Jennifer A. Kitchell

Prey selection naticid gastropods; experimental tests and application to the fossil record

Because predation by drilling gastropods is uniquely preservable in the fossil record, it represents important evidence for the study of coevolution. Previous studies of drilling gastropod predation have been largely descriptive and sometimes contradictory. We formulate and test a model of prey selection by naticid drilling gastropods. The model adequately predicts both prey species selection and prey size selection. Prey preferences parallel prey profitabilities, determined by calculating prey species-specific and predator size-specific cost-benefit functions. The model also specifically suggests the evolution of potential refugia from predation and the evolution of potential predatory attributes. Application of the model to several Miocene and Pliocene assemblages studied by Thomas (1976) corroborates the feasibility and utility of this approach in examining the evolutionary record of naticid predation, which extends from the Late Mesozoic. Apparent evolutionary stasis and convergent morphological trends among prey species may be consistent with continuous selection pressures against predation.

Biological selectivity of extinction; a link between background and mass extinction

The phenomenon of non-random or selective survival across major extinction boundaries in the geologic past is poorly understood but increasingly recognized as a critical area for future research. A current hypothesis, developedfrom a comparison of extinction patterns among Late Cretaceous molluscs, is that biological adaptations of organisms effectual during normal times of earth history are ineffectual during times of mass extinction. Microsampling of laminated biosiliceous marine sediments from the highlatitutde Alpha Ridge (-86? N lat.) provides evidence of an actively exploited biological adaptation by Late Cretaceous planktonic diatoms. Distinctive laminae reveal a life-history strategy comprised of alternating planktonic and nonplanktonic stages. Contrary to the hypothesis that mass extinctions are indifferent to biological adaptations, these data indicate a link between selection for traits in normal paleoenvironmental settings and differential survival during an unexpected episode of paleoenvironmental deterioration during a mass extinction. Planktonic diatoms, adapted locally to surviving periods of stress by leaving the plankton environment, may have differentially survived a global crisis at the end of the Cretaceous as a consequence of a life-history trait. The interaction of this proximate biological adaptation and the postulated end-Cretaceous extinction mechanisms may have played a major role in the unexpectedly high survival of planktonic diatoms, documenting a clear example of causal dependency between a biologic character selected for during times of normal or background extinction and macroevolutionary survivorship during times of crisis.

Periodicity of Extinctions in the Geologic Past: Deterministic Versus Stochastic Explanations

The temporal spacing and the magnitude of major extinctions over the past 250 and 570 million years, based on the use of different metrics of extinction probability, are analyzed by comparing deterministic and stochastic explanations. The best-fitting time series model is a stochastic autoregressive model that displays a pseudoperiodic behavior with a cycle length of 31 million years for the past 250 million years, regardless of the metric of extinction probability. The periodicity lengthens and weakens when the analysis is extended to the entire Phanerozoic. The history of the probability of extinction for the entire Phanerozoic, based on time series analysis, does not support the reported bipartite distribution of Van Valen. Rather, the probability of extinction has decreased uniformly over Phanerozoic time whereas the inertia or stability of the biotic system after the Late Permian crisis has increased.

Late Cretaceous—Paleogene paleogeography and paleocirculation: Evidence of north polar upwelling

Abstract Quantitative determination of biogenic silica in Late Cretaceous and Paleogene deep-sea sediment cores from the central Arctic Ocean provides evidence of open-ocean polar upwelling. The timing of polar upwelling coincides with periods of a weakened meridional thermal gradient, suggesting that heat transport to the poles by oceanic circulation may have been important. The timing of biogenic silica deposition in the Arctic precedes its deposition in both the Norwegian—Greenland Sea of the North Atlantic and he Bering Sea of the North Pacific. Tectonic events may be resposnible for the timingg and sitting of sites of deposition of biogenic silica in high northern latitudes, particularly the tectonic evolution of sites of deep-water exchange between the Arctic and the world ocean. We outline three phases in the post-mid-Cretaceous history of silica deposition in high northern latitudes. During Phase I, the Arctic is a silica sink, with deep-water formation but with no deep-water outflow. The transition to Phase II is brought about by opening of the Svalabard—Greenland Strait to deep-water outflow from the Arctic to the Norwegian—Greenland Sea. The transition to Phase III is initiated by submergence of the Faroe—Iceland Ridge and deep-water outflow from the Arctic to the North Atlantic. Climatic conditions in the Arctic during Late Cretaceous and Paleogene time are predicted to have favored open-ocean upwelling due to a circulation pattern dominated by cyclonic conditions, resulting from the establisment of a semi-permanent atmospheric low over the Alpha Ridge. Bathymetry of the Alpha Ridge may have intensified paleo-upwelling.

Abyssal traces and megafauna: comparison of productivity, diversity and density in the Arctic and Antarctic

The megafauna and associated behavioral traces of two deep-sea benthic environ- ments, the central Arctic and Antarctic, with a surface primary productivity differential of 104 were compared to assess the role of food availability in foraging strategy and community structure. Bottom photographs, analyzed for megafauna and trace density and diversity at comparable depths in the Arctic Canada Basin and the Antarctic Bellingshausen Basin, indicated that trace frequency was inversely proportional to organism density but that trace diversity directly reflected organism diversity. Those traces identified in the fossil record to represent efficient foraging strategies, i.e., the Nereites facies, were conspicuously absent at all depths in the Arctic and present at all depths in the Antarctic, in contradiction of the paradigm of in- creasing behavioral complexity and sediment exploitation as food availability decreases. Presence or absence of surface-grazing organisms seems to exert a greater influence on trace diversity than depth or nutrient supply. Trace density, however, may reflect episodic sedimentation events which intermittently influence the deep-sea trophic regime.

Dynamics of taxonomic diversity

A general model of taxonomic diversity, incorporating diversity-dependent rates of origination and extinction, is constructed to examine the dynamic responses of diversity to perturbation. The model predicts that the trajectories of diversification increase and decrease are substantially different. The trajectories of diversity during disequilibrium conditions are displayed in phase diagrams to permit a simple graphical analysis of stability. A positive displacement of diversity from equilibrium results in a rapid decline in diversity and may involve an initial overshoot of the equilibrium condition. A negative displacement of equal magnitude results in a gradual increase in diversity. The model is expressed as a nonlinear difference equation to incorporate intrinsically a delay time due to the characteristic noninstantaneous response of origination and extinction. The model initially assumes a parabolic curve expressing total taxon origination rate as a function of diversity. A second model, constructed assuming a sigmoidal total taxon origination rate derived from considerations of allopatric speciation, enhances the asymmetry of the diversity response. The delayed recovery of the Triassic fauna is shown to be characteristic of return to equilibrium from an undersaturated condition, whereas the more rapid “catastrophic” decline in the Late Permian fauna is shown to be characteristic of return to equilibrium from the oversaturated condition. It is proposed, although not assumed, that perturbation may include a degree of selectivity related to the dispersal abilities of organisms, thereby enhancing the observed asymmetry.

Predation at a snail's pace: what's time to a gastropod?

SummaryPredation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time.

Deep-sea foraging pathways; an analysis of randomness and resource exploitation

The foraging paradigm of trace fossil theory has historically accorded random behavior to non-food-limited deposit-feeders and non-random behavior to food-limited feeders. A series of random- ness measures derived from empirical modeling, simulation modeling, stochastic modeling and probability theory applied to foraging patterns observed in deep-sea bottom photographs from the Arctic and Ant- arctic yielded a behavioral continuum of increasing non-randomness. A linear regression of trace positions along the continuum to bathymetric data did not substantiate the optimal foraging efficiency-depth dependence model of trace fossil theory, except that all traces exhibited a greater optimization than that of simulated random foraging. It is hypothesized that optimization as evidenced by non-random foraging strategies represents maximization of the cost/benefit ratio of resource exploitation to risk of predation and that individual foraging patterns reflect an exploration response to the morphometry of a patchily distributed food resource. Differential predation and competition may account for the co-occurrence of random and non-random strategies within the same bathymetric zone.

Macroevolutionary Interpretations of Symmetry and Synchroneity in the Fossil Record

Quantitative analyses of global diversity in the marine fossil record over Phanerozoic time reveal an historically ordered pattern of sequential dominance and increasing diversity. Explanatory models applied to this empirical pattern lead to irreconcilable differences of interpretation. The issue may be resolved by determining the expected distributions and limits of temporal covariation among clades generated by a random branching process. Results also challenge the claim that asymmetries in intra-clade diversity variation provide a directional arrow for the history of life.

Testing for equality of rates of evolution

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