Where does environmental stochasticity most influence population dynamics? An assessment along a regional core-periphery gradient for prairie breeding ducks

2015 ◽  
Vol 24 (8) ◽  
pp. 896-904 ◽  
Author(s):  
Richard E. Feldman ◽  
Michael G. Anderson ◽  
David W. Howerter ◽  
Dennis L. Murray
Keyword(s):  
Population Dynamics ◽  
Environmental Stochasticity ◽  
Breeding Ducks

scholarly journals Breeding transients in capture–recapture modeling and their consequences for local population dynamics

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Daniel Oro ◽  
Daniel F. Doak
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Population Growth ◽  
Population Growth Rate ◽  
Local Population ◽  
Environmental Stochasticity ◽  
Adult Survival ◽  
Local Survival ◽  
First Reproduction ◽  
Capture Recapture

Abstract Standard procedures for capture–mark–recapture modelling (CMR) for the study of animal demography include running goodness-of-fit tests on a general starting model. A frequent reason for poor model fit is heterogeneity in local survival among individuals captured for the first time and those already captured or seen on previous occasions. This deviation is technically termed a transience effect. In specific cases, simple, uni-state CMR modeling showing transients may allow researchers to assess the role of these transients on population dynamics. Transient individuals nearly always have a lower local survival probability, which may appear for a number of reasons. In most cases, transients arise due to permanent dispersal, higher mortality, or a combination of both. In the case of higher mortality, transients may be symptomatic of a cost of first reproduction. A few studies working at large spatial scales actually show that transients more often correspond to survival costs of first reproduction rather than to permanent dispersal, bolstering the interpretation of transience as a measure of costs of reproduction, since initial detections are often associated with first breeding attempts. Regardless of their cause, the loss of transients from a local population should lower population growth rate. We review almost 1000 papers using CMR modeling and find that almost 40% of studies fitting the searching criteria (N = 115) detected transients. Nevertheless, few researchers have considered the ecological or evolutionary meaning of the transient phenomenon. Only three studies from the reviewed papers considered transients to be a cost of first reproduction. We also analyze a long-term individual monitoring dataset (1988–2012) on a long-lived bird to quantify transients, and we use a life table response experiment (LTRE) to measure the consequences of transients at a population level. As expected, population growth rate decreased when the environment became harsher while the proportion of transients increased. LTRE analysis showed that population growth can be substantially affected by changes in traits that are variable under environmental stochasticity and deterministic perturbations, such as recruitment, fecundity of experienced individuals, and transient probabilities. This occurred even though sensitivities and elasticities of these parameters were much lower than those for adult survival. The proportion of transients also increased with the strength of density-dependence. These results have implications for ecological and evolutionary studies and may stimulate other researchers to explore the ecological processes behind the occurrence of transients in capture–recapture studies. In population models, the inclusion of a specific state for transients may help to make more reliable predictions for endangered and harvested species.

scholarly journals Cooperative and non-cooperative behaviour in the exploitation of a common renewable resource with environmental stochasticity

2020 ◽  
Author(s):  
Michael Hackney ◽  
Alex James ◽  
Michael J. Plank
Keyword(s):  
Population Dynamics ◽  
Stochastic Game ◽  
Economic Value ◽  
Renewable Resource ◽  
Fishing Effort ◽  
Environmental Stochasticity ◽  
Agent Based ◽  
Stock Biomass ◽  
Optimal Policies ◽  
Fisheries Biology

AbstractClassical fisheries biology aims to optimise fisheries-level outcomes, such as yield or profit, by controlling the fishing effort. This can be adjusted to allow for the effects of environmental stochasticity, or noise, in the population dynamics. However, when multiple fishing entities, which could represent countries, commercial organisations, or individual vessels, can autonomously determine their own fishing effort, the the optimal action for one fishing entity depends on the actions of others. Coupled with noise in the population dynamics, and with decisions about fishing effort made repeatedly, this becomes an iterated stochastic game. We tackle this problem using the tools of stochastic optimisation, first for the monopolist’s problem and then for the duopolist’s problem. In each case, we derive optimal policies that specify the best level of fishing effort for a given stock biomass. Under these optimal policies, we can calculate the equilibrium stock biomass, the expected long-term return from fishing and the probability of stock collapse. We also show that there is a threshold stock biomass below which it is optimal to stop fishing until the stock recovers. We then develop an agent-based model to test the effectiveness of simple strategies for responding to deviations by an opponent from a cooperative fishing level. Our results show that the economic value of the fishery to a monopolist, or to a consortium of fishing agents, is robust to a certain level of noise. However, without the means of making agreements about fishing effort, even low levels of noise make sustained cooperation between autonomous fishing agents difficult.

Predicting the effects of climate change on bird population dynamics

2019 ◽  
pp. 74-90
Author(s):  
Bernt-Erik Sæther ◽  
Steinar Engen ◽  
Marlène Gamelon ◽  
Vidar Grøtan
Keyword(s):  
Climate Change ◽  
Population Dynamics ◽  
Population Size ◽  
Environmental Stochasticity ◽  
Population Estimates ◽  
Parameter Estimates ◽  
Vital Rates ◽  
Statistical Sense ◽  
High Level ◽  
Avian Populations

Climate variation strongly influences fluctuations in size of avian populations. In this chapter, we show that it is difficult to predict how the abundance of birds will respond to climate change. A major reason for this is that most available time series of fluctuations in population size are in a statistical sense short, thus often resulting in large uncertainties in parameter estimates. We therefore argue that reliable population predictions must be based on models that capture how climate change will affect vital rates as well as including other processes (e.g. density-dependences) known to affect the population dynamics of the species in question. Our survey of examples of such forecast studies show that reliable predictions necessarily contain a high level of uncertainty. A major reason for this is that avian population dynamics are strongly influenced by environmental stochasticity, which is for most species, irrespective of their life history, the most important driver of fluctuations in population size. Credible population predictions must therefore assess the effects of such uncertainties as well as biases in population estimates.

Reproductive value and analyses of population dynamics of age-structured populations

2021 ◽  
pp. 285-298
Author(s):  
Bernt-Erik Sæther ◽  
Steinar Engen
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Age Structure ◽  
Good Description ◽  
Age Distribution ◽  
Reproductive Rate ◽  
Environmental Stochasticity ◽  
Reproductive Value ◽  
Long Run ◽  
Age Structured

Many populations of especially long-lived species show large temporal variation in age structure, which can complicate estimating of important population parameters. This occurs because it can be difficult to disentangle whether variation in numbers is due to fluctuations in the environment or caused by changes in the age distribution. This chapter shows that fluctuations in the total reproductive value of the population, that is, the sum of all individual reproductive values, often provide a good description of the population dynamics but still is not confounded by fluctuations in age structure. Because the change in the total reproductive rate is exactly equal to the growth rate of the population, this quantity enables decomposition of the long-run growth rate into stochastic components caused by age-specific variation in demographic and environmental stochasticity. The chapter illustrates the practical application of this approach in stochastic demography by analyses of the dynamics of several populations of birds and mammals. It puts a strong focus on these methods being particularly useful in viability analyses of small populations of vulnerable or endangered species.

scholarly journals Evidence and implications of higher-order scaling in the environmental variation of animal population growth

2015 ◽  
Vol 112 (9) ◽  
pp. 2782-2787 ◽  
Author(s):  
Jake M. Ferguson ◽  
José M. Ponciano
Keyword(s):  
Population Dynamics ◽  
Density Dependence ◽  
Extinction Risk ◽  
Environmental Variation ◽  
Higher Order ◽  
Environmental Stochasticity ◽  
Population Variance ◽  
Environmental Variance ◽  
Animal Populations ◽  
Environmental Fluctuations

Environmental stochasticity is an important concept in population dynamics, providing a quantitative model of the extrinsic fluctuations driving population abundances. It is typically formulated as a stochastic perturbation to the maximum reproductive rate, leading to a population variance that scales quadratically with abundance. However, environmental fluctuations may also drive changes in the strength of density dependence. Very few studies have examined the consequences of this alternative model formulation while even fewer have tested which model better describes fluctuations in animal populations. Here we use data from the Global Population Dynamics Database to determine the statistical support for this alternative environmental variance model in 165 animal populations and test whether these models can capture known population–environment interactions in two well-studied ungulates. Our results suggest that variation in the density dependence is common and leads to a higher-order scaling of the population variance. This scaling will often stabilize populations although dynamics may also be destabilized under certain conditions. We conclude that higher-order environmental variation is a potentially ubiquitous and consequential property of animal populations. Our results suggest that extinction risk estimates may often be overestimated when not properly taking into account how environmental fluctuations affect population parameters.

scholarly journals Climate and density-dependent population dynamics: Lessons from a simple high-Arctic ecosystem

2021 ◽  
Author(s):  
Dominique Fauteux ◽  
Audun Stien ◽  
Nigel Yoccoz ◽  
Eva Fuglei ◽  
Rolf Ims
Keyword(s):  
Climate Change ◽  
Population Dynamics ◽  
Food Web ◽  
High Amplitude ◽  
High Arctic ◽  
Environmental Stochasticity ◽  
Food Web Structure ◽  
Annual Cycles ◽  
Density Dependent ◽  
The Impact

The strikingly diverse population dynamics of herbivorous small mammals, ranging from high-amplitude, multi-annual cycles to relatively stable dynamics, have puzzled ecologists for a century. Theory predicts that this diversity is shaped by density-dependent food web interactions and stochastic weather events. Recent disrupted cycles through amplitude dampening have been attributed to climate change. However, empirical testing has been hampered by the complexity of the food webs in which these herbivores normally are found. Here we analyze population dynamics of a grazing vole species in a uniquely simple high-Arctic food web without top-down regulation. In accordance with theory, the population dynamics was mostly ruled by overcompensatory density-dependence in winter that without environmental stochasticity would have yielded seasonality driven high-amplitude 2-year cycles. In this simple food web, rain-on-snow events disrupted cyclicity, but not through amplitude dampening. Our case study highlights how food web structure may modify the impact of climate change on population dynamics.

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