Children's competition in a natural setting: evidence for the ideal free distribution

Little is known of the foraging abilities of children in modern cultures, especially when children forage in groups. Here we present a test of optimal foraging theory in groups of street children working for money. The children we observed were selling bottles of water to drivers distributed in two lanes at a crossroad of Istanbul, Turkey. As predicted by the ideal free distribution (a model of optimal group foraging), the ratio of children working in the two lanes was sensitive to the ratio of cars (and therefore the ratio of potential buyers) present in each lane. Deviations from the ideal free model arose largely from numerical restrictions on the set of possible ratios compatible with a small group size. When these constraints were taken into account, optimal behavior emerged as a robust aspect of the children's group distribution. Our results extend to human children aspects of group foraging that were previously tested in human adults or other animal species.     

Vertical distribution of zooplankton: density dependence and evidence for an ideal free distribution with costs

Background  

In lakes with a deep-water algal maximum, herbivorous zooplankton are faced with a trade-off between high temperature but low food availability in the surface layers and low temperature but sufficient food in deep layers. It has been suggested that zooplankton (Daphnia) faced with this trade-off distribute vertically according to an "Ideal Free Distribution (IFD) with Costs". An experiment has been designed to test the density (competition) dependence of the vertical distribution as this is a basic assumption of IFD theory.     

Linking individual foraging behavior and population spatial distribution in patchy environments: a field example with Mediterranean blue tits

 In spite of recent theoretical interest, few field studies have addressed the links between individual behavioral decisions and population distribution. This work analyzes the foraging behavior of individuals and the spatial distribution of a population of blue tits (Parus caeruleus) just before the main breeding season, when blue tit foraging was not affected by central-place or flocking behaviors. The study was carried out in open holm oak Quercus ilex woodlands (dehesas) that are patchy for canopy-foraging birds because of the scattered arrangement of trees. Residence time on each tree was not correlated either with previous flight time or with prey abundance in trees. Flight distances between trees were larger than average distances estimated in random samples of holm oaks taken close to foraging birds. Trees were not selected by birds on the basis of their expected energy costs and rewards. Bird abundance was not related to food availability in trees or to tree size across dehesas. However, bird abundance was strongly correlated with tree density and with the availability of tree holes for nesting, to the extent that the proportion of tits matched the proportions of both tree abundance and hole abundance across study plots. Overall, neither the behavior of individuals nor the distribution of the population of blue tits corresponded with food resources, which appeared superabundant; instead, tits appeared to behave and be distributed according to the distribution of structural resources such as trees and tree holes for nesting. Received: 18 August 1996 / Accepted: 14 March 1997     

Activity patterns during food provisioning are affected by artificial light in free living great tits (Parus major)

Artificial light may have severe ecological consequences but there is limited experimental work to assess these consequences. We carried out an experimental study on a wild population of great tits (Parus major) to assess the impact of light pollution on daily activity patterns during the chick provisioning period. Pairs that were provided with a small light outside their nest box did not alter the onset, cessation or duration of their working day. There was however a clear effect of artificial light on the feeding rate in the second half of the nestling period: when provided with artificial light females increased their feeding rate when the nestlings were between 9 and 16 days old. Artificial light is hypothesised to have affected the perceived photoperiod of either the parents or the offspring which in turn led to increased parental care. This may have negative fitness consequences for the parents, and light pollution may thus create an ecological trap for breeding birds.     

Transition from a random to an ideal free to an ideal despotic distribution: the effect of individual difference in growth

Individual differences in growth can lead to a monopolistic form of food competition. We studied the long-term transition in the mode of competition and the distribution of individuals between food patches of the cloned salmonid fish, Oncorhynchus masou ishikawae, in the laboratory. This transition was accompanied by growth depensation, i.e., the increase over time in the variance of size between individuals resulting from the differences in individual growth rates. The 120-cm experimental tanks were divided into two compartments (patches) between which an opaque partition was placed. Fish were able to move freely between the patches and therefore were able to assess the patch quality using long-term memory, but they were not able to see the food input in the other patch directly. The distribution between the two food patches, the amount of food gained, and the growth and the agonistic behavior of four groups of six individuals were observed over 4 weeks. We found that (1) within-group variation in body weight increased with time; (2) on average, the better patch was used by more individuals than predicted by a random distribution but fewer individuals than predicted by an ideal free distribution, and (3) the distribution and pattern of resource use by the fish changed over the 4-week experimental period from a random distribution to an ideal free distribution and finally to an ideal despotic distribution. We suggest that growth depensation causes the long-term change in the spatial distribution and pattern of resource use by competitors. Received: December 19, 2000 / Accepted: March 19, 2001     

The ideal free distribution as an evolutionarily stable state in density‐dependent population games

In classical games that have been applied to ecology, individual fitness is either density independent or population density is fixed. This article focuses on the habitat selection game where fitness depends on the population density that evolves over time. This model assumes that changes in animal distribution operate on a fast time scale when compared to demographic processes. Of particular interest is whether it is true, as one might expect, that resident phenotypes who use density‐dependent optimal foraging strategies are evolutionarily stable with respect to invasions by mutant strategies. In fact, we show that evolutionary stability does not require that residents use the evolutionarily stable strategy (ESS) at every population density; rather it is the combined resident–mutant system that must be at an evolutionary stable state. That is, the separation of time scales assumption between behavioral and ecological processes does not imply that these processes are independent. When only consumer population dynamics in several habitats are considered (i. e. when resources do not undergo population dynamics), we show that the existence of optimal foragers forces the resident‐mutant system to approach carrying capacity in each habitat even though the mutants do not die out. Thus, the ideal free distribution (IFD) for the single‐species habitat selection game becomes an evolutionarily stable state that describes a mixture of resident and mutant phenotypes rather than a strategy adopted by all individuals in the system. Also discussed is how these results are affected when animal distribution and demographic processes act on the same time scale.     

Consumer–resource matching in a food chain when both predators and prey are free to move

The classical theory of the ideal free distribution (IFD) predicts that the spatial distribution of consumers should follow the distribution of the resources they depend on. Here, we study consumer–resource matching in a community context. Our model for the community is a food chain with three levels. We study whether the primary consumers are able to match resources both under predation risk and in its absence. Both prey and predators have varying degrees of knowledge of the global and local resource distribution. We present two versions of the model. In the "resource maximising" model, the consumers consider the availability of their resource only. In the "balancing" model, individual consumers minimise predation risk per unit of resource that they can gain access to. We show that both models can lead to perfect matching of consumers on resources and predators on consumers, assuming that individuals have full knowledge of the whole environment. However, when the consumers' information and freedom of movement are greater than those of the predators, then the predators generally undermatch the consumers. In the opposite case, we observe overmatching and high consumer movement rates. Furthermore, undermatching of predators on consumers tends to induce overmatching of consumers on resources.     

Foraging behaviour in tadpoles of the bronze frog<Emphasis Type="Italic">Rana temporalis</Emphasis>: Experimental evidence for the ideal free distribution

The ability of bronze frogRana temporalis tadpoles (pure or mixed parental lines) to assess the profitability of food habitats and distribute themselves accordingly was tested experimentally using a rectangular choice tank with a non-continuous input design. Food (boiled spinach) was placed at two opposite ends of the choice tank in a desired ratio (1:1, 1:2 or 1:4) to create habitat A and B. The tadpoles in Gosner stage 28–33, pre-starved for 24 h, were introduced in an open ended mesh cylinder placed in the center of the choice tank, held for 4 min (for acclimation) and then released to allow free movement and habitat selection. The number of tadpoles foraging at each habitat was recorded at 10, 15, 20, 25 and 30 min time intervals. The actual suitability,S _i (the food available in a habitat after colonization of tadpoles) of each habitat was obtained from the equationS _i =B _i−f _i (d _i) whereB _i is basic suitability (amount of food provided at each habitat before release of tadpoles),f _i is the rate of depletion of food (lowering effect) with introduction of each tadpole, andd _i is the density of tadpoles in habitati. The expected number of tadpoles at each habitat was derived from the actual suitability. With no food in the choice tank, movement of the tadpoles in the test arena was random indicating no bias towards any end of the choice tank or the procedure. In tests with a 1:1 food ratio, the observed ratio of tadpoles (11.71: 12.28) was comparable with the expected 12:12 ratio. The observed number of tadpoles in the habitats with a 1:2 food ratio was 8.71:15.29 and 7.87:16.13 for pure and mixed parental lines respectively. In both cases, the observed ratios were close to the expected values (7:17). Likewise, in experiments with a 1:4 food ratio, the observed number of tadpoles in the two habitats (10.78:37.22) did not differ significantly from the expected ratio of 7:41. In all tests, the number ofR. temporalis tadpoles matched ideally with habitat profitability (undermatching indexK ≜ 1. The study shows that tadpoles of the bronze frog exhibit an ideal free distribution while foraging regardless of whether they are siblings or non-siblings in a group, which correlates well with their group living strategy in nature.     

First evidence for relocation of stationary food resources during foraging in a strepsirhine primate (Microcebus murinus)

Field observations suggest that the diet of the Malagasy gray mouse lemur consists not only of non-stationary animal prey (invertebrates or small vertebrates), but also of stationary food resources such as gum or homopteran larvae secretions (HLS). We studied the foraging behavior of five mouse lemurs radiotelemetrically, each during six consecutive nights in the dry season, to explore to which extent they use these food resources and whether there is evidence for their relocation. We found that animals used all three different food categories. Mouse lemurs fed on gums and spent 68.5% (range 20.1-99.7%) of their feeding time eating this item. They were observed eating HLS in 8.4% (range 0-71.5%) of the feeding time and consuming small animals in 8.4% (range 0.3-26%) of their feeding time. The animals relocated stationary feeding sites significantly more frequently than non-stationary ones. They revisited the relocated stationary food sites about five times over the six nights. Furthermore, departure directions when leaving the sleeping site at dusk were not randomly distributed but showed a preferred orientation. Altogether, we provided first evidence for the relocation of stationary food resources in nature and thereby for the potential significance of spatial memory during foraging in a strepsirhine primate.     

地形对典型阔叶红松林灌木更新的影响

依托黑龙江凉水国家级自然保护区9 ha典型阔叶红松林动态监测样地的900个2 m×2 m样方,对灌木(H≥30 cm,DBH1 cm)进行了调查,基于2006年、2008年和2010年3次调查数据,分析了地形对灌木分布、死亡及新增的影响。结果表明:样地内共有灌木18种,2006、2008和2010年的灌木总数分别为18,253株/ha、27,383株/ha和23,300株/ha。地形对10种主要灌木的分布、死亡和新增均有显著的影响(P0.05),多数灌木种偏好坡中和山脊,且坡度6°的地形;坡向对大部分耐阴性较强的灌木的分布影响较小,而喜光的毛榛子(Corylus mandshurica)在阳坡和半阳坡的密度显著高于其他坡向。刺五加(Acanthopanax senticosus)、东北山梅花(Philadelphus schrenkii)、光萼溲疏(Deutzia gladata)、黄花忍冬(Lonicera chrysantha)、瘤枝卫矛(Euonymus pauciflorus)、毛榛子和早花忍冬(Lonicera praeflorens)7种灌木DBH1 cm的个体的分布、死亡和新增与其DBH≥1 cm的个体的分布表现基本一致。     

Seasonal ultrasonic acoustic emissions of <Emphasis Type="Italic">Quercus ilex</Emphasis> L. trees in a Mediterranean forest

Ultrasonic acoustic emissions were measured in Quercus ilex trees of a Mediterranean forest in Catalonia (NE Spain) each season from summer of 2004 to autumn of 2005. Acoustic emissions were maximum during hot and dry summer periods. Acoustic emissions started below 17% soil moisture, 0.85 RWC, and 2.5 MPa leaf water potential. They were negatively correlated with soil moisture and leaf water potential. The relationship between acoustic emissions and leaf water potential was the strongest, indicating that xylem tension is the most important factor inducing both cavitation (acoustic emissions) and a decrease in leaf water potential. Future increase of xylem cavitation derived from climate change may result in growth and survival limitations for this species in the drier southern limits of its current distribution.     

Trade-off between height growth and stem diameter growth for an evergreen Oak, Quercus glauca, in a mixed hardwood forest

1. Patterns of stem growth of a mid-successional evergreen Oak species ( Quercus glauca ) in a mixed hardwood forest were examined to explore the trade-off relationship between stem-diameter growth and height growth.
2. The mean cross-sectional area (and the corresponding mean diameter) of a stem at a point in time was defined as the stem volume divided by tree height. Based on this definition, a simple equation representing the trade-off relationship between the height growth and mean diameter growth was formulated.
3. In the long term, allocation to height growth was encouraged at the seedling stage and it gradually declined with time, with the decline in the suppressed seedlings being more pronounced than in the dominant trees.
4. However, both the suppressed and the dominant trees showed acceleration of height growth at various ages. Such a fluctuation in the allocation of biomass to height growth is likely to have been caused by chronological changes in light conditions, and meandered the trajectory of allometry between the height and mean diameter.
5. The observed stem growth patterns of the individual trees could explain the chronological changes in the diameter–height relationship of the population.     

Biomarker evidence for widespread anaerobic methane oxidation in Mediterranean sediments by a consortium of methanogenic archaea and bacteria. The Medinaut Shipboard Scientific Party

Although abundant geochemical data indicate that anaerobic methane oxidation occurs in marine sediments, the linkage to specific microorganisms remains unclear. In order to examine processes of methane consumption and oxidation, sediment samples from mud volcanoes at two distinct sites on the Mediterranean Ridge were collected via the submersible Nautile. Geochemical data strongly indicate that methane is oxidized under anaerobic conditions, and compound-specific carbon isotope analyses indicate that this reaction is facilitated by a consortium of archaea and bacteria. Specifically, these methane-rich sediments contain high abundances of methanogen-specific biomarkers that are significantly depleted in (13)C (delta(13)C values are as low as -95 per thousand). Biomarkers inferred to derive from sulfate-reducing bacteria and other heterotrophic bacteria are similarly depleted. Consistent with previous work, such depletion can be explained by consumption of (13)C-depleted methane by methanogens operating in reverse and as part a consortium of organisms in which sulfate serves as the terminal electron acceptor. Moreover, our results indicate that this process is widespread in Mediterranean mud volcanoes and in some localized settings is the predominant microbiological process.     

Home range and habitat use by the sable<Emphasis Type="Italic"> Martes zibellina brachyura</Emphasis> in a Japanese cool-temperate mixed forest

Home range and habitat use of the sable Martes zibellina brachyura were studied in a cool-temperate mixed forest in northernmost Japan. In both sexes, some sables showed a wide range of migration without establishing home ranges and the others had home ranges of 0.50–1.78 km² (mean: 1.12±SD 0.495 km², n =6) which were not significantly correlated with body weight or age. The analysis of canine tooth annuli revealed that the maximum age was 5.5 years. The home ranges of some sables overlapped so extensively that the home ranges and even the core areas did not appear exclusive to other sables. We determined resting sites and foraging routes in snow in winter. Comparison of vegetation at the resting sites and foraging routes with habitat availability suggested that the sables preferred resting in dense-tree forests with many tree species and debris probably in order to avoid predators (red foxes) and strong wind and foraging in forests of climax succession which are usually rich in their prey such as voles and mice.     

Inhibition of cathepsin K by nitric oxide donors: evidence for the formation of mixed disulfides and a sulfenic acid.

The cysteine protease cathepsin K is believed to play a key role in bone resorption as it has collagenolytic activity and is expressed predominantly and in high levels in bone resorbing osteoclast cells. The addition of nitric oxide (NO) and NO donors to osteoclasts in vitro results in a reduction of bone resorption, although the mechanism of this effect is not fully understood. The S-nitroso derivatives of glutathione (GSNO) and N-acetylpenicillamine (SNAP) and the non-thiol NO donors NOR-1 and NOR-3 all inhibited the activity of purified cathepsin K in a time- and concentration-dependent manner (IC(50) values after 15 min of preincubation at pH 7.5 of 28, 105, 0.4, and 10 microM, respectively). Cathepsin K activity in Chinese hamster ovary cells stably transfected with cathepsin K was also inhibited by the above NO donors with similar potencies. GSNO at 100 microM also completely inhibited the autocatalytic maturation at pH 4.0 of procathepsin K to cathepsin K. The inhibition of cathepsin K by GSNO was rapidly reversed by DTT, but inhibition by NOR-1 was not reversed by DTT, and analysis of the inhibited cathepsin K for S-nitrosylation using the Greiss reaction gave negative results in both cases. Analysis of the protein by electrospray liquid chromatography/mass spectrometry showed that the inhibition of cathepsin K by GSNO resulted in a mass increase of 306 +/- 2 Da, consistent with the formation of a glutathione adduct. Prior inhibition of cathepsin K by the active site thiol-modifying inhibitor E-64 blocked the modification by GSNO, indicating that the glutathione adduct is likely formed at the active site cysteine. Treatment of cathepsin K with NOR-1 resulted in a mass increase of between 30 and 50 Da, corresponding to the oxidation of a cysteine to sulfinic and sulfonic acids. Cotreatment of cathepsin K with NOR-1 plus the sulfenic acid reagent dimedone resulted in a mass increase of approximately 141 Da, which is consistent with the formation of a dimedone adduct. This result demonstrates that the NOR-1-dependent formation of cathepsin K sulfinic and sulfonic acids occurs via a sulfenic acid. These results show that inhibition of cathepsin K activity and its autocatalytic maturation represent two potential mechanisms by which NO can exert its inhibitory effect on bone resorption. This work also shows that oxidative thiol modifications besides S-nitrosylation should be considered when the effects of NO and NO donors on critical thiol-containing proteins are investigated.     

Pine stumps act as hotspots for seedling regeneration after pine dieback in a mixed natural forest dominated by <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>

Over the past few decades, rural forest ecosystems in Japan have experienced dynamic vegetation changes due to forest dieback and changes in land use, leading to the loss of local species populations and biodiversity. The aim of this study was to evaluate the importance of pine (Pinus densiflora) stumps and logs for tree seedling regeneration in a mixed natural forest in Kyoto Prefecture, Japan, that had previously experienced severe pine dieback, and to determine which factors most greatly affect seedling establishment. Seedlings of 17 tree species were recorded on pine stumps and logs in later stages of decay, among which Chamaecyparis obtusa and Rhododendron reticulatum were most dominant. Both of these species had a greater density on pine stumps than on logs or soil, despite stumps covering less than 0.5% of the study area. In addition, the seedling densities of both species were positively associated with moss cover on coarse woody debris, but negatively associated with wood pH. Brown rot in the sapwood and heartwood, which occurred more frequently in stumps than in logs, also positively associated with the seedling densities of both species. Predictive modelling showed that C. obtusa seedlings exhibited a stronger response to pH in stumps than in logs. Therefore, since brown-rotted wood is acidic due to fungal decay activities, brown-rotted pine stumps may present hotspots of C. obtusa seedling regeneration at the study site.     

Immunohistochemical localization of carbamoyl-phosphate synthetase (ammonia) in adult rat liver; evidence for a heterogeneous distribution

Different fixation media have been compared in order to find one that preserves the histological structure of rat liver and allows unambiguous immunohistochemical detection of carbamoyl-phosphate synthetase (ammonia). Fixation of rat liver in a mixture of methanol, acetone, and water yields the most intense immunohistochemical staining. Using a specific antiserum raised against rat liver carbamoyl-phosphate synthetase, less than 1% of the enzyme protein is extractable after this fixation procedure, and the histological structure is similar to that after fixation in Bouin's fixative. Specific immunohistochemical staining is localized exclusively in the cytoplasm of the parenchymal cells; its granular distribution is in accordance with the mitochondrial localization of carbamoyl-phosphate synthetase. Immunohistochemical staining shows a heterogeneous distribution within the liver acinus. Staining is most intense around the portal venules, decreases slowly toward the hepatic venules and is, after an abrupt decrease, virtually absent in a limited area surrounding these venules. The possible significance of the heterogeneous distribution of carbamoyl-phosphate synthetase for ammonia metabolism is discussed.