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Evolution in a pelagic planktic system: A paleobiologic test of models of multispecies evolution
- Antoni Hoffman, Jennifer A. Kitchell
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- Journal:
- Paleobiology / Volume 10 / Issue 1 / Winter 1984
- Published online by Cambridge University Press:
- 08 April 2016, pp. 9-33
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Two rival models of evolution in multispecies systems are tested against empirical species-level data. The two models are the Red Queen model of Van Valen as reformulated by Stenseth and Maynard Smith, which assumes that evolution is driven principally by biotic interactions, and the Stationary model of Stenseth and Maynard Smith, which assumes that evolution is propelled primarily by abiotic factors and will cease in the absence of changes in abiotic parameters. Testing refers to the models' predictions regarding the behavior of extinction and origination rates, and assumptions regarding equilibrium diversity and a constant effective environment. The data set includes the dates of origination and extinction for all coccolith, planktic foraminifer, and radiolarian species recorded in the Oligocene through Holocene, and all planktic diatom and silicoflagellate and ebridian species recorded in the Middle Miocene through Holocene in 111 DSDP sites of the low- to mid-latitude Pacific Ocean.
The condition of stable specific age distribution over geologic time is met, which allows one to perform survivorship analysis on extinction rates. The best fit survivorship curve is a decreasing function of age for both coccolith and foraminifer species, and an increasing function of age for radiolarian species. Neither model predicts age dependence of the probability of extinction. The small disparity between these curves and age-independent curves for each group indicates, however, that an age-independent interpretation of extinction probability is a reasonable first approximation. Rates of origination are analyzed in terms of species accretion, introduced to represent the cumulative origination of species within a higher taxon as a function of the age or duration of the community. Accretion analysis indicates that the probability of accretion is both diversity-dependent and absolute time-dependent.
The assumption of a constant effective environment is tested by polycohort analysis and nonparametric logistic regression analysis of true species cohorts. Both techniques indicate considerable variation in extinction probability over geologic time. When the predictions of the two evolutionary models are adjusted to take this variation into account, the results of both survivorship and accretion analysis seem to conform more closely to the predictions of the Red Queen than to the Stationary model. However, as the speed with which the effective environment changes is increased relative to speciation-extinction rates, it becomes increasingly difficult to differentiate patterns predicted by the two models. The assumption of equilibrium diversity can be neither corroborated nor rejected, since the species-level data are compatible with both an equilibrium and a nonequilibrium view of diversity behavior. Reservations concerning the basic assumptions of both models indicate an ultimate test requires that both models be reformulated to make precise and distinctive predictions under a varying effective environment.
Community paleoecology as an epiphenomenal science
- Antoni Hoffman
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- Journal:
- Paleobiology / Volume 5 / Issue 4 / Fall 1979
- Published online by Cambridge University Press:
- 08 February 2016, pp. 357-379
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The most important topics discussed thus far by community paleoecologists are: community approach to paleoenvironmental reconstruction, community development in evolutionary time, and community constraints upon species evolution. The first step in community-paleoecological analysis is to reconstruct the paleocommunity or paleoecosystem. However there are severe methodological limitations to any inference drawn from the composition and structure of a fossil assemblage. These result from various taphonomic biases. These constraints upon reliability of a community-paleoecological analysis are the least severe in the case of Cenozoic (and possibly Cretaceous) tropical to subtropical, molluskdominated, subtidal, benthic communities.
The basic assumption of community paleoecology is that communities or biocoenoses represent a distinct, real level of biotic organization achieved through ecological integration of and coevolution among the species. This assumption seems to be invalid for two reasons. (1) The actual degree of community integration is in general insufficient to induce any driving forces for a structural development as predicted by the system theory. (2) The concept of biological reality and distinctness of the community level of biotic organization implies assignment of a significant role to group selection. The assumption that ecological communities achieve with time an equilibrium state representing an optimum habitat partitioning among the component species is invalid, at least as a generalization. This idea is largely falsified and refuted by a variety of ecological studies. Ecological communities are then merely an epiphenomenon of the overlap in distributional patterns of various organisms. There is no intrinsic, biotic mechanism inducing community dynamics in either ecological, or evolutionary time.
In spite of this conclusion, the so-called “community approach” under favorable taphonomic conditions is among the most reliable methods of paleoenvironmental reconstruction, and the data on so-called “community evolution” are relevant to the problem of a relationship between actually realized niche patterns and their environmental framework. The latter problem can also be approached through analysis of longevity-frequency-distributions of chronospecies found living together in various habitats. A preliminary investigation may indicate that the precondition to optimization of niche dimensions through coevolution among ecologically related species was met in subtidal benthic habitats but not in pelagic ones. To account for a niche subdivision among planktonic organisms, one has therefore to invoke a stochastic pattern of speciation rather than coevolutionary mechanisms.
Randomness in the pattern of ‘mass extinctions’ and ‘waves of origination’
- Antoni Hoffman, Joe Ghiold
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- Journal:
- Geological Magazine / Volume 122 / Issue 1 / January 1985
- Published online by Cambridge University Press:
- 01 May 2009, pp. 1-4
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‘Mass extinctions’ and ‘waves of origination’ are defined as peaks in the average probability of family extinction and origination per geologic stage, respectively. A simple neutral model is proposed, assuming only that the average probabilities of family extinction and origination have varied independently and had equal chances of going up and down from one stage to another. As a null hypothesis, this model is not rejected by the available palaeontologic data on marine animal and nonmarine invertebrate families in the Phanerozoic. The only discrepancy between the model and the empirical pattern is due to a systematic bias introduced by Fossil-Lagerstätten. The alleged periodicity of Late Phanerozoic mass extinctions follows inevitably from the model.
Stable carbon and oxygen isotope record in the Paleogene La Meseta Formation, Seymour Island, Antarctica
- Andrzej Gaździcki, Michał Gruszczyński, Antoni Hoffman, Krzysztof Małkowski, Sergio A. Marenssi, Stanislaw Hałas, Andrzej Tatur
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- Journal:
- Antarctic Science / Volume 4 / Issue 4 / December 1992
- Published online by Cambridge University Press:
- 13 May 2004, pp. 461-468
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Stable carbon and oxygen isotopic relations have been analysed in brachiopod, gastropod, and bivalve fossils from the La Meseta Formation (Eocene-?early Oligocene), Seymour (Marambio) Island, West Antarctica. The results indicate a shift in δ13C by 6 permil beginning in the middle part of the Unit II of the formation. This shift may imply a change from a largely stratified to a vigorously mixed ocean. Such an interpretation is corroborated by changes in the elemental proportions in the shell material. Alternatively, the carbon isotopic shift may be regarded as reflecting a change in the local depositional enviornment. Such an interpretation agrees with isotopic data from the Weddell Sea, which do not confirm the pattern observed in the La Meseta Formation. In any event, the oxygen isotopic curve does not decline parallel to the carbon curve and may thus imply a considerable climatic cooling event. This effect is so profound that it might be interpreted as evidence for glaciation, especially when taking into account the fact that this phenomenon coincides with the well-known cooling trend throughout the Eocene. If this interpretation is correct, the hypothesized Glaciation may possibly be correlated with the Polonez Glaciation, the largest Cenozoic glaciation known in the Antarctic Peninsula sector. Alternatively, it may be regarded as a local phenomenon, predating development of the icesheet.