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Temporal changes in diversity
... According to CASWELL (1976), the loss of preclimax species may cause a decrease in species numbers in climax communities without altering the overall patterns of the community structure. Further it is usual to find dominant 'generalist' species in early successional community stages (GOULDEN 1969). New environments are typical low-diversity environments (SLOBODKIN & SAN-DERS 1969), and this diversity tends to increase with succession due to several factors (GRKY' 1978). ...
A volcanic eruption at Jan Mayen in 1970 created new submarine lava grounds. Eight years later the general ecology of the marine rocky-bottom macrofauna and the succession of colonisation were Studied. Benthos down to 30 m were collected from new and old grounds, using a diver-operated suction sampler.The faunae on the new and old grounds were more similar in the shallow waters (5–10 m) than in the deep waters (20–30 m). Above 15 m, motile animals, e.g. amphipods, were more frequent than sessile animals, and overall faunal diversity was low. It is suggested that the community at 5–10 m is controlled by physical factors such as strong water movements and scouring by sand and ice.At 20-30 m the new grounds had a lower diversity, less predators, and a dominance of filter feeders. Space was highly monopolized by Hiatella arctica L., which contributed more than 80 % of the total biomass. The old grounds had a higher faunal diversity with no one-species domination and with more predators. It is suggested that Strongylocentrotus droebachiensis (Müller) and Tealia felina (L.) are of ultimate importance to the community structure.These differences suggest that the new grounds below 15 m have not yet reached the same successional stage as the old grounds, while above 15 m, where more severe physical conditions limit the community complexity, the new grounds have reached a stage similar to that on the old grounds.
... As the figures cited here would suggest, mammalian faunal diversity was high in the Torrejonian, relatively low in the Tiffanian and Clarkforkian, and high again in the Wasatchian (see Rose, 1979, for a full analysis and documentation). Such low diversity as that observed in Tiffanian and Clarkforkian mammalian faunas is often associated with stress or unpredictability in the environment (Hutchinson, 1961;Goulden, 1969). Paleobotanical evidence indicates that temperatures and climatic equability were lower in the Tiffanian and Clarkforkian than at any other time during the Paleocene or early Eocene (Hickey, 1977, and this volume;Wolfe, 1978). ...
A richly fossiliferous stratigraphic section including late Cretaceous, Paleocene, and early Eocene faunas is exposed along Polecat Bench and the southern margin of the Clark's Fork Basin. Lancian, early Puercan, and late Torrejonian faunas are known from three concentrations in 200 m of section on the east side of Polecat Bench: Dumbbell Hill, Mantua Quarry, and Rock Bench Quarry, respectively. Tiffanian faunas occur a t 55 localities in about 800 m of section on the east, south, and west sides of Polecat Bench. Large faunal samples are known from Cedar Point Quarry (mid-Tiffanian) in the Foster Gulch area and Princeton Quarry (late Tiffanian) in the Clark's Fork Basin. Clarkforkian faunas occur at 135 localities in about 470 m of section on the south side of Polecat Bench and in the Clark's Fork Basin. Early and middle Wasatchian faunas occur at 105 localities in about 600 m of section in the southwestern part of the Clark's Fork Basin. The Tiffanian-Clark-forkian boundary is marked by the immigration of Rodentia, Tillodontia, Coryphodon, and Haplornylus, and the Clarkforkian-Wasatchian boundary is defined by the immigration of Artiodactyla, Perissodactyla, adapid and omomyid primates, and hyaenodontid creodonts. Faunal diversity was high in the Torrejonian, relatively low in the Tiffanian and Clarkforkian, and high again in the Wasatchian. I N T R O D U C T I O N One of the most complete stratigraphic sections spanning the Paleocene-Eocene boundary in conti-nental sediments is in the Clark's Fork Basin-Polecat Bench area of the northern Bighorn Basin. Mam-malian faunas from the Clark's Fork Basin were first described by W.
... Then, in the seventeenth and eighteenth centuries (830–570 cm), Chydorus sphaericus became less abundant and Graptoleberis testudinaria and Alona guttata increased, indicating a gradual shift towards meso-to oligotrophic conditions (Whiteside 1970; Brodersen et al. 1998) and thus confirming the decrease in diatom-inferred TP values (Figs. 3, 5). Factors such as the frequency and amplitude of catastrophic disturbance (Goulden 1969) similar to flood events in De Waay, habitat availability (Whiteside 1970), and food supply (Kerfoot et al. 1988) may also have had a strong influence on the cladoceran communities. It is therefore conceivable that flooding and elevated nutrient conditions in the lake influenced cladoceran communities indirectly. ...
We present a palaeolimnological study encompassing five centuries of trophic-state change of the dike-breach lake De Waay
located on the Rhine-Meuse delta (the Netherlands). Diatom-inferred total phosphorus (TP) concentrations indicate hypertrophic
epilimnetic conditions (>300μgl−1 TP) since the formation of the lake in the fifteenth century until the end of the eighteenth century. Cladocera data support
the reconstructed trophic state and indicate turbid conditions in lake De Waay during this period. High inferred TP concentrations
as well as the amount of Ti in the sediment reflect numerous flooding events. From the nineteenth century onwards reconstructed
TP concentrations decreased to 40–150μgl−1 due to improvements in sewage and dike systems that considerably diminished direct river flooding and seepage-derived nutrients.
As a consequence, the increased stability of littoral habitats led to an increased diversity of the Cladocera assemblages.
The most significant decrease in TP concentrations to ~40μgl−1 occurred between about 1900 and 1930. This mesotrophic phase was a consequence of the isolation of the lake from catchment
drainage and the introduction of a highly elaborate flood control during this period. However, since the mid twentieth century
a eutrophication trend is preserved in the record, likely related to increased agricultural activity in the vicinity of the
lake. Our results emphasize that land-use and trophic-state history must be taken into account when evaluating the ecological
status of lakes for water management and protection actions, especially for lakes in landscapes that are strongly modified
by human action.
KeywordsPalaeolimnology-Eutrophication-Diatoms-Cladocera-Phosphorous reconstruction
... As the figures cited here would suggest, mammalian faunal diversity was high in the Torrejonian, relatively low in the Tiffanian and Clarkforkian, and high again in the Wasatchian (see , for a full analysis and documentation). Such low diversity as that observed in Tiffanian and Clarkforkian mammalian faunas is often associated with stress or unpredictability in the environment (Hutchinson, 1961;Goulden, 1969). Paleobotanical evidence indicates that temperatures and climatic equability were lower in the Tiffanian and Clarkforkian than at any other time during the Paleocene or early Eocene (Hickey, 1977, and this volume;Wolfe, 1978). ...
1-146 http://deepblue.lib.umich.edu/bitstream/2027.42/48624/2/ID488.pdf
The concept of r and K strategems and their development during the evolution of organisms is certainly not new, although these particular terms to describe the process have been used for only a short period of time. As a matter of fact, the concept is implicit in some of the writings of Charles Darwin, among others. But, however old the basic theory is, there is presently a great deal of uncertainty as to how important these stratagems are in the functioning of organisms within ecological communities. There have also been questions as to whether or not genetic selection can proceed in the manner prescribed by the concept; even the appropriateness of the symbols “r” and “K” have been criticized. And to add to the dilemma, I suppose it is not altogether suitable to use the term “stratagem” when discussing the r and K theory since the dictionary defines stratagem as an artifice—a trick or way to deceive the enemy—and certainly this is a questionable manner in which to describe the process of evolution or development at any level of an ecosystem.
Cores of Holocene calcareous sediments (marls) from two small lakes (Putaanlampi and Ylimmainen Kuivajarvi) in Kuusamo, NE Finland, were analysed for pollen, Cladocera, and diatoms. The cladoceran planktonic / littoral ratio shows consistent trends through the Holocene, with parallel changes at both sites, suggesting regional changes in water balance and lake levels. The diatoms were extensively dissolved, but the down-core occurrence of remains of several mesohalobous taxa absent from the younger sediments indicates that the lakes must have undergone stages of elevated electrolyte concentration and, by inference, enhanced evaporation earlier in their history. The results are interpreted as indicating relatively dry conditions between 7000 and 5000 BP, with maximal dryness occurring around 6000 BP. The mid-Holocene dry interval is preceded and succeeded by periods of more humid conditions and higher lake levels. This pattern of Holocene humidity changes in NE Finland is closely comparable with the patterns previously suggested for Finnish Lapland and for south-central Sweden, but deviates from the pattern known from the southern parts of Fennoscandia.
Summary Patterns of species diversity and equitability, and the hypotheses suggested to explain them are examined in the terrestrial and marine environments, and the fossil record. Although all the hypotheses are important in explaining diversity, none of them singularly or in various combinations are sufficient to explain the observed patterns. Quantification of the variables suggested to explain the observations will no doubt help clarify and give more credibility to the explanation of diversity, but such studies are only in their infancy. Even the most casual observer notices that all parts of the globe do not contain the same number of species. The great increase in the number of species with decrease in latitude is particularly striking and has been the subject of discussion among biologists for many years. Among the most popular hypotheses suggested to explain this and other observed patterns of species diversity are time-stability-competition-predation-productivity-spa- tial heterogeneity and their various subcombinations (see Pianka 1966, for a review). Recently, there has been an increasing trend toward utilizing not only the number of species present but also measures which take into account the relative abundance of species (species dominance or equitability) as an aspect of species diversity. In this way the observer can utilize the information which previously could only be tabled as a listing of relative abundances. Although some studies of diversity arbitrarily group data from various habitats, such as the number of species present in large quadrats, there has been an increasing trend toward studying species diversity within habitats, and comparing trends between these habitats. In the present paper we will utilize data from both approaches. The purpose of the present study is to review recent and fossil patterns of species diversity and to attempt to make some assessment of our progress in explaining the observed patterns. It is by no means intended to be complete review of all papers dealing with species diversity, as that would require a book of some length and a knowledge of the literature probably beyond the capacity of a single individual. Rather, it is an attempt to summarize the patterns and the adequacy of the hypotheses suggested to explain them from a number of selected papers.
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Changes in the structure of an estuarine, subtidal, benthic deposit-feeding community have been investigated. Three quantitative samples were taken within a grid 10 m on a side every four weeks from May, 1971 to July, 1973. Each sample was washed over a 250 μm sieve. Streblospio benedicti Webster, Capitella capitata (Fabricius), Heteromastus filiformis (Claparède), Potydora ligni Webster, and Paranais litoralis (Müller) were the five dominant species on the basis of their total abundance, percentage occurrence, and biological index value. Repeatable cycles in diversity were observed for Fager's scaled standard deviation and scaled information measure, as well as for Lloyd and Ghelardi's equitability, but not for the unsealed information theory measure. McNaughton's dominance index was strongly inversely correlated with all diversity measures. Graphical measures of lognormal skewness and normal kurtosis, as applied to Whittaker's dominance diversity curves, followed repeatable cycles, whereas normal skewness and lognormal kurtosis did not. A strong relationship between Fager's scaled standard deviation diversity, dominance, and the degree to which resources were being shared by the deposit-feeding segment of the community was suggested. A decrease in average niche width and average niche overlap was observed as the community developed during the period of strong larval recruitment.
Sixteen mammalian assemblages from the middle Paleocene (Torrejonian) to early Eocene (Wasatchian) of western North America have been studied to determine their species composition and diversity. Torrejonian and Tiffanian faunas are dominated by small mammals of archaic aspect, while larger forms predominate in Clarkforkian assemblages and remain common in the Wasatchian. Both Clarkforkian and Wasatchian faunas are characterized by immigrant taxa, including representatives of more modern groups of mammals.Torrejonian assemblages have many species, and species abundances are relatively equitably distributed. Early and middle Tiffanian samples reveal a significant drop in both species richness and evenness, with predominance of one or two species; but diversity may have increased in the late Tiffanian. Clarkforkian assemblages resemble early-middle Tiffanian ones in their low species richness and evenness. Wasatchian assemblages, however, are somewhat richer in species and show much greater equitability of species abundances, thus resembling Torrejonian samples.The hypothesis is proposed that the observed pattern of species diversity is in part related to climatic disturbances (specifically changes in temperature) in the northern Western Interior. Consistent with this interpretation is the record of Paleocene-Eocene megafloras, which shows similar changes in species diversity. Thus, high diversity in the Torrejonian and Wasatchian coincided with warm, equable conditions. Lower diversity in the intervening Tiffanian and Clarkforkian was probably related to cooler temperatures, although a slight warming trend seems indicated in the Clarkforkian. Species diversity in the Clarkforkian and Wasatchian was also influenced by competition and predation directly related to major faunal immigrations.
Certain fossil communities may be recognized in collections from Early—mid-Middle Ordovician age rock units in the Inyo Mountains, California, and the Bare and Ranger Mountains in adjacent Nevada. These dominantly brachiopod—tribolite communities lived in several different, shallow shelf-sea environments. The communities appear to have maintained their diversity and evenness within relatively narrow limits for as long as the major aspects of the environments in which they lived, remained little changed (periods of about 1–2 m.y.). Some taxa occur in several communities (and are called wide-niched), and some occur in only a single community (and are called narrow-niched). Certain taxa that occur in large numbers in a single community appear to have been far more tolerant of particular environmental conditions than were associated taxa in the same community that are represented by few individuals. Counts of such abundant taxa that are restricted to a single community (and are thus considered narrow-niched) compared with counts of the individuals of those taxa found in several communities (and thus are considered wide-niched) indicate that the taxa highly tolerant of particular environmental conditions may be represented by more individuals than are the wide-niched taxa.
Principal component analysis is used to develop a technique for predicting the limnological characteristics of a lake from knowledge of its midsummer limnetic crustacean zooplankton community. Patterns of variation in zooplankton community structure are summarized in the principal components extracted, via the species covariance matrix, from the matrix of transformed proportionate numerical abundances of species in a sample of lakes. The relation between these patterns and the limnological characteristics of the lakes is determined from the first-order rank correlations of the limnological variables with the components. In relatively undisturbed lakes of northwestern Ontario, results indicate that lakes characterized by Cyclops bicuspidatus thomasi, Diaptomus minutus, and others are large and clear, whereas those characterized by Tropocyclops prasinus mexicanus, D. oregonensis, and others are smaller and of lower water clarity. These patterns are contrasted with those extracted from the same data using more subjective techniques. In the acid-stressed Killarney region, Ontario, lakes dominated by D. minutus are predicted to be acidic, small, and clear, whereas those dominated by Diaphanosoma leuchtenbergianum, Bosmina longirostris, Mesocyclops edax, and others will be less clear, larger, and with higher pH. In Haliburton lakes, Ontario, those with Diaptomus oregonensis, M. edax, and Ceriodaphnia lacustris are predicted to be small and productive, whereas those with D. minutus, D. sicilis, B. longirostris, and Daphnia dubia will be larger and less productive. The usefulness of the technique and some modifications are discussed. Key words: zooplankton communities, principal component analysis, ELA lakes, Haliburton lakes, Killarney lakes
Asymptotic increases in diversity, richness, and evenness are reported from a primary sand dune succession. Rapid increases in diversity and evenness were observed in the first 1000 years of the 4800 sampled; richness appears to increase little after 2000 years of succession.
Assemblages of living benthic invertebrates (predominantly bivalve molluscs) from the sand-channel habitat of two Southern California (U.S.A.) lagoons were sampled on ten occasions over a 37-month period. A one-time sampling of the corresponding assemblages of accumulating dead remains made possible a contrast of living and dead assemblages designed to assess the biasing effects of post-mortem transportation, shell dissolution, and time-averaging. Species-by-species comparisons of the living and dead molluscs found together in the same samples strongly suggested that post-mortem transportation is insignificant within this high-energy habitat. A similar conclusion arose from contrasting the pattern of spatial heterogeneity of the living community with that of the dead assemblage. Species presence-and-absence comparisons were generally more reliable than comparisons of relative abundances. Adjustments for experimentally determined rates of post-mortem shell dissolution proved significant and further decreased the correspondence in relative abundances between living and dead assemblages. Greater temporal variability of living populations at Mugu Lagoon, probably caused by a more harsh physical environment, increased the differences in composition between living and dead assemblages, which suggests that correspondence in relative abundances between living and dead assemblages generally should be expected to decrease as the life environment becomes more harsh.
The diversity, homogeneity and population structure of epifauna living on dead bivalve shells in a shallow marine bay are examined. Twenty-eight shells of Mercenaria mercenaria were artificially emplaced on each of three different sediment types in Buzzards Bay, Massachusetts, for one year. Living faunas (53,000 individuals assignable to 106 species) and preservable faunas (16,000 individuals assignable to 25 species) which colonized these shells are compared.Living epifaunas demonstrate a moderately good fit to the Preston truncated lognormal distribution but deviate consistently from the MacArthur broken-stick model. Homogeneity and diversity of living faunas are greater on shells resting on coarse sediments. The rarefaction methodology overestimates faunal diversity in both living and preservable faunas.Preservable epifaunas posses a higher homogeneity but one which is generally parallel to that of the living communities from which they are derived. The diversity of preservable epifaunas does not reflect the diversity of the living faunas from which they are derived.Abundant species living on shells are more likely to possess preservable hard parts than are rare species. This is indicative of the evolutionary success of various protective devices in epibenthic communities exposed to predation and environmental vagaries.
SUMMARY 1. Colonization and ecological development of postglacial freshwater communities was investigated in Glacier Bay National Park, south-eastern Alaska, following the rapid recession of a Neo-glacial ice sheet within the last 250 years.2. Environmental variables shown to be most significant in stream development were temperature, flow regime and sedimentation.3. The Chironomidae (Diptera) were the pioneer invertebrate colonizers of newly emergent streams arising as meltwater from receding ice sheets and displayed a distinct pattern of succession with stream maturity.4. Ephemeroptera and Plecoptera colonized warmer clearwater streams, but Trichoptera had a minimal role in invertebrate community development.5. Establishment and production of salmonid fish populations in the new streams related principally to stream flow and sediment characteristics.6. Future pathways along which the streams may develop is probably dependent on the degree of large organic debris input.7. Stream development, structure and function are summarized including reference to theories of ecosystem development, ecological succession and community stability.
Zooplankton species diversity and selected chemical parameters were investigated at three stations in Lake St. Clair, Ontario, Canada, from 15 June–26 August, 1971. Primary productivity and zooplankton species diversity were greatest at stations 1 and 2 which were enriched by the Thames River drainage. No significant correlation between total zooplankton diversity and chlorophyll a was found, however, within the Cladocera and Copepoda, positive correlations with chlorophyll a, reactive silicate and nitrate were shown at stations 2 and 3. Rotifer species diversity showed negative correlation with chlorophyll a, nitrate and reactive silicate.
Raptor counts in tropical and subtropical check areas in Southern Brazil, Paraguay, and Eastern Bolivia showed characteristic differences in the spectrum of species composition, which can only partly be caused by differences in altitude and climate. Changes in landscape structure under the influence of human economic management have caused the greatest influence on species composition and abundance. Numbers of species decrease markedly when human management increases, despite a strong increase of raptor abundance. This increase in numbers is due to improvment of environmental conditions to scavengers (vultures and caracaras). Without this group, the abundance of “true” Birds of Prey decreases with increasing human influences on landscape structure. In general this process is shown by a decreasing species diversity, which was calculated according toShannon's formula, a method suitable for calculations derived from the heterogene data collection gained in the course of the year of 1970 in the South American control areas. The shiftings within the species composition resulted in typical differences in the evenness (J′), which attained high values in the little influenced areas, moderate values in the more disturbed regions, and very low values in the thoroughly cultivated areas. From these results some consequences concerning the degree of stabilization of the shifted species composition can be derived which should be studied more in detail. It is likely that the ecological group “Birds of Prey” may be an usable indicator for community monitoring, but special investigations in landscape ecology must prove this assumption.
Comparisons of prehistoric (A.D. 1100–1400) and extant cricetine-dominated rodent faunas from two locations in New Mexico and one in Arizona reveal temporal changes in both species diversity and taxonomic composition. The archaeological context of the prehistoric faunas permitted them to be dated rather accurately; paleoenvironmental inferences generated from other materials recovered in the excavations such as pollen samples, agricultural remains, and tree-ring specimens provided evidence about prehistoric environmental conditions in the study areas. Both richness and evenness components of diversity are lower in the present day faunas than in their prehistoric counterparts. At the beta (between-habitat or valley-wide) level of diversity the increased prehistoric species richness as well as the nature of the differences in present and prehistoric taxonomic composition can be accounted for by small climatic shifts which were occurring between A.D. 1100 and 1300 in the Southwest and the resultant biogeogrphic responses of certain rodent species. Alpha (or within-habitat) diversity is similar for all analyzed faunas. This suggests basic similarities in very local species packing despite observed spatial and temporal variation in valley-wide diversities. Environmental changes stemming from climatic shifts provide a reasonable explanation of the observed patterns of rodent species occurrence and diversity. Habitat destruction resulting from agricultural practies of prehistoric human populations appears to have had only a limited impact on these rodent communities.
The European legislation (WFD) and the IPCC 2008 are both acknowledging the relevance of current and future problems with regard to water quality and quantity. Globally, many lakes are suffering from increased nutrient input (mainly phosphorus) leading to eutrophication. Eutrophication is diminishing ecosystems by causing toxic algal blooms, anoxic events, fish kills, and biodiversity degradation. Assessing the total phosphorus concentrations (TP) through the history of lakes is a key towards understanding the nature of eutrophication processes. In this dissertation the TP dynamics in eight Dutch and German lakes were quantitatively estimated for the past 30 to 13,000 years. In Sacrower See (Germany), the relationship between seasonal and interannual variability of modern diatoms and TP concentrations, temperature, and precipitation were assessed using sediment traps. On the basis of this data the fossil diatoms of Sacrower See could be interpreted and information on the length of summer stratification, winter circulation, and on the lake productivity could be inferred. The sediments of the past 130 years of Sacrower See were analyzed for diatom assemblages at a seasonal time-resolution. The results of this high-resolution analyses show that the sensitivity of diatom assemblages to meteorological parameters such as wind and temperature affected the diatoms for the past century. On a longer time scale (13,000 years), the palaeoreconstrution of Sacrower See indicated eutrophic conditions (TP ~70 g l-1) during the Younger Dryas cold event (12,700-11,600 years ago) which was caused by the abrupt temperature decrease that led to long-lasting ice cover and consequently the development of anoxic conditions with phosphorus release from the sediment. With the onset of the Holocene (11,600 years ago) and the increased temperatures, the lake became oxygenated again and became meso- to oligotrophic (TP ~10-30 g l-1), which prevailed throughout most of the Holocene. In the past 2500 years the nutrient concentrations increased as much as during the Younger Dryas, but now due to strong anthropogenic impact. Much in contrast to the foreseen effects of global warming, which imply increasing internal loading, the results from Sacrower See provide an unique example of increased TP concentrations due to climate cooling. In this thesis we carried out six trophic reconstructions of Dutch lakes. The results show small changes in the TP of these lakes during the past 30 to 100 years. The major controlling factor for nutrient enrichment in these lakes is the way they are fed (ground water, seepage,) and their catchment was managed. The reconstruction of past nutrient conditions in Lake De Waay (the Netherlands) shows hypertrophic to eutrophic conditions throughout the past 500 years were always evidenced. These results show that the idea of fitting the ecological status of lakes in the context of their natural state is therefore not recommended for lowland lakes. Overall, all case studies demonstrated that the classification of undisturbed environmental conditions should consider the possible effects of climate change and human influence on lake ecosystems when defining targets for ecological reference conditions or restoration of aquatic ecosystems.
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