Phylogenetic Endemism Hotspots of North American Birds Are Associated With Warm Temperatures and Long- and Short-Term Climate Stability

Abstract

Human activities have dramatically altered the distribution and abundance of species, and our impacts are likely to increase in the near future. Conservation efforts are typically faced with scarce resources, forcing us to prioritize areas based in part on estimates of their conservation value. Two major factors in conservation value are a species uniqueness and its extinction risk. Though these ideas are multidimensional, one important component of uniqueness is evolutionary distinctness, while risk is strongly related to geographic range size. These components are combined in an assemblage-level measure called phylogenetic endemism (PE), which measures the degree to which the species in an assemblage are small-ranged and phylogenetically distinct. Broad-scale patterns and correlates of PE are becoming better known for a variety of groups, and have been shown to depend on current climate, geographic isolation and long-term climate stability. Human impacts (e.g., land cover changes), are likely to shape PE as well, though the coarse resolution of most previous studies may make this difficult to detect. Overall, PE patterns at fine spatial and temporal resolutions are not well understood. Here, we fill this gap using data from the North American Breeding Bird Survey. These data comprise a long-term annual record with fine spatial resolution and a near-continental extent. We assess geographic patterns and trends in PE, and relate these to a range of putative predictor variables including measures of current climate, land cover, long-term and recent climate change. Bird PE is concentrated in three main hotspots: the west coast, the southeast and south-central Canada east of the Rockies. High PE values tended to occur in regions with high temperatures and stability in temperature, both in the long (21,000 year) and short (35 year) time scales. PE patterns are driven more strongly by patterns of range size than phylogenetic distinctiveness, and are trending gradually upward, driven by increasingly frequent sightings of small-ranged species. These results indicate the importance of climate stability on multiple time scales in influencing endemism patterns and suggest a surprisingly minor influence of direct human land use. The increase in PE through time may reflect successful conservation efforts that have led to population recoveries of some small-ranged species.

Disentangling the drivers of continental mammalian endemism

“…The relationship between endemism and climate velocity (which does not extricate climate change from topography) described previously (e.g., Sandel et al, 2011) may therefore be more strongly influenced by changes in climate than by topography. These results support the hypothesis that stable climate refugia foster greater numbers of range‐restricted species, whereas areas that underwent intense climatic changes (e.g., glaciation events) over the past 25,000 years are relatively endemic poor (Acevedo & Sandel, 2021; Harrison & Noss, 2017; Morueta‐Holme et al, 2013). Although it was slightly less influential than long‐term temperature stability, topographic complexity also exhibited a significant relationship to ecoregion‐level endemism (Figures 2b, 4, and 5).…”

“…These two measures of temperature change differ across the globe, especially in areas of high latitude and the Neotropics (Figure S1). Because different timescales of climate stability may influence rates of endemism differently (Acevedo & Sandel, 2021; Irl et al, 2015), we calculated the mean annual temperature range (seasonality) at each ecoregion across the eight time periods. Finally, we included the standard deviation of the annual precipitation in the ecoregion across time and the total change in precipitation as potential predictors.…”

“…However, two seemingly disparate physiographic processes have been identified as particularly important for structuring the current spatial patterns of endemism (Acevedo & Sandel, 2021; Murali et al, 2021). A greater prevalence of endemism is found in areas that are more climatically stable through time because of a repeated cycle of species range contractions (Acevedo & Sandel, 2021; Carnaval et al, 2014; Dynesius & Jansson, 2000; Harrison & Noss, 2017; Irl et al, 2015; Sandel et al, 2011). Areas of high topographic diversity are also linked to highly endemic regions because of geographic isolation, niche differentiation, and speciation (Badgley et al, 2017; Cadena et al, 2012; Igea & Tanentzap, 2021; Morales‐Barbero et al, 2018; Pellissier et al, 2018; Polato et al, 2018; Steinbauer et al, 2016, but see Knowles & Massatti, 2017).…”

“…The global pattern of vertebrate endemism observed today is an emergent property of many factors, including tectonic history (Huang et al, 2019; Pellissier et al, 2018), continental land area and shape (Flojgaard et al, 2011; Storch et al, 2012), and interspecific interactions (Paquette & Hargreaves, 2021). However, two seemingly disparate physiographic processes have been identified as particularly important for structuring the current spatial patterns of endemism (Acevedo & Sandel, 2021; Murali et al, 2021). A greater prevalence of endemism is found in areas that are more climatically stable through time because of a repeated cycle of species range contractions (Acevedo & Sandel, 2021; Carnaval et al, 2014; Dynesius & Jansson, 2000; Harrison & Noss, 2017; Irl et al, 2015; Sandel et al, 2011).…”

“…Patterns of speciation and extinction also influence the distribution of species range sizes within a region, with areas of high speciation leading to small range sizes and specialized niches across a community (Belmaker et al, 2012; Chejanovski & Wiens, 2014; Guo et al, 2022; Jetz et al, 2004). However, the effects of topography, climate stability, evolution, and ecology on vertebrate endemism have not been fully parsed (Harrison & Noss, 2017; Keppel et al, 2018; Sandel et al, 2020; Veron et al, 2019; but see Acevedo & Sandel, 2021; Zuloaga et al, 2019). Notably, when the various physiographic hypotheses explaining mammalian endemism are systematically tested, they do not effectively predict and reconstruct observed trends on continental scales (Zuloaga et al, 2019).…”