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

The exact timing of deglaciation is an important issue in the context of climatic feedback involving the deglacial rise in atmospheric CO2 seen in ice cores1–4. We have produced evidence, from box cores taken in the equatorial Atlantic, that the last deglaciation occurred in two major steps which were separated by a brief pause5. Here we propose that this pause is equivalent to the period of glacial readvance known as ‘Younger Dryas’, which lasted from about 11 to 10 kyr BP. If our correlation is correct, then the initiation of deglaciation occurred after 14 kyr BP, which disagrees with most other deep-sea timescales.

Timing of deglaciation from an oxygen isotope curve for Atlantic deep-sea sediments

Pulsations in the production of North Atlantic deep water (NADW) have been implicated in generating drastic climatic fluctuations during the Glacial–Holocene (G/H) transition1–3. The stable isotope record of benthic foraminifera in high-resolution cores from the Norwegian Sea suggests that such pulsations did occur4. Although the question of exact timing (and mechanism) is still open there is little doubt that NADW pulsations were important in climatic history because the rate of NADW production influences the rate of advection of heat to the northern North Atlantic5. Here we report that a sporadic shutdown of NADW may be recognizable in deep-sea carbonates with normal (low) sedimentation rates. Hence the possibility arises that relatively short-lived events (∼1,000–2,000 yr) in deep circulation can be mapped over large areas of the sea floor, despite the detrimental effects of bioturbation on signal resolution.

Sporadic shutdown of North Atlantic deep water production during the Glacial–Holocene transition?

Primary productivity in the western equatorial Pacific was distinctly higher during the last glacial period than today, judging from the abundance patterns of benthic foraminifers in box cores from the Ontong Java Plateau. The export of organic matter dropped by a factor of ∼1.7 during the last glacial to interglacial transition, on the basis of global calibration of estimated export against accumulation rates of benthic foraminifers. Using detailed information on δ 13 C stratigraphy of planktic and benthic foraminifers for the past 20 ka together with a simple two-box ocean model, we calculate that upward mixing and diffusion of subsurface waters decreased by a factor of 1.4, while nutrient content decreased by a factor of 1.2, over this time span.

Glacial to postglacial drop in productivity in the western equatorial Pacific: Mixing rate vs. nutrient concentrations

Benthic foraminifera in box core ERDC 112, Ontong Java Plateau

There are three fundamentally different proxies recording ocean productivity in sediments: those representing flux (that is, export production), those representing nutrient concentrations (e.g., nitrate or phosphate), and those representing aspects of the trophic structure of the pelagic environment. Flux proxies disagree due to different power-law relationships to the source term. The particular power-laws (expressed in terms of proxy exponents) change as a function of geography, and may change as a function of time. Modification of the accumulation rate by changing preservation on the sea floor (and within the sediment) is an important aspect of this problem.

Wolfgang H Berger

Papers

Timing of deglaciation from an oxygen isotope curve for Atlantic deep-sea sediments

Sporadic shutdown of North Atlantic deep water production during the Glacial–Holocene transition?

Glacial to postglacial drop in productivity in the western equatorial Pacific: Mixing rate vs. nutrient concentrations

Benthic foraminifera in box core ERDC 112, Ontong Java Plateau

Paleoproductivity: Flux Proxies Versus Nutrient Proxies and Other Problems Concerning the Quaternary Productivity Record