Climate change and the global redistribution of biodiversity: substantial variation in empirical support for expected range shifts

Abstract

Background: Among the most widely predicted climate change-related impacts to biodiversity are geographic range shifts, whereby species shift their spatial distribution to track their climate niches. A series of commonly articulated hypotheses have emerged in the scientific literature suggesting species are expected to shift their distributions to higher latitudes, greater elevations, and deeper depths in response to rising temperatures associated with climate change. Yet, many species are not demonstrating range shifts consistent with these expectations. Here, we evaluate the impact of anthropogenic climate change (specifically, changes in temperature and precipitation) on species' ranges, and assess whether expected range shifts are supported by the body of empirical evidence.

Methods: We conducted a Systematic Review, searching online databases and search engines in English. Studies were screened in a two-stage process (title/abstract review, followed by full-text review) to evaluate whether they met a list of eligibility criteria. Data coding, extraction, and study validity assessment was completed by a team of trained reviewers and each entry was validated by at least one secondary reviewer. We used logistic regression models to assess whether the direction of shift supported common range-shift expectations (i.e., shifts to higher latitudes and elevations, and deeper depths). We also estimated the magnitude of shifts for the subset of available range-shift data expressed in distance per time (i.e., km/decade). We accounted for methodological attributes at the study level as potential sources of variation. This allowed us to answer two questions: (1) are most species shifting in the direction we expect (i.e., each observation is assessed as support/fail to support our expectation); and (2) what is the average speed of range shifts?

Review findings: We found that less than half of all range-shift observations (46.60%) documented shifts towards higher latitudes, higher elevations, and greater marine depths, demonstrating significant variation in the empirical evidence for general range shift expectations. For the subset of studies looking at range shift rates, we found that species demonstrated significant average shifts towards higher latitudes (average = 11.8 km/dec) and higher elevations (average = 9 m/dec), although we failed to find significant evidence for shifts to greater marine depths. We found that methodological factors in individual range-shift studies had a significant impact on the reported direction and magnitude of shifts. Finally, we identified important variation across dimensions of range shifts (e.g., greater support for latitude and elevation shifts than depth), parameters (e.g., leading edge shifts faster than trailing edge for latitude), and taxonomic groups (e.g., faster latitudinal shifts for insects than plants).

Conclusions: Despite growing evidence that species are shifting their ranges in response to climate change, substantial variation exists in the extent to which definitively empirical observations confirm these expectations. Even though on average, rates of shift show significant movement to higher elevations and latitudes for many taxa, most species are not shifting in expected directions. Variation across dimensions and parameters of range shifts, as well as differences across taxonomic groups and variation driven by methodological factors, should be considered when assessing overall confidence in range-shift hypotheses. In order for managers to effectively plan for species redistribution, we need to better account for and predict which species will shift and by how much. The dataset produced for this analysis can be used for future research to explore additional hypotheses to better understand species range shifts.

Keywords: Depth; Distribution shift; Elevation; Global change; Latitude; Species redistribution; Vulnerability; Warming.

Fig. 1

Systematic Review workflow diagram

Fig. 2

Typology of range shifts used in this review. Leading edge or center of range increases and trailing edge decreases were considered to support our temperature-related range shift hypotheses. Lack of shifts in any parameter; decreases on the leading edge or in the mean/optimum; and increases on the trailing edge were all considered “fail to support”

Fig. 3

a Distribution of observations in the Database. An evaluation of how observations are distributed in the database, including by dimension, parameter, hemisphere, ecosystem type, and taxonomic group. Note: longitudinal shifts were considered only for precipitation-related analysis. b Global Distribution of Species in the Database. Counts reflect number of species assessed, rather than individual studies, represented in 1degree cells. Darker colors reflect more species

Fig. 3

a Distribution of observations in the Database. An evaluation of how observations are distributed in the database, including by dimension, parameter, hemisphere, ecosystem type, and taxonomic group. Note: longitudinal shifts were considered only for precipitation-related analysis. b Global Distribution of Species in the Database. Counts reflect number of species assessed, rather than individual studies, represented in 1degree cells. Darker colors reflect more species

Fig. 4

Model Results for temperature hypotheses. Estimated marginal mean probability and 95% confidence intervals of support for shifts poleward, upward, and deeper across dimensions (top left), ecosystem types (top right), parameters (bottom left), and taxonomic groups (bottom right); i.e., the predicted probability of support/fails to support after averaging across the methodological variables weighted proportionally to their occurrence in the original dataset. Letters show significant differences (p = 0.05) across within a given plot using post-hoc Tukey correction

Fig. 5

Magnitude of Shift. Estimated shifts by dimension (depth, elevation, and latitude) and by taxonomic group. Estimates by dimension (top row) show average range shifts by dimension, with 95% confidence intervals derived from single-dimension one-sample t-tests (Additional File 5: Table S7). Estimates by taxonomic group (bottom row) display estimated marginal means and associated 95% confidence intervals (Additional File 5: Table S8)