Abstract
AbstractFor mammals today, mountains are diverse ecosystems globally, yet the strong relationship between species richness and topographic complexity is not a persistent feature of the fossil record. Based on fossil-occurrence data, diversity and diversification rates in the intermontane western North America varied through time, increasing significantly during an interval of global warming and regional intensification of tectonic activity from 18 to 14 Ma. However, our ability to infer origination and extinction rates reliably from the fossil record is affected by variation in preservation history. To investigate the influence of preservation on estimates of diversification rates, I simulated fossil records under four alternative diversification hypotheses and six preservation scenarios. Diversification hypotheses included tectonically controlled speciation pulses, while preservation scenarios were based on common trends (e.g., increasing rock record toward the present) or derived from fossil occurrences and the continental rock record. For each scenario, I estimated origination, extinction, and diversification rates using three standard methods—per capita, three-timer, and capture–mark–recapture (CMR) metrics—and evaluated the ability of the simulated fossil records to accurately recover the underlying diversification dynamics. Despite variable and low preservation probabilities, simulated fossil records retained the signal of true rates in several of the scenarios. The three metrics did not exhibit similar behavior under each preservation scenario: while three-timer and CMR metrics produced more accurate rate estimates, per capita rates tended to better reproduce true shifts in origination rates. All metrics suffered from spurious peaks in origination and extinction rates when highly volatile preservation impacted the simulated record. Results from these simulations indicate that elevated diversification rates in relation to tectonic activity during the middle Miocene are likely to be evident in the fossil record, even if preservation in the North American fossil record was variable. Input from the past is necessary to evaluate the ultimate mechanisms underlying speciation and extinction dynamics.
Highlights
One of the outstanding questions in biology remains: How do patterns in species diversity arise and persist over space and time? Explanations for diversity gradients have frequently emphasized regional or temporal differences in diversification rates (e.g., Jablonski et al 2006; Weir and Schluter 2007; Mittelbach et al 2007; Rolland et al 2014)
I present results from four diversification models under six preservation scenarios to assess the fidelity of the simulated fossil records
Origination rates of fossil rodents from the Basin and Range Province, which has experienced a high degree of landscape change due to tectonic extension during the Neogene, were estimated based on three alternative metrics (Fig. 3, Supplementary Figs. 1–3)
Summary
One of the outstanding questions in biology remains: How do patterns in species diversity arise and persist over space and time? Explanations for diversity gradients have frequently emphasized regional or temporal differences in diversification rates (e.g., Jablonski et al 2006; Weir and Schluter 2007; Mittelbach et al 2007; Rolland et al 2014). One hypothesized mechanism for long-term variation in speciation and extinction rates is the influence of tectonic activity and broadscale landscape changes on species’ geographic ranges and diversification dynamics (Cracraft 1985; Badgley 2010; Hoorn et al 2010; Moen and Morlon 2014; Badgley et al 2017). The generation of topographic complexity and geographic barriers during tectonic activity reduces habitat continuity while increasing environmental heterogeneity along elevational gradients (e.g., Mulch 2016). These landscape changes can isolate populations, thereby promoting population divergence, allopatric speciation, and high species turnover at the regional scale (e.g., Coblentz and Riitters 2004; Renema et al 2008; Moen and Morlon 2014). Examples of the TDG in birds, plants, and mammals have been found on all continents where gradients in modern species richness strongly align with gradients in topographic complexity at the regional scale, resulting in elevated species richness in highrelief and often tectonically active regions
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