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1.
Optimal cytotoxic anticancer therapy, at the cellular level, requires effective and selective induction of cell death to achieve
a net reduction of biomass of malignant tissues. Standard cytotoxic chemotherapeutics have been developed based on the observations
that mitotically active cancer cells are more susceptible than quiescent normal cells to chromosomal, microtubular or metabolic
poisons. More recent development of molecularly targeted drugs for cancer focuses on exploiting biological differentials between
normal and transformed cells for selective eradication of cancers. The common thread of “standard” and “novel” cytotoxic drugs
is their ability to activate the apoptosis-inducing machinery mediated by mitochondria, also known as the intrinsic death
signaling cascade. The aim of this article is to provide an overview of the role of the mitochondria, an energy-generating
organelle essential for life, in mediating death when properly activated by cytotoxic stresses. 相似文献
2.
Pedersen PL 《Journal of bioenergetics and biomembranes》2007,39(1):1-12
This introductory article to the review series entitled “The Cancer Cell’s Power Plants as Promising Therapeutic Targets”
is written while more than 20 million people suffer from cancer. It summarizes strategies to destroy or prevent cancers by
targeting their energy production factories, i.e., “power plants.” All nucleated animal/human cells have two types of power
plants, i.e., systems that make the “high energy” compound ATP from ADP and P
i
. One type is “glycolysis,” the other the “mitochondria.” In contrast to most normal cells where the mitochondria are the
major ATP producers (>90%) in fueling growth, human cancers detected via Positron Emission Tomography (PET) rely on both types
of power plants. In such cancers, glycolysis may contribute nearly half the ATP even in the presence of oxygen (“Warburg effect”).
Based solely on cell energetics, this presents a challenge to identify curative agents that destroy only cancer cells as they
must destroy both of their power plants causing “necrotic cell death” and leave normal cells alone. One such agent, 3-bromopyruvate
(3-BrPA), a lactic acid analog, has been shown to inhibit both glycolytic and mitochondrial ATP production in rapidly growing
cancers (Ko et al., Cancer Letts., 173, 83–91, 2001), leave normal cells alone, and eradicate advanced cancers (19 of 19)
in a rodent model (Ko et al., Biochem. Biophys. Res. Commun., 324, 269–275, 2004). A second approach is to induce only cancer
cells to undergo “apoptotic cell death.” Here, mitochondria release cell death inducing factors (e.g., cytochrome c). In a
third approach, cancer cells are induced to die by both apoptotic and necrotic events. In summary, much effort is being focused
on identifying agents that induce “necrotic,” “apoptotic” or apoptotic plus necrotic cell death only in cancer cells. Regardless
how death is inflicted, every cancer cell must die, be it fast or slow. 相似文献
3.
Phytochemical research has revealed that organic sulfur-containing compounds (OSCs) from Allium species exert biological effects, that might be beneficial in the treatment or prevention of a range of diseases, such as
infections, cardiovascular and metabolic affections, cancers and related indispositions. Focusing physiological activities
of these compounds in the context of cancer, it became clear from both epidemiological studies in men and experimental studies
in diverse models, that the OSCs have a strong potential to prevent or to treat cancers even with selectivity against non-neoplastic
cells. Though underlying mechanisms are not yet fully understood, several parts of their modes and mechanisms of action were
elucidated: Pivotal molecular targets of as well chemoprevention as chemotherapy are metabolic, transporter or repair enzymes
strongly affecting cell death, proliferation and formation of metastases. Accordingly effects are not restricted to the run
of cell death programs, but they moreover comprise the strongly interdepending immune and inflammatory systems. Respectively,
several hypotheses exist which are based on chemical properties of sulfur as the “pharmacophor” of the compounds appearing
in up to ten different oxidation states (−2 to +6). Hence compounds can undergo redox-reactions and electrostatic interactions,
making reactive oxygen species (ROS) a key feature of their mechanisms of action. 相似文献
4.
Source-sink landscape theory and its ecological significance 总被引:2,自引:0,他引:2
Exploring the relationships between landscape pattern and ecological processes is the key topic of landscape ecology, for
which, a large number of indices as well as landscape pattern analysis model were developed. However, one problem faced by
landscape ecologists is that it is hard to link the landscape indices with a specific ecological process. Linking landscape
pattern and ecological processes has become a challenge for landscape ecologists. “Source” and “sink” are common concepts
used in air pollution research, by which the movement direction and pattern of different pollutants in air can be clearly
identified. In fact, for any ecological process, the research can be considered as a balance between the source and the sink
in space. Thus, the concepts of “source” and “sink” could be implemented to the research of landscape pattern and ecological
processes. In this paper, a theory of sourcesink landscape was proposed, which include: (1) In the research of landscape pattern
and ecological process, all landscape types can be divided into two groups, “source” landscape and “sink” landscape. “Source”
landscape contributes positively to the ecological process, while “sink” landscape is unhelpful to the ecological process.
(2) Both landscapes are recognized with regard to the specific ecological process. “Source” landscape in a target ecological
process may change into a “sink” landscape as in another ecological process. Therefore, the ecological process should be determined
before “source” or “sink” landscape were defined. (3) The key point to distinguish “source” landscape from “sink” landscape
is to quantify the effect of landscape on ecological process. The positive effect is made by “source” landscape, and the negative
effect by “sink” landscape. (4) For the same ecological process, the contribution of “source” landscapes may vary, and it
is the same to the “sink” landscapes. It is required to determine the weight of each landscape type on ecological processes.
(5) The sourcesink principle can be applied to non-point source pollution control, biologic diversity protection, urban heat
island effect mitigation, etc. However, the landscape evaluation models need to be calibrated respectively, because different
ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas.
This theory is helpful to further study landscape pattern and ecological process, and offers a basis for new landscape index
design.
__________
Translated from Acta Ecologica Sinica, 2006, 26(5): 1444–1449 [译自: 生态学报] 相似文献
5.
Leonard Arthur Stein 《Cell biochemistry and biophysics》1995,27(2):63-96
In the rapid “quench” kientics of myosin, the “initial phosphate burst” is the excess inorganic phosphate that is produced
during the early time-course of ATP hydrolysis by myosin subfragment-1 (S-1) or HMM. In general, the existence of a Pi burst
implies a rapid (i.e., generally an order of magnitude faster than the steady-state hydrolysis rate) lysis of the phospho-anhydride
bond within the ATP molecule, followed by one or more slower steps that are rate limiting for the process. Thus, the presence
of a Pi burst can provide an important clue to the mechanism of the reaction. However, in the case of actomyosin, this clue
as long been the subject of controversy and misunderstanding.
To measure the (initial) Pi burst, myosin S-1 (or HMM) is rapidly mixed with ATP and then the mixture is acid quenched after
a specific time period. The medium produced contains free Pi generated from hydrolysis of the ATP. The quantitative measure
of the phosphate generated in this way has always been significantly greater than that expected by steady-state “release”
of Pi alone, and it is that very difference between this measured Pi after the quench and that amount of Pi expected to be
released by steady-state considerations in that same time period that has been referred to as the “initial Pi burst”.
Recent investigations of the kinetics of Pi release have used an entirely new method that directly measures the release of
Pi from the enzyme-product complex. These studies have made reference to the properties of the “initial Pi burst” in the presence
of actin, as well as to a new kinetic entity: the “burst of Pi release”, and have been often vague concerning the true nature
of the initial Pi burst, as well as the properties of Pi release as predicted by the current models of the actin activation
of the myosin ATPase activity. The purpose of the current article is to correct this oversight, to discuss the “burst” in
some detail, and to display the kinetics predicted by the current models for the actin activation of myosin. Furthermore,
predictions for the kinetics of the new “burst of Pi release” are discussed in terms of its ability to discriminate between
the two current competing models for actin activation of the myosin ATPase activity. 相似文献
6.
Escape from apoptosis is a key attribute of tumour cells and facilitates chemo-resistance. The ‘BCL-2-regulated'' or ‘intrinsic'' apoptotic pathway integrates stress and survival signalling to govern whether a cancer cell will live or die. Indeed, many pro-apoptotic members of the BCL-2 family have demonstrated tumour-suppression activity in mouse models of cancer and are lost or repressed in certain human cancers. Conversely, overexpression of pro-survival BCL-2 family members promotes tumorigenesis in humans and in mouse models. Many of the drugs currently used in the clinic mediate their therapeutic effects (at least in part) through the activation of the BCL-2-regulated apoptotic pathway. However, initiators of this apoptotic pathway, such as p53, are mutated, lost or silenced in many human cancers rendering them refractory to treatment. To counter such resistance mechanisms, a novel class of therapeutics, ‘BH3-mimetics'', has been developed. These drugs directly activate apoptosis by binding and inhibiting select antiapoptotic BCL-2 family members and thereby bypass the requirement for upstream initiators, such as p53. In this review, we discuss the role of the BCL-2 protein family in the development and treatment of cancer, with an emphasis on mechanistic studies using well-established mouse models of cancer, before describing the development and already recognised potential of the BH3-mimetic compounds. 相似文献
7.
Baolu Zhao 《Neurochemical research》2009,34(4):630-638
“Modern” medicine and pharmacology require an effective medical drug with a single compound for a specific disease. This seams
very scientific but usually has unavoidable side effects. For example, the chemical therapy to cancer can totally damage the
immunological ability of the patient leading to death early than non-treatment. On the other hand, natural antioxidant drugs
not only can cure the disease but also can enhance the immunological ability of the patient leading to healthier though they
usually have several compounds or a mixture. For the degenerative disease such as Alzheimer’s disease (AD) and Parkinson’s
disease (PD), natural antioxidant drugs are suitable drugs, because the pathogenesis of these diseases is complex with many
targets and pathways. These effects are more evidence when the clinic trial is for long term treatment. The author reviews
the studies on the protecting effects of natural antioxidants on neurons in neurodegenerative diseases, especially summarized
the results about protective effect of green tea polyphenols on neurons against apoptosis of cellular and animal PD models,
and of genestine and nicotine on neurons against Aβ—induced apoptosis of hippocampal neuronal and transgenic mouse AD models.
Special issue in honor of Dr. Akitane Mori. 相似文献
8.
Sequence analysis of long FMR1 arrays in the Japanese population: insights into the generation of long (CGG)
n
tracts 总被引:10,自引:0,他引:10
Sperm chromosome abnormalities were assessed in testicular cancer patients before and after treatment with BEP (bleomycin,
etoposide, cisplatin). The frequencies of disomy for chromosomes 1, 12, X, Y and XY were assessed along with diploid frequencies
and sex ratios by multicolour fluorescence in situ hybridization (FISH). For each cancer patient, a minimum of 10 000 sperm
was assessed for each chromosome probe before and after chemotherapy (CT). Data was analysed “blindly” by coding the slides.
A total of 161 097 sperm were analyzed, 80 445 before and 80 642 after treatment. The mean disomy frequencies were 0.11% pre-CT
vs 0.06% post-CT for chromosome 1, 0.18% vs 0.15% for chromosome 12, 0.10% vs 0.9% for the X chromosome, 0.13% vs 0.10% for
the Y chromosome and 0.25% vs 0.20% for XY sperm. There was no significant difference in the frequency of disomy pre-CT vs
post-CT for any chromosome except that chromosome 1 demonstrated a significant decrease after CT. The “sex ratios” and frequency
of diploid sperm were also not significantly different in pre- and post-CT samples with 50.2% X-bearing sperm pre-CT and 50.5%
X post-CT and 0.14% diploid sperm pre-CT vs 0.15% diploid sperm post-CT. There was no significant donor heterogeneity among
the cancer patients. None of the values in the cancer patients differed significantly from 10 normal control donors. Thus
our study suggests that BEP chemotherapy does not increase the risk of numerical chromosomal abnormalities in human sperm.
Received: 11 June 1996 / Revised: 8 August 1996 相似文献
9.
Aigner A 《Applied microbiology and biotechnology》2007,76(1):9-21
Within the recent years, RNA interference (RNAi) has become an almost-standard method for in vitro knockdown of any target
gene of interest. Now, one major focus is to further explore its potential in vivo, including the development of novel therapeutic
strategies. From the mechanism, it becomes clear that small interfering RNAs (siRNAs) play a pivotal role in triggering RNAi.
Thus, the efficient delivery of target gene-specific siRNAs is one major challenge in the establishment of therapeutic RNAi.
Numerous studies, based on different modes of administration and various siRNA formulations and/or modifications, have already
accumulated promising results. This applies to various animal models covering viral infections, cancer and multiple other
diseases. Continuing efforts will lead to the development of efficient and “double-specific” drugs, comprising of siRNAs with
high target gene specificity and of nanoparticles enhancing siRNA delivery and target organ specificity. 相似文献
10.
P. Slurink 《Human Evolution》1993,8(4):265-273
In contrast to many other models of human evolution the “balance of power” theory of Alexander has a clear answer to the question
why a runaway selection process for unique social and moral capacities occurred in our ancestry only and not in other species:
“ecological dominance” is hypothesized to have diminished the effects of “extrinsic” forces of natural selection such that
withinspecies, intergroup competition increased (Alexander, 1989). Alexander seems to be wrong, however, in his claim that
already the common HUCHIBO (Humans, Chimps, Bonobo's)-ancestor has crossed the ecological dominance barrier. In this paper
an adapted version of Alexander's model is presented and several different ways are proposed to make this adapted version
testable. A preliminary survey of the available paleontological and paleoecological data suggests that there is some evidence
of a less vulnerable position towards predators in earlyHomo and that there are clear signs related to a crossing of the ecological dominance barrier inHomo sapiens sapiens. 相似文献
11.
Anatol Rapoport 《Bulletin of mathematical biology》1950,12(2):109-121
Aggregates of neurons are considered in which the frequency of occurrence of neurons with a specified value of the refractory
period follows certain probability distributions. Input-output functions are derived for such aggregates. In particular, if
input and output intensities are defined in terms of stimulus frequencies and firing frequencies per neuron respectively,
it is shown that a rectangular distribution of refractory periods leads to a logarithmic input-output curve. If input and
output are defined in terms of the total number of stimuli and firings in the aggregate, it is shown how the “mobilization”
picture leads to the logarithmic input-output curve.
By randomizing the intervals between stimuli received by a single neuron and by introducing an inhibitory neuron a very simple
“filter net” can be constructed whose output will be sensitive to a particular range of the input, and this range can be made
arbitrarily small. 相似文献
12.
Carlo R. Laing Thomas Frewen Ioannis G. Kevrekidis 《Journal of computational neuroscience》2010,28(3):459-476
Binocular rivalry occurs when two very different images are presented to the two eyes, but a subject perceives only one image
at a given time. A number of computational models for binocular rivalry have been proposed; most can be categorised as either
“rate” models, containing a small number of variables, or as more biophysically-realistic “spiking neuron” models. However,
a principled derivation of a reduced model from a spiking model is lacking. We present two such derivations, one heuristic
and a second using recently-developed data-mining techniques to extract a small number of “macroscopic” variables from the
results of a spiking neuron model simulation. We also consider bifurcations that can occur as parameters are varied, and the
role of noise in such systems. Our methods are applicable to a number of other models of interest. 相似文献
13.
Ewa D. Micewicz Chun-Ling Jung Dorthe Schaue Hai Luong William H. McBride Piotr Ruchala 《International journal of peptide research and therapeutics》2011,17(3):247-257
Many lung cancer treatment regimens include radiotherapy. We sought to improve the efficacy of such treatment by invoking
the targeted delivery of a model radiosensitizer (nicotinamide) to malignant tissues. Ephrin receptors (Eph), which are often
overexpressed in lung cancers, were selected as the target of our delivery system. Molecular targeting was achieved utilizing
a small peptide derived from the C-terminal portion of azurin, a copper-containing redox protein (“cupredoxin”) that is capable
of binding to ephrin receptors. We prepared and screened a sub-library of peptides derived from the C-terminal region of azurin
and found several small analogues that bound ephrin receptors EphA2, EphB2, and EphB4. One such peptide, termed AzV36, was
selected for conjugation with nicotinic acid via an amide bond to form AzV36-NicL. The resulting linear peptide contains 15
residues (including unusual and d-amino acids), is very stable in human serum, and can be easily manufactured. AzV36-NicL conjugate was tested in vivo for
its ability to radiosensitize Lewis lung carcinoma (LCC) in artificial metastasis and solid tumor engraftment models. The
compound increased the efficacy of radiotherapy with tumor colonies being ~2–13 fold lower than with radiation alone depending
on experimental schedule. In contrast, equimolar amounts of unconjugated peptide (AzV36-L) or nicotinamide alone only marginally
improved radiation efficacy. The targeted delivery of radiosensitizer(s) to ephrin receptors may enhance the efficacy of radiation
treatment of lung cancer and of other cancers that overexpress ephrin receptor(s). 相似文献
14.
S. V. Tillib 《Molecular Biology》2011,45(1):66-73
This short review provides an introduction to the rapidly developing field of generation and utilization of “camel nanoantibodies”
(or “nanobodies”). The term “nanoantibody” or “nanobody” was given to single-domain variable fragments of special type of
antibodies that naturally exist (in addition to classical types of antibodies) in blood of Camelidae family animals and in
some chondrichthyan fishes. The existence of very efficient technology of nanobody generation and some very useful characteristic
features promise a big potential for their use in immunobiotechnology and medicine. 相似文献
15.
Combinatorial treatments including vaccines,chemotherapy and monoclonal antibodies for cancer therapy 总被引:1,自引:0,他引:1
Accumulating evidence suggests that despite the potency of cytotoxic anticancer agents, and the great specificity that can
be achieved with immunotherapy, neither of these two types of treatment by itself has been sufficient to eradicate the disease.
Still, the combination of these two different modalities holds enormous potential for eliciting therapeutic results. Indeed,
certain chemotherapeutic agents have shown immunomodulatory activities, and several combined approaches have already been
attempted. For instance, chemotherapy has been proven to enhance the efficacy of tumor cell vaccines, and to favor the activity
of adoptively transferred tumor-specific T cells. A number of mechanisms have been proposed for the chemotherapy-triggered
enhancement of immunotherapy response. Thus, chemotherapy may favor tumor cell death, and by that enhance tumor-antigen cross-presentation
in vivo. Drug-induced myelosuppression may induce the production of cytokines favoring homeostatic proliferation, and/or ablate
immunosuppression mechanisms. Furthermore, the recently reported synergy between monoclonal antibodies and chemotherapy or
peptide vaccination is based upon the induction of endogenous humoral and cellular immune responses. This would suggest that
monoclonal antibodies may not only provide passive immunotherapy but can also promote tumor-specific active immunity. This
article will review several strategies in which immunotherapy can be exploited in preclinical and clinical studies in combination
with other agents and therapeutic modalities that are quite unique when compared with “conventional” combination therapies
(ie, treatments with chemotherapeutic drugs or chemotherapy and radiotherapy based protocols). The results from these studies
may have significant implications for the development of new protocols based on combinatorial treatments including vaccines,
chemotherapy and monoclonal antibodies, suggesting an exciting potential for therapeutic synergy with general applicability
to various cancer types. Given the complicity of immune-based therapies and cancer pharmacology, it will be necessary to bring
together cancer immunologists and clinicians, so as to provide a robust stimulus for realizing the successful management of
cancer in the near future. 相似文献
16.
Anatol Rapoport 《Bulletin of mathematical biology》1950,12(3):187-197
The output curve of a single neuron with a threshold of response with respect to the frequency of the stimuli is derived.
If the stimuli are regularly spaced in time, the output curve has discontinuities. If the threshold and/or refractory period
are sufficiently large, the output curve approaches the “all-or-none” curve.
In the case of completely randomized stimuli, the output curve is sigmoid. The equation of this curve is derived and some
properties are studied. Threshold and “all-or-none” effects can be achieved by “pyramiding” neurons of this type to converge
on neurons of higher order. 相似文献
17.
Pedersen PL 《Journal of bioenergetics and biomembranes》2007,39(3):211-222
As a new faculty member at The Johns Hopkins University, School of Medicine, the author began research on cancer in 1969 because
this frequently fatal disease touched many whom he knew. He was intrigued with its viscous nature, the failure of all who
studied it to find a cure, and also fascinated by the pioneering work of Otto Warburg, a biochemical legend and Nobel laureate.
Warburg who died 1 year later in 1970 had shown in the 1920s that the most striking biochemical phenotype of cancers is their
aberrant energy metabolism. Unlike normal tissues that derive most of their energy (ATP) by metabolizing the sugar glucose
to carbon dioxide and water, a process that involves oxygen-dependent organelles called “mitochondria”, Warburg showed that
cancers frequently rely less on mitochondria and obtain as much as 50% of their ATP by metabolizing glucose directly to lactic
acid, even in the presence of oxygen. This frequent phenotype of cancers became known as the “Warburg effect”, and the author
of this review strongly believed its understanding would facilitate the discovery of a cure. Following in the final footsteps
of Warburg and caught in the midst of an unpleasant anti-Warburg, anti-metabolic era, the author and his students/collaborators
began quietly to identify the key molecular events involved in the “Warburg effect”. Here, the author describes via a series
of sequential discoveries touching five decades how despite some impairment in the respiratory capacity of malignant tumors,
that hexokinase 2 (HK-2), its mitochondrial receptor (VDAC), and the gene that encodes HK-2 (HK-2 gene) play the most pivotal
and direct roles in the “Warburg effect”. They discovered also that like a “Trojan horse” the simple lactic acid analog 3-bromopyruvate
selectively enters the cells of cancerous animal tumors that exhibit the “Warburg effect” and quickly dissipates their energy
(ATP) production factories (i.e., glycolysis and mitochondria) resulting in tumor destruction without harm to the animals. 相似文献
18.
Yukio Takahata 《Primates; journal of primatology》1982,23(1):1-23
Some dyads of Japanese monkey adult males and females show remarkable spatial proximity and frequent exchanges of social behaviors.
It is suggested that some kind of “affinity” exists between them. Females obtain much unilateral benefit from “proximity effects”;
even lowranking females can dominate high-ranking females as long as they stay nearby their “affinitive” males. Males acquire
female followers in return. Mating relations and female mother-daughter relations play important roles in forming new “affinitive
relations.” Once monkeys have formed “affinitive relations,” however, they seldom mate with each other, as if they were kin-related.
Therefore, the acquisition of female followers appears inconsistent with a male's strategy for reproducing many genes in the
next generation.
This study was financed partly by the Cooperative Research Fund of the Primate Research Institute, Kyoto University. The outline
of this paper has already been published inTakahata (1980b). 相似文献
19.
A. J. Monforte M. J. Asíns E. A. Carbonell 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(4):706-713
A study of genotype-by-salinity interaction was carried out to compare the behavior of quantitative trait loci (QTLs) in
two F2 populations derived from crosses between the cherry tomato, Lycopersicon esculentum Mill. var. cerasiforme, and two wild relatives Lycopersicon pimpinellifolium (Jusl.) Mill. and Lycopersicon chesmannii f. minor (Hook. f.) Mull., grown at two environmental conditions (optimum and high salinity). QTLs for earliness and fruit yield could
be classified into four groups: “response-sensitive”, those detected only under control conditions or whose contribution significantly
decreased in salinity; “response-tolerant”, detected only in salinity or in which the direction of their additive effects
changed; “constitutive”, detected in both growing conditions; and “altered” QTLs, those where the degree of dominance changed
according to the presence or absence of salt. Epistatic interactions were also influenced by the salt treatment. This differential
allele effect at some (non-constitutive) QTLs induced by salt stress will make selection under an “optimum environment” unfruitful
for the “response-tolerant” QTLs. Similarly, selection under salinity will ignore “response-sensitive” QTLs. Given that salinity
is highly variable in the field, marker-assisted selection should take into account not only the “response-tolerant” but also
the “response-sensitive” QTLs although there might be cases where selection in some QTLs for both conditions is not feasible.
Comparing both populations, very few QTLs showed the same behavior.
Received: 5 August 1996 / Accepted: 25 October 1996 相似文献
20.
Hidden treatments in ecological experiments: re-evaluating the ecosystem function of biodiversity 总被引:68,自引:0,他引:68
Michael A. Huston 《Oecologia》1997,110(4):449-460
Interactions between biotic and abiotic processes complicate the design and interpretation of ecological experiments. Separating
causality from simple correlation requires distinguishing among experimental treatments, experimental responses, and the many
processes and properties that are correlated with either the treatments or the responses, or both. When an experimental manipulation
has multiple components, but only one of them is identified as the experimental treatment, erroneous conclusions about cause
and effect relationships are likely because the actual cause of any observed response may be ignored in the interpretation
of the experimental results. This unrecognized cause of an observed response can be considered a “hidden treatment.” Three
types of hidden treatments are potential problems in biodiversity experiments: (1) abiotic conditions, such as resource levels,
or biotic conditions, such as predation, which are intentionally or unintentionally altered in order to create differences
in species numbers for “diversity” treatments; (2) non-random selection of species with particular attributes that produce
treatment differences that exceed those due to “diversity” alone; and (3) the increased statistical probability of including
a species with a dominant negative or positive effect (e.g., dense shade, or nitrogen fixation) in randomly selected groups
of species of increasing number or “diversity.” In each of these cases, treatment responses that are actually the result of
the “hidden treatment” may be inadvertently attributed to variation in species diversity. Case studies re-evaluating three
different types of biodiversity experiments demonstrate that the increases found in such ecosystem properties as productivity,
nutrient use efficiency, and stability (all of which were attributed to higher levels of species diversity) were actually
caused by “hidden treatments” that altered plant biomass and productivity.
Received: 16 December 1996 / Accepted: 2 March 1997 相似文献