Collections of small urban parks consistently support higher species richness but not higher phylogenetic or functional diversity

When prioritizing regions for conservation protection, decisions are often
based on the principle that a single large (SL) reserve should support
more species than several small (SS) reserves of the same total area
(SLOSS). This principle remains a central paradigm in conservation
planning despite conflicting empirical evidence and methodological
concerns. In urban areas where small parks tend to dominate and policies
to promote biodiversity are becoming increasingly popular, determining the
most appropriate prioritization method is critical. Here, we document the
role of SLOSS in defining the seasonal diversity of birds in 475 parks in
21 US cities. Collections of small parks were consistently associated with
higher species richness, spatial turnover, and rarity. Collections of both
small and large parks were associated with higher phylogenetic and
functional diversity whose patterns varied across seasons and cities.
Thus, collections of small parks are a reliable source of species richness
driven by higher spatial turnover and rarity, whereas collections of both
small and large parks contain the potential to support higher phylogenetic
and functional diversity. The presence of strong intra-annual and
geographic variation emphasizes the need for regional prioritization
strategies where multiple diversity metrics are examined across parks and
seasons.