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, 286 (1904), 20182896

Conserving Evolutionary History Does Not Result in Greater Diversity Over Geological Time Scales

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Conserving Evolutionary History Does Not Result in Greater Diversity Over Geological Time Scales

J L Cantalapiedra et al. Proc Biol Sci.

Abstract

Alternative prioritization strategies have been proposed to safeguard biodiversity over macroevolutionary time scales. The first prioritizes the most distantly related species-maximizing phylogenetic diversity (PD)-in the hopes of capturing at least some lineages that will successfully diversify into the future. The second prioritizes lineages that are currently speciating, in the hopes that successful lineages will continue to generate species into the future. These contrasting schemes also map onto contrasting predictions about the role of slow diversifiers in the production of biodiversity over palaeontological time scales. We consider the performance of the two schemes across 10 dated species-level palaeo-phylogenetic trees ranging from Foraminifera to dinosaurs. We find that prioritizing PD for conservation generally led to fewer subsequent lineages, while prioritizing diversifiers led to modestly more subsequent diversity, compared with random sets of lineages. Importantly for conservation, the tree shape when decisions are made cannot predict which scheme will be most successful. These patterns are inconsistent with the notion that long-lived lineages are the source of new species. While there may be sound reasons for prioritizing PD for conservation, long-term species production might not be one of them.

Keywords: conservation; diversification; macroevolution; phylogenetic diversity.

Conflict of interest statement

We declare we have no competing interests.

Figures

Figure 1.
Figure 1.
Schematic workflow. For each tree, we set a series of time slices (dashed lines in (a)) at which we conserve a proportion of lineages (here in colours) based on diversity (PD-maximizing) or speciation rate (DR-maximizing) strategies (coloured lineages) (b). Each conservation strategy yields a subsequent diversity trajectory (c) represented by a lineages-through-time curve. These curves can be compared with the diversity trajectory obtained if the same number of lineages were conserved randomly (grey curve in (c)). At each time slice, the performance of the PD (or DR) maximizing algorithms is calculated (d) as the (logarithm of) the area under the diversity curve following a conservation strategy divided by the area under the diversity curve produced from random conservation. (Online version in colour.)
Figure 2.
Figure 2.
Datasets. The 10 fossil-rich phylogenetic datasets used in this study, ordered from largest to smallest. We report a series of tree metrics: the number of tips, the maximum root age over 100 trees from the posterior distribution of trees (in millions of years), average phylo-temporal clustering (PTC, the extent to which temporally synchronous divergence and extinction events are also phylogenetically clustered; see Material and methods and electronic supplementary material, figure S1), fossil γ (γf, the proportion of tree length held by the branches leading to the tips) and tree balance (β, the extent to which subclades in the tree are the same size). Note that the temporal axis below the trees reflects node depth and not necessarily absolute age. (Online version in colour.)
Figure 3.
Figure 3.
Performance at 30% conservation through time. The PD-based strategy is depicted with a solid line and the DR-based strategy with the dotted line. We show a LOESS fit to the data over 100 trees (except for Foraminifera), where the x-values are the times of the time slices in millions of years, and the y-values are (the log10 of) the area under the median LTT plot from our PD-maximizing strategy divided by the area obtained under the median LTT from random conservation. The thin horizontal line (at y = 0) represents the value below which random choice outperforms each conservation strategy. An optimal smoothing parameter for the LOESS fit was selected using an Akaike information criterion [27] so that the resulting curve captures the general trend, and reduces influence of extreme points. Shaded areas represent the 95% confidence interval of the LOESS fit. (Online version in colour.)
Figure 4.
Figure 4.
Overall conservation strategy performance. The percentage of time slices where prioritizing diversity, or PD-maximizing (a,c,e), and speciation, or DR-maximizing (b,d,f) strategies perform better than random conservation, plotted against phylo-temporal clustering, which reflects whether synchronous divergence and extinction events are also phylogenetically clustered. Each row represents performance under a different proportion of conserved lineages (from top to bottom: 15, 30, 60%). Coloured points reflect averaged metrics, and bars show ±s.d. across 100 trees (except for Foraminifera, for which we analyse one tree). The horizontal dashed line represents 50% performance: below this line, a given strategy performs worse than random conservation on average. (Online version in colour.)

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