Hypotheses that attempt to explain latitudinal gradients in species diversity are reviewed. Some hypotheses are circular, i.e. they are based on the assumption that some taxa have greater diversity in the tropics. These include explanations assuming different degrees of competition, mutualism, predation, epiphyte load, epidemics, biotic spatial heterogeneity, host diversity, population size, niche width, population growth rate, environmental harshness, and patchiness at different latitudes

Latitudinal gradients in species diversity: the search for the primary cause

1. Introduction.- 2. Taxonomy and Species Features.- 2.1 Introduction.- 2.2 Species List.- 2.2.1 Spinose Planktonic Foraminifera.- 2.2.2 Non-spinose Planktonic Foraminifera.- 3. Collecting and Culture Methods.- 3.1 Introduction.- 3.2 Collection for Ecological Studies.- 3.3 Fixation and Storing of Samples.- 3.4 Laboratory Preparations.- 3.5 Collection for Physiological and Ecological Studies.- 3.5.1 Net Collection.- 3.5.2 SCUBA Collection.- 3.6 Isolation and Preparation for Maintenance Culture.- 3.7 Maintenance Cultures.- 3.8 Monitoring Vitality and Growth of the Cultures.- 3.9 Feeding Techniques.- 3.9.1 Algal Prey.- 3.9.2 Animal Prey.- 3.10 Cataloguing and Storing Shells.- 3.11 Summary.- 4. Cellular Ultrastructure.- 4.1 Introduction.- 4.2 Fixation of Planktonic Foraminifera for Fine Structure Analysis.- 4.3 Cytoplasmic Streaming.- 4.4 Peripheral Cytoplasm and Rhizopodial Morphology.- 4.4.1 Cytoskeletal Structures.- 4.4.2 Filaments.- 4.5 Fine Structure of Cytoplasmic Organelles.- 4.5.1 Nucleus.- 4.5.2 Mitochondria.- 4.5.3 Peroxisomes.- 4.5.4 Endoplasmic Reticulum, Golgi Complex, and Vacuolar System.- 4.5.5 Fibrillar Bodies.- 4.5.6 Lipids and Various Cytoplasmic Inclusions.- 4.6 Comparative Fine Structure Data of Benthic and Planktonic Species.- 4.7 Comparative Fine Structure of Planktonic Foraminifera and Radiolaria.- 4.8 Summary.- 5. Host and Symbiont Relationships.- 5.1 Introduction.- 5.2 Symbiosis, Commensalism and Parasitism.- 5.3 Symbiont Morphology and Structural Association with Host.- 5.3.1 Dinoflagellate Symbiont Fine Structure.- 5.3.2 Chrysophycophyte Symbiont Fine Structure.- 5.4 Symbiont and Host Physiological Interactions.- 5.5 Origin of Symbionts.- 5.6 Major Features of Algal Symbionts.- 5.7 Summary.- 6. Trophic Activity and Nutrition.- 6.1 Introduction.- 6.2 Natural Prey.- 6.3 Laboratory Studies of Trophic Activity.- 6.3.1 Prey Acceptance and Rate of Digestion.- 6.3.2 Cannibalism.- 6.3.3 Fine Structure Studies of Prey Capture and Digestion.- 6.3.4 Trophic Activity and Longevity.- 6.3.5 Laboratory Studies of Omnivorous Feeding.- 6.4 Prey Abundance and Foraminiferal Distribution.- 6.5 Predators on Planktonic Foraminifera.- 6.6 Comparative Data with Benthic Foraminifera and Radiolaria.- 6.7 Summary.- 7. Reproduction.- 7.1 Introduction.- 7.2 Gametogenesis.- 7.2.1 Light Microscopic Data.- 7.2.2 Fine Structure Data.- 7.3 Morphological Changes during Gametogenesis.- 7.4 Reproductive Cycles.- 7.5 Comparisons with Benthic Foraminifera and Radiolaria.- 7.6 Summary.- 8. Shell Ontogeny.- 8.1 Introduction.- 8.2 Ontogenetic Concept for Spinose Species.- 8.2.1 Five Stage Concept.- 8.2.2 Ontogeny of Globigerinoides sacculifer.- 8.3 Variations in Developmental Morphology of Spinose Species.- 8.4 Variations in Developmental Morphology of Non-spinose Species.- 8.5 Quantitative Ontogeny.- 8.6 Coiling Directions.- 8.7 Taxonomic Applications.- 8.8 Summary.- 9. Shell Architecture.- 9.1 Introduction.- 9.2 Chamber Deposition and Pore Formation.- 9.2.1 Chamber Formation in Non-spinose Species.- 9.2.2 Pore Formation and Wall Thickening.- 9.2.3 Keel Development.- 9.2.4 Pustule Formation.- 9.3 Chamber Formation in Spinose Species.- 9.3.1 Spine Types.- 9.4 Wall Thickening and Gametogenic Calcification.- 9.5 Physiological Mechanism and Rates of Calcification.- 9.6 Organic Composition of the Calcitic Wall.- 9.7 Resorption and Repair Processes.- 9.8 Abnormal Shell Growth.- 9.9 Summary.- 10. Ecology.- 10.1 Introduction.- 10.2 Statistical Treatment and the Transfer Function.- 10.3 Stable Isotopes.- 10.4 Distributional Pattern of Planktonic Foraminifera.- 10.4.1 Horizontal Distribution.- 10.4.2 Seasonal Distribution.- 10.4.3 Vertical Distribution.- 10.4.4 Patchiness and Daily Vertical Migration.- 10.4.5 General Sea Surface Temperature in the Past.- 10.5 Population Dynamics.- 10.5.1 Reproductive Strategies.- 10.5.1.1 Lunar Periodicity.- 10.5.1.2 Annual Periodicity.- 10.5.2 Water Mass Boundary Effects.- 10.6 Experimental Studies.- 10.7 Summary.- 11. Sedimentation - Settlement of Shells.- 11.1 Introduction.- 11.2 Shells Released by Reproduction and Juvenile Mortality.- 11.3 Aggregates - Sedimentation.- 11.4 Predation.- 11.5 Residence Time and Sinking Velocity.- 11.6 Seasonal Fluctuations in the Settlement.- 11.7 Dissolution in the Deep Water.- 11.8 Summary.- 12. Concluding Remarks.- 12.1 Effects Influencing the Isotopic Signal.- 12.1.1 Temperature Effect.- 12.1.2 GlacialEffect.- 12.1.3 Water Mass Effect.- 12.1.4 VitalEffect.- 12.1.5 Selective Production.- 12.1.6 Differential Dissolution.- 12.2 Carbon Isotopes.- 12.3 Summative Perspective.- 13. References.- 14. Glossary.- 15. Index.

Modern Planktonic Foraminifera

Tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale, making use of improved chronostratigraphic control and additional Oligocene isotope data Synchronous changes in both benthic and planktonic δ18O values which occurred in the Oligocene to Miocene (36–52 Ma) are interpreted, in part, to represent ice growth and decay The inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records This association is consistent with a link between Oligocene to Miocene erosional events and rapid (>15 m/my) glacioeustatic lowerings of about 50 m High benthic foraminiferal δ18O values suggest the presence of continental ice sheets during much of the Oligocene to Recent (36–0 Ma) Substantially ice-free conditions probably existed throughout the Paleocene and Eocene (66–36 Ma) The mechanisms and rates of sea level change apparently were different between the early and late Tertiary, with glacioeustatic changes restricted to the past 36 my Pre-Oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes We apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands, stimulating slope failure and submarine erosion The different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late Tertiary on passive continental margins This speculation needs to be confirmed by examination of data from several passive margins

Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion

Oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on Antarctica since the earliest Oligocene (circa 35 Ma). The growth and decay of ice sheets during the Oligocene to modern “ice house world” caused glacioeustatic sea level changes. The early Eocene was an ice-free “greenhouse world,” but it is not clear if ice sheets existed during the middle to late Eocene “doubt house world.” Benthic foraminiferal δ18O records place limits on the history of glaciation, suggesting the presence of ice sheets at least intermittently since the earliest Oligocene. The best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic δ18O records. Although planktonic isotope records from the western equatorial regions are limited, subtropical planktonic foraminifera may also record such ice volume changes. It is difficult to apply these established principles to the Cenozoic δ18O record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events. We improved Oligocene to Miocene correlations of δ18O records and erected eight oxygen isotope zones (Oi1-Oi2, Mi1-Mi6). Benthic foraminiferal δ18O increases which are associated with the bases of Zones Oil (circa 35.8 Ma), Oi2 (circa 32.5 Ma), and Mil (circa 23.5 Ma) can be linked with δ18O increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near Antarctica. Our new correlations of middle Miocene benthic and western equatorial planktonic δ18O records show remarkable agreement in timing and amplitude. We interpret benthic-planktonic covariance to reflect substantial ice volume increases near the bases of Zones Mi2 (circa 16.1 Ma), Mi3 (circa 13.6 Ma), and possibly Mi5 (circa 11.3 Ma). Possible glacioeustatic lowerings are associated with the δ18O increases which culminated with the bases of Zone Mi4 (circa 12.6 Ma) and Mi6 (circa 9.6 Ma), although low-latitude planktonic δ18O records are required to test this. These inferred glacioeustatic lowerings can be linked to seismic and rock disconformities. For example, we link 12 Oligocene-early late Miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries (= inferred eustatic lowerings) of Haq et al. (1987).

Unlocking the Ice House: Oligocene‐Miocene oxygen isotopes, eustasy, and margin erosion

The middle Miocene climatic transition: East Antarctic ice sheet development, deep ocean circulation and global carbon cycling

Oxygen isotopic analyses of planktonic foraminifera have provided a picture of many aspects of the evolution of the temperature structure of surface and near-surface oceans during the Miocene. In time slice studies oceanographic conditions have been interpreted from synoptic maps of isotopic data at between 22 and 27 locations in the Atlantic, Pacific and Indian Oceans. Three time slice intervals were examined: 22 Ma (foraminifera! zone N4B) and 16 Ma (N8) in early Miocene time; and 8 Ma (N17) in late Miocene time. In time series studies, the evolution of oceanographic conditions at single localities during an extended period of time were inferred from <5O values of planktonic foraminifera. Surface waters warmed throughout the early Miocene at almost all localities examined. At 22 Ma, the Pacific Ocean was characterized by relatively uniform temperatures in the equatorial region but a marked east-west asymmetry in the tropical South Pacific, with higher temperatures in the west. Between 22 Ma and 16 Ma, tropical Pacific surface waters warmed, but wanned more in the east than the west. At 16 Ma, the asymmetric distribution of temperatures in the South Pacific Ocean remained, and the latitudinal temperature gradient, inferred from the isotopic data, was gentler than that of either the late Miocene or Modern ocean. Between the late early Miocene and late Miocene, surface waters at most lowlatitude Pacific sites warmed while those at high latitudes cooled or remained unchanged. However, surface waters at high northern latitudes in the Atlantic Ocean as well as in the eastern equatorial Atlantic cooled, while water temperatures remained •Present address: Department of Geological and Geophysical Science, Princeton University, Princeton, New Jersey 08540.

Margaret Nesbitt Murphy

Papers

The evolution of Miocene surface and near-surface marine temperatures: Oxygen isotopic evidence

Growth and Development of the Young Child

Rand, Sweeny and Vincent's Growth and development of the young child