The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Lu Zhunwei - One of the best experts on this subject based on the ideXlab platform.
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A note on the asymptotic behaviour of the Extinction Probability in supercritical population-size-dependent branching processes with independent and identically distributed random environments
Journal of Applied Probability, 2004Co-Authors: Lu Zhunwei, Peter JagersAbstract:In supercritical population-size-dependent branching processes with independent and identically distributed random environments, it is shown that under certain regularity conditions there exist constants 0 < α 1 ≤α 0 < + ∞ and 0 < C 1, C 2 < + ∞ such that the Extinction Probability starting with k individuals is bounded below by C 1 k -α 0 and above by C 2 k -α 1 for sufficiently large k. Moreover, a similar conclusion, which follows from a result of Höpfner, is presented along with some remarks.
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THE ASYMPTOTIC BEHAVIOUR OF Extinction Probability IN THE SMITH-WILKINSON BRANCHING PROCESS
Advances in Applied Probability, 1993Co-Authors: D. R. Grey, Lu ZhunweiAbstract:Under some regularity conditions, in the supercritical Smith-Wilkinson branching process it is shown that as k, the starting population size, tends to infinity, the rate of convergence of qk, the corresponding Extinction Probability, to zero is similar to that of:
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The asymptotic behaviour of Extinction Probability in the Smith–Wilkinson branching process
Advances in Applied Probability, 1993Co-Authors: D. R. Grey, Lu ZhunweiAbstract:Under some regularity conditions, in the supercritical Smith–Wilkinson branching process it is shown that as k, the starting population size, tends to infinity, the rate of convergence of qk, the corresponding Extinction Probability, to zero is similar to that of:k–θ, if there exists at least one subcritical state in the random environment space; xkk–α, if there exist only supercritical states in the random environment space; exp , if there exists at least one critical state and the others are supercritical in the random environment space.Here θ, x, α and c are positive constants determined by the process.
John W. Hargrove - One of the best experts on this subject based on the ideXlab platform.
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Uncertainty and sensitivity analyses of Extinction probabilities suggest that adult female mortality is the weakest link for populations of tsetse (Glossina spp).
PLoS neglected tropical diseases, 2020Co-Authors: Elisha B. Are, John W. HargroveAbstract:Background A relatively simple life history allows us to derive an expression for the Extinction Probability of populations of tsetse, vectors of African sleeping sickness. We present the uncertainty and sensitivity analysis of the Extinction Probability, to offer key insights into factors affecting the control or eradication of tsetse populations. Methods We represent tsetse population growth as a branching process, and derive closed form estimates of population Extinction from that model. Statistical and mathematical techniques are used to analyse the uncertainties in estimating Extinction Probability, and the sensitivity of the Extinction Probability to changes in input parameters representing the natural life history and vital dynamics of tsetse populations. Results For fixed values of input parameters, the sensitivity of Extinction Probability depends on the baseline parameter values. Extinction Probability is most sensitive to the Probability that a female is inseminated by a fertile male when daily pupal mortality is low, whereas the Extinction Probability is most sensitive to daily mortality rate for adult females when daily pupal mortality, and Extinction probabilities, are high. Global uncertainty and sensitivity analysis show that daily mortality rate for adult females has the highest impact on the Extinction Probability. Conclusions The high correlation between Extinction Probability and daily female adult mortality gives a strong argument that control techniques which increase daily female adult mortality may be the single most effective means of ensuring eradication of tsetse population.
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The weakest link: uncertainty and sensitivity analysis of Extinction Probability estimates for tsetse (Glossina spp) populations
2019Co-Authors: Elisha B. Are, John W. HargroveAbstract:Abstract Background A relatively simple life history allows us to derive an expression for the Extinction Probability of populations of tsetse, vectors of African sleeping sickness. We present the uncertainty and sensitivity analysis of Extinction Probability for tsetse population, to offer key insights into parameters in the control/eradication of tsetse populations. Methods We represent tsetse population growth as a branching process, and derive closed form estimates of population Extinction from that model. Statistical and mathematical techniques are used to analyse the uncertainties in estimating Extinction Probability, and the sensitivity of the Extinction Probability to changes in input parameters representing the natural life history and vital dynamics of tsetse populations. Results For fixed values of input parameters, the sensitivity of Extinction Probability depends on the baseline parameter values. For example, Extinction Probability is more sensitive to the Probability that a female is inseminated by a fertile male when daily pupal mortality is low, whereas the Extinction Probability is more sensitive to daily mortality rate for adult females when daily pupal mortality, and Extinction probabilities, are high. Global uncertainty and sensitivity analysis showed that daily mortality rate for adult females has the highest impact on the Extinction Probability. Conclusions The strong correlation between Extinction Probability and daily female adult mortality gives a strong argument that control techniques to increase daily female adult mortality may be the single most effective means of ensuring eradication of tsetse population. Author summary Tsetse flies (Glossina spp) are vectors of Trypanosomiasis, a deadly disease commonly called sleeping sickness in humans and nagana in livestock. The relatively simple life history of tsetse enabled us to model its population growth as a stochastic branching process. We derived a closed-form expression for the Probability that a population of tsetse goes extinct, as a function of death, birth, development and insemination rates in female tsetse. We analyzed the sensitivity of the Extinction Probability to the different input parameters, in a bid to identify parameters with the highest impact on Extinction Probability. This information can, potentially, inform policy direction for tsetse control/elimination. In all the scenarios we considered, the daily mortality rate for adult females has the greatest impact on the magnitude of Extinction Probability. Our findings suggest that the mortality rate in the adult females is the weakest link in tsetse life history, and this fact should be exploited in achieving tsetse population control, or even elimination.
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Extinction probabilities, times to Extinction, basic reproduction number and growth rates for tsetse (Glossina spp) populations as a function of temperature
bioRxiv, 2019Co-Authors: John W. HargroveAbstract:Abstract Increases in temperature over recent decades have led to a significant reduction in the populations of tsetse flies (Glossina spp) in parts of the Zambezi Valley of Zimbabwe. If this is true for other parts of Africa, populations of tsetse may actually be going extinct in some parts of the continent. Extinction probabilities for tsetse populations have not so far been estimated as a function of temperature. We develop a time-homogeneous branching process model for situations where tsetse flies live at different levels of fixed temperatures. We derive a Probability distribution pk(T) for the number of female offspring an adult female tsetse is expected to produce in her lifetime, as a function of the fixed temperature at which she is living. We show that pk(T) can be expressed as a geometric series: its generating function is therefore a fractional linear type. We obtain expressions for the Extinction Probability, expected number of female offspring per female tsetse, and time to Extinction. No tsetse population can escape Extinction if subjected, for extended periods, to temperatures outside the range 16 °C - 32°C. Extinction Probability increases more rapidly as temperatures approach and exceed the upper and lower limits. If the number of females is large enough, the population can still survive even at high temperatures (28°C - 31°C). Small decreases or increases in constant temperature in the neighbourhoods of 16°C and 31°C, respectively, can drive tsetse populations to Extinction. Further study is needed to estimate Extinction probabilities for tsetse populations in field situations where temperatures vary continuously. Author summary Tsetse flies (Glossina spp) are the vectors of the African sleeping sickness. We derived an expression for the Extinction Probability, and mean time to Extinction, of closed populations of the flies experiencing different levels of fixed temperatures. Temperatures play a key role in tsetse population dynamics: no tsetse populations can escape Extinction at constant temperatures 32°C. The effect of temperature is more severe if tsetse populations are already depleted. Increasingly high temperatures due to climate change may alter the distribution of tsetse populations in Africa. The continent may witness local Extinctions of tsetse populations in some places, and appearances in places hitherto too cold for them.
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Extinction probabilities, times to Extinction, basic reproduction number and growth rates for tsetse (Glossina spp) populations as a function of temperature
bioRxiv, 2019Co-Authors: John W. HargroveAbstract:Abstract Increases in temperature over recent decades have led to a significant reduction in the populations of tsetse flies (Glossina spp) in parts of the Zambezi Valley of Zimbabwe. If this is true for other parts of Africa, populations of tsetse may actually be going extinct in some parts of the continent. Extinction probabilities for tsetse populations have not so far been estimated as a function of temperature. We develop a time-homogeneous branching process model for situations where tsetse flies live at different levels of fixed temperatures. We derive a Probability distribution pk(T) for the number of female offspring an adult female tsetse is expected to produce in her lifetime, as a function of the fixed temperature at which she is living. We show that pk(T) can be expressed as a geometric series: its generating function is therefore a fractional linear type. We obtain expressions for the Extinction Probability, expected number of female offspring per female tsetse, and time to Extinction. No tsetse population can escape Extinction if subjected, for extended periods, to temperatures outside the range 16 °C - 32°C. Extinction Probability increases more rapidly as temperatures approach and exceed the upper and lower limits. If the number of females is large enough, the population can still survive even at high temperatures (28°C - 31°C). Small decreases or increases in constant temperature in the neighbourhoods of 16°C and 31°C, respectively, can drive tsetse populations to Extinction. Further study is needed to estimate Extinction probabilities for tsetse populations in field situations where temperatures vary continuously. Author summary Tsetse flies (Glossina spp) are the vectors of the African sleeping sickness. We derived an expression for the Extinction Probability, and mean time to Extinction, of closed populations of the flies experiencing different levels of fixed temperatures. Temperatures play a key role in tsetse population dynamics: no tsetse populations can escape Extinction at constant temperatures 32°C. The effect of temperature is more severe if tsetse populations are already depleted. Increasingly high temperatures due to climate change may alter the distribution of tsetse populations in Africa. The continent may witness local Extinctions of tsetse populations in some places, and appearances in places hitherto too cold for them.
Irene Pérez - One of the best experts on this subject based on the ideXlab platform.
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exurban sprawl increases the Extinction Probability of a threatened tortoise due to pet collections
Ecological Modelling, 2012Co-Authors: José D. Anadón, Irene Pérez, Andrés Pedreño, Alicia Tenza, Julia Martinezfernandez, Andrés GiménezAbstract:Abstract Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors’ own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations.
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Exurban sprawl increases the Extinction Probability of a threatened tortoise due to pet collections
Ecological Modelling, 2012Co-Authors: Irene Pérez, José D. Anadón, Andrés Pedreño, Alicia Tenza, Julia Martínez-fernández, Andrés GiménezAbstract:Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors' own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations. © 2012 Elsevier B.V.Peer Reviewe
Andrés Giménez - One of the best experts on this subject based on the ideXlab platform.
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exurban sprawl increases the Extinction Probability of a threatened tortoise due to pet collections
Ecological Modelling, 2012Co-Authors: José D. Anadón, Irene Pérez, Andrés Pedreño, Alicia Tenza, Julia Martinezfernandez, Andrés GiménezAbstract:Abstract Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors’ own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations.
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Exurban sprawl increases the Extinction Probability of a threatened tortoise due to pet collections
Ecological Modelling, 2012Co-Authors: Irene Pérez, José D. Anadón, Andrés Pedreño, Alicia Tenza, Julia Martínez-fernández, Andrés GiménezAbstract:Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors' own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations. © 2012 Elsevier B.V.Peer Reviewe
D. R. Grey - One of the best experts on this subject based on the ideXlab platform.
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THE ASYMPTOTIC BEHAVIOUR OF Extinction Probability IN THE SMITH-WILKINSON BRANCHING PROCESS
Advances in Applied Probability, 1993Co-Authors: D. R. Grey, Lu ZhunweiAbstract:Under some regularity conditions, in the supercritical Smith-Wilkinson branching process it is shown that as k, the starting population size, tends to infinity, the rate of convergence of qk, the corresponding Extinction Probability, to zero is similar to that of:
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The asymptotic behaviour of Extinction Probability in the Smith–Wilkinson branching process
Advances in Applied Probability, 1993Co-Authors: D. R. Grey, Lu ZhunweiAbstract:Under some regularity conditions, in the supercritical Smith–Wilkinson branching process it is shown that as k, the starting population size, tends to infinity, the rate of convergence of qk, the corresponding Extinction Probability, to zero is similar to that of:k–θ, if there exists at least one subcritical state in the random environment space; xkk–α, if there exist only supercritical states in the random environment space; exp , if there exists at least one critical state and the others are supercritical in the random environment space.Here θ, x, α and c are positive constants determined by the process.
