Research ArticleECOLOGY

Late Quaternary horses in Eurasia in the face of climate and vegetation change

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Science Advances  25 Jul 2018:
Vol. 4, no. 7, eaar5589
DOI: 10.1126/sciadv.aar5589
  • Fig. 1 Horse occurrences through time.

    (A) Horse occurrences through time. Histograms showing the number of horse observations in Europe (left panel) and Asia (right panel) for each time bin (top) and for climatic period (bottom). Only time bins with more than 10 observations (black horizontal line) have been considered for the SDM analyses. From 22 ka B.P. backward (gray vertical line), time bins cover 2 ka following the available paleoclimatic reconstructions. The central map shows the boundaries considered while defining European and Asian regions, with the black line representing the Urals. The zoomed area shows the geographical resolution of the climatic reconstructions, with each pixel representing a grid cell. (B) Geographic distribution of horse occurrences. Maps showing horse occurrences for each climatic period in Europe (left) and Asia (right).

  • Fig. 2 Climatic niche of European and Asian horses.

    (A) PCA of the estimated values of four environmental variables: Annual minimum temperature (tmin), mean temperature in the warmest month (tmax), total yearly precipitation (totprec), and mean annual NPP. The lighter points represent locations randomly sampled from the two continents (100 per time bin), while the darker points show locations where horses have been found. (B) Niche representation of the horse populations in Europe and Asia, in a PCA environmental space. The red and dark blue surfaces represent the European and Asian realized environmental niche of the horse, respectively. The overlap among the two, in purple, represents the common conditions occupied by the two populations. The arrow shows the centroids of the two realized niches. The continuous lines show the total environmental space of Europe (in red) and Asia (in dark blue) across all time intervals. Axes represent the two first principal components and the respective explained variance of the total environmental space. D shows the overlap of the niche of each horse subpopulation. (C) Histogram of the niche overlap values of the resampling analysis. Bars represent counts of each niche overlap value in 100 repetitions. The x axis shows the realized environmental niche overlap of the European-Asian horse subpopulations, while the dotted line represents the original estimate obtained using all European occurrences. (D) NPP in locations where horses have been found in Europe (highest series) and Asia (lowest series).

  • Fig. 3 Climatic suitability.

    (A) Cumulative climatic suitability for the past 44 ka based on simulation on the European (left), Eurasian (middle), and Asian (right) data sets. To correct for sampling bias in the Eurasian data set, for each time slice, all estimates and projections for Eurasia are performed considering 100 random resampling of European occurrences in the same number as Asian occurrences. The darker the colors, the more stable the climatic suitability for horses (climatic niche = p-Hor) through time. (B) Projection of climatic suitability across Eurasia in different climatic periods based on occurrences in Europe (left), Eurasia (middle), and Asia (right). Because of the scarcity of data available for Asia, no models for the Holocene have been possible for both Asia and Eurasia, with the exception of 5 and 3 ka B.P. (both included in the “Recent” period).

  • Fig. 4 Analyses of the European data set and biome frequency.

    (A) Distribution through time of the frequency of horse remains in Europe calculated as NISP of horses versus other ungulates. (B) Density of horse remains through time in Europe, calculated as NISP of horses versus other ungulates. The numbers at the bottom of each bar represent the number of observations falling in each class, from 0 to >5%. (C) Climatic suitability for horses in Europe between 10 and 3 ka B.P. (D) Climatic suitability per time period. Percentage of land cells in Europe with a value of suitability for horses (p-Hor) > 0.5 and p-Hor > 0.8. (E) Holocene climatic amelioration. Difference in p-Hor in Europe comparing five successive time bins during the Holocene: 9, 8, 7, 6, and 5 ka B.P. Each map shows the difference in the more recent distribution compared to the previous one. (F) Environmental reconstructions in the macro area surrounding horse finds in Europe (left) and Asia (right) per climatic period. The lighter the color, the less forested is the region. The numbers at the bottom of the bars show the number of occurrences in closed environments over all the observations. The dotted line represents a frequency of 0.5.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/7/eaar5589/DC1

    Fig. S1. PCA based on faunal assemblages from Holocene sites, PC1 (38.5%) versus PC2 (19.2%).

    Fig. S2. PCA based on faunal assemblages from Holocene sites, PC2 (19.2%) versus PC4 (11.8%).

    Fig. S3. Projections of the horse climatic niche for each time bin based on occurrences in Europe.

    Fig. S4. Projections of the horse climatic niche for each time bin based on occurrences in Asia.

    Fig. S5. Projections of the horse climatic niche for each time bin based on occurrences in Eurasia.

    Fig. S6. Evaluation of the ensemble models for Europe (44 to 14 ka B.P.).

    Fig. S7. Evaluation of the ensemble models for Europe (14 to 2 ka B.P.).

    Fig. S8. Evaluation of the ensemble models for Asia.

    Table S1. Database of radiocarbon dates associated with horse remains and with archaeological layers where horses have been excavated in Europe and Asia.

    Table S2. Database of horse frequency with respect to other ungulates in archaeological layers from European sites.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. PCA based on faunal assemblages from Holocene sites, PC1 (38.5%) versus PC2 (19.2%).
    • Fig. S2. PCA based on faunal assemblages from Holocene sites, PC2 (19.2%) versus PC4 (11.8%).
    • Fig. S3. Projections of the horse climatic niche for each time bin based on occurrences in Europe.
    • Fig. S4. Projections of the horse climatic niche for each time bin based on occurrences in Asia.
    • Fig. S5. Projections of the horse climatic niche for each time bin based on occurrences in Eurasia.
    • Fig. S6. Evaluation of the ensemble models for Europe (44 to 14 ka B.P.).
    • Fig. S7. Evaluation of the ensemble models for Europe (14 to 2 ka B.P.).
    • Fig. S8. Evaluation of the ensemble models for Asia.

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    Other Supplementary Material for this manuscript includes the following:

    • Table S1 (Microsoft Excel format). Database of radiocarbon dates associated with horse remains and with archaeological layers where horses have been excavated in Europe and Asia.
    • Table S2 (Microsoft Excel format). Database of horse frequency with respect to other ungulates in archaeological layers from European sites.

    Files in this Data Supplement:

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