Low contribution of rare species to resilience and adaptive capacity in novel spatial regimes arising from biome shifts caused by global change

Human activity causes biome shifts that alter biodiversity and spatial resilience patterns, ultimately challenging conservation. Rare species, often considered vulnerable to change and endangered, can be a critical element of resilience by providing adaptive capacity in response to disturbances. However, little is known about changes in rarity and dominance patterns of communities once a biome transitions into a novel spatial regime, and how this affects conservation. We used time series modeling to identify species rarity and dominance patterns in an expanding terrestrial (southern) spatial regime in the North American Great Plains and another (northern) regime that will become encroached by the southern regime in the near future. In this approach, presumably rare and abundant species show stochastic and deterministic dynamics, respectively. We specifically assessed how stochastic species of the northern spatial regime influence the resilience and adaptive capacity of a novel spatial regime once it has been encroached by the southern regime by either becoming deterministic or staying stochastic. Using 47 years (1968 - 2014) of breeding bird survey data and a space-for-time substitution, we found half of the stochastic species from the northern regime to be either deterministic or stochastic in the southern regime. However, the overall contribution of these species to the community of the southern regime was low, manifested in marginal contributions to resilience and adaptive capacity of this regime. Also, none of these species were of conservation concern, suggesting limited need for revised species conservation action in the novel spatial regime. From a systemic perspective our result suggest that while stochastic species can potentially compensate for the loss of dominant species after disturbances and maintain the system in its current regime, they may only marginally contribute to resilience and adaptive capacity in a new spatial regime after fundamental ecological changes have occurred.