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Residential gardens are a principal component of urban green infrastructure throughout the world and their potential positive contributions to biodiversity are increasingly recognised. But the characteristics of gardens reflect the needs, values and interests of individual households. The present review summarises evidence from studies of garden biodiversity published in the scientific literature, describes major themes and identifies important knowledge gaps. A search of the Web of Science database identified 408 published articles on the biodiversity of residential gardens (1981–2022), with numbers increasing over time and a strong bias towards Europe (32.1%) and North America (23.8%). Plants and invertebrates were most frequently studied, and species diversity was often correlated with garden size and habitat complexity. Botanic composition and vegetation cover were often positively associated with the diversity and abundance of fauna. Non-native plants contributed substantially to garden plant diversity and evidence from some studies indicated benefits to other species linked to their functional attributes. Intensive management including frequent lawn mowing, fertiliser and pesticide application, and a more formal, 'neater' garden appearance were often associated with reduced biodiversity. However, results varied amongst studies, for example in relation to the impacts of mowing frequency on lawn diversity. There was a general paucity of experimental evidence on the impacts of different management regimes on garden biodiversity and few replicated experimental tests of recommended 'wildlife-friendly practices'. Several studies identified the importance of connectivity amongst gardens and with other green infra-structure for species dispersal and ecosystem functioning. Emerging threats to garden biodiversity include their replacement by development, conversion to hard surfaces and declining plot sizes. Managing these challenges and maximising the biodiversity value of residential gardens requires greater engagement from policymakers and planners, and partnerships between public bodies and private households to co-ordinate local initiatives. [ABSTRACT FROM AUTHOR]

Attempts to assess the magnitude of global biodiversity have focusedon estimating species richness. However, this is but one component of biodiversity, and others, such as numbers of individuals or biomass, are at least as poorly known and just as important to quantify. Here, we use a variety of methods to estimate the global number of individuals for a single taxon, birds. The different methods yield surprisingly consistent estimates of a global bird population of between 200billion and 400 billion individuals (1 billion = 109 ). We discuss some of the implications of this figure. [ABSTRACT FROM AUTHOR]

The taxonomic impediment to biodiversity studies may be influenced radically by the application of new technology, in particular, desktopimage analysers and neural networks. The former offer an opportunityto automate objective feature measurement processes, and the latter provide powerful pattern recognition and data analysis tools which are able to 'learn' patterns in multivariate data. The coupling of these technologies may provide a realistic opportunity for the automationof routine species identifications. The potential benefits and limitations of these technologies, along with the development of automatedidentification systems are reviewed. [ABSTRACT FROM AUTHOR]