配方案。
3. 人类人口密度是影响28个鸟类物种记录率的重要驱动因子。“避城种（urban avoider）”、“适城种（urban adapter）”与“嗜城种（urban exploiter）”的响应曲线存在显著差异。针对研究区域当前的人口规模，最优土地分配方案同时兼具土地共享与土地 sparing模式的特征。然而，在人口规模增长的情景下，最优分配方案将收敛于土地 sparing模式。
5. 综合与应用。城市区域是由多种土地利用类型构成的镶嵌体，可为生物提供质量各异的栖息生境。基于在居住区中维持生物群落的土地共享模式，由于无法支撑依赖自然或半自然生境的物种，在所有情景下均表现不佳。若要在城市区域维持同质化鸟类群落之外的生物多样性，必须在城市环境内部或毗邻区域保留大片天然植被。随着城市人口与土地利用不可避免地扩张，保护城市边缘的自然区域将成为未来守护自然的关键举措。