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1.
Marshall Abrams 《Biology & philosophy》2007,22(1):115-130
Recent debate on the nature of probabilities in evolutionary biology has focused largely on the propensity interpretation
of fitness (PIF), which defines fitness in terms of a conception of probability known as “propensity”. However, proponents
of this conception of fitness have misconceived the role of probability in the constitution of fitness. First, discussions
of probability and fitness have almost always focused on organism effect probability, the probability that an organism and its environment cause effects. I argue that much of the probability relevant to fitness
must be organism circumstance probability, the probability that an organism encounters particular, detailed circumstances within an environment, circumstances which
are not the organism’s effects. Second, I argue in favor of the view that organism effect propensities either don’t exist
or are not part of the basis of fitness, because they usually have values close to 0 or 1. More generally, I try to show that
it is possible to develop a clearer conception of the role of probability in biological processes than earlier discussions
have allowed. 相似文献
2.
Linda Van Speybroeck 《Theorie in den Biowissenschaften》2000,119(3-4):187-208
Summary Whereas genetics refers to the study and mapping of linear nucleotide sequences, their mutations and inheritance, epigenetics refers to the structural organization and evolution of the genome. Epigenetic studies indicate that not all heritable information
leading to the phenotype is “inscribed” in the DNA base sequence. In this sense, epigenetics — as the term indicates — goes
beyond genetics, thereby (1) leaving behind the gene-centered view from within molecular biology itself, and (2) urging bio-philosophers
to change their focus from criticizing the central dogma to evaluating new developments in molecular research.
In the epigenetic approach, a hierarchy of genomic contexts can be revealed, consisting basically of an intracellular, an
intercellular, and an organismic level. The first explorations on the organismic level suggest that under certain conditions
the somatic constitution of the organism and how it stands in close interaction with its environment are to be taken into
account as factors influencing the genomic constitution. Depending on the specificity of these conditions, the organism and
its history and actuality can be seen as a crucial genomic context — leading to a more complex perception of the local dynamics and the structure of the genome and its consequences for development
and evolution.
This “organism in the world” view fits well with the philosophical tradition of Developmental Systems Theory, although epigeneticists
seek to enlarge the genetic picture of biology by gradually expanding the range of molecular processes which influence the
genome, thereby decentralizing the sovereign role of the genome, without loosing track of experimental demands. 相似文献
3.
Fernando Moya 《Theorie in den Biowissenschaften》2000,119(3-4):318-333
Summary For Aristotle, living entities are exemplars of substance being. This means that they show a unity of matter and form on the
one hand and of potency and act on the other, in contrast to the duality shown in these respects by accidental beings, exemplified
by artefacts. An animal, although composed of the same elements (arche) considered by presocratic philosophers, is defined as an individual unity, generated and maintained by an organisation which
relates its parts in a hierarchical and functional way. Crucial to his understanding of the living is the hierarchy in which
each part is defined by fitness to a function, as an instrument (organon), performing within the whole. The whole being is also an instrument (an organism) for a specific kind of life, which actualises
an internal and specific principle (psuche).
Both the regularity of appearance of each organism and its fitness to a specific function justify the introduction, in addition
to the study of necessary causes, of an additional way of analysis in terms of hypothetical necessities, or necessary conditions
for a goal to be attained. Fitness to a function and regularity of appearance make necessary the analysis not just of the
elementary components, but of another principle (eidos, form) which defines a structure directed to a goal. While for accidental beings matter can survive their destruction, the
corruption (pthora) of living entities causes the disruption of the entire unity of matter and form. Living entities, both as matter and form,
show therefore a temporal limitation in being generated and corrupted, although they persist as specific forms since they
generate offspring which regularly share their differential characteristics defined in their form.
After reviewing recent interpretations of Aristotle’s biological writings, I will suggest the usefulness of this conceptual
framework to analyse some problems approached by current developmental biology. 相似文献
4.
Lawrence J. Schneiderman 《Journal of bioethical inquiry》2011,8(2):123-131
It probably should not be surprising, in this time of soaring medical costs and proliferating technology, that an intense
debate has arisen over the concept of medical futility. Should doctors be doing all the things they are doing? In particular,
should they be attempting treatments that have little likelihood of achieving the goals of medicine? What are the goals of
medicine? Can we agree when medical treatment fails to achieve such goals? What should the physician do and not do under such
circumstances? Exploring these issues has forced us to revisit the doctor-patient relationship and the relationship of the
medical profession to society in a most fundamental way. Medical futility has both a quantitative and qualitative component.
I maintain that medical futility is the unacceptable likelihood of achieving an effect that the patient has the capacity to appreciate as a benefit. Both emphasized terms are important. A patient is neither a collection of organs nor merely an individual with desires.
Rather, a patient (from the word “to suffer”) is a person who seeks the healing (meaning “to make whole”) powers of the physician.
The relationship between the two is central to the healing process and the goals of medicine. Medicine today has the capacity
to achieve a multitude of effects, raising and lowering blood pressure, speeding, slowing, and even removing and replacing
the heart, to name but a minuscule few. But none of these effects is a benefit unless the patient has at the very least the
capacity to appreciate it. Sadly, in the futility debate wherein some critics have failed or refused to define medical futility
an important area of medicine has in large part been neglected, not only in treatment decisions at the bedside, but in public
discussions—comfort care—the physician’s obligation to alleviate suffering, enhance well being and support the dignity of
the patient in the last few days of life. 相似文献
5.
Scarcelli N Tostain S Vigouroux Y Luong V Baco MN Agbangla C Daïnou O Pham JL 《Genetica》2011,139(8):1055-1064
The relative role of sexual reproduction and mutation in shaping the diversity of clonally propagated crops is largely unknown.
We analyzed the genetic diversity of yam—a vegetatively-propagated crop—to gain insight into how these two factors shape its
diversity in relation with farmers’ classifications. Using 15 microsatellite loci, we analyzed 485 samples of 10 different
yam varieties. We identified 33 different genotypes organized in lineages supported by high bootstrap values. We computed
the probability that these genotypes appeared by sexual reproduction or mutation within and between each lineage. This allowed
us to interpret each lineage as a product of sexual reproduction that has evolved by mutation. Moreover, we clearly noted
a similarity between the genetic structure and farmers’ classifications. Each variety could thus be interpreted as being the
product of sexual reproduction having evolved by mutation. This highly structured diversity of farmer-managed varieties has
consequences for the preservation of yam diversity. 相似文献
6.
Hugh C. Crenshaw 《Bulletin of mathematical biology》1993,55(1):231-255
Organisms that move along helical trajectories change their net direction of motion largely by changing the direction, with
respect to the body of the organism, of their rotational velocity (Crenshaw and Edelstein-Keshet, 1993,Bull. math. Biol.
55, 213–230). This paper demonstrates that an organism orients to a stimulus field, such as a chemical concentration gradient
or a ray of light, if the components of its rotational velocity, with respect to the, body of the organism, are simple functions
of the stimulus intensity encountered by the organism. For example, an organism can orient to a chemical concentration gradient
if the rate at which it rotates around its anterior-posterior axis is proportional to the chemical concentration it encounters.
Such an orientation can be either positive or negative. Furthermore, it is true taxis—orientation of the axis of helical motion
is direct. It is neither a kinesis nor a phobic response—there is no random component to this mechanism of orientation. 相似文献
7.
Reinhard Agerer 《Mycological Progress》2012,11(2):425-434
Hygrophorus olivaceoalbus has long been known as an ectomycorrhizal fungus, formerly designated with the artificial binomen Piceirhiza gelatinosa. Recently, it has been found to be abundant and very frequent under double ambient ozone free air fumigation of mature Norway
spruce trees. As it has already been reported that this fungus can form intercellular hyphae within the root meristem, a more
detailed study was performed to clarify its type of root colonization. The present study not only revealed intercellular hyphae
within the meristematic zone but also intracellular hyphae within root cortex cells which grow towards and into large tannin
droplets—phenolic compounds usually deposited as defensive aids—to finally fill them completely. The hyphal assemblages become
globular which at first sit as separated hyphal balls within cells still containing cytoplasm. Later on, they are apparently
released from the root cells, presumably as microsclerotia for dispersal of the species. Old ectomycorrhizae (ECM) show an
apical pore, and later a large orifice of a tube-like cylinder formed by the thick, persistent hyphal mantle. The root tissue
is progressively degrading towards proximal parts. Disintegrating root cells apparently liberate the microsclerotia through
the orifice. Further studies have to find out the mechanism by which the microsclerotia are liberated and whether they operate
as asexual propagules and lastly how and by whom they are propagated. As these ECM are found under ozone stress, and with
identical features at higher altitudes, stress impact on trees might be the causative agent for the high frequency and abundance
of Hygrophorus olivaceoalbus ECM. 相似文献
8.
Most plants are constructed from repeating modular units such as phytomers, merophytes, and cell packets. Even an organism
as simple as the filamentous cyanobacterium Anabaena shows recurrent patterns of differentiated cellular structures, notably with respect to its heterocysts. These examples reflect
the inherent rhythms established within developmental processes of living organisms. In the present article, attention is
paid to repetitious production of idioblasts—isolated cells, or clusters of cells, with an identity different to that of neighbouring
cells from which they are derived. In higher plant root tissues, idioblasts are contained within cell packets that grow up
from mother cells during the course of a number of cycles of cell production. The heterocysts of Anabaena are also discussed; they, too, are a type of idioblast. The idioblasts of root tissues originate as small cells which result
from unequal cell divisions. Such divisions are usually the final ones within a cell packet which has already undergone a
number of division cycles and are characteristically located at one or both ends of a packet. The packet end walls are suggested
to have a role in regulating division asymmetry. Idioblastic systems discussed are root cortical trichosclereids and diaphragm
cells; in their earliest stage, the cells from which lateral root primordia arise are also considered as clusters of idioblasts
because they, too, are the products of asymmetric divisions of pericyclic mother cells. The division patterns of all these
idioblastic systems were modelled in a consistent way using L-systems, with the assumption that the age of a cell-packet end
wall plays a special role in cell determination.
This article is dedicated to Vsevelod Ya. Brodsky, doyen of Russian studies of rhythms in cell division and development, who
celebrates his 80th birthday on August 4, 2008
This article was presented in original. 相似文献
9.
N. L. Wallin 《Human Evolution》2000,15(3-4):199-242
Musical experience and creativity are regarded to be largely depending on cultural conditions and hence on higher cognitive
functions. True as this may be, there are, however, numerous responses to music-the urge to make music taken into account-which
derive from deeper levels of the human organism, namely from arousing alternatively moderating vegetative and limbic functions.
Although the behavioral intensity and quality emanating from such evolutionary early nervous structures may be affected by
cultural influence, they still seem to be essentially independent. Similar specific responses to acoustical and/or motor patterned
stimuli are found among some other higher vertebrates which like humans are equipped with sophisticated mechanisms for hearing,
sound production and locomotion, well tuned to each other. However, it is even today an open question whether these manifestations
of auditive-phonatory-locomotor abilities just are analogues or if they share a common evolutionary background. The current
discussion on this matter has accumulated data which apparently support the latter view pointing to that sexual selection
would be the common force, first suggested by Charles Darwin (153). Other, and still more recent data in genetics and neuroscience,
may be interpreted as hints at that the common origin would be a more elemental organismic feature, a metabolic-homeostatic
variable which due to its evolutionary strength eventually created the platform for a radiation of adaptations concerning
species-specific patterned sounds and locomotions with a broad spectrum of tasks, among them sexual selection. This line of
reasoning is here, under reference to recent biological data, made the basis for a hypothetical model of music as an expression
of an early homeostatic feedback mechanism.
Accordingly, in music there is a central variable, a “heart” or a “core”, which is not to be found exclusively in music but
appears globally as a releasing mechanism for basic endocrine, autonomous and elementally cognitive functions. It is of acoustical
or motoric nature, or of a combination of these characters, and is performed in repetitive trains of impulses. It is further
assumed that the target of its operations is mainly proteins with a regulatory effect on the cellular and synaptic states.
The principal representatives for these proteins are growth factors, especially the NGF which originally was regarded as a
growth stimulator within the peripheral and sympathetical systems but which eventually appeared to be also a synergetic modulator
of neuro-endocrine-immuno-reactions, i.e. of the three central homeostatic systems (5, 80). One can speculate that this variable
is functionally active at an elemental level such that it has escaped to be knocked out by forceful “higher” and evolutionary
younger factors (49:13).
This hypothesis — that music has its roots within and is a part of a globally occurring natural acoustical-motoric stimulus,
manifested in a great variety of auditory and motoric behavior in humans and among some other higher vertebrates — implies
that humankind has developed this stimulus into a category of acoustical structures which oscillate round an instable point
of equilibrium. Exactly such structures, not stochastic but neither too predictable, affect the organism mainly on a sensory-vegetative
level (59, 102, 137, 151). They are in addition perceptionally optimal in creating cortical space-temporal neural patterns
with strong interhemispheric coherence (110, 130).
According to this scenario, music did not originate from a human need of communication or as an aspect of sexual selection.
It emerged from elemental processes within the individual organism with the aspiration to maintain his bodily and mental fitness,
thus on a pre-social level. What was beneficial to the single individual in his fight for survival, was good also for the
group and its survival. Starting from that platform music has evolved in symbiosis with dance and play within a large spectrum
of social functions, where sexual selection and ritual and autonomously aesthetical tasks got a focal role that increased
over time and always was accompanied by emotional events. Behind, the ticking in the deep structure of music of this in cultural-ethical
terms totally value-neutral archaic mechanism goes on without pause, contributing to the maintenance of an optimal functional
balance in body and mind of the individual, and the group as well. 相似文献
10.
Wolf U. Blanckenhorn 《Evolutionary ecology》2000,14(7):627-643
Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A
unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response
or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were
investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were
controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between
egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a
cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness
consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg
and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature
corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead,
this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate
temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24 °C had reduced
survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation
of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint)
of unclear adaptive value.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
11.
Age-related variations in chemical composition of egg matter were found in females in some studies, but they do not seem to
be a universal phenomenon. In contrast, egg size can be well predicted from female age. The relationship has a parabolic shape,
but the predicted size decrease of eggs from old females has not always been documented. Female size is an important contributor
to egg size, both at intra- and inter-specific levels. Dependence of fecundity on body size has usually been described by
a power function. A trade-off between egg number and size is considered in light of life history strategies. During a spawning
season egg size may differ between successive batches, but lack of effects of egg batch sequence was reported in some studies.
In yolk-feeding fish three discrete periods of elevated mortality are typically observed: shortly after egg activation, during
hatching, and at final yolk resorption. The positive relationships between female size, egg size and offspring size/resistance
to starvation and predation are a key pathway in parent–egg–progeny relationships. Both maternal and paternal effects contribute
to the total survival of offspring, but they operate in different ways and at different times. In contrast to the importance
of female size, no paternal size effects were revealed, but density and motility of spermatozoans were decisive. Typically,
paternal effects diminish earlier in ontogeny. Major factors governing embryonic survival (fertilisation success and hatching
success) differ from factors to which starvation mortality of yolk-feeding larvae is related. Embryonic survival is affected
by female age via egg matter composition, by egg ripeness and paternal factors such as sperm density and motility. In contrast, starvation
mortality of yolk-feeding larvae depends largely on female attributes (age, size and fecundity) via egg size, and, in some batch spawners, on egg batch sequence. Among teleost species egg size varies across a wide range (from
0.3 to 85–90 mm in diameter). Species that spawn large eggs are relatively rare. Caloric value of egg dry matter varies within
a narrow range of 20–30 J mg−1. Ecosystem and evolutionary components, and reproductive style are factors that contribute to egg endowment and yolk quality.
During the last decade considerable progress was made in the methodology and understanding of paternal effect on progeny performance
in fishes. This paper reviews these of parent–egg–progeny relationships. 相似文献
12.
Chester M 《Acta biotheoretica》2012,60(3):289-302
Proposed here is that an overriding principle of nature governs all population behavior; that a single tenet drives the many regimes observed in nature—exponential-like growth, saturated growth, population decline, population extinction, and oscillatory behavior. The signature of such an all embracing principle is a differential equation which, in a single statement, embraces the entire panoply of observations. In current orthodox theory, this diverse range of population behaviors is described by many different equations—each with its own specific justification. Here, a single equation governing all the regimes is proposed together with the principle from which it derives. The principle is: The effect on the environment of a population’s success is to alter that environment in a way that opposes the success. Experiments are suggested which could validate or refute the theory. Predictions are made about population behaviors. 相似文献
13.
Kepa Ruiz-Mirazo Juli Peretó Alvaro Moreno 《Origins of life and evolution of the biosphere》2010,40(2):203-213
In the present, post-genomic times, systemic or holistic approaches to living phenomena are compulsory to overcome the limits
of traditional strategies, such as the methodological reductionism of molecular biology. In this paper, we propose that theoretical
and philosophical efforts to define life also contribute to those integrative approaches, providing a global theoretical framework
that may help to deal with or interpret the huge amount of data being collected by current high-throughput technologies, in
this so-called ‘omics’ revolution. We claim that two fundamental notions can capture the core of the living, (basic) autonomy and open-ended evolution, and that only the complementary combination of these two theoretical constructs offers an adequate solution to the problem
of defining the nature of life in specific enough—but also encompassing enough—terms. This tentative solution should also
illuminate, in its most elementary version, the leading steps towards living beings on Earth. 相似文献
14.
A simple family of models of a bacterial population in a time varying environment in which cells can transit between dormant
and active states is constructed. It consists of a linear system of ordinary differential equations for active and dormant
cells with time-dependent coefficients reflecting an environment which may be periodic or random, with alternate periods of
low and high resource levels. The focus is on computing/estimating the dominant Lyapunov exponent, the fitness, and determining
its dependence on various parameters and the two strategies—responsive and stochastic—by which organisms switch between dormant
and active states. A responsive switcher responds to good and bad times by making timely and appropriate transitions while
a stochastic switcher switches continuously without regard to the environmental state. The fitness of a responsive switcher
is examined and compared with fitness of a stochastic switcher, and with the fitness of a dormancy-incapable organism. Analytical
methods show that both switching strategists have higher fitness than a dormancy-incapable organism when good times are rare
and that responsive switcher has higher fitness than stochastic switcher when good times are either rare or common. Numerical
calculations show that stochastic switcher can be most fit when good times are neither too rare or too common.
This research was supported by NSF Grant DMS 0414270, Department of Mathematics, Arizona State University, Tempe, AZ. 相似文献
15.
This commentary examines conventional and recent ideas regarding the interpretation of species richness-productivity relationships
(SRPR) in terrestrial vegetation. A new conceptual modelling approach — cascading graph diagrams — is used to search for maximum
parsimony by distilling and clarifying synthetic linkages between several potential causes of variation and co-variation in
these two vegetation attributes at three distinctly different spatial scales: global/continental scale (variation between
climatic/geographic regions within a continent, or across latitudes); regional scale (variation between local communities
representing different habitat (soil) fertility types or different habitat disturbance levels within a climatic/geographic
region); and local community scale (variation between neighbourhood plots within a particular plant community/habitat). In
contrast with a number of interpretations in recent literature, the approach developed here emphases that SRPR at each scale
in terrestrial vegetation involve a “cascade” of several intermediary causational variables that have not been generally accounted
for in previous studies of SRPR. Accordingly, SRPR are expected usually to be correlational, sometimes indirectly causational,
but never directly causational, at any scale. Rather than suggesting that causational mechanisms “scale up”, the analysis
here illustrates that several mechanistic features may be shared across scales and that in some cases, mechanisms may “scale
down”. This has crucial implications for identifying testable and un-confounded hypotheses for future research and for selecting
effective experimental designs and appropriate methods of data analyses for the interpretation of SRPR in natural vegetation. 相似文献
16.
Many autotrophs vary their allocation to nutrient uptake in response to environmental cues, yet the dynamics of this plasticity
are largely unknown. Plasticity dynamics affect the extent of single versus multiple nutrient limitation and thus have implications
for plant ecology and biogeochemical cycling. Here we use a model of two essential nutrients cycling through autotrophs and
the environment to determine conditions under which different plastic or fixed nutrient uptake strategies are adaptive. Our
model includes environment-independent costs of being plastic, environment-dependent costs proportional to the rate of plastic
change, and costs of being mismatched to the environment, the last of which is experienced by both fixed and plastic types.
In equilibrium environments, environment-independent costs of being plastic select for tortoise strategies—fixed or less plastic
types—provided that they are sufficiently close to co-limitation. At intermediate levels of environmental fluctuation forced
by periodic nutrient inputs, more hare-like plastic strategies prevail because they remain near co-limitation. However, the
fastest is not necessarily the best. The most adaptive strategy is an intermediate level of plasticity that keeps pace with
environmental fluctuations, but is not faster. At high levels of environmental fluctuation, the environment-dependent cost
of changing rapidly to keep pace with the environment becomes prohibitive and tortoise strategies again dominate. The existence
and location of these thresholds depend on plasticity costs and rate, which are largely unknown empirically. These results
suggest that the expectations for single nutrient limitation versus co-limitation and therefore biogeochemical cycling and
autotroph community dynamics depend on environmental heterogeneity and plasticity costs. 相似文献
17.
Sasha Daskalova Alex McCormac Nigel Scott Harry Van Onckelen Malcolm Elliott 《Plant Growth Regulation》2007,51(3):217-229
A transgenic approach to manipulation of endosperm development has been investigated. Nicotiana tabacum cv. Xanthi, an endosperm-containing dicotyledon, has been used as a model plant and the 2.6 kb wheat high molecular weight
(HMW) glutenin subunit 12 promoter has been used fused either to the gus reporter gene (HMWgus construct)—to study promoter characteristics—or to the Agrobacterium ipt gene—to study the effect of cytokinin (CK) over-expression on assimilate accumulation in the seed. In transgenic tobacco
the promoter:gus fusion showed that HMW is an endosperm-specific promoter with maximum expression 20 days after anthesis (DAA), corresponding
to the mid to late stages of seed development. Transgenic plants containing the HMWipt construct showed no morphological abnormalities but they had an average increase in seed weight and total ethanol-insoluble
carbohydrates and protein content of 8.1%, 7.0% and 8.3%, respectively. SDS PAGE analysis demonstrated that the effect on
protein accumulation was non-specific. The highest values of the parameters analysed correlated with moderate increases in
the levels of biologically active CKs. These results suggest that ectopic expression of small amounts of CKs can be used to
increase storage assimilate accumulation without a detrimental effect on development. 相似文献
18.
Sinéad Collins 《Evolutionary biology》2011,38(1):3-14
Experimental microbial evolution has focused on the particular ecological scenario where a population is placed suddenly in
an environment where its fitness is low, and then adapts while the environment remains stable. In line with this, most microbial
evolution studies use fitness measures that report how evolved genotypes fare when competed directly against their own distant
ancestor while other studies compare life history traits (such as growth rates) of ancestral and evolved genotypes. This standard
way of measuring and reporting changes in fitness has resulted in a consistent body of literature that explains adaptation
when populations evolve in this “standard ecological scenario.” Here, I suggest that for experimental evolution to investigate
adaptation in other ecological scenarios, such as fluctuating or persistently changing environments, measures of fitness must
be expanded such that they not only continue to be comparable between experiments, but also account for evolution and demographic
effects in all environments that an evolving lineage experiences. I examine two non-standard measures of fitness—fitness flux
and the total number of reproductive events—as potential ways to quantify adaptation by integrating historical information
about selection over many environments. This approach could allow us to make quantitative and biologically-meaningful comparisons
of adaptation across diverse ecological scenarios. I use the case study of understanding how phytoplankton communities may
respond to global change, where environmental variables change continuously, to explore concrete ways of using non-standard
fitness measures that consider both demographic effects and selection in changing, rather than in changed, environments. 相似文献
19.
Jørgen Kristiansen 《Biodiversity and Conservation》2008,17(2):419-426
The silica-scaled chrysophytes—here mainly represented by the freshwater genera Mallomonas and Synura—have special problems in dispersal from one habitat to another because they cannot tolerate desiccation. Their dispersal
is limited by the fragile construction and aquatic habit. Dispersal from one water body to another involves dangerous changes
of the environment, and the ability to avoid desiccation during transport is crucial. So, air-borne and ectozoic dispersal
by birds or mammals can only work at short distances. This danger may be avoided by endozoic dispersal of thick-walled cysts;
as far as they can tolerate the digestion fluids in the intestine. In spite of these difficulties, Chrysophytes have been
dispersed worldwide, but they display various distinct distribution patterns, e.g., cosmopolitan, arctic-northern temperate,
bipolar, and tropical. Quite a large proportion may be considered endemic, occurring only within a restricted area. Even if
the exact dispersal methods are elusive, the distribution of chrysophytes around the world proves their ability for dispersal.
On the other hand, the different degree of distribution shows the varying success of the individual species. The distribution
of a species at a given time depends on several factors: dispersal capacity—available vectors—suitable available habitats—and
most important: sufficient time for dispersal. It is remarkable that the chrysophytes—in spite of their fragile cell construction
and apparently low dispersal capacity—show distribution types comparable to those found in, e.g., blue–greens and desmids,
whose cell construction appears much better adapted for dispersal.
Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner 相似文献
20.
As a reflection on recent debates on the value of wild animals we examine the question of the intrinsic value of wild animals
in both natural and man-made surroundings. We examine the concepts being wild and domesticated. In our approach we consider
animals as dependent on their environment, whether it is a human or a natural environment. Stressing this dependence we argue
that a distinction can be made between three different interpretations of a wild animal’s intrinsic value: a species-specific,
a naturalistic, and an individualistic interpretation. According to the species-specific approach, the animal is primarily
considered as a member of its species; according to the naturalistic interpretation, the animal is seen as dependent on the
natural environment; and according to the individualistic approach, the animal is seen in terms of its relationship to humans.
In our opinion, the species-specific interpretation, which is the current dominant view, should be supplemented—but not replaced
by—naturalistic and individualistic interpretations, which focus attention on the relationship of the animal to the natural
and human environments, respectively. Which of these three interpretations is the most suitable in a given case depends on
the circumstances and the opportunity for the animal to grow and develop according to its nature and capabilities. 相似文献