Disequilibrium in Trait-Climate Relationships of Trees and Birds

Abstract

Climate change is expected to drive changes in the structure of ecological assemblages, but these responses might show considerable time lags. If these lags are large, then the observed composition of assemblages will fall out of equilibrium with current climatic conditions. This disequilibrium has several expected signatures, including trends in the magnitude of climate relationships through time and stronger climate relationships across space than through time. Here, I describe spatial and temporal patterns of functional assemblage composition of birds and trees and ask whether there is evidence of disequilibrium between climate and functional assemblage structure. I used bird assemblage data from the Breeding Bird Survey (BBS) and tree data from the Forest Inventory and Analysis program (FIA), in both cases spanning the continental United States and covering the time period 1970-2016. To describe functional assemblage composition, I used the community weighted means of five functional traits for trees and six traits for birds, and fit linear models to explain the variation in composition through time and across space. For most traits, spatial relationships were much stronger than temporal relationships, consistent with lagged responses of assemblages to climate change. Several of the traits showed trends over the study period, in some cases associated with trends in mean annual temperature. Others showed dynamics in the spatial relationships between climate and trait values. For example, the mean clutch size of birds depended only weakly on temperature in the early study period, but the relationship became strongly negative by 2016. While precipitation was often an important predictor of spatial patterns of functional composition, it was typically weakly correlated with the temporal patterns. This likely reflects the fact that temperature experienced more consistent long-term trends over the study period, whereas large year-to-year fluctuations in precipitation prevent composition from ever coming into equilibrium with precipitation in a particular year. Overall, there was substantial evidence of disequilibrium between functional assemblage composition and climate.

Mismatches between birds' spatial and temporal dynamics reflect their delayed response to global changes

“…Identifying the impact of lagged response in empirical biodiversity patterns is important to assess the accuracy of punctual biological surveys of the current and local state of biodiversity, and whether they are still imprinted by past environmental changes (Sandel et al 2011, Sandel 2019). For now, successful approaches have either focused on particular environmental forces such as climate change, habitat loss (Halley et al 2016) and landscape change (Adriaens et al 2006), or have confronted current biodiversity states with past and present conditions (Dupouey et al 2002, Halley et al 2016, Ordonez and Svenning 2016, Blonder et al 2018).…”

Space‐for‐time substitutions in climate change ecology and evolution

“…Transplant studies are also used to study genetic markers, with the motivation usually to identify the genetic loci underlying climate-phenotype relationships, rather than direct correlations between genotypes and climate (Fournier-Level et al, 2011;de Villemereuil et al, 2018;Housset et al, 2018). Nonetheless, where the focus of transplant studies is on fitness-associated genotypes, it is possible to estimate climate-genotype relationships (Fournier-Level et al, 2011) and make predictions about how allele frequencies will respond to future climate change (Exposito-Alonso et al, 2018, 2019.…”

Space-for-time substitutions in climate change ecology and evolution

“…Where temporal and spatial data are available, inferences can also be made about the presence of a lag in the temporal community response to climate change (Fig. 2b), using the same approaches as for phenotypes (comparing spatial and temporal climate-biotic response slopes (Sandel, 2019;Gaüzère et al, 2020); Section III(1)) or species distributions (comparing current observations to predictions based on historically-calibrated models (Menéndez et al, 2006); Section III(3)). These lags can also be quantified in terms of geographic distance (Distance of biotic lag, Fig.…”

“…SFTS validation of changes in community compositions and traits has been assessed using historical data (Lemoine, Schaefer & Böhning-Gaese, 2007;Algar et al, 2009;Blois et al, 2013;Maguire et al, 2016;Bjorkman et al, 2018). Another approach for assessing SFTS validation has involved a comparison of the spatial and temporal relationships between climate and community traits (La Sorte et al, 2009;Elmendorf et al, 2015;Sandel, 2019;Gaüzère et al, 2020) or community composition (Lemoine & Böhning-Gaese, 2003;White & Kerr, 2006;Adler & Levine, 2007;La Sorte et al, 2009). Similarly, warming and water addition experiments have been used to validate in situ gradient SFTS for species interactions (Kazenel et al, 2019) and trait compositions (Sandel et al, 2010).…”