Niche breadth and geographic range size as determinants of species survival on geological time scales

Abstract

Aim Determining which species are more prone to extinction is vital for conserving Earth's biodiversity and for providing insight into macroevolutionary processes. This paper utilizes the Pliocene to Recent fossil record of mollusks to identify determinants of species' extinction over the past three million years of Earth history. Location Western Atlantic.Methods We focus on 92 bivalve and gastropod species that lived during the mid-Pliocene Warm Period (mPWP; ∼3.264-3.025 Ma) and have either since gone extinct or are still extant. We used ecological niche modeling (ENM) to assess the vulnerability of these species to extinction as a function of both fundamental (FN) and realized (RN) niche breadth proxies, geographic range size, and amount of suitable area available to them during the Last Glacial Maximum (LGM; ∼21 Ka).Results Geographic range size emerged as a key predictor of extinction for the studied mollusk species, with RN breadth and amount of suitable area available during the LGM as secondary predictors. By contrast, FN breadth was not a significant predictor of extinction risk. Main conclusionsThe failure to recover FN breadth as a predictor of extinction may suggest that extinction resistance is achieved when species are more successful in filling the geographic extent of their fundamental tolerances. That is, when it comes to species' survival, being a generalist or specialist sensu stricto may be secondary to the unique historical, dispersal, and biotic constraints that dictate a species' occupation of suitable environments, and consequently of geographic space, at a particular time. Identifying the factors that promote extinction is important because of the time-intensive nature of estimating extinction risk for individual species and populations, and because of the rising concerns about the future of marine ecosystems and biodiversity.

Impacts of Niche Breadth and Dispersal Ability on Macroevolutionary Patterns

“…This strict criterion was chosen purposefully in keeping with our goals of simplifying reality and exploring generalizable results from extreme conditions. The low numbers of extinctions under these conditions is interesting, however, in that it supports the prediction that extinction rates in nature are not structured by loss of suitable habitat alone (Martínez-Meyer et al 2004;O'Grady et al 2004;Mace et al 2008;Harnik 2011;Harnik et al 2012b;Saupe et al 2015). Additional factors-such as population-size thresholds, Allee effects, biotic interactions, or random stochastic events-may, therefore, play an important role in structuring empirical patterns of extinction.…”

“…We predicted a primary role for species' abiotic requirements in affecting speciation and extinction rates, since this trait determines the amount and structure of suitable area that a species can occupy and how this area changes as the environment fluctuates (e.g., a specialist species may experience more volatility in the amount and structure of suitable habitat than a generalist species). Previous work has shown that degree of specialization is often positively correlated with speciation and extinction potential (Eldredge 1979(Eldredge , 1989Vrba 1980;Stanley 1990;Kammer et al 1997Kammer et al , 1998Nürnberg and Aberhan 2013;Saupe et al 2015): specialist species are more likely to form isolated populations during times of environmental change, increasing opportunities for allopatric speciation (but see Fisher-Reid et al 2012). Similarly, niche breadth is expected to correlate negatively with extinction rates, as environmental change is more likely to remove all suitable habitat (leading to extinction) for narrow-tolerance species.…”

Including environmental niche information to improve IUCN Red List assessments

“…This additional information is most valuable in cases where geographic space is only minimally affected by extinctions but niche size shows strong shrinkage (e.g., Sedum rubens in Figure 4). The risk of extinction is increasing with decreasing niche breadth (Kotiaho et al, 2005;Pearson et al, 2014;Saupe et al, 2015), and thus, the realized niche size reflects the environmental spread of extinction risk corresponding to the spatial spread of extinction risk measured by EOO. The widespread occurrence of locally adapted populations (Hereford, 2009) implies that the loss of geographically peripheral populations leads to reduced genetic diversity, which in turn could hamper fitness and long-term survival of a species (Frankham, 2005;Rehm et al, 2015).…”

Getting somewhere with the Red Queen: chasing a biologically modern definition of the hypothesis

“…We diverge from this proposal as this set of conditions is probably unachievable, because a period of constancy of any potential abiotic factors is virtually absent from the geological record [14]. Another challenge to evaluating the RQH is that biotic and abiotic factors can interact to drive macroevolution [54,55], making it hard to differentiate primary biotically driven evolution from secondary biotically driven evolution instigated by abiotic forcing. Because of these challenges, here we focus on an alternative method to assess the validity of the RQH sensu Van Valen [1].…”