Changes In Faunal Assemblages Research Articles

Historical changes in bird communities at Quitobaquito Springs, Arizona and impacts of climate, spring flow, and shift from Indigenous to federal-agency management

For nearly a century, bird communities at the oasis of Quitobaquito Springs in the Sonoran Desert have attracted desert ecologists. This spring-fed oasis is among the most biologically and culturally significant sites in arid southwestern North America, but has experienced marked changes in management and is threatened by climate change, border, and other development. We assembled data on birds at Quitobaquito across 83 years (1939–2022) and evaluated the patterns and potential drivers of changes in communities. We found evidence of marked community shifts that included apparent loss and replacement of species dependent on riparian and wetland vegetation, mud flats, agricultural fields, and human settlements, to species that use deeper more open-water environments, generalists, and desertscrub. Strong associations between community composition and shift from Indigenous to federal-agency management, temperature, and spring flow suggest important drivers of change, but associations with precipitation and border development were weaker. Such patterns match those for bird communities at broader scales in nearby and other aridlands and indicate impacts of increasing aridification. Our work represents the first analysis of changes in faunal assemblages at Quitobaquito that quantitatively assesses potential drivers of change, and provides insights for management and conservation.

Climate-driven habitat shifts of high-ranked prey species structure Late Upper Paleolithic hunting

Changing climates in the past affected both human and faunal population distributions, thereby structuring human diets, demography, and cultural evolution. Yet, separating the effects of climate-driven and human-induced changes in prey species abundances remains challenging, particularly during the Late Upper Paleolithic, a period marked by rapid climate change and marked ecosystem transformation. To disentangle the effects of climate and hunter-gatherer populations on animal prey species during the period, we synthesize disparate paleoclimate records, zooarchaeological data, and archaeological data using ecological methods and theory to test to what extent climate and anthropogenic impacts drove broad changes in human subsistence observed in the Late Upper Paleolithic zooarchaeological records. We find that the observed changes in faunal assemblages during the European Late Upper Paleolithic are consistent with climate-driven animal habitat shifts impacting the natural abundances of high-ranked prey species on the landscape rather than human-induced resource depression. The study has important implications for understanding how past climate change impacted and structured the diet and demography of human populations and can serve as a baseline for considerations of resilience and adaptation in the present.

Modern and early Holocene ice shelf sediment facies from Petermann Fjord and northern Nares Strait, northwest Greenland

Based on sediment cores and geophysical data collected from Petermann Fjord and northern Nares Strait, NW Greenland, an Arctic ice shelf sediment facies is presented that distinguishes sub and pro ice shelf environments. Sediment cores were collected from sites beneath the present day Petermann Ice Tongue (PIT) and in deglacial sediments of northern Nares Strait with a focus on understanding the glacial and oceanographic history over the last 11,000 cal yr BP. The modern sub ice shelf sediment facies in Petermann Fjord is laminated and devoid of coarse clasts (IRD) due to strong basal melting that releases debris (debris filtering) from the basal ice at the grounding zone driven by buoyant subglacial meltwater and entrained Atlantic Water. Laminated sediments in the deep basin proximal to the gounding zone comprise layers of fine mud formed by suspension settling from turbid meltwater plumes (plumites) interrupted by normally graded very fine sand to medium silt layers with sharp basal contacts and rip-up clasts of mud, interpreted as turbidites. An inner fjord sill limits distribution of sediment gravity flows from the grounding zone to the deep inner fjord basin, such that sites on the inner sill and beyond the ice tongue largely only comprise plumites. Bioturbation and foraminiferal abundances increase with distance from the grounding zone. The benthic foraminiferal species, Elphidium clavatum is absent beneath the ice tongue, but dominant in the turbid meltwater influenced environment beyond the ice tongue. The very sparse IRD in sediments beneath the PIT and in the fjord beyond the PIT derives mainly from englacial debris in the ice tongue, side valley glaciers, rock falls from the steep fjord walls and sea ice.We use the modern ice shelf sediment facies characteristics to infer the past presence of ice shelves in northern Nares Strait using analyses of sediment cores from several cruises (OD1507, HLY03, 2001LSSL, RYDER19). On bathymetric highs, bioturbated mud with dispersed IRD overlies a 10–15 m thick, distinctly laminated silt and clay unit with rare coarse clasts and sparse foraminifera which forms a sediment drape of nearly uniform thickness. We interpret these laminated sediments to represent glaciomarine deposition by meltwater plumes emanating from ice streams that terminated in floating ice shelves. IRD layers, shifts in sediment composition (qXRD, MS and XRF) and faunal assemblage changes in the laminated unit document periods of ice-shelf instability sometimes, but not always, coupled with grounding zone retreat. Our deglacial reconstruction, including ice shelves, begins ∼10.7 cal ka BP, with confluent ice streams grounded in Hall Basin fronted by the Robeson Channel ice shelf. Ice shelf breakup and grounding zone retreat to relatively stable grounding zones at Kennedy Channel and the mouth of Petermann Fjord was accomplished by 9.4 cal ka BP when the Hall Basin ice shelf was established. This ice shelf broke up and reformed once prior to the final break up at 8.5 to 8.4 cal ka BP marking ice stream collapse, separation of Greenland and Innuitian ice sheets, and the opening of Nares Strait for Arctic-Atlantic throughflow. The Petermann ice shelf remained in Hall Basin until the Petermann Glacier retreated from the fjord mouth ∼7.1 cal ka BP. The resilience of these northern ice streams to strong early Holocene insolation and subsurface Atlantic Water advection is attributed to their northern aspect, buttressing by narrow passages, and high ice flux from the Greenland Ice Sheet (GIS).

Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar’s Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role.

Faunal assemblage changes, bioturbation and benthic storms at an abyssal station in the northeastern Pacific

This study investigates the evolution of deep-sea lebensspuren assemblages before, during, and after five high-energy episodes over a storm-events period lasting 25 days. Bioturbational changes were characterized through brief benthic storm events in the northeastern Pacific at the abyssal time-series site Station M (4000 m depth). Quantification of seafloor coverage was processed to evaluate variations on the substratum type. A total of 15 lebensspuren morphotypes were identified. Most traces could be associated with feeding faecal casts, crawling tracks, dwellings and resting structures. Lebensspuren assemblages were similar before and after the storm-events period; full assemblage was re-established in one week. This high energy period was associated with an impoverishment of lebensspuren abundance and assemblage diversity. Only elpidiid holothurian feeding faecal casts recorded a notable increase in abundance during this period of high energy. In addition, this energetic stage involved the appearance of exhumed surface patches. Holothurian feeding activity appeared to have been primarily influenced by the local-scale erosion and re-suspension of unconsolidated surface sediment, which led to the reorganization of organic matter resources. We propose the mobility of elpidiid holothurians allowed them to gain a competitive advantage in obtaining these new resources. This research presents a novel relationship between lebensspuren, faunal activity, and bottom currents that broadens our understanding of benthic community responses to deep-sea bottom currents. Finally, we discuss these results as they pertain to the fossil record to assess how bioturbational structure development could be controlled by substratum type, organic matter availability and duration of energetic episodes.

Biodiversity across the Guadalupian-Lopingian Boundary: first results on the ostracod (Crustacea) fauna, Chaotian section (Sichuan Province, South China)

The Middle Permian-Late Permian boundary (Guadalupian-Lopingian boundary, GLB) interval is characterised by important faunal assemblage changes. This extinction-turnover episode is considered by some authors to be the first step of the end-Permian biodiversity drop. The forty-five meters thickness of sediment encompassing the GLB in Chaotian section (Sichuan Province, South China) was sampled and processed for ostracod study. This study presents the first analysis of ostracod faunas in the GLB interval. A total of 154 species belonging to 29 genera are identified. Three species are described as new: Bairdia chaotianensis Zazzali, n. sp., Microcheilinella wujiapingensis Zazzali, n. sp., Microcheilinella pagodaensisZazzali, n. sp. All the ostracods discovered in the section belong to shallow marine taxa. So these results are not consistent with previous interpretations (lagoonal environment or deep water setting) based on other evidences. Abundance and diversity present a rapid and noticeable decline in the Early Capitanian. Recovery is then recorded about three meters above the GLB. At specific level, a 93% extinction rate and a 96% turnover rate are recorded at the GLB. Moreover, Palaeocopida, straight dorsal border ostracods known to progressively disappear from the Late Permian to the basal Middle-Triassic, are here less abundant and diversified after the GLB. This could reflect the first step of their disappearance at the end of the Palaeozoic.

Sea-level reconstruction for Turonian sediments from Tanzania based on integration of sedimentology, microfacies, geochemistry and micropaleontology

Despite many advances in sea-level research, the nature of cyclic eustatic sea-level fluctuations during warm periods without, or with much reduced, polar ice remains enigmatic. Recently published δ18O records from extremely well-preserved Turonian microfossils from Tanzania do not support the contentious idea of glacio-eustatic control of global sea-level changes during the warmest period of the Cretaceous. For the same locality (site TDP 31) we reconstruct relative sea-level changes based on sequence stratigraphy and integration of sedimentology, microfacies, geochemistry, and micropaleontology. Four local sequence boundaries (SBs TuTz1–4) are recognized: at the base, middle, and top of the Helvetoglobotruncana helvetica Zone and in the Late Turonian. The lowstands are characterized by increased grain size, enhanced organic carbon flux, faunal assemblage changes, and bulk δ13Corg and foraminiferal δ13Cf and δ18Of minima. Strong benthic and planktic foraminiferal turnovers above the top Middle Turonian SB TuTz3 probably reflect shallowing (from upper slope to outer shelf) and/or eutrophication.The TDP 31 age model is refined through inter-regional comparison of planktic foraminiferal ranges and δ13C records from three other South-Tethyan localities (ODP Holes 762C and 763B, Exmouth Plateau, and the Guru section, Tibet). This age model enables correlation of the regressive events at a global scale and suggests that, within stratigraphic uncertainty, the TDP 31 depositional sequences are synchronous with the global Turonian third-order sequences and are likely driven by eustasy. These correlations, together with recent astrochronological and radiometric dating, indicate a considerably younger age (91.17±0.52Ma) for the top H. helvetica Zone than currently assumed, resulting in zonal duration of 2.35±0.52 myr. Foraminiferal stable-isotope data from TDP 31 indicate slight surface- and bottom-water warming during the regressions and possibly a minor surface-water salinity decrease, which is inconsistent with glacio-eustatic forcing of Turonian third-order sea-level cycles and is more in line with the model of aquifer-eustasy.

Climate change impacts on zooplankton and benthic communities in Lake Unterer Giglachsee (Niedere Tauern Alps, Austria)

AbstractWe examined a sediment core from a climatically sensitive High Alpine lake Unterer Giglachsee in the Niedere Tauern Alps in Austria. Our aim was to investigate long‐term climate change impacts on aquatic invertebrates (Chironomidae, Cladocera) with a special focus on the ending of the Little Ice Age and the present climate warming. Although the changes in faunal assemblages were relatively subtle through the sedimentary record, a mutual faunal breakpoint at ∼1900 AD was distinguished. In addition, the faunal dynamics correlated closely with instrumental Alpine temperature records and with reconstructed Northern Hemisphere climate development over the examined time period. In particular, significant relationships between relative taxa abundance and temperature were found with chironomids Sergentia, Paracladius, Paratanytarsus austriacus‐type, Cricotopus (I.) intersectus‐type, and Cricotopus cylindraceus‐type and with cladocerans Daphnia and Alonella excisa. Our results also suggested that the most recent assemblages represent unique community compositions. We conclude that our study lake is sensitive to climate warming and the composition of the aquatic ecosystem in Unterer Giglachsee has changed due to the impact of increasing temperatures. We predict that the further increasing temperatures will have direct but also cascading effects on the sensitive lake, potentially causing an ecosystem turnover where the key taxon Paracladius may play an important role.

A review of the taxonomy of chondrichthyan fishes: a modern perspective

Taxonomic clarity is a fundamental requirement as it forms the foundation of all other life sciences. In the last decade, chondrichthyan taxonomy has undergone a scientific renaissance with >180 new species formally described. This effort encompasses c. 15% of the global chondrichthyan fauna, which consists of 1185 currently recognized species. The important role of chondrichthyan taxonomy for conservation management has been highlighted in recent years with new species descriptions or taxonomic resolution of a number of threatened species. These include Australian gulper (genus Centrophorus) and speartooth sharks (genus Glyphis) in coastal waters of Australia and Borneo. Closer examination of other wide-ranging species, for which the taxonomy was thought to be stable, has shown that they consist of species complexes, e.g. manta rays (Manta spp.) and spotted eagle rays (the Aetobatus narinari complex), and highlights the need for critical re-examination of other wide-ranging species. Molecular methods have provided another useful tool to taxonomists and they have proven to assist greatly with identifying cryptic species and species complexes. The limitations of particular molecular methods being used need, however, to be carefully considered and there are some concerns about how these are being integrated with classical taxonomy. The fundamental importance of taxonomic nomenclature to life sciences is often poorly understood but striving for nomenclatural stability is a critical component of taxonomy. Similarly, biological collections are an extremely vital asset to both taxonomists and the broader scientific community. These collections are becoming increasingly important due in part to molecular species identification initiatives such as the Barcode of Life which has resulted in a large number of voucher specimens linked to tissue samples being deposited. Biological collections are also proving to be imperative in biodiversity studies as they contain a 'gold mine' of historical collection information important for assessing changes in faunal assemblages. Resources are typically limited for taxonomic research and the ageing taxonomic community is another issue of concern for the future of taxonomy on this important group. Succession planning and better resource allocation will be essential to ensure that this fundamental discipline is maintained into the future.

Symposium review: long-term shifts in faunal assemblages in eastern North American estuaries: a review of a workshop held at the biennial meeting of the Coastal and Estuarine Research Federation (CERF), November 2007, Providence, Rhode Island

A workshop held at the fall 2007 meeting of the Coastal and Estuarine Research Federation addressed the topic of long-term changes in the faunal assemblages of estuaries along the east coast of North America. The workshop, organized by Rodney Rountree and Francis Juanes, brought together researchers who have examined data sets spanning greater than 20 years and who related their findings to various drivers. Changes in faunal assemblages were well-documented by most researchers and were associated with fishing pressure, eutrophication, warmer seawater temperatures, alterations of hydrology, natural environmental factors, and the interactions among these drivers.

Facies and faunal assemblage changes in response to the Holocene transgression in the Lagoon of Mayotte (Comoro Archipelago, SW Indian Ocean)

This paper documents the facies change in response to the Holocene transgression within five sediment cores taken in the lagoon of Mayotte, which contain a Type-1 depositional sequence (lowstand, transgressive and highstand deposits underlain by an erosive sequence boundary). Quantitative compositional analysis and visual examination of the bioclasts were used to document the facies changes. The distribution of the skeletal and non-skeletal grains in the lagoon of Mayotte is clearly controlled by (1) the rate and amplitude of the Holocene sea-level rise, (2) the pre-Holocene basement topography and (3) the growth-potential of the barrier reef during sea-level rise, and the changes in bathymetry and continuity during this period. The sequence boundary consists of the glacial karst surface. The change-over from the glacial lowstand is marked by the occurrence of mangrove deposits. Terrigenous and/or mixed terrigenous-carbonate muds to sandy muds with a mollusc or mollusc-ostracod assemblage dominate the transgressive deposits. Mixed carbonate-siliciclastic or carbonate sand to gravel with a mollusc-foraminifer or mollusc-coral-foraminifer assemblage characterize the early highstand deposits on the inner lagoonal plains. The early highstand deposits in the outer lagoonal plains consist of carbonate muds with a mollusc-foraminifer assemblage. Late highstand deposits consist of terrigenous muds in the nearshore bays, mixed terrigenous-carbonate sandy muds to sands with a mollusc-foraminifer assemblage on the inner lagoonal plains and mixed muds with a mollusc-foraminifer assemblage on the outer deep lagoonal plains. The present development stage of the individual lagoons comprises semi-enclosed to open lagoons with fair or good water exchange with the open ocean.

Variation in the response of intertidal infaunal invertebrates to nutrient additions: field manipulations at two sites within Port Phillip Bay, Australia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 250:35-49 (2003) - doi:10.3354/meps250035 Variation in the response of intertidal infaunal invertebrates to nutrient additions: field manipulations at two sites within Port Phillip Bay, Australia Liz Morris1,2,*, Michael J. Keough2 1Department of Zoology, University of Melbourne, Melbourne 3010, Australia 2Present address: Marine and Freshwater Resources Institute, PO Box 114, Queenscliff 3225, Australia *Email: liz.morris@nre.vic.gov.au ABSTRACT: Nutrient addition experiments are one way of testing the importance of nutrients in ecological systems and can be undertaken relatively easily in soft sediments. We added nutrients (Osmocote®) at 2 sites in Port Phillip Bay, Australia, which differed in proximity to sources of nutrient loading. Changes in faunal assemblages were assessed over an 18 wk experimental period in 1998. At the Sand Island site, nitrate levels were elevated in the high dose treatments and 3 taxa showed responses to nutrient additions, with differences in densities between control and dosed plots of between 50 and 600%. Assemblage-level measures of total abundance and diversity were approximately 20 to 80% greater in dosed plots relative to controls at the end of the experimental period. In contrast, at the more enriched Western Treatment Plant site, 3 of the 10 most dominant taxa were affected by the nutrient additions, with changes of between 50 and 200% observed during the course of the experiment. At this site none of the assemblage level measures of abundance, biomass and diversity reflected an effect of the dose treatments. These results are broadly consistent with other studies that suggest that in areas of low ambient nutrient availability diversity is likely to increase, while in areas with high background nutrient loadings there is likely to be a decrease. At Sand Island, changing the nutrient status of the area is liable to result in rapid changes in several deposit-feeding populations. At the Western Treatment Plant, the same absolute change in N may have less impact on the invertebrate fauna. KEY WORDS: Western Treatment Plant · Swan Bay · Victoria · Benthos · Macroinvertebrates · Field experiments · Experimental power Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 250. Online publication date: March 26, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Sr/Ca, Mg/Ca ratios and Sr and stable isotopes of biogenic carbonates from the Late Miocene Velona Basin (central Apennines, Italy) provide evidence of unusual non-marine Messinian conditions

The Sr/Ca and Mg/Ca ratios of fossil ostracod and mollusc shells from a Late Miocene (Early Messinian) lacustrine sequence in the Velona Basin (central Apennines, Italy) were used to calculate the Sr/Ca and Mg/Ca of waters in which these taxa lived. Sr/Ca of these waters were always higher than the Sr/Ca calculated for the Messinian seawater, despite the broad salinity ranges (fresh water-oligo/mesohaline) inferred from the paleontological analyses. The estimated Mg/Ca water from the Velona samples are below the Mg/Ca value for coeval seawater even though they represent relatively high values when compared with many non-marine waters. The salinity variations of the Velona lacustrine system, recorded by changes in faunal assemblages, are linked to variable inputs of Na–Cl from deep groundwaters and are not reflected in significant changes in Sr/Ca and Mg/Ca of the waters calculated from shell chemistry. The combination of δ 18O signatures and Sr isotopic ratios from molluscs from the Velona Basin suggests a non-marine environment. During some episodes of the lake history, given the saline inputs, the waters in the lake would attain a large solute concentration (oligo to mesohaline), although they retained the meteoric δ 18O signature. We compare the paleohydrochemical inferences from the studied sequence with other Messinian records, and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions.

NE Atlantic benthic foraminifera: modern distribution patterns and palaeoecological significance

Microfaunal evidence is presented from a region in the NE Atlantic Ocean characterized by well‐constrained and very uniform physiochemical water mass properties, but a significant gradient in surface ocean productivity. Notable changes in the species composition of benthic foraminiferal assemblages can be directly related to surface productivity and particulate organic matter supply to the deep ocean floor. Because of the labile nature of much organic matter as it reaches the sea floor, it is argued that benthic foraminifera, which exhibit a high preservation potential in most marine sediments, provide a better proxy for estimating past fluxes than bulk sediment organic carbon (OC) content. Three distinct assemblage groups are recognized: a Cassidulina laevigata group which is dominated by infaunal species and a relatively high sediment OC content; a Rhizammina spp. group which is also dominated by infaunal species; and an Epistominella exigua group dominated by epifaunal taxa and falling sediment OC content. Significant faunal assemblage changes appear to be independent of grain size.

Distribution of planktic foraminifera at the ice margin in the Arctic (Fram Strait)

Planktic foraminifera were collected in net tows (>63 μm) along two east-west transects at 78 ° and 80 °N in the Fram Strait (northern Nordic Seas) at five concurrent depth intervals in the upper 200 m of the water column. In the ice-free zone, absolute abundances in the upper 200 m of the water column up to 500 individuals/m 3 were obtained. Along the ice margin the absolute abundances reached up to 1250 ind/m 3, while in the ice-covered areas not more than 50 ind/m 3 have been found. Surprisingly, these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice-free and the ice-covered regions. Neogloboquadrina pachyderma is the dominant species in most samples, making up to 60% of the total faunal assemblage. Globigerina quinqueloba contributes 38%, and all other species combined make up only 2% of the total fauna. Both, absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used. Using smaller mesh sizes provides a wider species spectrum, which is of special interest for paleoceanographic reconstructions in the Nordic Seas, where fossil assemblages >150 μm often consist of only one species. The specific hydrographic conditions in the Fram Strait, with warm Atlantic waters underlying cold Polar surface waters, result in a rather atypical depth distribution of the planktic foraminifera. All species seem to prefer the temperate Atlantic waters (between 50 m and 200 m). Thus, the species composition as well as geochemical tracers do not reflect the surface ocean conditions, which again has potentially interesting implications for paleoceanographic reconstructions.

Biotic response to a Middle Ordovician paleoceanographic event in eastern North America

Global paleontological events such as mass extinctions have been the focus of attention in recent years, yet regional biotic events account for a greater proportion of extinction in the fossil record and should receive greater attention if we are to fully understand extinction processes over the Phanerozoic. We use a sequence stratigraphic framework to document a major extinction and migration episode that occurred in the Middle and Late Ordovician of North America. This event is characterized in eastern North America by coordinated changes in faunal assemblages, carbonate lithologies, siliciclastic influx, and phosphatization. We ascribe these changes to a regional paleoceanographic event brought on by thrust-driven flexural subsidence and sea-level fluctuations that lowered water temperature and increased turbidity and nutrient input.

Is causal ecological biogeography a progressive research program?

Various spacial and temporal time scales need to be taken into account in the interpretation of biological events. Omission of these aspects can lead to purely descriptive studies of changes in faunal assemblages, which are severely limited in scope. Terrestrial molluscs, which are very sensitive to environmental and climatic changes, provide a good example to illustrate this problem. Using an ecological biogeographic approach, a review of mollusc assemblages from holsteinian tufas in western Europe is presented. The analysis permits the definition of the Lyrodiscus biome, which corresponds to a temperate mixed forest community which developed under a particularly warm oceanic climate, and never occurred in Western Europe since that time.

Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktonic foraminifera from Brazos River, Texas

High‐resolution planktonic foraminiferal analysis of three Brazos River sections indicates a nearly continuous Cretaceous/Tertiary [K/T] boundary sedimentary record second only to the world's most complete record at El Kef, Tunisia. Species extinctions occur over an extended period of time and with two major extinction episodes. The first extinction episode with 46% of the species extinct occurs at and just below [10–15 cm] a short hiatus at the base of a sandy shell hash and clay‐sand unit which was interpreted by Bourgeois et al. [1988] to represent a tsunami bed generated by the K/T boundary bolide impact. The top of this tsunami bed is about 17–20 cm below the K/T boundary as defined by the first appearance of Tertiary planktonic foraminifera. The second extinction phase with 45% of the species extinct occurs 25 cm above the K/T boundary [Zone P0/P1a boundary]. Of the remaining seven surviving Cretaceous species, six gradually disappear during planktonic foraminiferal Subzones P1a and basal P1b. No species extinctions or major faunal assemblage changes are directly associated with the K/T boundary. Iridium distribution is ambiguous, with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined K/T boundary. Relative abundances of dominant species are stable through the Late Maastrichtian, and only minor abundance changes coincide with the first extinction episode or the K/T boundary. The first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in Subzone P1a. Species disappearing at the two extinction episodes [46% and 45%] constitute only a small percentage [8% and 5%] of the individuals of the total planktonic foraminiferal population. This suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes. Magnetostratigraphy indicates that the first extinction phase began about 310,000 years before the K/T boundary, and the second extinction phase occurred 50,000 years after the K/T boundary. This stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling. The hypothesis of a global catastrophic mass extinction at the K/T boundary caused by a large extraterrestrial impact is not supported by the Brazos River planktonic foraminiferal data.

FORESTS, DISTURBANCES, AND INSECTS

AbstractRecent developments in ecological theory pertaining to the coexistence of insect species in response to forest disturbance are reviewed, and the findings are applied to the requirements for the Biological Survey of the Insects of Canada. It is important that a data collection system have a sound theoretical base, otherwise it will probably be found inadequate for the purpose for which it was designed. Questions about changes in faunal assemblages should be related to the scale of disturbance relative to the replacement time of the forest. Recommendations for research on faunal assemblage disturbance relationships are made for the Forest Insect and Disease Survey of Canada, and for the northern boreal forest.