Repeatability of taxon longevity in successive foraminifera radiations and a theory of random appearance and extinction

Abstract

An analysis of taxonomic longevity for species of the two Cenozoic radiations of Caribbean planktonic foraminifera shows strong similarity in longevity for extinct taxa, though extant species of the latter radiation are biased towards longer-lived forums. In this case, the present is not the key to the past. A simple one-parametric stochastic model predicts generally the shape of the distributions, though there is an excess of species with model longevity and a deficiency of longer-lived forms, relative to the prediction of the model. Although the one parameter may relate to the biology of the group under consideration, the distribution about the mode may reflect random appearance-extinction processes.Interest among paleontologists in the tempo of speciation and extinction can be traced to Simpson (1) and Newell (2), who both voiced the opinion that much of the evolutionary record reflects deterministic responses of biotas to the physical and biotic environment. Patterns of appearance and extinction were related by these pioneers to intertaxon competition, paleogeographic change, and environmental change.More recently, many have revived the argument; some have introduced more deterministic parameters, such as sea-floor spreading and continental drift (3), and interspecific interactions (4), while others have claimed that the overall pattern of appearance and extinction follows essentially a stochastic process (5). This argument parallels the controversy in island biogeography over interactions among species on islands that might regulate species diversity (6).Raup and colleagues (7) simulated speciation and extinction and claimed that computer-geqerated clades could not be distinguished easily from data obtained from the fossil record. In particular, the average time of maximal taxon richness was midway between the first and last appearance of the clade in both simulations and fossil data. Although Flessa and Levinton (8) To obtain the longevity spectrum, we used a corrective equation (Fig. 1) that related a length of ranges on a stratigraphic range chart to independent radiometric dates presented by Saunders et al. (11). We used an exponential fit, but any of a number of other fits do not substantially alter our results. Longevity reckoned by number of foraminiferal zones is not as useful, because zone longevity increases by a factor of 2 in the Oligocene, decreases to approximate Paleocene-Eocene levels [ca. 1-1.5 million years (my)] in the Miocene, and then decreases dramatically towards the present. With this data set, we cannot correct for pseudoextinction, the transition of one taxonomic form to another, due to phyletic evolution. This effect tends to decrease taxon longevity by confounding it with morphological evolution. In the case in which pseudoextinction dominates, our estimate of longevity is simply a measure of the lifespan of a given morphotype.Using the calibration, Fig. 2 shows the distribution of longevities for the Paleogene (N -128) and Neogene (N = 59) radiations. They point to a r...

Extinction dynamics of age-structured populations in a fluctuating environment.

“…The r(i) have serial correlation caused by the time lag or "momentum" inherent in age-structured populations, in addition to possible environmentally induced autocorrelation in the vital rates. Therefore, as t -X 00 [5] and C'al~)-AO0)] ---o.Ti1 + 2 7=11) = a2, [6] where the expectation and variance are across sample paths.…”

“…The distribution of extinction times is positively skewed, with third central moment 3xRoo4/1I I5, so that the mode (the most probable extinction time) is less than the mean. When A = 0 the moments do not exist, but the mode is at x6/3o-2 (5 (Fig. 1).…”

“…In natural populations subject to substantial abiotic and biotic perturbations, environmental stochasticity is usually far more important than demographic stochasticity in causing extinction (6,7). Previous analytical models of stochastic population growth and extinction either lacked age structure or dealt only with demographic stochasticity (1)(2)(3)(4)(5)(6)(7).…”

Vertical niche partitioning between cryptic sibling species of a cosmopolitan marine planktonic protist

“…Planktonic foraminifera have been frequently used as model system to investigate speciation patterns in the plankton (e.g. Levinton & Ginzburg 1984;Norris et al 1996;Norris 2000;Allen et al 2006). Today, there are about 50 morphospecies inhabiting the world ocean, the majority of which show a cosmopolitan distribution within their preferred temperature range (e.g.…”

The evolution of diversity in ancient ecosystems: a review

“…So far as it has an aim, it is to touch on areas that perhaps have su¡ered from either relative neglect or are particularly topical. To forestall justi¢able criticism I should say that among the many potential topics that will not be considered here are: the problem of selectivity in extinctions (see, for example, Bennett & Owens 1997), apart from some passing comments at the end of this paper any detailed discussion of the mathematical treatment of diversity (see, for example, Patterson & Fowler 1996;; the questions of stratigraphic completeness and the sampling of the fossil record (see, for example, Foote & Raup 1996;Marshall 1997); variable species longevity (see, for example, Levinton & Ginzburg 1984;Kammer et al 1997); biogeographical changes engendered by continental splitting; the in£uence of seawater chemistry (Grotzinger 1990;Harper et al 1997); the patterns of onshore^o¡shore diversity (see, for example, Sepkoski 1991); the merits (or otherwise) of Linnean taxa versus cladistic methodologies (see, for example, Sepkoski & Kendrick 1993;Foote 1996); the stability of taxonomic concepts (Hughes & Labandeira 1995); and the important role of refugia as`ecological bunkers' in times of adversity and also`evolutionary museums' of archaic diversity (see Oji 1996). Finally, no serious attempt is made to cover the in£uence of climate on diversity in terms of either originations (see Cronin 1985), extinctions (Clarke 1993;Coope 1987Coope , 1994, or faunal replacements (Janis 1989;Jackson 1994).…”