Definitions of diversity. Measuring species diversity. Choosing an index and interpreting diversity measures. Sampling problems. Structural diversity. Applications of diversity measures. Summary.

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Ecological Diversity and its Measurement

Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

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Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.

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Historical overfishing and the recent collapse of coastal ecosystems.

Interactions between organisms are a major determinant of the distribution and abundance of species. Ecology textbooks (e.g., Ricklefs 1984, Krebs 1985, Begon et al. 1990) summarise these important interactions as intra- and interspecific competition for abiotic and biotic resources, predation, parasitism and mutualism. Conspicuously lacking from the list of key processes in most text books is the role that many organisms play in the creation, modification and maintenance of habitats. These activities do not involve direct trophic interactions between species, but they are nevertheless important and common. The ecological literature is rich in examples of habitat modification by organisms, some of which have been extensively studied (e.g. Thayer 1979, Naiman et al. 1988).

Organisms as ecosystem engineers

The management and conservation of the world's oceans require synthesis of spatial data on the distribution and intensity of human activities and the overlap of their impacts on marine ecosystems. We developed an ecosystem-specific, multiscale spatial model to synthesize 17 global data sets of anthropogenic drivers of ecological change for 20 marine ecosystems. Our analysis indicates that no area is unaffected by human influence and that a large fraction (41%) is strongly affected by multiple drivers. However, large areas of relatively little human impact remain, particularly near the poles. The analytical process and resulting maps provide flexible tools for regional and global efforts to allocate conservation resources; to implement ecosystem-based management; and to inform marine spatial planning, education, and basic research.

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A Global Map of Human Impact on Marine Ecosystems

Ocean history is largely read from deep-sea sediments, using microscopic fossils, notably foraminifers. Ice age fluctuations in the ocean's sediments provided for a new geologic understanding of climate change. The discovery of rapid decay of ice masses at the end of glacial periods was especially important, yielding rates of sea level rise reaching values of 1 to 2 m per century for millennia. Thanks to deep-ocean drilling, the overall planetary cooling trend in the Cenozoic was recognized as occurring in three large steps. The first step is at the Eocene–Oligocene boundary and is marked by a great change in sedimentation patterns; the second is in the middle Miocene, associated with a major pulse in the buildup of Antarctic ice masses and the intensification of upwelling regimes; and the third is within the late Pliocene and led into the northern ice ages. Evolution in the sea is linked to these various steps.

Geologist at sea: aspects of ocean history.

Over much of the tropical ocean, late Quaternary productivity patterns show maxima associated with glacial periods, minima during warm times. Also, biogenic opal deposition tends to parallel the accumulation rates of organic carbon and related productivity proxies. This pattern is found in the eastern equatorial Pacific, for example. However, in the western equatorial Pacific, while productivity is normally high during glacials, opal deposition is reduced. In Santa Barbara Basin, both organic matter supply and opal supply are reduced during the last glacial period, showing a reversed productivity pattern. Silicate/phosphate ratios at 100 m depth in Pacific waters and elsewhere suggest that present circulation greatly favors silicate enrichment of the thermocline in the North Pacific, presumably through large-scale deep upwelling, which prevents segregation of silicate from phosphate through partial recycling in the uppermost water column. If so, it appears that the opal supply to Santa Barbara Basin may indicate the nutrient content of the North Pacific thermocline. We suggest that during the last glacial period the nutrient content of the thermocline was low, and large-scale deep upwelling was absent. The records of organic matter supply and laminations show patterns that call for additional factors, presumably changing wind strength, changing shelf exposure, and local feedback effects.

Silica depletion in the thermocline of the glacial North Pacific: corollaries and implications

On the pteropod pavement of the eastern Rio Grande Rise

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Wolfgang H Berger

Papers

Geologist at sea: aspects of ocean history.

Silica depletion in the thermocline of the glacial North Pacific: corollaries and implications

On the pteropod pavement of the eastern Rio Grande Rise

CO2 Increase and Climate Prediction: Clues from Deep-Sea Carbonates

Glacial deep-water properties in the west-equatorial Pacific : bathyal thermocline near a depth of 2000 m