A new approach to loop analysis is presented in which decompositions of the total elasticity of a population projection matrix over a set of life history pathways are obtained as solutions of a constrained system of linear equations. In loop analysis, life history pathways are represented by loops in the life cycle graph, and the elasticity of the loop is interpreted as a measure of the contribution of the life history pathway to the population growth rate. Associated with the life cycle graph is a vector space -- the cycle space of the graph -- which is spanned by the loops. The elasticities of the transitions in the life cycle graph can be represented by a vector in the cycle space, and a loop decomposition of the life cycle graph is then defined to be any nonnegative linear combination of the loops which sum to the vector of elasticities. In contrast to previously published algorithms for carrying out loop analysis, we show that a given life cycle graph admits of either a unique loop decomposition or an infinite set of loop decompositions which can be characterized as a bounded convex set of nonnegative vectors. Using this approach, loop decompositions which minimize or maximize a linear objective function can be obtained as solutions of a linear programming problem, allowing us to place lower and upper bounds on the contributions of life history pathways to the population growth rate. Another consequence of our approach to loop analysis is that it allows us to identify the exact tradeoffs in contributions to the population growth rate that must exist between life history pathways. 相似文献
Several animal species have cyclic population dynamics with phase-related cycles in life history traits such as body mass,
reproductive rate, and pre-reproductive period. Although many mechanisms have been proposed there is no agreement on the cause
of these cycles, and no population equation that deduces both the abundance and the life history cycles from basic ecological
constraints has been formulated. Here I deduce a population dynamic equation from the selection pressure of density dependent
competitive interactions in order to explain the cyclic dynamics in abundance and life history traits. The model can explain
cycles by evolutionary changes in the genotype or by plastic responses in the phenotype. It treats the population dynamic
growth rate as an initial condition, and its density independent fundament is Fisher’s (1930, The Genetical Theory of Natural Selection, Oxford: Clarendon) fundamental theorem of natural selection that predicts a hyper-geometrical increase in abundance. The
predicted periods coincide with the cyclic dynamics of Lepidoptera, and the Calder hypothesis, which suggests that the period
of population cycles is proportional to the 1/4 power of body mass, follows from first principles of the proposed density
dependent ecology. 相似文献
Demographic data provide a basis for understanding the life history and ecology of species, factors which are vital for informing
conservation efforts; however, little is known regarding the population ecology of most snake species, including the threatened
Eastern Indigo Snake (Drymarchon couperi). We used 11 years (1999–2009) of capture-mark-recapture (CMR) and 2.5 years (2003–2005) of radiotelemetry data from southeastern
Georgia, USA, in a CMR modeling framework to estimate apparent survival, capture and transition probabilities, and evaluate
factors influencing these parameters. The model-averaged estimate of overall apparent annual survival probability was 0.700
(±0.030 SE) and is comparable to that obtained from known fate analysis (radiotelemetry) at the same site. Body size positively
influenced survival, regardless of sex. Capture probability differed seasonally by sex, suggesting lower capture probability
for females in fall and males in winter. There was no evidence for effect of precipitation or site-specific differences in
survival. Model averaged estimate of annual adult survival estimated using multistate CMR models was 0.738 ± 0.030 and 0.515 ± 0.189
for subadults. We estimated population growth rate (λ) and elasticity (proportional sensitivity) of λ to vital rates using a stage-structured matrix population model. Population growth rate ranged from 0.96 to 1.03 depending
on the value of the probability of transitioning from subadult to adult stage. The λ was proportionally most sensitive to changes in adult survival rate, followed by subadult survival. Our results suggest that
protecting adult snakes and their habitats would result in the highest likelihood of long-term population stability and growth. 相似文献
Summary. Angles (λ) at which parallel cortical microtubules (cMTs) were oriented with respect to the longitudinal direction were measured
in Helianthus annuus hypocotyl epidermal cells. Histograms showing λ frequencies in cell populations at the instant of epidermis fixation were
obtained. Analysis of the histograms indicates that, in a particular position within a cell, the angle λ changes periodically
with time, i.e., there is a cycle of λ change at that position. This cycle is most likely rotational rather than oscillatory,
i.e., the change in λ has a defined chirality (clockwise or counterclockwise). The full diversity of histograms can be consistently
explained by rotational cycles with a variable velocity of λ change, and with a cMT rebuilding stage taking place at a different
phase of the cycle. The rotational cycles also provide the simplest explanation of cMT arrays in which the angle λ changes
along a cell (fixed) and no parallel orientation of cMTs is apparent at a certain position. This explanation assumes a gradient
in the phase of the rotational cycle along the cell. The symmetry of the angular characteristics of the rotational cycle,
with respect to the morphological directions in cells, leads to the concept that these directions typically represent the
principal directions of a certain tensor quantity, which may control the cycling. Possible interactions between the rotational
cycle of cMT reorientation and the helicoidal cycle during cell wall formation are discussed.
Correspondence and reprints: Department of Biophysics and Cell Biology, Silesian University, ulica Jagiellonska 28, 40-032
Katowice, Poland. 相似文献
Recently, several authors have proposed that the availability of intermediate hosts (IHs) for definitive hosts (DHs) may contribute to determining the dynamics and evolutionary ecology of parasites with facultative complex life cycles. The protozoa Toxoplasma gondii may be transmitted to DHs either via predation of infected IHs through a complex life cycle (CLC) or directly from a contaminated environment through a simple life cycle (SLC). This parasite is also present in contrasting host density environments. We tested the hypothesis that the relative contributions of the CLC and SLC along an urban-rural gradient depend on the IH supply. We built and analysed a deterministic model of the T. gondii transmission cycle. The SLC relative contribution is important only in urban-type environments, i.e., with low predation rate on IHs. In contrast, the parasite is predominantly transmitted through a CLC in suburban and rural environments. The association of the two cycles enables the parasite to spread in situations of low IH availability and low DH population size for which each cycle alone is insufficient. 相似文献
The study of population regulation and demography in natural habitats is critical for the conservation of rare and endangered
species. We address the impact of cattle exclusion on the demographics of Magnolia dealbata (Magnoliaceae), an endangered species according to IUCN and Federal Mexican laws. Sixteen permanent plots were established,
eight of which were enclosed to livestock, in the mountain cloud forest in Coyopolan, Mexico, which has the largest population
of M. deadlbata. Censuses of the plots were undertaken annually during three annual cycles to record seed number, recruitment, mortality,
and growth (defined as length and diameter at breast height). The effects of two treatments (with and without livestock exclusion)
on the dynamics of M. dealbata were investigated using transition matrix models and life table response experiment (LTRE) analysis. Contrary to expectations,
there was no significant effect of cattle exclusion on population growth rates (λ). Furthermore, the λ, estimated from the mean transition matrix for both treatments was greater than one. The transitions with the highest elasticity
values were similar between the two treatments, while reproductive stage contributed more to differences in population growth
rate and were less variable than the non-reproductive stage. LTRE analysis showed that treatment differences had little effect
on λ. Livestock exclusion appears to lead more to differences in the arrangement of the values of the transition matrix than to
the rate of population growth for M. dealbata.相似文献
Fuel economy and emissions of heavy-duty trucks greatly vary based on vehicular/environmental conditions. Large-scale infrastructure construction projects require a large amount of material/equipment transportation. Single-parameter generic hauling models may not be the best option for an accurate estimation of hauling contribution in life cycle assessment (LCA) involving construction projects; therefore, more precise data and parameterized models are required to represent this contribution. This paper discusses key environmental/operational variables and their impact on transportation of materials and equipment; a variable-impact transportation (VIT) model accounting for these variables was developed to predict environmental impacts of hauling.
Methods
The VIT model in the form of multi-nonlinear regression equations was developed based on simulations using the U.S. Environmental Protection Agency (EPA)’s Motor Vehicle Emission Simulator (MOVES) to compute all the impact categories in EPA’s TRACI 2.1 and energy consumption of transportation. Considering actual driving cycles of hauling trucks recorded during a pavement rehabilitation project, the corresponding environmental impacts were calculated, and sensitivity analyses were performed. In addition, an LCA case study based on historical pavement reconstruction projects in Illinois was conducted to analyze the contribution of transportation and variability of its impacts during the pavements’ life cycle.
Results and discussion
The importance of vehicle driving cycles was realized from simulation results. The case study results showed that considering driving cycles using the VIT model could increase the contribution of hauling in total life cycle Global Warming Potential (GWP) and total life cycle GWP itself by 2–4 and 3–5%, respectively. In addition to GWP, ranges of other hauling-related impact categories including Smog, Ozone Depletion, Acidification, and Primary Energy Demand from fuel were presented based on the case study. Ozone Depletion ranged from 9 to 45%, and Smog ranged from 11 to 48% of the total relevant life cycle impacts. The GWP contribution of hauling in pavement LCA ranged between 5 and 32%. The results indicate that the contribution of hauling transportation can be significant in pavement LCA.
Conclusions
For large-scale roadway infrastructure construction projects that need a massive amount of material transportation, high fidelity models and data should be used especially for comparative LCAs that can be used as part of decision making between alternatives. The VIT model provides a simple analytical platform to include the critical vehicular/operational variables without any dependence on an external software; the model can also be incorporated in those studies where some of the transportation activity data are available.
Demographic loop analysis is one of the basic methods applied in life cycle analysis in population ecology. Here, we developed an R package called “loop” to implement the algorithmic approach of loop analysis developed by a previous work. Additionally, the package can provide flexible network plotting and food web analysis as well. In this paper we illustrated the loop decomposition analysis using the life-cycle graph of a tropical tree species Vouacapoua americana; and performed food web statistics for the two real food webs for illustrating food web plotting and detecting key species in securing food web persistence. The package, including source code and binary versions, is available at the following URL: http://cran.r-project.org/web/packages/loop/. 相似文献
The concept of fitness is often reduced to a single component, such as the replication rate in a given habitat. For species with multi-step life cycles, this can be an unjustified oversimplification, as every step of the life cycle can contribute to the overall reproductive success in a specific way. In particular, this applies to microbes that spend part of their life cycles associated to a host. In this case, there is a selection pressure not only on the replication rates, but also on the phenotypic traits associated to migrating from the external environment to the host and vice-versa (i.e., the migration rates). Here, we investigate a simple model of a microbial lineage living, replicating, migrating and competing in and between two compartments: a host and an environment. We perform a sensitivity analysis on the overall growth rate to determine the selection gradient experienced by the microbial lineage. We focus on the direction of selection at each point of the phenotypic space, defining an optimal way for the microbial lineage to increase its fitness. We show that microbes can adapt to the two-compartment life cycle through either changes in replication or migration rates, depending on the initial values of the traits, the initial distribution across the two compartments, the intensity of competition, and the time scales involved in the life cycle versus the time scale of adaptation (which determines the adequate probing time to measure fitness). Overall, our model provides a conceptual framework to study the selection on microbes experiencing a host-associated life cycle.Subject terms: Microbial ecology, Symbiosis, Theoretical ecology, Evolution, Microbiome相似文献
The dynamics of plant populations in arid environments are largely affected by the unpredictable environmental conditions
and are fine-tuned by biotic factors, such as modes of recruitment. A single species must cope with both spatial and temporal
heterogeneity that trigger pulses of sexual and clonal establishment throughout its distributional range. We studied two populations
of the clonal, purple prickly pear cactus, Opuntia macrocentra, in order to contrast the factors responsible for the population dynamics of a common, widely distributed species. The study
sites were located in protected areas that correspond to extreme latitudinal locations for this species within the Chihuahuan
Desert. We studied both populations for four consecutive years and determined the demographic consequences of environmental
variability and the mode of reproduction using matrix population models, life table response experiments (LTREs), and loop
and perturbation analyses. Although both populations seemed fairly stable (population growth rate, λ∼1), different demographic parameters and different life cycle routes were responsible for this stability in each population.
In the southernmost population (MBR) LTRE and loop and elasticity analyses showed that stasis is the demographic process with
the highest contributions to λ, followed by sexual reproduction, and clonal propagation contributed the least. The northern population (CR) had both higher
elasticities and larger contributions of stasis, followed by clonal propagation and sexual recruitment. Loop analysis also
showed that individuals in CR have more paths to complete a life cycle than those in MBR. As a consequence, each population
differed in life history traits (e.g., size class structure, size at sexual maturity, and reproductive value). Numerical perturbation
analyses showed a small effect of the seed bank on the λ of both populations, while the transition from seeds to seedlings had an important effect mainly in the northern population.
Clonal propagation (higher survival and higher contributions to vital rates) seems to be more important for maintaining populations
over long time periods than sexual reproduction. 相似文献
Forest-insect systems frequently show cyclic dynamics which has been of considerable interest to both experimental and theoretical ecologists. One important issue has been the manner in which density-dependence acting on the host population through resource competition influences the likelihood of population cycles. Existing models make contradictory predictions. Here, we explore two models that allow different forms of density-dependence to be examined. We find that host density-dependence can influence the persistence of the host-pathogen interaction, the likelihood of population cycles and the stability of the host-pathogen interaction. In particular, over-compensatory density-dependence is likely to lead to host-pathogen cycles while under-compensatory density-dependence can promote stability. We discuss these differences with reference to the different forms of intraspecific competition and recent developments in insect population ecology. 相似文献
The results of long-term studies of two bank vole (Myodes glareolus) populations in stationary sites in the central part and periphery of its species area are described. Four phases of a multiannual
population cycle and two of its structural parts have been detected for both populations. The first part of the cycle is “determined,”
with the “peak” phase passing into a “depression” (population collapse). This transition is mainly determined by intrapopulation
processes and is weakly dependent on the external conditions of each individual year. The second part is “stochastic,” starting
from a stable point in the cycle in the depression phase. The duration of the second part is determined by the state of the
population and its ability to increase its size, as well as by the weather and food factors, predation pressure, and location
of the population within the species area. The transition from the peak phase to the depression phase (the determined part)
for both populations takes place during one fall-winter-spring season and has no effect on the cycle duration. The duration
of the stochastic part in the core of the species area (the period from depression phase to peak phase) is 1–3 years and in
the periphery, 2–4 years. 相似文献
Nine types with 11 variations of nuclear cycle and associated metabasidium development were distinguished in microcyclic
rust fungi. An additional type was recognized in rust fungi with an expanded life cycle. A significant proportion of rust
fungi with a reduced life cycle is assumed to have lost a sexual genetic recombination process, being either apomictic or
asexual in reproduction. Most species that retain a sexual process in the microcyclic life cycle seem to have become homothallic.
During life cycle evolution by the omission of spore stages, these traits might have had a selective advantage for those species
that had less opportunity to encounter a genetically different but sexually compatible mate because of isolated patchy distribution
or a short growing season. The findings that different populations of a morphologically identifiable species exhibit two or
more distinct patterns of nuclear cycle and different metabasidium development indicate that microcyclic lineages might have
evolved independently and repeatedly from a macrocyclic parental species. Those lineages are morphologically the same but
would differ from each other in their genetics and biology.
Received: July 5, 2002 / Accepted: August 5, 2002
Acknowledgment This work was supported in part by a Grant-in-Aid for Scientific Research (no. 09640744) from the Ministry of Education,
Science and Culture (now the Ministry of Education, Culture, Sports, Science and Technology), Japan.
Correspondence to:Y. Ono 相似文献
Northern pike (Esox lucius) are often considered to be specialist piscivores, but under some circumstances will continue to eat invertebrates as adults.
To examine effects of fish assemblage composition on the trophic ecology of pike, we combined stable isotope analysis (SIA)
of carbon and nitrogen and stomach content analysis (SCA) on pike from five lakes in northern Alberta, three of which contain
only pike (“pike-only”) and two that also contain yellow perch (Perca flavescens) or white sucker (Catostomus commersoni) (“pike-other”). Fish were more important as prey and empty stomachs, which often characterize piscivores, were significantly
more frequent in pike-other than in pike-only lakes. However, even though invertebrates were more important for pike in pike-only
lakes, SIA and SCA indicated that invertebrates were also an important component of pike diets in pike-other lakes. SIA and
SCA also revealed considerable intrapopulation variation in trophic ecology, with individuals in some populations differing
by as much as two trophic levels. Comparisons of stomach contents and isotope signatures of the same fish suggested that within
these variable populations, specialization on invertebrates or fish was a long-term trait of some individuals. SIA indicated
that trophic position increased and diets shifted to a greater importance of littoral prey as pike grew in pike-only lakes,
but not in lakes with other fish present. Trophic adaptability in northern pike is expressed at both the population level,
where the trophic ecology is sensitive to differences in prey regimes, and at the organismal level, in the form of intrapopulation
variation and individual specialization.
Received: 1 July 1998 / Accepted: 3 February 1999 相似文献
There is a need to assess social impacts of products along the full life cycle, not only to be able to address the “social
dimension” in sustainability, but also for potentially improving the circumstances of affected stakeholders. This paper presents
a case study for a social life cycle assessment (S-LCA) based on the recently published “Guidelines for Social Life Cycle
Assessment of Products” developed by the United Nations Environment Programme/Society of Environmental Toxicology and Chemistry
(UNEP/SETAC) working group. General aim is to “try out” the proposed method. The case study itself compares the impacts of
rose production in Ecuador with the Netherlands. Furthermore, the objective is to identify differences and similarities in
environmental and social life cycle modelling and both social and environmental hot spots in each of the life cycles. 相似文献
Wildlife populations in the northern reaches of the globe have long been observed to fluctuate or cycle periodically, with dramatic increases followed by catastrophic crashes. Focusing on the early work of Charles S. Elton, this article analyzes how investigations into population cycles shaped the development of Anglo-American animal ecology during the 1920s–1930s. Population cycling revealed patterns that challenged ideas about the “balance” of nature; stimulated efforts to quantify population data; and brought animal ecology into conversation with intellectual debates about natural selection. Elton used the problem of understanding wildlife population cycles to explore a central tension in ecological thought: the relative influences of local conditions (food supply, predation) and universal forces (such as climate change and natural selection) in regulating wild animal populations. He also sought patronage and built research practices and the influential Bureau of Animal Population around questions of population regulation during the 1930s. Focusing on disease as a local population regulator that could interact with global climatic influences, Elton facilitated an interdisciplinary and population-based approach in early animal ecology. Elton created a network of epidemiologists, conservationists, pathologists and mathematicians, who contributed to population cycle research. I argue that, although these people often remained peripheral to ecology, their ideas shaped the young discipline. Particularly important were the concepts of abundance, density, and disease; and the interactions between these factors and natural selection. However, Elton’s reliance on density dependence unwittingly helped set up conditions conducive to the development of controversies in animal ecology in later years. While ecologists did not come to consensus on the ultimate causes of population cycles, this phenomenon was an important early catalyst for the development of theory and practice in animal ecology. 相似文献
The analysis of population systems is carried out on the basis of the spatial and functional classification of populations
developed by V.N. Beklemishev. The population system is a functional part of a particular community. Steady interrelationships
between population systems of different species within the community (referred to as ”community links”) appear to be a prerequisite
for the formation of a complex of population systems. A prominent example of this is the parasitic system. The parasitic system
is the population system of a parasite with all the connected populations of its hosts. The complexity of a parasitic system
depends on: (1) peculiarities of the life cycle of the parasite, since its population system is the organizing component of
the parasitic system and (2) subdivision of the environment for the parasites. The first trait is discussed from the standpoint
of the phase structure of populations, which is clearly seen in parasites. The second one comprises the organization of the
parasites’ environment according to the scale of variability (interspecies, interpopulation or intrapopulation) of hosts.
These make it possible to recognize spatial and functional parts in the framework of the parasitic system. A critical review
of the terminology is presented together with a list of the pertaining vocabulary.
Received: 15 January 1998 / Accepted: 15 October 1998 相似文献
Growth rates and life cycles of D. reticulatum and A. intermediusare described and compared at different temperatures. D. reticulatummatures earlier in the cycle than A. intermedius and is moresensitive to changes in temperature. These differences are discussedin relation to the natural life cycles and ecology of thesespecies. (Received 9 February 1981; 相似文献
Background, Aims and Scope Although LCA is frequently used in product comparison, many practitioners are interested in identifying and assessing improvements
within a life cycle. Thus, the goals of this work are to provide guidelines for scenario formulation for process and material alternatives
within a life cycle inventory and to evaluate the usefulness of decision tree and matrix computational structures in the assessment
of material and process alternatives. We assume that if the analysis goal is to guide the selection among alternatives towards
reduced life cycle environmental impacts, then the analysis should estimate the inventory results in a manner that: (1) reveals
the optimal set of processes with respect to minimization of each impact of interest, and (2) minimizes and organizes computational
and data collection needs.
Methods A sample industrial system is used to reveal the complexities of scenario formulation for process and material alternatives
in an LCI. The system includes 4 processes, each executable in 2 different ways, as well as 1 process able to use 2 different
materials interchangeably. We formulate and evaluate scenarios for this system using three different methods and find advantages
and disadvantages with each. First, the single branch decision tree method stays true to the typical construction of decision
trees such that each branch of the tree represents a single scenario. Next, the process flow decision tree method strays from
the typical construction of decision trees by following the process flow of the product system, such that multiple branches
are needed to represent a single scenario. In the final method, disaggregating the demand vector, each scenario is represented
by separate vectors which are combined into a matrix to allow the simultaneous solution of the inventory problem for all scenarios.
Results For both decision tree and matrix methods, scenario formulation, data collection, and scenario analysis are facilitated in
two ways. First, process alternatives that cannot actually be chosen should be modeled as sub-inventories (or as a complete
LCI within an LCI). Second, material alternatives (e.g., a choice between structural materials) must be maintained within
the analysis to avoid the creation of artificial multi-functional processes. Further, in the same manner that decision trees
can be used to estimate ‘expected value’ (the sum of the probability of each scenario multiplied by its ‘value’), we find
that expected inventory and impact results can be defined for both decision tree and matrix methods.
Discussion For scenario formulation, naming scenarios in a way that differentiate them from other scenarios is complex and important
in the continuing development of LCI data for use in databases or LCA software. In the formulation and assessment of scenarios,
decision tree methods offer some level of visual appeal and the potential for using commercially available software/ traditional
decision tree solution constructs for estimating expected values (for relatively small or highly aggregated product systems).
However, solving decision tree systems requires the use of sequential process scaling which is difficult to formalize with
mathematical notation. In contrast, preparation of a demand matrix does not require use of the sequential method to solve
the inventory problem but requires careful scenario tracking efforts.
Conclusions Here, we recognize that improvements can be made within a product system. This recognition supports the greater use of LCA
in supply chain formation and product research, development, and design. We further conclude that although both decision tree
and matrix methods are formulated herein to reveal optimal life cycle scenarios, the use of demand matrices is preferred in
the preparation of a formal mathematical construct. Further, for both methods, data collection and assessment are facilitated
by the use of sub-inventories (or as a complete LCI within an LCI) for process alternatives and the full consideration of
material alternatives to avoid the creation of artificial multi-functional processes.
Recommendations and Perspectives The methods described here are used in the assessment of forest management alternatives and are being further developed to
form national commodity models considering technology alternatives, national production mixes and imports, and point-to-point
transportation models.
ESS-Submission Editor: Thomas Gloria, PhD (t.gloria@fivewinds.com) 相似文献
Worldwide, river fragmentation is primarily responsible for the decline of populations of migrating fish. In particular, anadromous
fish species, which necessarily migrate to fresh water to reproduce, are endangered since many are no longer able to reach
their natural spawning sites. In addition, pollution of rivers effectively prevents upstream or downstream movements and blocks
access to spawning grounds. This article investigates how poor water quality interferes with the life history cycle of twaite
shad Alosa fallax fallax (Lacépède, 1803), an anadromous clupeid fish, in the watershed of River Scheldt, a heavily impacted environment in West Europe.
We used two models based on known ecological and environmental information to explain past and present twaite shad distribution
within the watershed and to make inferences about a future population recovery and juvenile habitat value. We demonstrated
that historical spawning areas satisfy water quality conditions necessary to support spawning and successful development of
early life history stages of the twaite shad. However, poor water quality conditions just upstream the freshwater–saltwater
boundary still act as an effective migration barrier for upstream movement. As a consequence, spawning grounds are inaccessible
and the population is dominated by seasonal adults occurring in the lower estuarine part of the watershed. This article provides
testable and diagnostic information to the watershed management in that it identifies habitat and water quality requirements
needed to support the expected recovery of an endangered anadromous fish population.
Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot
Fish and diadromy in Europe (ecology, management, conservation) 相似文献