Biodiversity trends are stronger in marine than terrestrial assemblages

  1. Shane Blowes
  2. Sarah Supp
  3. Laura Antão
  4. Amanda Bates
  5. Helge Bruelheide
  6. Jon Chase
  7. Faye Moyes
  8. Anne Magurran
  9. Brian McGill
  10. Isla Myers-Smith
  11. Marten Winter
  12. Anne Bjorkman
  13. Diana Bowler
  14. Jarrett E.K. Byrnes
  15. Andrew Gonzalez
  16. Jes Hines
  17. Forest Isbell
  18. Holly Jones
  19. Laetitia M. Navarro
  20. Patrick Thompson
  21. Mark Vellend
  22. Conor Waldock
  23. Maria Dornelas

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Abstract

Human activities have fundamentally altered biodiversity. Extinction rates are elevated and model projections suggest drastic biodiversity declines. Yet, observed temporal trends in recent decades are highly variable, despite consistent change in species composition. Here, we uncover clear spatial patterns within this variation. We estimated trends in the richness and composition of assemblages in over 50,000 time-series, to provide the most comprehensive assessment of temporal change in biodiversity across the planet to date. The strongest, most consistent pattern shows compositional change dominated by species turnover, with marine taxa experiencing up to fourfold the variation in rates of change of terrestrial taxa. Richness change ranged from no change to richness gains or losses of ~10% per year, with tropical marine biomes experiencing the most extreme changes. Earth is undergoing a process of spatial reorganisation of species and, while few areas are unaffected, biodiversity change is consistently strongest in the oceans.

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  1. PREreview

    This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/7728068.

    OIST E&E PREreview JC "Biodiversity trends are stronger in marine than terrestrial assemblages"

    Biodiversity trends are stronger in marine than terrestrial assemblages

    Shane Blowes, Sarah Supp, Laura Antao, Amanda Bates, Helge Bruelheide, Jonathan Chase, Faye Moyes, Anne Magurran, Brian McGill, Isla Myers-Smith, Marten Winter, Anne Bjorkman, Diana Bowler, Jarrett EK Byrnes, Andrew Gonzalez, Jes Hines, Forest Isbell, Holly Jones, Laetitia Navarro, Patrick Thompson, Mark Vellend, Conor Waldock, Maria Dornelas

    bioRxiv, October 30th, 2018

    doi: https://doi.org/10.1101/457424

    Overview and take-home messages:

    Blowes et al. tackle an impressive and large undertaking in this paper by attempting to disentangle global biodiversity trends through a meta-analysis of data from 358 studies. By dividing the available data by biome and taxa, the authors were able to detect different biodiversity trends in marine and terrestrial biomes. Tropical marine biomes, particularly the Caribbean, have a more negative deviation from the mean trend in species richness and more positive deviations from the overall trend in species turnover--species are turning over more quickly in marine biomes. The analyses demonstrate that mean local species richness is not decreasing, but many individual regions deviate significantly from the overall mean. The results have important implications for how we discuss changes in biodiversity in the anthropocene, but it is important to make clear that locally static species richness does not equate to globally static species richness, and species are going extinct at an alarming rate. Overall, this paper presents careful analyses and is clearly written, however, there are a few issues that, if addressed, we feel could improve future versions of the manuscript.  

    Major concerns:

    • The authors make excellent use of a public, curated time-series database to facilitate this study. A major limitation in interpreting the results is the uneven distribution of data across regions (33 marine biomes v. 10 terrestrial and 5 freshwater) and the gap in data from tropical terrestrial ecosystems. It is feasible that inclusion of tropical terrestrial systems would change the mean trend in local species richness and eliminate the differential deviance between marine and terrestrial biomes from the overall trend. While we understand that including tropical terrestrial ecosystems in the current analysis is probably not possible, we would appreciate more discussion of both the cause and effects of this limitation. Why are data unavailable for tropical terrestrial systems? Have they not been collected or did they not meet the selection criteria for the database? While selection criteria for the database is likely discussed in the publication describing its initiation, it may be helpful to readers to briefly describe how data was selected for inclusion in the database and the current study.

    • The authors clearly state that baseline availability and selection is a major issue in time-series studies and they did an impressively thorough job in their sensitivity analyses examining the effect of baseline selection on their results. Regardless, it is extremely difficult to compare studies with such varied lengths as 2-95 years and the length of the time series should affect the change in biodiversity observed. While it would cause an undesired reduction in data, we are curious if the authors considered pruning the data to include studies that cover a minimum number of years within a specified time period (e.g. at least 10 years of observations with at least 1 observation before 1980). We are curious how many studies would pass such filters and how it would affect the results. Alternatively, baselines might be set to the mean richness in all observations for a given time-series with changes in richness as the difference from the mean rather than the difference from an earlier observation. This method has been used to assess the impact of extreme events, such as hurricanes, on community compositions. 

    • While ecologically fascinating that the mean local species richness is not changing over time, it could easily be conflated with global species richness remaining unchanged if the paper is not read carefully. We are slightly concerned that non-specialist readers, including the press, may interpret the results to mean that global biodiversity is not decreasing and use the paper in rhetoric challenging the reality of climate change. Lines 311-314 are paramount to this work, and deserve potentially even more emphasis, but we feel some treatment of the difference between the subject of the study (changes in local species richness) and global extinction rate could be useful. Despite the results presented here, climate change is causing species extinction (?). If there are global species richness/abundance data available, it could be helpful to include or discuss them.

    Minor concerns:

    • The first paragraph of the discussion adeptly summarizes the most important and interesting findings of this study. It may be helpful to highlight this finding in the title.

    • In figures 2 and 4 the backgrounds of the individual density ridges are opaque instead of transparent and therefore occlude other data and the grey shading for the confidence interval. Figures 2 and 4 may be more clear to readers if the biomes in panel a are sorted by latitudinal band to match the sorting in panel b. Visually distinguishing realms in panel a could also be improved. Several members of our group initially thought it was a mistake that the space next to "marine" in the Realm legend was blank. Authors may consider distinguishing realms with 3 more distinct line types.

    • In figure 5, panel b, we believe that the color should be set to discrete rather than continuous. Our interpretation of the description of these results calls for 2 shades of blue and 2 shades of green, but there appear to be 3+ shades of blue and green.

    • On line 69, "reliable" should be "reliably."

    • We found it extremely interesting that the overall trend in biodiversity loss was not significantly different than zero. It is absolutely fascinating that while global biodiversity is decreasing, local biodiversity is essentially remaining the same due to species turnover. We would love to hear more of the authors interpretation possible consequences. We are especially curious about what these results may mean for ecosystem function over time. Do the authors feel that that ecosystem function will be maintained even in an era of extinction due to this turnover effect?  

    It was a great pleasure reading this interesting and exciting work and we are extremely grateful to the authors for posting it as a preprint on bioRxiv and for their obvious commitment to open, reproducible science. In addition to most of the data used in this paper being available in a public data base, the code for the analyses is extremely well commented and available on Zenodo. Meta-analyses like this, while difficult, are absolutely necessary to illuminate larger ecological trends, and we thoroughly appreciate the effort made here. We sincerely hope that our comments are useful to the authors and we look forward to reading the final version when it is published. 

    Very best wishes,

    The OIST Ecology and Evolution Preprint Journal Club

  2. Version published to 10.1101/457424v1 on bioRxiv