Martin A. Buzas

Species Diversity: Benthonic Foraminifera in Western North Atlantic

Maximum species diversity occurs at abyssal depths of greater than 2500 meters. Other diversity peaks occur at depths of 35 to 45 meters and 100 to 200 meters. The peak at 35 to 45 meters is due to species equitability, whereas the other two peaks correspond to an increase in the number of species.

A statistical evaluation of the microhabitats of living (stained) infaunal benthic foraminifera

Abstract A total of 66 statistical analyses were made on published data for 48 taxa from replicate cores ranging in water depths from At Our assignment of taxa into SI or DI infaunal habitats based on their morphology had a 75% accuracy. The data suggest that as more observations are made, it becomes increasingly difficult to assign a species exclusively to a specific habitat category.

Species Diversity: Patterns in Modern and Miocene Foraminifera of the Eastern Margin of North America

Patterns of foraminiferal species diversity were examined along the eastern margin of North America by utilizing the number of species, S, the information function, H(S), and species equitability, E. The 350 modern samples we studied extended from the Arctic to the Gulf of Mexico at depths ranging from a few meters to more than 5,000 m. In addition, 29 samples from Miocene strata of the Atlantic Coastal Plain and continental shelf were studied. Modern species diversity as measured by S and H(S) generally increases as depth increases and latitude decreases. Some notable exceptions occur, however, which are difficult to explain. For example, species diversity in the Arctic depth interval of 0 to 100 m is as high or higher than that found immediately south of Nova Scotia, in the Gulf of Maine, on Browns and Georges Banks, and even off the Gulf of Mexico deltas. At the moderate depth interval of 100 to 1,000 m, however, the entire margin north of Browns and Georges Banks has lower diversities than that to the south. The highest diversity by far in this depth interval occurs in the northeastern Gulf of Mexico. At the depth interval greater than 1,000 m, the more southern areas studied generally have a higher species diversity than the more northern Cape Cod to Maryland area. An exception to this is the northwestern Gulf of Mexico; this area is also an exception in that species diversity is significantly lower in the deeper waters than in the shallower waters in the same area. The measure of species equitability, E, showed no clear pattern with depth or latitude. This may be so because no simple pattern of species proportions exists or because the sampling was inadequate to measure it. Samples from the Miocene strata show a striking resemblance in species diversity to modern samples at similar depths and latitudes. Our observations indicate that species diversity and equitability have not increased during the last 15 × 106 yrs. The fossil and modern data indicate that each environment has its own carrying capacity and that this capacity is reached rather quickly. Although time and environmental stability are undoubtedly important in determining species diversity, as presently defined they are inadequate to explain all observed patterns. Long-term observations in various environments will be required to determine the relative importance of variables that affect species diversity.

FORAMINIFERAL DENSITIES OVER FIVE YEARS IN THE INDIAN RIVER LAGOON, FLORIDA: A MODEL OF PULSATING PATCHES

Densities of 5 taxa along with 7 environmental variables were measured monthly with 4 replicates at each of 3 stations over a period of 5 years. The 720 observations of density for each taxon were analyzed by General Linear Models with density as the dependent variable. Differences among stations, years, seasons and their interactions are all significant. When treated as covariates environmental variables contributed little to explaining the observed variability in densities. However, the observed densities of the taxa are highly correlated and when a single taxon is treated as a covariate most of the variability in the density of a related taxon is explained. There are no significant differences among replicates (taken within a square meter) or their interactions. Consequently, the biotic or abiotic factor(s), although unknown, responsible for the simultaneous density variation of the taxa operate on a relatively small spatial scale. Based on these observations and previous studies, we propose a model wherein individual foraminifers are spatially distributed as a heterogeneous continuum forming patches with different densities that are only meters apart; reproduction is asynchronous causing pulsating patches that vary in space and time. Thus, we would expect significant differences among stations, years, seasons and their interaction. At the same time, no long-term increase or decrease in density for any of the taxa is observed. Evidently, long-term stability is achieved through considerable short-term variability in space and time. Although observations at a single station are not indicative of a larger area at any particular time, the concept of pulsating patches indicates that observations at a station will in the long-term give an assessment of a larger area.

Biodiversity resolution: an integrated approach

Fifty years of ecological research have failed to achieve an integrated, quantitative analysis suitable for both marine and terrestrial biodiversity. We present a new approach that reconciles the interrelationship of the number of individuals and species with population structure. Sample size dependency, always the primary obstacle, here is recognized as the primary missing requirement for biodiversity analysis. With this key, and a new decomposition formula, we solve the two historically intractable problems of (1) inability to separate species effects of richness and evenness within the same system, and (2) correlation of diversity measures and non- specificity of statistical distributions with sample size. In addition to providing resolution for ecological investigations, this approach reveals ordered structure in inventory and monitoring situations, undetectable by any other approach. As an example, Bolivian and Guyanan trees are shown to exhibit uniquely distinct and heretofore unseen diversity patterns.

Global latitudinal species diversity gradient in deep-sea benthic foraminifera

Global scale patterns of species diversity for modern deep-sea benthic foraminifera, an important component of the bathyal and abyssal meiofauna, are examined using comparable data from five studies in the Atlantic, ranging over 138° of latitude from the Norwegian Sea to the Weddell Sea. We show that a pattern of decreasing diversity with increasing latitude characterises both the North and South Atlantic. This pattern is confirmed for the northern hemisphere by independent data from the west-central North Atlantic and the Arctic basin. Species diversity in the North Atlantic northwards from the equator is variable until a sharp fall in the Norwegian Sea (ca. 65°N). In the South Atlantic species diversity drops from a maximum in latitudes less than 30°S and then decreases slightly from 40 to 70°S. For any given latitude, North Atlantic diversity is generally lower than in the South Atlantic. Both ecological and historical factors related to food supply are invoked to explain the formation and maintenance of the latitudinal gradient of deep-sea benthic foraminiferal species diversity. The gradient formed some 36 million years ago when global climatic cooling led to seasonally fluctuating food supply in higher latitudes.

Latitudinal difference in biodiversity caused by higher tropical rate of increase

Tropical diversity has generally exceeded temperate diversity in the present and at points in the past, but whether measured differences have remained relatively constant through time has been unknown. Here we examine tropical vs. temperate diversities from the Neogene to Recent using the within-habitat diversity measure Fishers alpha of Cenozoic benthic foraminifera from the temperate Central Atlantic Coastal Plain and the tropical Central American Isthmus. During the Neogene, the mean value of alpha at temperate latitudes increased 1.4 times or 40%, whereas in the tropics it increased 2.1 times or 106%. Thus, while both areas exhibit an increase of diversity with time, past differences in the rate of increase have generated a more pronounced gradient today (164%) than existed in the Miocene (80%). These data disagree with the suggestion that the world reached an equilibrium number of species during the Paleozoic and demonstrate the need to consider both temperate and tropical components in global diversity assessments.

Species Pool and Dynamics of Marine Paleocommunities

Foraminiferal communities in the Cenozoic shelf deposits of the North American Atlantic Coastal Plain exhibit little unity during almost 55 million years of successive transgressions and regressions. Transgression communities are composed of a dynamic mixture of immigrants and newly evolved species. During regressions, species within these communities either became extinct or emigrated. Some emigrants returned during subsequent transgressions, but many did not. The neritic species of the Atlantic and Gulf continental margins constitute a species pool. Immigrants and emigrants transferred into and out of the species pool, while extinctions and originations repeatedly altered its species composition. While the results indicate a lack of local community unity, at the same time they demonstrate the necessity of a species pool to sustain species diversity.

On richness and evenness within and between communities

Abstract Although there is extraordinary interest in the quantitative measurement of species diversity, published statements on the behavior of the components of species diversity are contradictory and lead to opposite conclusions. In this paper, we demonstrate that the confusion is due to two key oversights: (1) whether or not biological sampling is carried out within or between communities; and (2) determination of the statistical distribution underlying a biological community, which is crucial for the evaluation of all of the components of diversity measurement. The problem of sampling “within” a population or community is basically distinct from the equivalent integration of structure and diversity measurement “between” differing multispecies populations. “Within-community sampling” is defined as a set of biological samples from a statistical population that has a particular statistical distribution or a constant value for the associated parameter(s). As the number of individuals increases along with the number of species, for a log series distribution, the diversity measures of Shannons H, log series or Fishers α, and Simpsons Index 1/λ remain constant while the evenness measures of Buzas-Gibsons E and Pielous J decrease. For a log-normal distribution, J will remain constant while E decreases and α, 1/λ, and H increase. No single measure of evenness remains constant over all statistical distributions, so if constancy as a type of independence is required, the appropriate distribution must first be determined. Each species ensemble is mathematically fixed by the applicable statistical distribution. In contrast, “between-community sampling” is defined as a set of biological samples from different statistical distributions and/or the same distribution with differing parametric values. If sampling is between communities and S increases while the number of individuals remains constant, then all the other measures considered here increase. The exception is the broken stick, for which E remains constant while H, J, α, and 1/λ increase. Herein we propose and justify the use of the log-series distribution (with regression on the information decomposition equation) as a null model for determination of community structure and demonstrate that the community structure of a Miocene bed at Calvert Cliffs, Maryland, is a log series by use of this new unified methodology.

On the distribution of species occurrence

The distribution of species abundance (number of individuals per species) is well documented. The distribution of species occurrence (number of localities per species), however, has received little attention. This study investigates the distribution of species occurrence for five large data sets. For modern benthic foraminifera, species occurrence is examined from the Atlantic continental margin of North America, where 875 species were recorded 10,017 times at 542 localities, the Gulf of Mexico, where 848 species were recorded 18,007 times at 426 localities, and the Caribbean, where 1149 species were recorded 6684 times at 268 localities. For Late Cretaceous molluscs, species occurrence is examined from the Gulf Coast where 716 species were recorded 6236 times at 166 localities and a subset of this data consisting of 643 species recorded 3851 times at 86 localities. Logseries and lognormal distributions were fitted to these data sets. In most instances the logseries best predicts the distribution of species occurrence. The lognormal, however, also fits the data fairly well, and, in one instance, better. The use of these distributions allows the prediction of the number of species occurring once, twice, …, n times. Species abundance data are also available for the molluscan data sets. They indicate that the most abundant species (greatest number of individuals) usually occur most frequently. In all data sets approximately half the species occur four or less times. The probability of noting the presence of rarely occurring species is small, and, consequently, such species must be used with extreme caution in studies requiring knowledge of the distribution of species in space and time.