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Turtle biodiversity losses suggest coming sixth mass extinction

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Abstract

Biodiversity losses in the face of climate change are among the most important issues facing humanity today. Vertebrate extinction is at an all-time high, and losses of reptiles are no exception. The turtles are a unique vertebrate group of grave conservation concern. I compared recent declines in turtle biodiversity to the losses of Testudinata (Cryptodira + Pleurodira) and non-dinosaurian reptiles during the most recent mass extinction. Fuzzy arithmetic was used because of its suitability to deal with uncertainty in these kinds of data sets and the questions that arise with comparing geological data with those from recent times. This revealed that extinctions of turtles in modern times massively exceed losses observed at the Cretaceous–Paleogene border. Further, if turtle extinctions continued at their current level, massive losses of these charismatic animals could occur within our lifetime and loss of the entire group could occur in just a few centuries. We must ask ourselves, how much more can we lose before we also disappear.

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Data Availability

All data are publicly available from the IUCN Red List of Threatened and Endangered Species. This author was responsible for all aspects of this manuscript.

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Funding

The study was self-funded and it did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

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  1. Department of Agriculture and Natural Resources, Langston University, Langston, OK, 73050, USA

    Malcolm L. McCallum

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  1. Malcolm L. McCallum
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Appendix

Appendix

Minimum percentage of extant turtle species that became extinct since 1500

$$\left( {N_{{\text{recent extinctions}}} /N_{{\text{extant species}}} } \right)\; \times \;{1}00$$

Point estimate

$$\left( {{9}/{258}} \right)\; \times \;{1}00\; = \;{3}.{48}\%$$

Fuzzy estimate

$${\text{Recent Extinctions}}\; = \;\left[ {{\text{N}}\;{-}\;{1}0\% ,{\text{ N}},{\text{ N}}\; + \;{1}0\% } \right]$$
$${\text{Extant species }} = \, \left[ {{\text{evaluated }}{-}{ 1}0\% ,{\text{ evaluated}},{\text{ described}},{\text{ described }} + { 1}0\% } \right]$$
$$\left( {\left[ {{8}.{1},{ 9},{ 9}.{9}} \right]/\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]} \right)\; \times \;{1}00\; = \;\left[ {{2}.{85},{ 3}.{49},{ 4}.{26}} \right]\%$$

Number of extinctions expected since 1500 AD based on the marine invertebrate background extinction rate

(Nspecies/Nall species) × marine invertebrate background extinction rate × 513 years.

Point estimate

$$\left( {{258}/{14,}00,000} \right))\; \times \;\left( {0.{25}/{1}0,00,000} \right)\; \times \;{513}\; = \;0.000{18428}\; \times \;0.000000{25}\; \times \;{513}\; = \;{2}.{36}\; \times \;{1}0^{{ - {8}}}$$

Fuzzy estimate

$$\begin{gathered} \left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]/\left[ {{12,6}0,000,\;\;{14,}00,000,\;\;{1,}00,00,000} \right]} \right) \times \left( {0.{25}/{1}0,00,000} \right)\; \times \;{\text{513 years}}\; \hfill \\ = \;\left[ {{2}.{98}\; \times \;{1}0^{{ - {9}}} ,{ 2}.{36}\; \times \;{1}0^{{ - {8}}} ,{ 2}.{89}\; \times \;{1}0^{{ - {8}}} } \right]{\text{ expected turtle extinctions since 15}}00{\text{ AD}} \hfill \\ \end{gathered}$$

Per taxon rate of extinction (per million species years) since 1500 AD

\(\left( {N_{{{\text{extinctions}}}} /N_{{{\text{species}}}} } \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 years}}} \right)\; = \;{\text{per taxon rate}}\)(the N that would go extinct in 1 MY given the available number of turtle species with potential to go extinct).

Point estimate

$$\left( {{9}.0/{258}} \right)\; \times \;\left( {{1}0^{{6}} /{513}} \right)\; = \;{\text{68 species}}/{\text{1 MY}}.$$
$$\left( {\left[ {{8}.{1},{ 9}.0,{ 9}.{9}} \right]/\left[ {{232}.{2},{ 258},{ 283}.{8}} \right)} \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 years}}} \right)\; = \;\left[ {{55},{ 68},{ 83}} \right]{\text{ extinctions in 1 MY}}$$

Comparison of post-1500 extinctions to K–Pg extinction rate

$$\left( {\left[ {N_{{{\text{extinctions}}}} \; \times \;{\text{CI}}} \right]} \right)/\left( {\left[ {N_{{\text{extant species}}} } \right]\; \times \;\left( {{\text{CI}}\; \pm \;{1}0\% } \right)} \right]\; \times \;\left( {{1}0^{{6}} /{\text{T}}_{{{\text{obs}}}} } \right)\; \times \;\left( {{1}/{\text{R}}_{{{\text{K}} - {\text{Pg}}}} } \right)$$

There are three available estimates for completedness for turtles (Suppl. 1).

RK–Pg = [0.1, high estimate, high estimate × 1.1] (there are eight estimates) (0.1 was substituted for zero for RK–Pg to avoid dividing by zero).

Point estimate

$$\left( {{\text{9}\; \times \; }0.{7}0{4}} \right)/\left( {{\text{258}\; \times \;}0.{7}0{4}} \right)\; \times \;\left( {{1}0^{{6}} /{513}} \right)\; \times \;\left( {{1}/0.{73}} \right)\; = \;{99}.{\text{24 times K}} - {\text{Pg}}$$

Fuzzy estimate

$$\begin{gathered} \left( {\left( {\left[ {{8}.{1},{ 9}.0,{ 9}.{9}} \right] \, \times \, \left[ {0.{684},\;0.{7}0{4},\;0.{75}0,0.{8}0{2}} \right]} \right)/\left( {\left[ {{3297},\;{3663},\;{9547},\;{1}0{5}0{2}} \right]\; \times \;\left[ {0.{575},\;0.{7}0{4},\;0.{75}0,\;0.{825}} \right]} \right)} \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 yr}}} \right)\; \times \hfill \\ \, \left( {{1}/\left[ {0.{1},0.{11},0.{73},0.{83}} \right]} \right)\; = \;\left[ {{57},{ 87},{ 658},{ 916}} \right]{\text{ times K}} - {\text{Pg}}. \hfill \\ \end{gathered}$$

Comparison of post-1500 extinctions to K–Pg extinction rate for each taxon with data deficient species included

$$\left( {\left( {\left[ {N_{{\text{taxon extinctions}}} \; \times \;{\text{CI}}} \right]\; + \;\left[ {N_{{\text{data deficient}}} } \right]} \right)/\left[ {{\text{N}}_{{\text{extant species}}} \; \times \;\left( {{\text{CI}}\; \pm \;N_{{\text{data deficient}}} } \right)} \right]} \right)\; \times \;\left( {{1}0^{{6}} /{\text{T}}_{{{\text{obs}}}} } \right)\; \times \;\left( {{1}/{\text{R}}_{{{\text{K}} - {\text{Pg}}}} } \right)$$

Point estimate

$$\left( {\left( {{9}*0.{75}0} \right)/{258}} \right)\; \times \;\left( {0.{75}0} \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 yr}}} \right)\; \times \;\left( {{1}/0.{22}} \right)\; = \;{\text{174 times K}} - {\text{Pg}}$$

Fuzzy estimate

$$\begin{gathered} \left( {\left( {\left[ {{8}.{1},{ 9}.0,{ 2}0} \right] \, \times \, \left[ {0.{684}, \, 0.{7}0{4}, \, 0.{75}0, \, 0.{8}0{2}} \right]} \right)/\left( {\left[ {{247},{ 258},{ 269}} \right]\; \times \;\left[ {0.{575},0.{7}0{4},0.{75}0,0.{825}} \right]} \right)} \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 yr}}} \right)\; \times \;\left( {{1}/\left[ {0.0{7}, \, 0.{22}, \, 0.{75}} \right]} \right) \hfill \\ \; = \;\left[ {{65},{ 29}0,{ 329},{ 3145}} \right]{\text{ times K}} - {\text{Pg}} \hfill \\ \end{gathered}$$

Comparison of post-1500 extinctions to K-Pg extinction rate with data deficient, and impaired species included

$$\left( {\left( {\left( {\left[ {N_{{{\text{extinctions}}}} } \right]\; \times \;{\text{CI}}} \right)\; + \;\left[ {N_{{\text{data deficient}}} } \right]\; + \;\left( {\left[ {N_{{\text{impaired species}}} } \right]\; \times \;{\text{CI}}} \right)} \right)/\left[ {N_{{\text{extant species}}} } \right]\; \times \;\left( {{\text{CI }} \pm { 1}0\% } \right)} \right)\; \times \;\left( {{1}0^{{6}} /{\text{T}}_{{{\text{obs}}}} } \right)\; \times \;\left( {{1}/_{{{\text{RK}} - {\text{Pg}}}} } \right)$$

There are three available estimates for completedness (Suppl. 1).

RK–Pg = [0.1, high estimate, high estimate × 1.1] (there are seven estimates).

Point estimate

$$\left( {\left( {{171}\; \times \;0.{75}0} \right)/\left( {{258}\; \times \;0.{75}} \right)} \right)\; \times \;\left( {{1}0^{{6}} /{513}} \right)\; \times \;\left( {{1}/0.{22}} \right)\; = \;{\text{5873 times K}} - {\text{Pg}}.$$

Fuzzy estimate

$$\begin{gathered} \left( {\left( {\left( {\left[ {{154},{ 171},{ 182}} \right]} \right) \times \, \left[ {0.{684},0.{7}0{4},0.{75}0,0.{8}0{2}} \right]} \right)/\left( {\left[ {{247},{258},{ 269}} \right] \, \times \, \left[ {0.{575},0.{7}0{4},0.{75}0,0.{825}} \right]} \right)} \right) \, \\ \quad \quad \quad \times \, \left( {{1}0^{{6}} /{\text{513 yr}}} \right) \, \times \, \left( {{1}/\left[ {0.0{7}, \, 0.{22}, \, 0.{75}} \right]} \right) \, \hfill \\ \quad \quad \quad = \, \left[ {{1234},{ 5512},{ 6256},{ 28619}} \right] \hfill \\ \end{gathered}$$

Number of extinctions expected since 1500 AD based on the marine invertebrate background extinction rate

$$\left( {N_{{\text{turtle species}}} /N_{{\text{extant species}}} } \right)\; \times \;{\text{marine invertebrate background extinction rate}}\; \times \;{\text{513 years}}$$

Point estimate

$$\left( {{258}/{14,}00,000} \right)\; \times \;\left( {0.{25}/{1}0,00,000} \right)\; \times \;{\text{513 years }} = { 2}.{36}\; \times \;{1}0^{{ - {8}}} {\text{expected turtle extinctions in 513 years}}.$$

Fuzzy estimate

$$\begin{gathered} \left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]/\left[ {{12,6}0,000,\;\;{14,}00,000,\;\;{1,}00,00,000} \right]} \right)\; \times \;\left( {0.{25}/{1}0,00,000} \right)\; \\ \quad \quad \quad \times \;{\text{513 years}}\; = \; \left[ {{2}.{\text{98e}}^{{ - {9}}} ,{ 2}.{\text{36e}}^{{ - {8}}} ,{ 2}.{\text{89e}}^{{ - {8}}} } \right]{\text{ turtle extinctions}} \hfill \\ \quad \quad\quad {\text{ expected in 513 years}} \hfill \\ \end{gathered}$$

Per taxon rate of extinction (per million species years) since 1980 AD

\(\left( {N_{{\text{turtle extinctions}}} /N_{{\text{turtle species}}} } \right)\; \times \;\left( {{1}0^{{6}} /{\text{513 years}}} \right)\; = \;{\text{per taxon rate}}\) (the N expected to go extinct in 1 MY given the available number of species in that taxon with potential to go extinct).

Point estimate

$$\left( {{2}/{258}} \right)\; \times \;\left( {{1}0^{{6}} /{\text{39 years}}} \right)\; = \;{2}0{\text{6 species expected to go extinct in 1 MY}}.$$
$$\left( {\left[ {{1}.{8},{ 2}.0,{ 2}.{2}} \right]/\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]} \right)\; \times \;\left( {{1}0^{{6}} /{\text{39 years}}} \right)\; = \;\left[ {{168},{ 2}0{6},{ 252}} \right]{\text{ extinctions in 1 MY}}$$

Minimum post-1500 magnitude of extinction predicted per million years for each taxon

$$\left( {N_{{\text{recent turtle extinctions}}} /{\text{513 years}}} \right)\; \times \;{1}0^{{6}}$$

Point estimate

$$\left( {{9}/{513}} \right)*{1}0^{{6}} = \;{17},{544}$$

Fuzzy estimate

$$\left( {\left[ {{8}.{1},{9}.0,{9}.{9}} \right]/{513}} \right)\; \times \;\left( {{1}0^{{6}} } \right)\; = \;\left[ {{15,789},{ 17,544},{ 19,298}} \right]{\text{ extinctions in 1 MY}}$$

Years until turtle extinction based on post-1500 extinction rate

$$\left( {N_{{\text{extant species}}} \; \times \;{\text{513 years}}} \right)/{\text{ N}}_{{\text{recent turtle extinctions}}} )$$

Point estimate

$$\left( {{258}*{513}} \right)/{9}\; = \;{14},{7}0{\text{6 years}}$$

Fuzzy estimate

$$\left( {\left( {\left[ {{232}.{2},{ 258},{ 283}} \right]*{513}} \right)/\left[ {{8}.{1},{9},{9}.{9}} \right]} \right)\; = \;\left[ {{12,}0{32},{ 14,7}0{6},{ 17,923}} \right]{\text{ years}}$$

Years until total extinction based on post-1500 extinction including impaired and data deficient species as extinct

$$\left( {N_{{\text{extant turtle species}}} \; \times \;{\text{513 years}}} \right)/\left( {{\text{N}}_{{\text{recent turtle extinctions}}} \; + \;N_{{\text{impaired taxa}}} } \right)$$

Point estimate

$$\left( {{\text{258x513}}} \right)/\left( {{171}} \right) = \;{\text{774 years}}$$

Fuzzy estimate

$$\left( {\left( {\left[ {{232}.{2},\;\;{258},\;\;{283}.{8}} \right]*{513}} \right)/\left( {\left[ {{153}.{9},\;{171},\;{182}} \right]} \right)} \right)\; = \;\left[ {{654},{ 774},{ 946}} \right]{\text{ years}}$$

Minimum percentage of extant species that became extinct since 1980

$$\left( {N_{{\text{recent extinctions}}} /N_{{\text{extant species}}} } \right)\; \times \;{1}00$$

Point estimate

$$\left( {{2}/{258}} \right)\; \times \;{1}00\; = \;0.{7}\%$$

Fuzzy estimate

Recent Extinctions = [N – 10%, N, N + 10%].

Extant species = [evaluated – 10%, evaluated, described, described + 10%]

$$\left( {\left[ {{1}.{8},{ 2}.0,{ 2}.{2}} \right]/\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]} \right)\; \times \;{1}00\; = \;\left[ {0.{63}, \, 0.{78}, \, 0.{95}} \right]\%$$

Comparison of post-1980 extinctions to K-Pg extinction rate

$$\left( {\left[ {N_{{\text{turtle extinctions}}} \; \times \;{\text{CI}}} \right]/\left[ {N_{{\text{extant turtle species}}} } \right)\; \times \;\left( {{\text{CI }} \pm { 1}0\% } \right)} \right])\; \times \;\left( {{1}0^{{6}} /{\text{T}}_{{{\text{obs}}}} } \right)\; \times \;\left( {{1}/{\text{R}}_{{{\text{K}} - {\text{Pg}}}} } \right)$$

There are three available estimates for completedness (Suppl. 1).

RK–Pg = [0.1, high estimate, high estimate × 1.1] (there are eight estimates) (0.1 was substituted for zero for RK–Pg to avoid dividing by zero).

Point estimate

$$\left( {{2}/{258}} \right)*\left( {{1}0^{{6}} /{39}} \right)*\left( {{1}/0.{22}} \right)\; = \;{9}0{\text{3 times K}} - {\text{Pg}}$$

Fuzzy estimate

$$\begin{gathered} \left( {\left( {\left[ {{1}.{8},{ 2}.0,{ 2}.{2}} \right]\; \times \;\left[ {0.{684}, \, 0.{7}0{4}, \, 0.{75}0, \, 0.{8}0{2}} \right]} \right)/\left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]\; \times \;\left[ {0.{575}, \, 0.{7}0{4}, \, 0.{75}0, \, 0.{825}} \right]} \right)} \right)\; \\ \quad \quad \quad \times \;\left( {{1}0^{{6}} /{\text{39 years}}} \right)\; \times \;\left( {{1}/\left[ {0.0{7}, \, 0.{22}, \, 0.{75}} \right]} \right) \, \hfill \\ \quad \quad \quad= \, \left[ {{78}0,{ 9}0{3},{ 1}0{38}} \right]{\text{ times K}} - {\text{Pg}} \hfill \\ \end{gathered}$$

Comparison of post-1980 extinctions to K-Pg extinction rate with impaired and data deficient species included

$$\left( {\left[ {N_{{{\text{extinctions}}}} \; \times \;{\text{CI}}} \right]/\left[ {N_{{\text{extant species}}} \; \times \;\left( {{\text{CI}}\; \pm \;{1}0\% } \right)} \right]} \right)\; \times \;\left( {{1}0^{{6}} /{\text{T}}_{{{\text{obs}}}} } \right)\; \times \;\left( {{1}/{\text{R}}_{{{\text{K}} - {\text{Pg}}}} } \right)$$

There are three available estimates for completedness (Suppl. 1).

RK–Pg = [0.1, high estimate, high estimate × 1.1] (there are eight estimates) (0.1 was substituted for zero for RK–Pg to avoid dividing by zero).

Point estimate

$$\left( {{164}/{258}} \right)*\left( {{1}0^{{6}} /{39}} \right)*\left( {{1}/0.{22}} \right)\; = \;{74},0{\text{86 times K}} - {\text{Pg}}$$

Fuzzy estimate

$$\begin{gathered} \left( {\left( {\left[ {{16}0,\;\;{164},\;\;{175}} \right]\; \times \;\left[ {0.{684}, \, 0.{7}0{4}, \, 0.{75}0, \, 0.{8}0{2}} \right]} \right)/\left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]\; \times \;\left[ {0.{575}, \, 0.{7}0{4}, \, 0.{75}0, \, 0.{825}} \right]} \right)} \right)\; \\ \quad \quad \quad \times \; \left( {{1}0^{{6}} /{\text{39 years}}} \right)\; \times \;\left( {{1}/\left[ {0.0{7}, \, 0.{22}, \, 0.{75}} \right]} \right) \hfill \\ \, \quad \quad \quad= \, \left[ {{15,98}0,{ 69,542},{ 78,927},{ 3,85,}0{52}} \right]{\text{ times K}} - {\text{Pg}} \hfill \\ \end{gathered}$$

Minimum post-1980 magnitude of extinction predicted per million years

$$\left( {N_{{\text{recent taxon extinctions}}} /{\text{39 years}}} \right)\; \times \;{1}0^{{6}}$$

Point estimate

$$\left( {{2}/{39}} \right)\; \times \;{1}0^{{6}} \; = \;{51},{\text{282 extinctions}}/{\text{MY}}$$
$$\left( {\left[ {{1}.{8},{ 2}.0,{ 2}.{2}} \right]/{39}} \right)\; \times \;\left( {{1}0^{{6}} } \right)\; = \;\left[ {{46},{154},{ 51,282},{ 56,41}0} \right]{\text{ extinctions}}/{\text{ MY}}$$

Years until total extinction based on post-1980 extinction rate

$$\left( {{\text{N}}_{{\text{extant taxon species}}} \; \times \;{\text{39 years}}} \right)/N_{{\text{recent extinctions}}}$$

Point estimate

$$\left( {{258}\; \times \;{39}} \right)/{2}\; = \;{5}0{\text{31 years}}$$

Fuzzy estimate

$$\left( {\left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]*{39}} \right)/\left[ {{1}.{8},{ 2}.0,{ 2}.{2}} \right]} \right)\; = \;\left[ {{4116},{ 5}0{31},{ 6149}} \right]\;{\text{years}}$$

Years until total extinction for each taxon based on post-1980 extinction rate including impaired species and DD species

$$\left( {N_{{\text{extant species}}} \; \times \;{\text{39 years}}} \right)/\left( {N_{{\text{recent taxon extinctions}}} \; + \;N_{{{\text{impaired }} + {\text{ DD taxa}}}} } \right)$$

Point estimate

$$\left( {{258}\; \times \;{39}} \right)/{171}\; = \;{\text{59 years}}$$
$$\left( {\left( {\left[ {{232}.{2},{ 258},{ 283}.{8}} \right]} \right)*{39}} \right)/\left[ {{153}.{9},{ 171},{182}} \right])\; = \;\left[ {{5}0,{ 59},{ 72}} \right]{\text{ years}}$$

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McCallum, M.L. Turtle biodiversity losses suggest coming sixth mass extinction. Biodivers Conserv 30, 1257–1275 (2021). https://doi.org/10.1007/s10531-021-02140-8

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