Equilibrium in plant functional trait responses to warming is stronger under higher climate variability during the Holocene

Abstract

Aim: The functional trait composition of plant communities is thought to be determined largely by climate, but relationships between contemporary trait distributions and climate are often weak. Spatial mismatches between trait and climatic conditions are commonly thought to arise from disequilibrium responses to past environmental changes. We aimed to investigate whether current trait-climate disequilibrium is likely to emerge during plant functional responses to Holocene climate warming. Location: North America. Time period: 14-0 ka. Major taxa studied: Terrestrial plants. Methods: We joined global trait data with palaeoecological time series and climate simulations on 425 sites. We estimated plant community functional composition for three leaf traits involved in resource use. We then quantified disequilibrium in plant trait temporal responses to climate change during two contrasted periods: a period of high climate variability (14-7 ka) and a period of low climate variability (7-0 ka). Results: Functional trait composition showed consistent deviation from climatic equilibrium during both periods. The temporal dynamics of trait composition tends to be positively correlated with climate equilibrium expectations during Holocene climate warming (14-7 ka), but not during a subsequent period of low climate variability (7-0 ka). Main conclusions: Long-term functional responses of plants to climate change showed mixed evidence for both equilibrium and disequilibrium responses. Temporal trait dynamics were closer to the expectations of spatial dynamics under high climate variability, indicating that the relevance of space-for-time substitution might be dependent, in part, on climate variability. Our results also suggest that current mismatches between trait and climatic conditions might arise because of a divergence of factors influencing trait dynamics during periods of low climate variability. These findings provide a counterpoint to the common assumption that contemporary traitclimate mismatches result from lagged responses to past climate warming. Our study also demonstrates the need for a deeper investigation of the potential influence of non-climatic factors on functional plant community dynamics. | 2053 GAÜZÈRE Et Al.

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

“…Conversely, positive deviation indicates a population relatively small but with higher growth rate than expected for this size. This approach is in line with recent empirical studies showing mismatches between species distributions and performance (Bohner and Diez 2020) in one hand, and between temporal and spatial patterns (Gaüzère et al 2020a) on the other hand. Thus, our approach stands for overall population size, but also for species‐scale population sizes, community‐scale measures such as species richness or biomass, or more generally for any relevant ecological metric that can be computed in space and time.…”

“…Those observations are in line with the positive versus negative influence of global changes on the species depending on their traits (Julliard et al 2003). Such patterns suggest that differential responses of species population depend on their sensitivity to climate and land use changes (Julliard et al 2003, Jiguet et al 2007), and on complex trait–environment relationships that differ in space and time (Gaüzère et al 2020a). This variability complexifies the interpretation of environmental drivers, but also suggests that the effects of our set of predictors on space–time deviations are structuring at community level.…”

“…This space‐for‐time substitution is commonly used to infer temporal dynamics from spatial patterns (Fukami and Wardle 2005, La Sorte et al 2009) and has been extensively used to explain and predict the effects of global change on biodiversity, for example via species distribution modelling (SDM) applied to future scenarios of climate or land use changes. Although it is relevant to rely on space‐for‐time substitution in several specific situations (Walker et al 2010, Blois et al 2013, Gaüzère et al 2020a), many studies have emphasized substantial deviations between spatial patterns and temporal ecological dynamics (Johnson and Miyanishi 2008). For example, changing environmental conditions over time coupled with long organismal lifespans allows species to persist within suboptimal environmental conditions (Bisbing et al 2022021).…”

“…Depending on the rate of environmental change, taxa characteristics and temporal processes at stake (Blonder et al 2017), biodiversity responses can be synchronous (Adriaens et al 2006), lagged (Brooks et al 1999, Ovaskainen and Hanski 2002) or uncorrelated (Gaüzère et al 2018) with temporal environmental change (Pironon et al 2017). Such mismatches in biotic responses to environmental changes might create deviations between spatial and temporal ecological patterns (Halley et al 2016, Gaüzère et al 2018, 2020a).…”

“…Many studies have questioned the relevance of space‐for‐time substitution approaches to describe and forecast biodiversity dynamics (Blois et al 2013, Bonthoux et al 2013), but the potential meaning of the deviation between spatial patterns and temporal dynamics has received less attention. Recent theoretical developments in disequilibrium ecology (Blonder et al 2017) and their empirical application (Gaüzère et al 2018) suggest that this deviation can inform on the disequilibrium state of a community (Gaüzère et al 2020a). These approaches, however, consider a single environmental variable (e.g.…”