Stephen J. Brooks

Quantification of biotic responses to rapid climatic changes around the Younger Dryas — a synthesis

To assess the presence or absence of lags in biotic responses to rapid climatic changes, we: (1) assume that the δ18O in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the Younger Dryas without any lag at our two study sites of Gerzensee and Leysin, Switzerland; (2) derive a time scale by correlating the δ18O record from these two sites with the δ18O record of the GRIP ice core; (3) measure δ18O records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes; (4) analyse at Gerzensee and Leysin as well as at two additional sites (that lack carbonates and hence a δ18O record) pollen, plant macrofossils, chironomids, beetles and other insects, and Cladocera; (5) estimate our sampling resolution using the GRIP time scale for the isotope stratigraphies and the biostratigraphies; and (6) summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis. We conclude that, at the major climatic shifts at the beginning and end of the Younger Dryas, hardly any biotic lags occur (within the sampling resolution of 8–30 years) and that upland vegetation responded as fast as aquatic invertebrates. We suggest that the minor climatic changes associated with the Gerzensee and Preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site, but were more distinct at higher altitudes. Individualistic responses of plant and animal species to climatic change may reflect processes in individuals (e.g. productivity and phenology), in populations (e.g. population dynamics), in spatial distributions (e.g. migrations), and in ecosystems (e.g. trophic state). We suggest that biotic responses may be telescoped together into relatively short periods (50 to 150 years), perhaps disrupting functional interactions among species and thus destabilising ecosystems.

Chironomid-inferred late-glacial air temperatures at Whitrig Bog, southeast Scotland

This paper presents the first chironomid-inferred mean July air temperature reconstruction for the Late-glacial in Britain. The reconstruction suggests that the thermal maximum occurred early in the interstadial, with temperatures reaching about 12 degreesC. There was then a gradual downward trend to about 11 degreesC, punctuated by four distinct cold oscillations of varying intensity. At the beginning of the Younger Dryas, mean July temperatures fell to about 7.5 degreesC but gradually increased to about 9 degreesC before a rapid rise at the onset of the Holocene. The chironomid-inferred temperature curve agrees closely, both in general trends and in detail, with the GRIP ice-core oxygen-isotope curve. The reconstructed temperatures are 2-4 degreesC lower than coleopteran-inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium-line altitudes during the Younger Dryas. Copyright (C) 2000 John Wiley & Sons, Ltd.

An identification guide to subfossil Tanypodinae larvae (Insecta: Diptera: Chrironomidae) based on cephalic setation

Tanypodinae usually form an important component in subfossil Chironomidae assemblages but can be difficult to identify beyond subfamily level due to fragmentation of subfossil material. However, generic identification of most subfossil specimens can be achieved by reference to the arrangement of cephalic setae. This paper presents the first identification guide to Holarctic Tanypodinae genera based on the cephalic setae. A total of 33 genera is described and illustrated, of which 9 were previously undescribed, and 26 descriptions are based on new material. A total of 42 species is illustrated to show intrageneric and intraspecific variation. Improved taxonomic resolution will enhance the performance of chironomid-environmental variable inference models and chironomid biostratigraphy.

Looking forward through the past : identification of 50 priority research questions in palaeoecology

Summary 1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on timescales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. This article is protected by copyright. All rights reserved. Accepted Article 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human–environment interactions in the Anthropocene; biodiversity, conservation, and novel ecosystems; biodiversity over long timescales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes, and the continued application of long-term data for better-informed landscape management. 7. Synthesis Palaeoecology is a vibrant and thriving discipline and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.

An intercontinental comparison of chironomid palaeotemperature inference models: Europe vs North America.

Abstract Chironomid-temperature inference models based on North American, European and combined surface sediment training sets were compared to assess the overall reliability of their predictions. Between 67 and 76% of the major chironomid taxa in each data set showed a unimodal response to July temperature, whereas between 5 and 22% of the common taxa showed a sigmoidal response. July temperature optima were highly correlated among the training sets, but the correlations for other taxon parameters such as tolerances and weighted averaging partial least squares (WA-PLS) and partial least squares (PLS) regression coefficients were much weaker. PLS, weighted averaging, WA-PLS, and the Modern Analogue Technique, all provided useful and reliable temperature inferences. Although jack-knifed error statistics suggested that two-component WA-PLS models had the highest predictive power, intercontinental tests suggested that other inference models performed better. The various models were able to provide good July temperature inferences, even where neither good nor close modern analogues for the fossil chironomid assemblages existed. When the models were applied to fossil Lateglacial assemblages from North America and Europe, the inferred rates and magnitude of July temperature changes varied among models. All models, however, revealed similar patterns of Lateglacial temperature change. Depending on the model used, the inferred Younger Dryas July temperature decrease ranged between 2.5 and 6°C.

The chronology of palaeoenvironmental changes during the Last Glacial-Holocene transition: towards an event stratigraphy for the British Isles

The overall aim of the TIGGER IIb project is to increase our understanding of the manner and rates by which ecosystems responded to climate changes during the Last Glacial-Holocene transition. Success in this venture requires better constrained palaeoenvironmental reconstructions than have been achieved thus far, and the TIGGER project focused, in particular, on three main aims: (1) off-setting the limitations of conventional radiocarbon dating, in order to provide a more secure chronology of events; (2) increasing the resolution and precision of palaeoclimatic reconstructions; (3) widening the scope of site-specific palaeoecological investigations. In this paper we focus on the first of these strategies, and describe the progress made in developing a more coherent timescale for the climate history of the Lateglacial period. This has been achieved by using a number of independent methods, including calibration of AMS radiocarbon dates obtained from terrestrial plant macrofossils, MCR estimates of summer temperatures based on coleopteran records, analysis of stable carbon isotope ratios in terrestrial plant macrofossils and tephrochronology. Following Björck et al.s 1998 recommendations, we integrate the new results to construct a provisional event stratigraphy for the Last Glacial-Holocene transition in the British Isles, which is based on a sequence of features that are believed to be time-parallel. This approach is considered to provide a more coherent framework for direct comparison of the palaeoenvironmental evidence from Britain with that from elsewhere.

Present-day temperatures in northern Scandinavia during the last glaciation

Scandinavia is generally considered to have been covered extensively with ice throughout marine isotope stages (MIS) 4–2 between 75 and 10 ka. Here we present evidence for ice-free, warm conditions in the central area of the Scandinavian glaciations during MIS 3. Our multiproxy data obtained from a lacustrine sequence in northern Fin-land reveal not only significant response in the northeastern sector of the Scandinavian Ice Sheet to warming during the early part of MIS 3, but also indicate rapid climate warming to present-day temperatures in this ice-free period. New climate-model simulations for interstadial conditions in MIS 3 confirm the high mean July temperatures northeast of the Scandinavian Ice Sheet in response to the high insolation values and the presence of the ice sheet during MIS 3.

Discovering the True Chrysoperla carnea (Insecta: Neuroptera: Chrysopidae) Using Song Analysis, Morphology, and Ecology

Abstract What was once considered a single Holarctic species of green lacewing, Chrysoperla carnea (Stephens), has recently been shown to be a complex of many cryptic, sibling species, the carnea species group, whose members are reproductively isolated by their substrate-borne vibrational songs. Because species in the complex are diagnosed by their song phenotypes and not by morphology, the current systematic status of the type species has become a problem. Here, we attempt to determine which song species corresponds to Stephens’ 1835 concept of C. carnea, originally based on a small series of specimens collected in or near London and currently housed in The Natural History Museum. With six European members of the complex from which to choose, we narrow the field to just three that have been collected in England: C. lucasina (Lacroix), Cc2 ‘slow-motorboat’, and Cc4 ‘motorboat’. Ecophysiology eliminates C. lucasina, because that species remains green during adult winter diapause, while Cc2 and Cc4 share with Stephens’ type a change to brownish or reddish color in winter. We then describe the songs, ecology, adult morphology, and larval morphology of Cc2 and Cc4, making statistical comparisons between the two species. Results strongly reinforce the conclusion that Cc2 and Cc4 deserve separate species status. In particular, adult morphology displays several subtle but useful differences between the species, including the shape of the basal dilation of the metatarsal claw and the genital ‘lip’ and ‘chin’ of the male abdomen, color and coarseness of the sternal setae at the tip of the abdomen and on the genital lip, and pigment distribution on the stipes of the maxilla. Furthermore, behavioral choice experiments involving playback of conspecific versus heterospecific songs to individuals of Cc2 and Cc4 demonstrate strong reproductive isolation between the two species. Comparison of the adult morphology of song-determined specimens to that of preserved specimens in the original type series and in other collections in The Natural History Museum, London, indicate that the ‘true’ Chrysoperla carnea (Stephens) is Cc4. Cc2 cannot be confidently associated with any previously described species and is therefore assigned a new name, Chrysoperla pallida sp. nov., and formally described.

Climate Change and Biosphere Response: Unlocking the Collections Vault

Natural history collections (NHCs) are an important source of the long-term data needed to understand how biota respond to ongoing anthropogenic climate change. These include taxon occurrence data for ecological modeling, as well as information that can be used to reconstruct mechanisms through which biota respond to changing climates. The full potential of NHCs for climate change research cannot be fully realized until high-quality data sets are conveniently accessible for research, but this requires that higher priority be placed on digitizing the holdings most useful for climate change research (e.g., whole-biota studies, time series, records of intensively sampled common taxa). Natural history collections must not neglect the proliferation of new information from efforts to understand how present-day ecosystems are responding to environmental change. These new directions require a strategic realignment for many NHC holders to complement their existing focus on taxonomy and systematics. To set these new priorities, we need strong partnerships between NHC holders and global change biologists.

Validation of climate model-inferred regional temperature change for late-glacial Europe

Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized paleoclimate datasets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earths recent past. Here we present a new chironomid-based paleotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our paleotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.