bluuebunny/crossref_metadata_2025 huggingface dataset:
Handgrip Strength and Cause‐Specific and Total Mortality in Older Disabled Women: Exploring the Mechanism
Authors: Rantanen Taina , Volpato Stefano , Luigi Ferrucci MD , Eino Heikkinen MD , Fried Linda P. , Guralnik Jack M.
Published: December 2004

OBJECTIVES: To examine the association between muscle strength and total and cause‐specific mortality and the plausible contributing factors to this association, such as presence of diseases commonly underlying mortality, inflammation, nutritional deficiency, physical inactivity, smoking, and depression.

DESIGN: Prospective population‐based cohort study with mortality surveillance over 5 years.

SETTING: Elderly women residing in the eastern half of Baltimore, Maryland, and part of Baltimore County.

PARTICIPANTS: Nine hundred nineteen moderately to severely disabled women aged 65 to 101 who participated in handgrip strength testing at baseline as part of the Women's Health and Aging Study.

MEASUREMENTS: Cardiovascular disease (CVD), cancer, respiratory disease, other measures (not CVD, respiratory, or cancer), total mortality, handgrip strength, and interleukin‐6.

RESULTS: Over the 5‐year follow‐up, 336 deaths occurred: 149 due to CVD, 59 due to cancer, 38 due to respiratory disease, and 90 due to other diseases. The unadjusted relative risk (RR) of CVD mortality was 3.21 (95% confidence interval (CI) = 2.00–5.14) in the lowest and 1.88 (95% CI = 1.11–3.21) in the middle compared with the highest tertile of handgrip strength. The unadjusted RR of respiratory mortality was 2.38 (95% CI = 1.09–5.20) and other mortality 2.59 (95% CI = 1.59–4.20) in the lowest versus the highest grip‐strength tertile. Cancer mortality was not associated with grip strength. After adjusting for age, race, body height, and weight, the RR of CVD mortality decreased to 2.17 (95% CI = 1.26–3.73) in the lowest and 1.56 (95% CI = 0.89–2.71) in the middle, with the highest grip‐strength tertile as the reference. Further adjustments for multiple diseases, physical inactivity, smoking, interleukin‐6, C‐reactive protein, serum albumin, unintentional weight loss, and depressive symptoms did not materially change the risk estimates. Similar results were observed for all‐cause mortality.

CONCLUSION: In older disabled women, handgrip strength was a powerful predictor of cause‐specific and total mortality. Presence of chronic diseases commonly underlying death or the mechanisms behind decline in muscle strength in chronic disease, such as inflammation, poor nutritional status, disuse, and depression, all of which are independent predictors of mortality, did not explain the association. Handgrip strength, an indicator of overall muscle strength, may predict mortality through mechanisms other than those leading from disease to muscle impairment. Grip strength tests may help identify patients at increased risk of deterioration of health.
Income‐Related Differences in the Use of Evidence‐Based Therapies in Older Persons with Diabetes Mellitus in For‐Profit Managed Care
Authors: Brown Arleen F. , Gross Amy G. , Gutierrez Peter R. , Jiang Luohua , Shapiro Martin F. , Mangione Carol M.
Published: December 2004

OBJECTIVES: To determine whether income influences evidence‐based medication use by older persons with diabetes mellitus in managed care who have the same prescription drug benefit.

DESIGN: Observational cohort design with telephone interviews and clinical examinations.

SETTING: Managed care provider groups that contract with one large network‐model health plan in Los Angeles County.

PARTICIPANTS: A random sample of community‐dwelling Medicare beneficiaries with diabetes mellitus aged 65 and older covered by the same pharmacy benefit.

MEASUREMENTS: Patients reported their sociodemographic and clinical characteristics. Annual household income (≥$20,000 or <$20,000) was the primary predictor. The outcome variable was use of evidence‐based therapies determined by a review of all current medications brought to the clinical examination. The medications studied included use of any cholesterol‐lowering medications, use of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitors (statins) for cholesterol lowering, aspirin for primary and secondary prevention of cardiovascular disease, and angiotensin‐converting enzyme (ACE) inhibitors in those with diabetic nephropathy. The influence of income on evidence‐based medication use was adjusted for other patient characteristics.

RESULTS: The cohort consisted of 301 persons with diabetes mellitus, of whom 53% had annual household income under $20,000. In unadjusted analyses, there were lower rates of use of all evidence‐based therapies and lower rates of statin use for persons with annual income under $20,000 than for higher‐income persons. In multivariate models, statin use was observed in 57% of higher‐income versus 30% of lower‐income respondents with a history of hyperlipidemia (P = .01) and 66% of higher‐income versus 29% of lower‐income respondents with a history of myocardial infarction (P = .03). There were no differences by income in the rates of aspirin or ACE inhibitor use.

CONCLUSION: Among these Medicare managed care beneficiaries with diabetes mellitus, all of whom had the same pharmacy benefit, there were low rates of use of evidence‐based therapies overall and substantially lower use of statins by poorer persons.
Exercise Training as a Therapy for Chronic Heart Failure: Can Older People Benefit?
Authors: Witham Miles D. , Struthers Allan D. , Fesc  , McMurdo Marion E. T.
Published: December 2004

Despite recent advances in pharmacological therapy, chronic heart failure remains a major cause of morbidity and mortality in older people. Studies of exercise training in younger, carefully selected patients with heart failure have shown improvements in symptoms and exercise capacity and in many pathophysiological aspects of heart failure, including skeletal myopathy, ergoreceptor function, heart rate variability, endothelial function, and cytokine expression. Data on mortality and hospitalization are lacking, and effects on everyday activity, depression, and quality of life are unclear. Exercise therapy for patients with heart failure appears to be safe and has the potential to improve function and quality of life in older people with heart failure. To realize these potential benefits, exercise programs that are suitable for older, frail people need to be established and tested in an older, frail, unselected population with comorbidities.
Maintenance of integrity and function of isolated hepatocytes during extended suspension culture at 25°C
Authors: Wigg Alan J. , Phillips John W. , Berry Michael N
Published: December 2004

Abstract: Isolated hepatocytes in suspension provide a number of advantages for use in bioartificial liver device, however, poor stability of this cell preparation at physiological temperatures is an apparent barrier preventing their use. We therefore investigated the integrity and differentiated function of isolated rat hepatocytes under conditions of mild hypothermia. Isolated hepatocytes were suspended in a bicarbonate buffered saline medium, supplemented with glucose and bovine serum albumin (BSA), and maintained for 48 h at 25 °C on a rotary shaker under an atmosphere of 95% O2 and 5% CO2. Under these conditions there was no significant decline in cell viability and good preservation of cellular morphology on transmission electron microscopy for at least 24 h. Isolated hepatocytes in suspension at 25 °C were also able to maintain normal Na +  and K +  ion gradients. The cellular energy status ([ATP], ATP/ADP ratio, cytoplasmic and mitochondrial redox potentials), metabolic function (urea synthesis and ammonia removal), albumin synthesis and phase I and phase II drug detoxification activity of these cells were also maintained for at least 24 h post isolation. These observations demonstrate the robust nature of mildly hypothermic isolated hepatocytes in suspension and encourage further studies re‐examining the feasibility of using this cell preparation in bioartificial livers.
Water‐ and nutrient‐use efficiency of a deciduous species, Vaccinium myrtillus, and an evergreen species, V. vitis‐idaea, in a subalpine dwarf shrub heath in the southern Alps, Italy
Authors: Gerdol Renato , Iacumin Paola , Marchesini Roberta , Bragazza Luca
Published: December 2004

Periodic measurements of gas‐exchange rates and determinations of foliar N and P concentrations were used for evaluating instantaneous water‐use efficiency and photosynthetic nutrient‐use efficiency in two co‐existing dwarf shrubs of different growth form (V. myrtillus,
deciduous, and V. vitis‐idaea, evergreen) in a subalpine heath in
the southern Alps of Italy. Those data were compared with cumulative
assessments of water‐use efficiency and photosynthetic nutrient‐use
efficiency obtained by measuring leaf carbon isotope discrimination in
leaf tissues and by estimating nutrient resorption from senescing leaves.
V. myrtillus presented higher dry‐weight based rates of net
photosynthesis (Aweight) compared to V.
vitis‐idaea. Aweight was positively correlated with
foliar‐nutrient status and intercellular‐to‐ambient gradient in
CO2 concentrations. Aweight was,
furthermore, negatively correlated with leaf specific mass. Instantaneous
photosynthetic nutrient‐use efficiency did not differ between the two
species but the percentages of N and P pools resorbed from senescing
leaves were somewhat higher in the deciduous species. The evergreen
species showed lower P concentrations in senescing leaves which indicated
a higher proficiency in resorbing phosphorus compared to the deciduous
species. In addition, the evergreen species achieved a higher carbon gain
per unit foliar N and P, due to a longer mean residence time of both
nutrients. The two species did not differ from each other with respect to
both instantaneous and long‐term water‐use efficiency. This was
consistent with the climatic pattern, showing no sign of water deficiency
through the growing season. Current‐year V. vitis‐idaea leaves had
a significantly higher Δ13C compared to previous‐year leaves, possibly mirroring a long term acclimation of evergreen leaves, as far as they age, to the habitat conditions in the understory where evergreen species are usually confined within mixed dwarf‐shrub communities.
Cannibals and parasites: conflicting regulators of bimodality in high latitude Arctic char, Salvelinus alpinus
Authors: Hammar Johan
Published: December 2004

Unexploited populations of Arctic char (Salvelinus alpinus)
sampled in autonomous lake ecosystems in northern Svalbard demonstrate
extraordinary catch curves with age and size frequency distributions
characterized by discrete bimodality. Analyses of size‐age relationship,
summer diet and food‐related intestinal parasite intensities of modal
char groups revealed a pattern of discrete ontogenetic niche shifts.
Life‐history changes at age 10–15 and size 200–300
mm/50–300 g involved shifting from an initial mode of small‐sized,
slow‐growing and sexually mature individuals feeding on micro‐crustaceans
and aquatic insects (Chironomidae, Trichoptera), to a terminal mode of
large‐sized and fast‐growing cannibals. Cannibalism, however, was found
to result in accumulation of cestodan parasites, of which
Diphyllobothrium ditremum increases age‐related mortality rates
and may be lethal at 1500–2000 plerocercoids. Genetically
allopatric populations with cannibalism demonstrated a female‐biased sex
ratio, primarily in the initial mode, suggesting sexual asynchrony in
their ontogeny. By contrast, a small population of large‐sized,
non‐cannibalistic Arctic char feeding exclusively on the large amphipod
Gammaracanthus lacustris, demonstrated unimodal size and age frequency distribution, faster growth, an excess of males and lower parasite burden. Seasonal prey shortage and slow juvenile growth in association with fitness components favoring large body size is a suggested mechanism for inducing cannibalism. Although not the basic cause of bimodality as such, it is concluded that ontogenetic niche shift by cannibalism reinforces discrete age modal divergence resulting in the numerical preponderance of large‐sized individuals in these marginal char populations. Cannibalism is thus considered an important strategy for survival of landlocked Arctic char in the High Arctic. As a conflicting cost to the more efficient use of available energy by larger individuals, the accumulation of cestodan parasites in cannibals, however, will reduce the survival rate of old individuals and accelerate their termination within this modal group.
The influence of patch demographics on metapopulations, with particular reference to successional landscapes
Authors: Johnson Mark P.
Published: December 2004

The classical view of metapopulations relates the regional abundance of a species to the balance between the extinction and colonization dynamics of identical local populations. Species in successional landscapes may represent the most appropriate examples of classical metapopulations. However, Levins‐type metapopulation models do not explicitly separate population loss due to successional habitat change from other causes of extinction. A further complication is that the chance of population loss due to successional habitat change may be related to the age of a patch. I developed simple patch occupancy models to include succession and included consideration of patch age structure to address two related questions: what are the implications of changes in patch demographic rates and when is a move to a structured patch occupancy model justified? Age‐related variation in patch demography could increase or decrease the equilibrium fraction of the available habitat occupied by a species when compared to the predictions of an unstructured model. Metapopulation persistence was enhanced when the age class of patches with the highest species occupancy suffered relatively low losses to habitat succession. Conversely, when the age class of patches with the highest species occupancy also had relatively high successional loss rates, extinction thresholds were higher that would be predicted by a simple unstructured model. Hence age‐related variation in patch successional rate introduces biases into the predictions of simple unstructured models. Such biases can be detected from field surveys of the fraction of occupied and unoccupied patches in each age class. Where a bias is demonstrated, unstructured models will not be adequate for making predictions about the effects of changing parameters on metapopulation size. Thinking in successional terms emphasizes how landscapes might be managed to enhance or reduce the patch occupancy by any particular metapopulation
Single‐ or multistage regulation in complex life cycles: does it make a difference?
Authors: Hellriegel Barbara
Published: December 2004

Data on the different stages of complex life cycles are often rather unbalanced, especially those concerning the effects of density. How does this affect our understanding of a species’ population dynamics? Two discrete three‐stage models with overlapping generations and delayed maturation are constructed to address this question. They assume that survival or emigration in any life stage and/or reproduction can be density dependent. A typical pond‐breeding amphibian species with a well‐studied larval stage serves as an example. Numerical results show that the population dynamics resulting from density dependence at a single (e.g. the larval) stage can be decisively and unpredictably modified by density dependence in additional stages. Superposition of density‐dependent processes could thus be one reason for the difficulties in identifying density dependence in the field. Moreover, in a simulated source‐refuge system with habitat‐specific density‐dependent dispersal of juveniles density dependence in multiple stages can stabilize or destabilize the dynamics and produce misleading age structures. From an applied perspective this model shows that excluding multistage regulation prematurely clearly affects our ability to predict consequences of human impacts.
Effects of CO2 and light on tree phytochemistry and insect performance
Authors: Agrell Jep , McDonald Evan P. , Lindroth Richard L.
Published: December 2004

Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acer saccharum) were grown under ambient (387±8 μL/L) and elevated (696±2 μL/L) levels of atmospheric CO2, with low and high light availability (375 and 855 μmol×m−2×s−1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white‐marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short‐term (fourth instar) feeding trials were conducted with insects fed detached leaves.

 Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO2, respectively.

 The long‐term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general, CO2 effects were pronounced in high light and decreased along the gradient aspen birch maple. For larvae reared on high light aspen, enriched CO2 resulted in 62% fewer survivors, with increased development time, and reduced pupal mass. For maple‐fed insects, elevated CO2 levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO2 effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO2 significantly reduced total consumption, especially by insects on high light aspen and low light maple.

 This research demonstrates that effects of CO2 on phytochemistry and insect performance can be strongly light‐dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO2 availability appeared to increase the defensive capacity of early‐successional species primarily under high light conditions, and of late‐successional species under low light conditions. Due to the interactive effects of tree species, light, CO2, and herbivory, community composition of forests may change in the future.
Reproductive synchrony in the intertidal amphipod Corophium volutator
Authors: McCurdy Dean G. , Boates J. Sherman , Forbes Mark R.
Published: December 2004

Following logic of the mate‐availability hypothesis, females are expected to show asynchronous reproduction in those species where operational sex ratios are female‐biased and under circumstances where an individual female is sexually receptive only for short durations. We show that females of the intertidal amphipod Corophium volutator are receptive to mating only for a few days following their moult and are unable to hasten onset of moulting in the presence of a male. Despite meeting the conditions of the mate‐availability hypothesis, reproduction was synchronous for female C. volutator across spatial and temporal scales relevant to mate‐searching abilities of males. As such, some females are not expected to mate between moults, which coincide with their ability to mate. However, females do moult frequently (relative to males) which should increase their likelihood of mating over their lifetimes. It is unlikely that seasonal constraints, predation, or competition can account for the high degree of synchrony among breeding female amphipods. We suggest that dispersal of females or their offspring may constrain activity of females, as they moulted almost entirely during spring tides (although not always during the same set of spring tides). Female reproductive synchrony also has implications for reproductive behaviour of males, in particular, the possibility of harem‐defence polygyny.
On the invasibility of persistent protist communities
Authors: Law Richard , Weatherby Anita J. , Warren Philip H.
Published: December 2004

We investigate the rate of increase of protists introduced at low density into experimental communities comprising different sets of coexisting species. The experiment separates (1) the main effect of six introduced species, (2) the main effect of eleven resident communities, and (3) the introduction×community interaction. Introduced species differ markedly in their capacity to invade, and only one, Paramecium, invades all of the communities. Most of the introduced species invade some communities, and there is a large introduction×community interaction that comes about from bringing together particular combinations of species. For example, the rate of increase of Amoeba is greater when introduced into communities containing Paramecium than when introduced into communities in which Paramecium is absent. The omnivore Blepharisma increases faster in the presence of one of its prey Tetrahymena, notwithstanding the fact that it is also a potential competitor with this prey for bacteria. There is little indication that the species richness of resident communities (over the limited range available) affects the success of invasion. The results suggest that understanding invasions depends as much on detailed knowledge of idiosyncratic biological interactions as on general properties of community structure.
Does interspecific competition affect territorial distribution of birds? A long‐term study on Siberian Phylloscopus warblers
Authors: Bourski Oleg V. , Forstmeier Wolfgang
Published: December 2004

Seven species of Phylloscopus warblers breed in the middle taiga subzone of Central Siberia. We studied their territorial distribution over 18 breeding seasons between 1978 and 1996.

 Phylloscopus inornatus, the most abundant breeding bird species in the study area, breeds in dense clusters of territories. In some habitats, these clusters are very unstable from year to year, providing an excellent opportunity to study the influence of P. inornatus on the territorial distribution of other species. We present a method for quantifying decreases in a species’ breeding density caused by the presence of a competing congener. Analysing all possible combinations of species, we found reciprocal territorial avoidance between P. inornatus and P. proregulus as well as between P. inornatus and P. collybita. This is consistent with the hypothesis that territorial avoidance occurs between the species of greatest morphological similarity. The occurrence of territorial avoidance is not explained by habitat characteristics such as vegetation cover and productivity. However low productivity may be necessary for territorial avoidance to occur.

 An alternative explanation for the observed territorial separation of some species, derived from the Fretwell‐Lucas model of habitat occupancy, is examined and rejected. Causes and implications of clustering behaviour of P. inornatus are also discussed.
Interactive effects of soil fertility and herbivory on Brassica nigra
Authors: Meyer Gretchen A.
Published: December 2004

Soil nutrient availability may affect both the amount of damage that plants receive from herbivores and the ability of plants to recover from herbivory, but these two factors are rarely considered together. In the experiment reported here, I examined how soil fertility influenced both the degree of defoliation and compensation for herbivory for Brassica nigra plants damaged by Pieris rapae caterpillars. Realistic levels of defoliation were obtained by placing caterpillars on potted host plants early in the life cycle and allowing them to feed until just before pupation on the designated plant. Percent defoliation was more than twice as great at low soil fertility compared to high (48.2% and 21.0%, respectively), even though plants grown at high soil fertility lost a greater absolute amount of leaf area (38.2 cm2 and 22.1 cm2, respectively). At both low and high soil fertility, total seed number and mean mass per seed of damaged plants were equivalent to those of undamaged plants. Thus soil fertility did not influence plant compensation in terms of maternal fitness. However, the pathways used to achieve compensation in seed production were different at low and high soil fertility. At low soil fertility, relative leaf growth rates (area added per inital area per day) of damaged plants were drastically reduced over the second week of caterpillar feeding. Damaged plants recovered the leaf area lost to herbivory in the two weeks following insect removal by increasing leaf relative growth rates above the levels seen for undamaged plants, but the replacement of leaf tissue lost to herbivory came at the expense of stem biomass. At high soil fertility, relative leaf growth rates of damaged plants were similar to those of undamaged plants both over the second week of caterpillar feeding and following caterpillar removal, and stem biomass was not affected by herbivory. These results suggest that higher levels of soil nutrients increased the ability of plants to stay ahead of their herbivores as they were being eaten. Because damaged plants at high soil fertility were able to maintain leaf growth rates to a greater extent than damaged plants at low soil fertility, they did not fall as far behind undamaged plants over the period of insect feeding and did not have as much catching up to do after feeding ended to compensate for herbivory.
A comparative study of seed number, seed size, seedling size and recruitment in grassland plants
Authors: Jakobsson Anna , Eriksson Ove
Published: December 2004

In this study we analyse relationships between seed number, seed size, seedling size and recruitment success in grassland plants. The often hypothesised trade‐off between seed size and seed number was supported by a cross‐species analysis and by an analysis of 35 phylogenetically independent contrasts, derived from a data‐set of 72 species. Apart from among‐species relatedness, we also controlled for possible confounding effect of plant size that may influence both seed size and seed number. A sowing experiment with 50 species was performed in the field. The seeds were sown in a grassland and subjected to two treatments, disturbance and undisturbed sward. Evidence for seed‐limited recruitment was obtained for 45 of the species. Disturbance had a significant, or nearly significant, positive effect on recruitment for 16 of the 45 species. The relative recruitment in undisturbed sward increased with increased seed size, and both recruitment success and seedling size were positively related to seed size. We suggest that a trade‐off between competitive ability and number of recruitment opportunities follows from the trade‐off between seed size and seed number, through a causal chain from seed size via seedling size to recruitment success. The relationships between seed size, seed number and recruitment may be an important underlying mechanism for abundance and dynamics of plant species in grassland vegetation. This is an example of a direct link between evolutionary life‐history theory, and theory of plant community structure.
Patterns within patterns: abundance‐size relationships within the Hemiptera of tropical rain forest or why phylogeny matters
Authors: Hodkinson Ian D. , Casson David S.
Published: December 2004

Our data are for a large composite sample of bugs (Insecta Hemiptera and Homoptera) from a tropical rain forest area in Sulawesi, Indonesia, collected by various sampling techniques at several representative localities over one year. We demonstrate how an overall relationship between log abundance and log body length in a large sample, which at first sight might appear to be of the polygonal form identified by Blackburn and Gaston, can be broken down into a consistent series of stronger linear relationships based around the composition of taxonomic clades with differing gradients. Furthermore, we show that the number of species within superfamily/family clades is negatively related to the mean body size of the clade, suggesting that taxa with a small body size tend to be represented by more species, thus further distorting the form of any overall relationship. The significance of these findings is discussed in the context of the current debate about species abundance, species size and distribution area relationships.
Are insects flower constant because they use search images to find flowers?
Authors: Goulson Dave
Published: December 2004

Many insects which gather nectar or pollen exhibit flower constancy, a learned fidelity to a particular species of plant. Recent studies suggest that foraging insects may use a perceptual mechanism akin to a search image to detect flowers, in a manner analogous to the way that predators search for prey. This has emerged as an alternative (but not mutually exclusive) explanation for flower constancy to that proposed by Darwin, who suggested that it may result from a limited ability to learning or remember the handling skills appropriate for particular flowers. However, search images are thought to be a mechanism for locating cryptic prey. Plants which are pollinated by animals have evolved brightly coloured flowers to attract the attention of their pollinators. It thus seems implausible to argue that flowers may actually be cryptic. One possible explanation for this apparent contradiction is that flowers are effectively cryptic when viewed against a background which contains many other flowers of similar colour. I present experimental evidence which suggests that a background of flowers of similar colour does reduce foraging efficiency of bumblebees, but that a background of dissimilarly coloured flowers has no effect. This I interpret as evidence that flowers may be cryptic, suggesting that pollinators may indeed use a search image in location of flowers. However, the relative importance of constraints on foragers’ abilities to locate flowers versus their abilities to handle them as causes of flower constancy remain to be elucidated.
Fine‐scale movement behaviors of calopterygid damselflies are influenced by landscape structure: an experimental manipulation
Authors: Jonsen Ian D. , Taylor Philip D.
Published: December 2004

We explore the effect of differences in landscape structure, arising from habitat loss, on the fine‐scale movement behaviors of two congeneric damselflies –Calopteryx aequabilis and C. maculata.
Both species require streams for breeding and naiad development and both
often use forest for foraging. We compare movement behaviors across three
types of landscape: forested landscapes, where stream and forest habitat
are adjacent; partially forested landscapes, where streams and forest
habitat are disjunct, and non‐forested landscapes, where little to no
forest habitat is available. We employ a reciprocal transplant experiment
to determine the extent to which movement along and away from streams is
influenced by landscape structure and historical behavior or
morphological adaptations. For both species, we show that both the
propensity to move away from streams and rates of net displacement differ
among landscape types. Both species move away from streams on landscapes
with high or moderate levels of forest cover but neither moves away from
streams on landscapes with little or no forest. Furthermore, C.
maculata native to predominantly forested landscapes are more likely
to move away from streams, regardless of the landscape structure they
encounter, than are individuals native to moderately forested or
non‐forested landscapes. There was no effect of natal landscape on C.
aequabilis. Comparisons with microlandscape studies suggest that there may be some general similarities among the different systems but these are clouded by uncertainty regarding the similarity of the underlying processes responsible for observed behavioral responses to landscape structure. Despite this uncertainty, animal movement behaviors are contingent upon the structure of the broader landscape, regardless of the absolute scale of the landscape.
Interspecific variation in extraction of buried seeds within an assemblage of sparrows
Authors: Whalen David M. , Watts Bryan D.
Published: December 2004

Most North American sparrows forage almost exclusively on herbaceous seeds during the winter months. Limited availability of surface seeds forces some birds to scratch for seeds buried beneath soil, snow, or litter. Artificial seed trays were used to test the ability of five different sparrow species to extract seeds buried at different depths in soil. The results suggest three functional groups based on relative scratching ability. Strong scratchers, which included eastern towhee and song and white‐throated sparrows, met or exceeded their energetic requirements when foraging on seeds buried at all depths (down to a maximum depth of 1.50–2.25 cm). A weak scratching species, Savannah sparrow, scratched with the same frequency as the strong scratchers, but experienced negative energy budgets when forced to forage on sub‐surface seeds. Finally, a non‐scratching species, field sparrow, failed to extract any buried seeds.  Level of scratching ability may influence foraging efficiency at low resource densities. As a result, interspecific differences in scratching ability may contribute to habitat selection. Strong scratchers may be adapted to foraging near woody vegetation where intense resource competition and abundant litter limit the availability of surface seeds. Weak scratchers, on the other hand, may be forced to feed away from areas where surface seeds are limited. Since woody vegetation serves as a primary source of protective cover in early successional habitats, a tradeoff between foraging efficiency and the risk of predation may promote the local coexistence of species that differ in relative scratching ability and adaptations to evading predators.
Effects of bryophytes and lichens on seedling emergence of alvar plants: evidence from greenhouse experiments
Authors: Zamfir Manuela
Published: December 2004

Emergence of seedlings of four alvar grassland species (Arenaria
serpyllifolia, Festuca ovina, Filipendula vulgaris and
Veronica spicata) in bryophyte and lichen carpets was analysed in
a series of greenhouse experiments. The aspects investigated were: the
influence of thickness of moss mats, both in dry and moist conditions,
the effects of thick Cladonia spp. clumps, and of living vs dead
moss shoots and lichen podetia. Overall, Festuca seedlings emerged
best whereas the small‐seeded species, Arenaria and Veronica
, had the lowest emergence. Moisture had a significant effect only on the
emergence of Festuca seedlings, which emerged better in the dry
treatment than in the moist. A thick moss cover negatively affected
seedling emergence of Arenaria and Veronica but did not
affect the emergence of Festuca. Filipendula showed lower
seedling emergence in both thick and thin moss than on bare soil only in
the dry treatment, whereas in the moist treatment emergence did not
differ among the three substrates. Arenaria seedlings emerged less
in thick and thin moss than on bare soil in the dry treatment, whereas in
the moist treatment emergence in the thin moss was not different from
bare soil. Thus, in relatively dry environments even a thin moss cover
may inhibit rather than facilitate seedling emergence. The lichen clumps
inhibited only the emergence of the forbs. Both living moss shoots and
lichen podetia inhibited emergence of Veronica seedlings but did
not affect Festuca. In contrast, emergence in the presence of dead mosses and lichens did not differ from emergence in their absence for both species. Hence, inhibition of seedling emergence by bryophytes and lichens of at least some vascular plant species may be mediated by some biotic factor. However, the effect of differences in substrate properties on germination cannot be excluded
Small‐scale processes in desert locust swarm formation: how vegetation patterns influence gregarization
Authors: Despland E. , Collett M. , Simpson S. J.
Published: December 2004

Desert locusts (Schistocerca gregaria) change phase in response to population density: ‘solitarious’ insects avoid one another, but when crowded they shift to the gregarious phase and aggregate. This individual‐level process is the basis for population‐level responses that may ultimately include swarm formation. We have recently developed an individual‐based model of locust behavior in which contagious resource distribution leads to phase change. This model shows how population gregarization can result from simple processes operating at the individual level. In the present study, we performed a series of laboratory experiments in which vegetation pattern and locust phase state were assigned quantitative, measurable indices. The pattern of distribution of the resource was represented via fractal dimension; the phase state was evaluated using a behavioral assay based on logistic regression analysis. Locusts were exposed to different patterns of food resource in an artificial arena, after which their behavioral phase state was assayed. These experiments showed that when the distribution of the vegetation was patchy, locusts were more active, experienced higher levels of crowding, and became more gregarious. These results are consistent with simulation predictions and field observations, and demonstrate that small‐scale vegetation distribution influences individual behavior and phase state and plays a role in population‐level responses.
The radiation of Calochortus: generalist flowers moving through a mosaic of potential pollinators
Authors: Dilley James D. , Wilson Paul , Mesler Michael R.
Published: December 2004

Few studies have surveyed the insects visiting flowers at many sites and for many related species. Calochortus, a genus of about 60
species with its center of diversity in California, has flowers with a
wide range of appearances. Insects visiting Calochortus flowers in
25 species were censused at 40 sites. Visitors at coflowering plants were
also censused at each site. Calochortus flowers attracted insects
in several orders, especially beetles that feed at glands on the petals
and bees that often collect pollen. Species in Calochortus section
Calochortus had a somewhat narrower spectrum of visitors than
species in section Mariposa. The diversity of visitor species at
Mariposa flowers was often greater than the diversity at
coflowering species. On the whole, Calochortus flowers seem to be
generalists in terms of their pollinators. Differences in visitor
assemblage were greater between Calochortus populations at
different sites than between visitors to Calochortus versus
coflowering species at a site. Nevertheless, there were always
significant differences in the proportions of various insects at
Calochortus versus coflowering plants. In addition, proportions of
visitors also differed between species of Calochortus at the same
site. Thus, Calochortus flowers have diverged in the visitors they
attract, and evidently they have done so without permanently specializing
(except to a limited degree at the sectional level). What we know of the
radiation of Calochortus lilies is consistent with an interpretation of adaptive wandering through a spatiotemporal mosaic of pollinator communities.
Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus
Authors: Pietikäinen Janna , Kiikkilä Oili , Fritze Hannu
Published: December 2004

Wildfires produce a charcoal layer, which has an adsorbing capacity resembling activated carbon. After the fire a new litter layer starts to accumulate on top of the charcoal layer, which liberates water‐soluble compounds that percolate through the charcoal and the unburned humus layer. We first hypothesized that since charcoal has the capacity to adsorb organic compounds it may form a new habitat for microbes, which decompose the adsorbed compounds. Secondly, we hypothesized that the charcoal may cause depletion of decomposable organic carbon in the underlying humus and thus reduce the microbial biomass. To test our hypotheses we prepared microcosms, where we placed non‐heated humus and on top one of the adsorbents: non‐adsorptive pumice (Pum), charcoal from Empetrum nigrum (EmpCh), charcoal from humus (HuCh) or activated
carbon (ActC). We watered them with birch leaf litter extract. The
adsorbing capacity increased in the order Pum<HuCh<EmpCh<ActC,
the adsorbents being capable of removing 0%, 26%, 42% and 51% of the
dissolved Corg in the litter extract, respectively. After one month, all adsorbents harboured microbes, but their amount and basal respiration was largest in EmpCh and HuCh, and smallest in Pum. In addition, different kinds of microbial communities with respect to their phospholipid fatty acid and substrate utilization patterns were formed in the adsorbents. The amount of microbial biomass and number of bacteria did not differ between humus under different adsorbents, although different microbial communities developed in humus under EmpCh compared with Pum, which is obviously related to the increased pH of the humus under EmpCh, and also ActC. We suggest that charcoal from burning can support microbial communities, which are small in size but have a higher specific growth rate than those of the humus. Although the charcoal layer induces changes in the microbial community of the humus, it does not reduce the amount of humus microbes.
An experimental test of the effect of plant functional group diversity on arthropod diversity
Authors: Symstad Amy J. , Siemann Evan , Haarstad John
Published: December 2004

Characteristics used to categorize plant species into functional groups for their effects on ecosystem functioning may also be relevant to higher trophic levels. In addition, plant and consumer diversity should be positively related because more diverse plant communities offer a greater variety of resources for the consumers. Thus, the functional group composition and richness of a plant community may affect the composition and diversity of the herbivores and even higher trophic levels associated with that community. We tested this hypothesis by sampling arthropods with a vacuum sampler (34 531 individuals of 494 species) from an experiment in which we manipulated plant functional group richness and composition. Plant manipulations included all combinations of three functional groups (forbs, C3 graminoids,
and C4 graminoids) removed zero, one, or two at a time from grassland plots at Cedar Creek Natural History Area, MN. Although total arthropod species richness was unrelated to plant functional group richness or composition, the species richness of some arthropod orders was affected by plant functional group composition.  Two plant characteristics explained most of the effects of plant functional groups on arthropod species richness. Nutritional quality, a characteristic related to ecosystem functioning, and taxonomic diversity, a characteristic not used to designate plant functional groups, seemed to affect arthropod species richness both directly and indirectly. Thus, plant functional groups designated for their effects on ecosystem processes will only be partially relevant to consumer diversity and abundance.
Resource heterogeneity and ungulate population dynamics
Authors: Illius A. W. , O'Connor T. G.
Published: December 2004

It has been suggested that climatic variation has the effect on the dynamics of arid and semi‐arid grazing systems of reducing animal numbers below the level at which they have much impact on vegetation or soils, and that spatial heterogeneity in resource availability serves to buffer herbivores against climatic variation. Modelling was used to test these hypotheses and to examine the interacting effects of temporal and spatial variability in plant production on animal population dynamics and defoliation intensity. The model distinguishes areas of the range that are accessible during wet and dry seasons, and examines the effect of seasonal restrictions in foraging area. It was established that the animal population is in long‐term equilibrium with dry‐season resources, on which it depends for survival; that dry season resource areas and outlying areas thus operate in a source‐sink manner; and that the ratio of these areas determines the strength of consumer‐resource coupling outside the dry‐season range. A high ratio of dry season to wet season resources may support a sufficiently large animal population to impose non‐trivial defoliation impacts on the outlying range. Increasing degrees of variability in primary production on areas used by animals for surviving the dry season increased the annual variation in animal abundance and reduced the mean. By comparison with a stable environment, for which the model predicts virtually stable animal numbers and constant, low defoliation intensity, variation in annual rainfall causes wide fluctuations in animal numbers and defoliation intensity. Under climatic variation, animal numbers can build up enough to impose much higher defoliation intensities than under a constant regime. Periodic intense defoliation is a consequence of climatic variability which is likely to make these environments more, not less, prone to ecological change.
Density dependence in induced plant resistance to herbivore damage: threshold, strength and genetic variation
Authors: Underwood Nora
Published: December 2004

The density‐dependent effect of induced plant resistance on herbivore populations depends on the relationship between the amount of herbivore damage and the level of induced resistance produced by the plant. This relationship should influence the interaction of induced resistance and herbivore population dynamics, and if the relationship varies among plant genotypes, it could be subject to natural selection by herbivores. In this study the relationship between percent leaf area damaged and level of induced resistance was characterized for four genotypes of soybeans grown in a greenhouse. Damage ranging from 8 to 92% of leaf area was imposed using Mexican bean beetle larvae, and induced resistance was measured by bioassay using Mexican bean beetle adults. The level of induced resistance was significantly affected by the amount of damage, and the level of induced resistance varied significantly among the four genotypes. There was also a marginally significant interaction of damage and plant genotype, suggesting that the form of density dependence varies among these four genotypes of soybeans. These results suggest that these genotypes of plants might affect herbivore populations differently. If this variation is heritable, the form of density‐dependent effects of induced resistance has the potential to evolve in this system.