Mammalian niche conservation through deep time.

Climate change alters species distributions, causing plants and animals to move north or to higher elevations with current warming. Bioclimatic models predict species distributions based on extant realized niches and assume niche conservation. Here, we evaluate if proxies for niches (i.e., range areas) are conserved at the family level through deep time, from the Eocene to the Pleistocene. We analyze the occurrence of all mammalian families in the continental USA, calculating range area, percent range area occupied, range area rank, and range polygon centroids during each epoch. Percent range area occupied significantly increases from the Oligocene to the Miocene and again from the Pliocene to the Pleistocene; however, mammalian families maintain statistical concordance between rank orders across time. Families with greater taxonomic diversity occupy a greater percent of available range area during each epoch and net changes in taxonomic diversity are significantly positively related to changes in percent range area occupied from the Eocene to the Pleistocene. Furthermore, gains and losses in generic and species diversity are remarkably consistent with ~2.3 species gained per generic increase. Centroids demonstrate southeastern shifts from the Eocene through the Pleistocene that may correspond to major environmental events and/or climate changes during the Cenozoic. These results demonstrate range conservation at the family level and support the idea that niche conservation at higher taxonomic levels operates over deep time and may be controlled by life history traits. Furthermore, families containing megafauna and/or terminal Pleistocene extinction victims do not incur significantly greater declines in range area rank than families containing only smaller taxa and/or only survivors, from the Pliocene to Pleistocene. Collectively, these data evince the resilience of families to climate and/or environmental change in deep time, the absence of terminal Pleistocene "extinction prone" families, and provide valuable insights to understanding mammalian responses to current climate change

Relationships between changes in species, genera, and percent range area occupied through time.

<p>A) Minimum genera change and range area change (% occupied; R² = 0.25, <i>p</i><0.0001); B) minimum species change and range area change (% occupied; R² = 0.17, <i>p</i><0.001); and, C) minimum genera change and minimum species change (R² = 0.79, <i>p</i><0.0001) from the Eocene to Oligocene (red diamonds), Oligocene to Miocene (orange circles), Miocene to Pliocene (green triangles), and Pliocene to Pleistocene (blue Xs), with linear regression trend lines noted in solid black for all data and dashed colored lines corresponding to specific epochs (Eocene to Oligocene, R² = 0.91, <i>p</i><0.0001; Oligocene to Miocene, R² = 0.56, <i>p</i><0.001; Miocene to Pliocene, R² = 0.76, <i>p</i><0.0001; Pliocene to Pleistocene, R² = 0.69, <i>p</i><0.0001).</p

Concordance of ranks across geologic epochs.

*<p>X² values calculated by Friedman's test, a repeated measures comparison for k related groups.</p>§<p>Significance value (noted in bold) pertains to both the X² statistic and Kendall's W, a coefficient of concordance that represents a normalization of Friedman's test.</p

Relationship between minimum number of genera or minimum number of species and percent range area occupied during each epoch.

<p>Significant <i>p</i>-values and subsequent R² values are noted in bold. All slopes/relationships are positive.</p

Correlation between Pliocene and Pleistocene relative range size.

<p>(R² = 0.64, <i>p</i><0.001).</p

Centroid shifts between epochs, demonstrating a general southeastern trend through time.

<p>Centroid shifts between epochs, demonstrating a general southeastern trend through time.</p

Range size and rank of North American families from the Eocene to Pleistocene.

<p>Range sizes are converted to a log₁₀ scale and a percentage based on the total range size of all terrestrial mammalian families included during each epoch. Rank of family within each epoch is relative to other families present in that epoch through the Pleistocene: Eocene-Pleistocene (<i>n</i> = 10), Oligocene-Pleistocene (<i>n</i> = 16), Miocene-Pleistocene (<i>n</i> = 22), Pliocene-Pleistocene (<i>n</i> = 28).</p>1<p>Families containing taxa that went extinct during the terminal Pleistocene extinction in North America <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035624#pone.0035624-Faith1" target="_blank">[37]</a>.</p>2<p>Families completely absent in North America, excluding re-introductions.</p>3<p>Families containing at least one extinct or extant megafaunal taxon (≥45 kg; based on data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035624#pone.0035624-Paleobiology1" target="_blank">[22]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035624#pone.0035624-Nowak1" target="_blank">[33]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035624#pone.0035624-Janis2" target="_blank">[39]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035624#pone.0035624-Reynolds1" target="_blank">[42]</a>).</p

Range area polygons during each epoch for (A) Camelidae, (B) Equidae, (C) Sciuridae, and (D) Tapiridae.

<p>Range area polygons during each epoch for (A) Camelidae, (B) Equidae, (C) Sciuridae, and (D) Tapiridae.</p