New York's nature: a review of the status and trends in species richness across the metropolitan region

The world's population is urbanizing, yet relatively little is known about the ecology of urban areas. As the largest metropolitan area in the USA, New York City is an ideal location to study the effects of urbanization. Here, we aim to produce a better understanding of the state of the research for species richness of flora and fauna across the New York metropolitan region. New York metropolitan region, USA. We conducted a review of the published and grey literature, in which we targeted studies of species richness, and categorized each study by habitat, location and taxonomic group. We found 79 studies reporting location-specific species richness data, resulting in 261 location-taxonomic group records. Of these, 26 records had data from multiple time periods; 17 showed decreases in species richness, six reported increases and three showed stable species richness. Of these 26 records, most declines were attributed to anthropogenic causes, such as habitat loss/degradation and invasive species, while most increases reflected recovery from major habitat loss or increases in exotic species. Overall, most records (84) were terrestrial, followed by those in freshwater (72) and mixed habitats (61). When parsed by taxonomic group, the most commonly studied groups were plants (76) and mammals (48). In general, we discovered fewer studies than expected reporting species richness, especially studies reporting species richness for more than one point in time. Most studies that did contain data over time reported declines in species richness, while several studies reporting increasing or stable species richness reflected increases in exotic species. This survey provides a crucial first step in establishing baseline ecological knowledge for the New York metropolitan region that should help prioritize areas for protection, research and development. Furthermore, this research provides insights into the impacts of urbanization across the USA and beyond and should help establish similar frameworks for ecological understanding for other metropolitan regions throughout the world.