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111.
Indriķis Krams 《Behavioral ecology and sociobiology》2000,48(2):147-153
The risk of predation may influence the acquisition of energy and the feeding activity of animals. Feeding activity and body
reserves of wintering great tits Parus major in response to the priority to food access were studied in two areas differing in incidence of predators. The one-predator
area contained sparrowhawks Accipiter nisus only, whereas the two-predator area contained both sparrowhawks and pygmy owls Glaucidium passerinum, whose hunting periods overlap at dawn and dusk. In the two-predator area dominant great tits arrived at feeders significantly
later in the morning, and left earlier in the evening, than their subordinate flock-mates. Hence, feeding day length of dominants
was found to be significantly shorter. The reverse was true for the one-predator area. In addition, dominants carried significantly
greater reserves than subordinates in the area inhabited by two predators. Factors constraining subcutaneous energy reserves
were also studied in removal experiments. After the removal of dominant individuals, subordinate great tits did not reduce
their body reserves in the two predator area. In contrast, subordinate great tits significantly reduced evening body reserves
in the single-predator area. I concluded that the presence of the two predators increases unpredictability in feeding conditions
for great tits. Dominant individuals responded to this by shortening their feeding day and increasing body reserves at dusk.
Received: 8 December 1999 / Received in revised form: 15 March 2000 / Accepted: 31 March 2000 相似文献
112.
Kurt Kotrschal Josef Hemetsberger John Dittami 《Behavioral ecology and sociobiology》1993,33(5):289-295
Summary To investigate the dynamics of the winter flock patch exploitation, feeding experiments were performed with 140 semi-tame, free-roaming greylag geese (Anser anser). Three different initial densities of barley were offered on a 50-m2 patch: low (1600 grains/m2), intermediate (3300/m2) and high (I 1500/m2). Goose numbers on the patch, peck rates, and frequencies of agonistic encounters and of alert postures were observed by scanning the flock and in focal individuals. At low and intermediate initial food densities, peck rates decreased with food density, whereas at high food density, peck rates decreased only slightly over the feeding bout. Agonistic interactions increased as food decreased. A switch from exploitation to interference competition occurred at a threshold of approximately 900 remaining grains per square meter. With high initial food density, agonistic encounters began to increase gradually after 20–30 min. The same general patterns were observed for frequency of alertness. Family members occupied the patch for the longest time periods. The family female and the offspring fed most intensely. The family gander however, fed significantly less but was more aggressive and vigilant than all other social categories. Solitary geese spent their time on the patch doing little else but feeding and were the first to leave. It seems that high-ranking families and low-ranking singles adopt different competitive strategies, the former being superior interference competitors whereas the latter are forced scramble competitors.This study is dedicated to the memory of Konrad Lorenz
Correspondence to: K. Kotrschal 相似文献
113.
Policies that arise out of conflict or collaboration between specific interest groups and government agencies are often explained
by theoretical constructs that fall under the umbrella of group theory. Triangulation theory is one of these constructs and
serves to explain the mutuality of interests that exist between government agencies and interest groups expressed as points
linking geometric forms. Conflict tends to occur when competing interest groups are excluded from the linkage, in this case
between the opponents and proponents of hormone herbicides in the Tala area in Natal, South Africa. In opposition to the use
of hormone herbicides were vegetable farmers and their supporters: in linked support were agricultural interest groups who
used hormone herbicides, the manufacturers of the herbicides, and the government agency responsible for agriculture. Because
of the influence exerted through mutual support by the proponents of hormone herbicides, the formulation of policy decisions
directed towards the resolution of the conflict was delayed. When the minister of agriculture finally intervened, the policy
decisions were designed to secure the support of those opposing the use of hormone herbicides by introducing issues that cut
across those maintaining the discord. 相似文献
114.
Utilising the Synergy between Plants and Rhizosphere Microorganisms to Enhance Breakdown of Organic Pollutants in the Environment (15 pp) 总被引:1,自引:0,他引:1
Chaudhry Q Blom-Zandstra M Gupta S Joner EJ 《Environmental science and pollution research international》2005,12(1):34-48
Background Phytoremediation is a promising technology for the cleanup of polluted environments. The technology has so far been used mainly to remove toxic heavy metals from contaminated soil, but there is a growing interest in broadening its applications to remove/degrade organic pollutants in the environment. Both plants and soil microorganisms have certain limitations with respect to their individual abilities to remove/breakdown organic compounds. A synergistic action by both rhizosphere microorganisms that leads to increased availability of hydrophobic compounds, and plants that leads to their removal and/or degradation, may overcome many of the limitations, and thus provide a useful basis for enhancing remediation of contaminated environments.Main Features The review of literature presented in this article provides an insight to the nature of plant-microbial interactions in the rhizosphere, with a focus on those processes that are relevant to the breakdown and/or removal of organic pollutants. Due consideration has been given to identify opportunities for utilising the plant-microbial synergy in the rhizosphere to enhance remediation of contaminated environments.Results and Discussion The literature review has highlighted the existence of a synergistic interaction between plants and microbial communities in the rhizosphere. This interaction benefits both microorganisms through provision of nutrients by root exudates, and plants through enhanced nutrient uptake and reduced toxicity of soil contaminants. The ability of the plant-microbial interaction to tackle some of the most recalcitrant organic chemicals is of particular interest with regard to enhancing and extending the scope of remediation technologies.Conclusions Plant-microbial interactions in the rhizosphere offer very useful means for remediating environments contaminated with recalcitrant organic compounds.Outlook A better knowledge of plant-microbial interactions will provide a basis for improving the efficacy of biological remediations. Further research is, however, needed to investigate different feedback mechanisms that select and regulate microbial activity in the rhizosphere. 相似文献
115.
Spillover of Agriculturally Subsidized Predators as a Potential Threat to Native Insect Herbivores in Fragmented Landscapes 总被引:3,自引:0,他引:3
Abstract: Habitat loss and fragmentation can have strong negative impacts on populations of some native species. Spillover of generalist natural enemies from the surrounding landscape matrix is one mechanism potentially generating such effects, yet this has been rarely studied in insects. We examined the influence of habitat conversion to agriculture on the abundance and potential effects of predatory coccinellid beetles on native insect herbivores within 12 grassland remnants in central Nebraska (U.S.A.). Results of sweep sampling revealed that coccinellids were three to six times more abundant at native grassland sites embedded within cropland-dominated landscapes compared with control sites in grassland-dominated landscapes over the 3 years of the study. Exclusion experiments further demonstrated that predation intensity was strongly related to coccinellid abundances across sites and that coccinellids can dramatically reduce densities of a native aphid herbivore. In contrast to studies of specialized insect parasitoids, which have generally found reduced enemy pressure in fragmented landscapes, our results suggest that native herbivores may in some cases experience increased consumer pressure in landscapes with increasing habitat loss because of spillover of generalist predators from surrounding cropland habitats. 相似文献
116.
Summary. Feeding by belowground herbivores may induce systemic changes in shoot defence levels that affect the performance of above
ground herbivores and higher trophic levels. In this paper two wild Brassica species, B. nigra and B. oleracea were experimentally infested with 10 larvae of the cabbage root fly, Delia radicum. Plant dry masses and glucosinolate levels in shoots, main roots, and fine roots were determined at 3, 7, 12 and 14 days
after infestation and compared to those of control plants.
The systemic response in the leaves differed between plant species. In B. nigra shoot glucosinolate levels in D. radicum infested plants steadily increased with time until they were almost twice those of controls 14 days after infestation. B. oleracea plants infested with D. radicum did not show significant changes in shoot glucosinolate levels within 14 days, which may be due to the unexpected poorer
performance of D. radicum on this species.
Both plant species showed a local increase in indole glucosinolates in the main roots, which are the preferred feeding site
of D. radicum larvae. B. oleracea plants however showed a stronger (1.9 – 4.7 times) increase in indole glucosinolate levels than B. nigra (1.5 – 2.6 times). The increase in indole glucosinolates in B. nigra main roots, was counterbalanced by a significant decrease in aromatic glucosinolate levels. These differences in local responses
to D. radicum feeding between the two species may have contributed to the slower growth rates of the larvae on B. oleracea. D. radicum feeding did not result in altered glucosinolate levels in the fine roots in either plant species. The differences in glucosinolate
induction patterns between the summer annual B. nigra and the perennial B. oleracea are discussed in the light of their different life histories. 相似文献
117.
The model of Hastings and Powell describes a tritrophic food chain that exhibits chaotic dynamics. The model assumes that the populations are homogeneously mixed, so that the probability that any two individuals interact is uniform and space can be ignored. In this paper we propose a spatial version of the Hastings and Powell model in which predators seek their preys only in a finite neighborhood of their home location, breaking the mixing hypothesis. Treating both space and time as discrete variables we derive a set of coupled equations that describe the evolution of the populations at each site of the spatial domain. We show that the introduction of local predator–prey interactions result in qualitatively distinct dynamics of predator and prey populations. The evolution equations for the predators involve averages over the local density of preys, whereas the equations for the preys involve double averages, where the local density of both preys and predators appear. Our numerical simulations show that local predation also leads to spontaneous pattern formation and to qualitative changes in the global dynamics of the system. In particular, depending on the size of the predation neighborhoods, the chaotic strange attractor present in the original model of Hastings and Powell can be replaced by a stable fixed point or by an attractor of simpler topology. 相似文献
118.
119.
Large-scale effects of diffuse heavy metals pollution on terrestrial ecosystems are still underestimated. We studied the relation between the biodiversity of vascular plants and the feeding Lepidoptera, in our case leaf-miners and pollinating adult butterflies, in a Dutch nature reserve over a period of five years. We found that 5% of the 56 plants species which provide food and habitat to Microlepidoptera during their larval stage were affected by heavy metal pollution. Furthermore, the numerical abundance of leaf-mining larvae remained rather constant, despite of significant increases of the concentrations of Cd, Cu, Ni and Zn pollutants in leaves and litter. 相似文献
120.
Ranking of individual mountain birch trees in terms of leaf chemistry:
seasonal and annual variation
Marianna?RiipiEmail author Erkki?Haukioja Ky?sti?Lempa Vladimir?Ossipov Svetlana?Ossipova Kalevi?Pihlaja 《Chemoecology》2004,14(1):31-43
Summary. The quality of tree leaves as food for herbivores changes rapidly especially
during the spring and early summer. However, whether the quality of an individual
tree in relation to other trees in the population changes during the growing season
and between years is less clear. We studied the seasonal and annual stability of
chemical and physical traits affecting leaf quality for herbivores. Rankings of trees
in terms of the contents of two major groups of phenolics in their leaves, hydrolyzable
tannins and proanthocyanidins (condensed tannins), were very stable from the early
spring to the end of the growing season. There were also strong positive within-season
correlations in the levels of some other groups of phenolics in the leaves (kaempferol
glycosides, myricetin glycosides and p-coumaroylquinic
acid derivatives). The contents of individual sugars and the sum content of protein-bound amino
acids showed patterns of seasonal consistency in mature leaves, but not in young developing leaves.
The seasonal correlations in leaf water content and toughness were also strongest in mature leaves.
The correlations between two years at corresponding times of the growing season were strongly
positive for the major groups of phenolics throughout the season, but were more variable
for the contents of proteins and some sugars. Leaf toughness and water content showed strong
positive correlations in mature leaves. Despite the consistency of tree ranking in terms
of leaf phenolics, the relative resistance status of trees may, however, change during
a growing season because there was a negative correlation between the content of hydrolyzable
tannins (early-season resistance compounds) in leaves early in the season and the content of
proanthocyanidins (late-season resistance compounds) late in the season, and vice versa.
Thus, assuming that phenolics affect herbivore preference and performance, different
plants may suffer damage at different times of the growing season, and the overall
variation between trees in the fitness consequences may be low. In addition, the
adaptation of herbivorous insects to mountain birch foliage in general, as well as
to specific tree individuals, may be constrained by variation in the relative resistance
status of the trees. 相似文献