Protected areas (PAs) are the primary strategy for slowing terrestrial biodiversity loss. Although expansion of PA coverage is prioritized under the Convention on Biological Diversity, it remains unknown whether PAs mitigate declines across the tetrapod tree of life and to what extent land cover and climate change modify PA effectiveness1,2. Here we analysed rates of change in abundance of 2,239 terrestrial vertebrate populations across the globe. On average, vertebrate populations declined five times more slowly within PAs (−0.4% per year) than at similar sites lacking protection (−1.8% per year). The mitigating effects of PAs varied both within and across vertebrate classes, with amphibians and birds experiencing the greatest benefits. The benefits of PAs were lower for amphibians in areas with converted land cover and lower for reptiles in areas with rapid climate warming. By contrast, the mitigating impacts of PAs were consistently augmented by effective national governance. This study provides evidence for the effectiveness of PAs as a strategy for slowing tetrapod declines. However, optimizing the growing PA network requires targeted protection of sensitive clades and mitigation of threats beyond PA boundaries. Provided the conditions of targeted protection, adequate governance and well-managed landscapes are met, PAs can serve a critical role in safeguarding tetrapod biodiversity.
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All data were from open sources listed in Supplementary Table 15. Population time series are from living datasets and are freely accessible from the Living Planet Index database at www.livingplanetindex.org and the BioTIME database at http://biotime.st-andrews.ac.uk/. The WorldClim climate data used in this study are available from www.worldclim.org, and the land cover data are available from https://luh.umd.edu for land use harmonization data and www.esa-landcover-cci.org for ESA CCI land cover products. The final harmonized datasets analysed in this study are available on Figshare: https://doi.org/10.6084/m9.figshare.14821644.
The code for the main statistical models presented in this study is available on Figshare: https://doi.org/10.6084/m9.figshare.14821644.
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We thank the many scientists and organizations that funded, collected and made available the open data underlying this study. We are also grateful to WWF and the Zoological Society of London for curating the Living Planet database and to the BioTIME team for maintaining the BioTIME database. L. M’Gonigle provided technical feedback on the manuscript. A.J.N. was supported by a joint Smithsonian-Conservation International Postdoctoral Fellowship.
The authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Distributions of vertebrate population time series and the mean effect of protected areas (PAs) on vertebrate population trends across latitudinal zones (n = 2,239 time series).
Histograms show the frequency of time series in the harmonized dataset for all taxa (a), amphibians (n = 159) (b), reptiles (n = 81) (c), birds (n = 1,368) (d), and mammals (n = 631) (e). PA impact – estimated as the difference between mean population trends inside versus outside PAs – does not differ significantly between temperate and tropical zones (f) (Supplementary Table 9). Error bars are 95% Bayesian credible intervals and violin plots represent 500 samples of the posterior for each estimate. The map shows the distribution of population time series in temperate (blue) and tropical (orange) regions (g). Bird and mammal silhouettes © 2003-2023 Shutterstock, Inc. Landmasses in map displayed using Natural Earth data (https://www.naturalearthdata.com).
Extended Data Fig. 2 The mean effect of protected areas (PAs) on vertebrate population trends does not differ across biogeographic realms (n = 2,239 time series).
Estimated PA impact is the difference between mean population trends inside versus outside PAs for each biogeographic realm (a). Realms with few time series – Antarctic, Indo-Malay, and Oceanic realms – were combined with adjacent realms. Error bars are 95% Bayesian credible intervals and violin plots represent 500 samples of the posterior for each estimate. The map shows the distribution of population time series in each realm (b). Landmasses in map displayed using Natural Earth data (https://www.naturalearthdata.com).
Extended Data Fig. 3 Age, area, and type of protected areas had negligible effect on trends (n = 930 time series).
We evaluated the effect of age, area, and type (IUCN category) of protected areas (PAs) on vertebrate trends using a multilevel model wherein we controlled for variables used in pre-analysis matching in addition to governance, regional rates of climate change, and land use change. The model was fit to a subset of population trends that occurred only within PAs. Records with missing values for PA age or area were excluded from the analysis. Points represent mean estimates from a multilevel model and error bars represent 80% (thick) and 95% (narrow) Bayesian credible intervals. Asterisks indicate statistical support for effects – 95% BCIs exclude zero.
Extended Data Fig. 4 The effect of protected areas (PAs) on mean trends within each vertebrate class does not differ significantly between temperate and tropical zones (n = 2,239 time series).
Estimated PA impact is the difference between mean population trends inside PAs (circles) versus outside PAs (triangles) for each class. Error bars are 95% Bayesian credible intervals (BCI) and violin plots represent 500 samples of the posterior for each estimate. 95% BCIs include 0 for all interaction terms.
Extended Data Fig. 5 The effect of protected areas (PAs) on mean trends within each vertebrate class does not vary significantly across biogeographic realms (n = 2,239 time series).
Estimated PA impact is the difference between mean population trends inside PAs (circles) versus outside PAs (triangles) for each biogeographic realm. 95% BCIs include 0 for all interaction terms. Realms with few time series – Antarctic, Indo-Malay, and Oceanic realms – were combined with adjacent realms. Error bars are 95% Bayesian credible intervals and violin plots represent 500 samples of the posterior for each estimate. The map shows the distribution of population time series in each realm. Landmasses in map displayed using Natural Earth data (https://www.naturalearthdata.com).
Extended Data Fig. 6 Responses of terrestrial vertebrates to converted land cover across latitudinal zones and between non-threatened and threatened species (n = 1,721 time series).
(a) Amphibians and reptiles responded more negatively to converted land cover, irrespective of site protection, in tropical than in temperate zones (Supplementary Table 10). (b) Threatened birds experienced greater declines in landscapes with greater proportions of converted land cover, irrespective of site protection (Supplementary Table 11). Threatened taxa in other classes were not more sensitive to habitat conversion; though, samples sizes of threatened species were small for amphibians and reptiles. To examine effects of converted land cover across latitudinal zones and by threatened status, we modeled the interactive effect of class, zone (or IUCN status), and land cover on population trends. Converted land cover was measured as the mean proportion of anthropogenic habitats within a 10 km radius around each site. Symbols represent mean trends of individual time series estimated from a multilevel model. Transparent symbols are estimates that are indistinguishable from zero. Error bars are 95% credible intervals. Heavy lines represent the mean predicted effect of land cover on population trends. Shaded areas represent 95% credible bands. Bird and mammal silhouettes © 2003-2023 Shutterstock, Inc.
Extended Data Fig. 7 Ectothermic and endothermic vertebrate classes exhibit different responses to climate change across latitudinal zones (n = 2,239 time series).
To examine whether responses of vertebrate classes to climate change differ between temperate and tropical zones, irrespective of site protection, we modeled the interactive effect of class, latitudinal zone, and climate change on population trends (a)(Supplementary Table 12). To examine whether responses of vertebrate classes to climate change differ between temperate and tropical zones and inside versus outside of protected areas (PAs), we modeled the interactive effect of class, PA, and climate change on population trends separately for tropical (b) and temperate zones (c). The negative effects of climate change on trends of tropical amphibians and reptiles are greater outside than inside of PAs (b). Symbols represent mean trends of individual time series estimated from a multilevel model. Transparent symbols are estimates that are indistinguishable from zero. Error bars are 95% credible intervals. Heavy lines represent the mean predicted effect of climate change on population trends. Shaded areas represent 95% credible bands. Bird and mammal silhouettes © 2003-2023 Shutterstock, Inc.
Extended Data Fig. 8 The overall positive effect of governance on population trends does not depend on class or whether a population was inside or outside of a protected area (PA) (n = 2,239 time series).
To examine whether national governance modifies PA effectiveness, we modeled the interactive effect of class, PA, and governance on population trends (Supplementary Table 13). Symbols represent mean trends of individual time series estimated from a multilevel model. Transparent symbols are estimates that are indistinguishable from zero. Error bars are 95% credible intervals. Heavy lines represent the mean predicted effect of governance on population trends. Shaded areas represent 95% credible bands. Bird and mammal silhouettes © 2003-2023 Shutterstock, Inc.
Extended Data Fig. 9 When analyzing only species with populations both inside and outside of protected areas (PAs), population trends remain higher overall in protected areas, again with the most prominent benefits for amphibians and birds (n = 1,356 time series).
Data were subset to 373 species for which population time series were available both inside and outside of PAs. Results from this narrower dataset are qualitatively consistent with those of the larger dataset of 1,032 species. We evaluated (a) the overall effect of protected areas on vertebrate trends and (b) whether all terrestrial vertebrate classes benefit equally from PAs. We used multilevel models wherein we controlled for variables used in pre-analysis matching in addition to governance, regional rates of climate change, and land cover change. To evaluate whether all vertebrate lineages benefit equally from PAs (b), we modeled the interactive effect of class and PA on population trends. Points represent mean estimates from a multilevel model and error bars represent 80% (wide) and 95% (narrow) Bayesian credible intervals (BCI). Asterisks indicate statistical support for effects and contrasts – 95% BCIs exclude zero. In panel b, small symbols represent individual population trends, and transparent symbols are estimates that are indistinguishable from zero.
This file contains supplementary methods, discussion, data figures, tables and references. Supplementary methods: description of analyses of climate velocity, an extended description of model structure and evaluation of the sensitivity of analyses to different modelling decisions. Supplementary discussion: extended discussion of main results, discussion of results from analyses of effects of precipitation changes and climate velocity on population trends, and the value of multiple biodiversity metrics for assessing protected area effectiveness. Supplementary data: display items 1–13 show summaries of the evidence base for the effectiveness of protected areas, variation in population trend estimates from the current study, estimates of land cover effects at different spatial extents, correlations among covariates, evaluation of model fit and assessment of spatial autocorrelation. Supplementary Tables: Tables 1–15 provide summaries of the datasets and model estimates.
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Justin Nowakowski, A., Watling, J.I., Murray, A. et al. Protected areas slow declines unevenly across the tetrapod tree of life. Nature 622, 101–106 (2023). https://doi.org/10.1038/s41586-023-06562-y