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

History is rich in examples of the impact of climatic change on the well-being of human populations, and the various possible connections between climatic variability, food shortages, epidemic diseases, and large-scale migrations have generated much discussion in recent years (Ladurie, 1971; Lamb, 1977, 1982; Schneider, 1976; Rotberg and Rabb, 1981). Famine due to bad harvests resulting from bad weather is a phenomenon as old as agriculture itself. However, with the rapid growth of populations since the industrial revolution, and the evolution of a world food and energy market, famines now affect more people and more nations than ever before. Thus, the vicissitudes of climate have begun to loom large in world affairs.

Abrupt Climatic Change — An Introduction

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Ocean: Reflections on a Century of Exploration

Sites 143 and 144

The success of Milankovitch Theory — which states that ice age cycles are real and are a result of orbital forcing — has made climate cycle research thoroughly respectable. This was not the case when E. Bruckner (1862–1927) pioneered climate cycles on the scale of decade-to-century, for the last 1000 years, publishing a century ago. In the last 20 years or so, Bruckner’s claim that climate cycles exist at this scale has received much support. Work on solar-forced climate cycles suggests that such cycles interfere with the assessment of human-induced global warming. A portion of the general warming observed over the last century may be owing to solar activity. If so, this shows considerable sensitivity of climate to modest changes in forcing. The original Bruckner cycle of 35 years is here suggested to be of tidal origin (twice the lunar perigee period). Likewise, the 1470-y Greenland cycle is proposed to be tidal in nature (as a beat between nodal and perigee cycles, effective during the summer season).

Wolfgang H Berger

Papers

Abrupt Climatic Change — An Introduction

Ocean: Reflections on a Century of Exploration

Sites 143 and 144

A case for climate cycles: orbit, sun and moon

Varved sediments of the Arabian Sea