The global diversity of birds in space and time

Journal name:
Nature
Volume:
491,
Pages:
444–448
Date published:
DOI:
doi:10.1038/nature11631
Received
Accepted
Published online

Current global patterns of biodiversity result from processes that operate over both space and time and thus require an integrated macroecological and macroevolutionary perspective1, 2, 3, 4. Molecular time trees have advanced our understanding of the tempo and mode of diversification5, 6, 7 and have identified remarkable adaptive radiations across the tree of life8, 9, 10. However, incomplete joint phylogenetic and geographic sampling has limited broad-scale inference. Thus, the relative prevalence of rapid radiations and the importance of their geographic settings in shaping global biodiversity patterns remain unclear. Here we present, analyse and map the first complete dated phylogeny of all 9,993 extant species of birds, a widely studied group showing many unique adaptations. We find that birds have undergone a strong increase in diversification rate from about 50 million years ago to the near present. This acceleration is due to a number of significant rate increases, both within songbirds and within other young and mostly temperate radiations including the waterfowl, gulls and woodpeckers. Importantly, species characterized with very high past diversification rates are interspersed throughout the avian tree and across geographic space. Geographically, the major differences in diversification rates are hemispheric rather than latitudinal, with bird assemblages in Asia, North America and southern South America containing a disproportionate number of species from recent rapid radiations. The contribution of rapidly radiating lineages to both temporal diversification dynamics and spatial distributions of species diversity illustrates the benefits of an inclusive geographical and taxonomical perspective. Overall, whereas constituent clades may exhibit slowdowns10, 11, the adaptive zone into which modern birds have diversified since the Cretaceous may still offer opportunities for diversification.

At a glance

Figures

  1. Diversification of all birds through time.
    Figure 1: Diversification of all birds through time.

    a, b, Estimates of the tree-wide lineage net diversification (speciation – extinction) rate (a) and speciation rate (b), calculated in 5 million year intervals (line segments). These are estimated to be very similar (see Supplementary Discussion). The shaded region represents the area between the 5th and 95th quantiles for 525 assessed trees with the mean rate traced in black. Intervals outside 67.5 and 2.5Myr ago are not shown due to lack of data (≤30 lineages per interval) and the difficulty of accounting for ongoing speciation events, respectively. c, Lineage-through time plot for 1,000 trees (in grey), with mean waiting times to speciation in black. Green background is the tree depicted in Fig. 2. Geologic time periods are delineated at the bottom of the plot. Ju, Jurassic period; Qu, Quaternary period.

  2. Diversification across the avian tree.
    Figure 2: Diversification across the avian tree.

    Diversification rate shifts identified by MEDUSA and the species level diversification rate metric (DR) are displayed on a representative avian tree. Nodes with shifts in diversification rate identified in at least 25% of the tested trees are indicated by pie-charts (labelled A–Y, see Table 1). Black and grey areas show the proportion of trees with a shift at the focal node and with shifts that are nested within (more recent than) the focal node, respectively. Shifts are counted only once (for example, shifts at node U do not contribute to the prevalence of nested shifts at node T). Prevalence of shifts may be lowered by a ‘trickle-down’ effect where combinations of nested shifts are rarely identified in the same tree (see also Supplementary Discussion Fig. 6 for discussion). Branches are coloured according to the mean diversification rate of descendant branches. We colour branches for visualization purposes to highlight tree-wide variation in diversification rate and do not analyse values for internal branches. Diversification rate quantifies the splitting rate along branches leading to a species and offers species-level detail for clade-level diversification rate (see Supplementary Methods). The inset shows the scale and frequency distribution of diversification rate values across species. Concentric grey circles show time from the present in 20 million year intervals.

  3. Geographic variation in species-level lineage diversification rate and the richness of high-diversification rate species.
    Figure 3: Geographic variation in species-level lineage diversification rate and the richness of high-diversification rate species.

    ac, Mean assemblage diversification rate (see Fig. 2), calculated as the geometric mean of all species in a grid cell assemblage, weighted by the inverse of their range size. a, All species; b, non-passerines; c, passerines. This visualization limits the overbearing (pseudo-replicating) effect wide-ranging species have on perceived spatial patterns of assemblage summaries4. df, Relative (d) and absolute (e) richness of top 25% diversification rate species (DR0.243 species Myr−1); f shows the richness of all 9,993 bird species for comparison. Grid cell size is 110×110km for all panels (Behrman projection).

  4. Latitudinal gradient in species-level lineage diversification rate.
    Figure 4: Latitudinal gradient in species-level lineage diversification rate.

    Each black point represents a single species diversification rate (DR) at the centroid latitude of its global breeding range. Only the 75% species with small to moderate latitudinal extent (<26.4°, N = 7,493) are included to ensure comparable centroid positions (see Supplementary Discussion Fig. 7 for very similar patterns and results including all species). There is no significant association between diversification rate and absolute centroid latitude (Pavg = 0.51, f(P<0.05) = 0/100) or for intra- (<23° latitude) against extra-tropical centroid location (Pavg = 0.16, f(P<0.05) = 31/100). The solid line is a loess smooth over all data (span = 0.2, degree = 2). The dashed line indicates the threshold identifying the quartile of species with highest diversification rate (DR0.243 Myr−1). Darker brown shading highlights greater density of species points.

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Author information

  1. These authors contributed equally to this work.

    • W. Jetz,
    • G. H. Thomas &
    • J. B. Joy

Affiliations

  1. Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, Connecticut 06520-8106, USA

    • W. Jetz
  2. Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK

    • G. H. Thomas
  3. Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada

    • J. B. Joy &
    • A. O. Mooers
  4. Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 49, Hobart, Tasmania 7001, Australia

    • K. Hartmann

Contributions

W.J., A.O.M., and G.H.T. conceived of the study; K.H., W.J., J.B.J., A.O.M. and G.H.T. developed the methods; W.J., J.B.J. and G.H.T. collected the data; W.J., J.B.J. and G.H.T. conducted the analyses; W.J., J.B.J., A.O.M. and G.H.T. wrote the paper. W.J., J.B.J, G.H.T. and A.O.M. contributed equally to the study.

Competing financial interests

The authors declare no competing financial interests.

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