Space can substitute for time in predicting climate-change effects on biodiversity

Abstract

"Space-for-time" substitution is widely used in biodiversity modeling to infer past or future trajectories of ecological systems from contemporary spatial patterns. However, the foundational assumption-that drivers of spatial gradients of species composition also drive temporal changes in diversity-rarely is tested. Here, we empirically test the space-for-time assumption by constructing orthogonal datasets of compositional turnover of plant taxa and climatic dissimilarity through time and across space from Late Quaternary pollen records in eastern North America, then modeling climatedriven compositional turnover. Predictions relying on space-for-time substitution were ∼72% as accurate as "time-for-time" predictions. However, space-for-time substitution performed poorly during the Holocene when temporal variation in climate was small relative to spatial variation and required subsampling to match the extent of spatial and temporal climatic gradients. Despite this caution, our results generally support the judicious use of space-for-time substitution in modeling community responses to climate change.fossil pollen | global change | paleoecology | generalized dissimilarity modeling V iewed broadly, space-for-time substitution encompasses analyses in which contemporary spatial phenomena are used to understand and model temporal processes that are otherwise unobservable, most notably past and future events. Many fields have developed and debated methods relying on space-for-time substitution, such as ecological chronosequences to study longterm nutrient cycling and plant succession (1-3) and transfer functions for inferring past environmental changes from geological proxies (4, 5). The assumption of space-for-time substitutability has been queried and debated most closely in chronosequence studies, with conclusions ranging from strong support (6) to strong rejection (2) of space-for-time substitution. Increasingly, space-for-time substitution is being applied in biodiversity modeling to project climate-driven changes in species distributions, species richness, and compositional turnover (7-11). Examination of transferability of models for individual species has exposed concerns regarding the projection of these spatial models across time (12-15), and it has been suggested that models based on collective biodiversity properties might be more robust (9,16,17). However, the fundamental assumption that spatial relationships between climate and biodiversity can be used to project temporal trajectories of biodiversity under changing climates remains largely untested (but see refs. 16 and 18).The turnover of species among communities is particularly well suited for testing space-for-time substitution because it can be quantified independently across space or through time and because compositional turnover strongly correlates to climate variations in both space and time (19)(20)(21). However, other factors, such as species history, site history, and species interactions, also influence compositional turnover, independently or...

Effects of increased temperature on plant communities depend on landscape location and precipitation

“…These effects could be related to differences in biophysical properties of the soil (Elmendorf et al., 2015) or to differences in species composition between the two locations. Some studies point to space‐for‐time substitution, that is, the study of spatial variation such as ecosystems existing across a gradient in field age or up a mountainside, as insight into the potential impact of the same variations over time, such as succession or global changes, as a helpful approach to understanding impacts of future climate change (Blois, Williams, & Fitzpatrick, 2013), but see (Metz & Tielbörger, 2016). If space‐for‐time is applicable in our system, then we would expect the warmer, drier upper slope to support a plant community predictive of future, climate‐induced changes on the lower slope.…”

Community ecology in a changing environment: Perspectives from the Quaternary

“…A growing body of work has demonstrated that environmental variability affects species diversity on short time scales (33,101,102), suggesting a species-time relationship (103) as an analog to the species-area relationship. However, key differences between spatial and temporal processes imply that they may have unique diversity-scaling relationships (103,104). In addition, space and time constrain one another, motivating theoretical formulation and empirical testing of integrated species-time-area relationships (103, 105).…”

Deoxygenation alters bacterial diversity and community composition in the ocean’s largest oxygen minimum zone

“…Although no approach can completely mimic large-scale global changes such as ocean deoxygenation, use of natural gradients to 'substitute space for time' is a robust approach for modelling ecological responses to environmental change 21 ; ocean deoxygenation research has examined the distribution of organisms along oxygen gradients in present OMZs, and related these data to historical deoxygenation 3 . Our approach is analogous, and our OMZ transect captures variation in DO with limited variation in other respects.…”