A population cycle occurs when the growth rate of population varies over time in some fairly recognizable fashion. This might be due to changes in patterns of migration, or fluctuations in birth and death rates.
What is the population cycle in ecology?
Population cycle. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.
What are the causes of population change?
There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.
How can we better understand the drivers of population cycles?
Barraquand et al. [ 93] in a recent overview of modelling cyclic dynamics, concluded that by ‘gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss’. This throws the gauntlet back to the field ecologists.
What is population fluctuations?
Population fluctuations are undoubtedly one of the most fascinating phenomena in ecology. Some of the earliest writings known to man describe outbreaks of pests, such as the fabled locust plagues in Egypt. Some species, such as the snowshoe hare or larch budmoth, cycle through changes in abundance as regular as clockwork.
What factors can cause population fluctuations?
Three primary factors account for population change, or how much a population is increasing or decreasing. These factors are birth rate, death rate, and migration.
What is an example of a population cycle?
Some of the best examples of population cycles in animals are described from the boreal forest regions; for example, lynx (Lynx canadensis), snowshoe hares (Lepus americanus), arctic ground squirrels (Spermophylus parryi), red squirrel (Tamiasciurus hudsonius), and boreal red-backed vole (Clethrionomys rutilus) in ...
What are the four general types of population cycles?
1. Four general types of population fluctuations in nature are: stable, irruptive, cyclic, and irregular.
What are the 4 processes that determine population growth?
Population growth rate is how fast a population changes in size over time. Population growth is determined by rates of birth, death, immigration, and emigration.
What does it mean to say that a population cycles?
A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems.
What is population life cycle?
The demographic cycle, or population cycle, refers to the evolution over time of the population profile of a country, region or other defined geographical area. A population cycle theory has been postulated in terms of the socio-economic history of industrialized countries.
What are the 6 factors that affect population size?
Population growth rate is affected by birth rates, death rates, immigration, and emigration. If a population is given unlimited amounts of food, moisture, and oxygen, and other environmental factors, it will show exponential growth.
Which condition can cause a population crash?
The causes of a population crash are somewhat varied, but include scarcity of environmental resources that are needed for survival, growth and reproduction, predation, and waste accumulation. It can also be caused by an initially overpopulated group and competition between members of the same species.
What are the 3 phases of a population's life cycle?
The phases of logistic population growth include birth or initiation phase and growth phase. The other two phases are deceleration phase and stationary phase. In birth or initiation phase, the growth rate is slow. In growth phase, the population grows rapidly due to the presence of large amount of resources.
What are the five causes of population growth?
The Causes of OverpopulationFalling Mortality Rate.Underutilized Contraception.Lack of Female Education.Ecological Degradation.Increased Conflicts.Higher Risk of Disasters and Pandemics.
What causes population growth and decline?
A reduction over time in a region's population can be caused by sudden adverse events such as outbursts of infectious disease, famine, and war or by long-term trends, for example sub-replacement fertility, persistently low birth rates, high mortality rates, and continued emigration.
What are 3 effects of population growth?
Rapid growth has led to uncontrolled urbanization, which has produced overcrowding, destitution, crime, pollution, and political turmoil. Rapid growth has outstripped increases in food production, and population pressure has led to the overuse of arable land and its destruction.
What are the five stages of demographic cycle?
Demographic cycle(1) FIRST STAGE (High stationary) It is characterized by both. ... (2) SECOND STAGE (Early expanding) It begins with the. ... (3) THIRD STAGE (Late expanding) *Death rate declines further and. ... (4) FOURTH STAGE (Low stationary) This stage is characterized with. ... (5) FIFTH STAGE: (Declining)
Why do populations exhibit cyclic growth?
Cyclic changes in population growth can be caused by seasonal, or other environmental changes, or can be driven by density-dependent processes, such as predation, like the snowshoe hare and lynx example depicted here.
What is the predator/prey cycle?
Predator-prey cycles are based on a feeding relationship between two species: if the prey species rapidly multiplies, soon afterwards the number of predators increases - until the predators eventually eat so many prey that the prey population goes down again.
What is population fluctuation and the factors affecting it?
Factors affecting population fluctuation Density-independent factors, such as weather and climate, exert their influences on population size regardless of the population's density. In contrast, the effects of density-dependent factors intensify as the population increases in size.
What is a population cycle?
A population cycle is a roughly periodic variation over time in the size or composition of a population. Here, composition refers to the component structure of the population, for example into distinct age classes. The formal theory of population cycles consists of mathematical tools that yield qualitative and quantitative information about the characteristics of cycles, such as their amplitude or period. There are three broad types of cycle: transient cycles are a response to a perturbation of finite duration such as a fertility transition; externally driven cycles are triggered and sustained by a persistent external perturbation such as an economic cycle; internally driven cycles are maintained by interactions within the population such as a feedback between cohort size and cohort fertility. This article discusses the theory for these three types of cycles, dealing mainly with age-structured populations, although other aspects of population structure are mentioned.
How long are small mammals' cycles?
Small mammal cycles tend to be 2–4 years in length. Krebs (2013) concludes that predation and social behavior are the most critical factors for understanding small mammal population fluctuations although winter food can influence survival ( Johnsen et al., 2017 ). Small mammal populations are amenable to manipulation and much work has been devoted ...
How does a large cohort affect childbearing?
The linkage between birthrates and adverse economic and social effects causes the emergence of ‘crowding mechanisms’ operating within three major social institutions: family, school, and labor market. The result of the ‘crowding mechanisms’ is that the appearance of social stress factors are quite different in large and small cohorts. A large cohort adapts in order to avoid deterioration of its living standard compared with that of its parents. One such adaptation is that family formation takes place later in life. Another is that a woman in such a situation finds herself compelled to combine labor force participation with childbearing, which reduces her natality. By means of such demographic adaptation the large cohort strives to maintain its economic status compared with that of its parents. For a small cohort the situation is again reversed. Its members have no need to make any demographic adaptation in order to preserve an economic status that is favorable from the outset.
Why are bank voles increasing?
Bottom-up regulation of food quantity and quality is probably the major driver of population increase in bank voles ( Tersago et al., 2009) and deer mice ( Calderon et al., 1999). Accordingly, results from field studies and modeling efforts mentioned above suggest that it might be sufficient to forecast the phase of the multiannual population cycle of rodent reservoir populations instead of hantavirus prevalence within reservoirs in order to predict human hantavirus infection risk - at least for the systems bank vole – PUUV and Peromyscus maniculatus – SNV. The sooner in trophic cascades the forecast can be made, the more useful the prediction will be because more lead-up time is achieved ( Mills et al., 2010 ).
How is demographic behavior determined in the Easterlin model?
The most essential difference between the two approaches is that, according to the Easterlin model, demographic behavior is determined by incomes and consumption relative to expectations , whereas in the neoclassical theory demographic behavior is determined by absolute incomes and actual levels of consumption .
What is the meaning of the term "a group of people born during a given period"?
A group of people born during a given period are marked by the same code of values and attitudes in many respects. Easterlin believes it possible to identify an important underlying reason why values and attitudes may vary from one cohort to another.
Why do married women participate in the labor force more often?
Married women in a large cohort will participate in the labor force more often because of the family's difficult economic situation. Unmarried women have high nonmarital fertility, also resulting from social stress factors. Alcoholism is also regarded as more common in a large cohort.
What is a population cycle?
A population cycle is a roughly periodic variation over time in the size or composition of a population. Here, composition refers to the component structure of the population, for example into distinct age classes. The formal theory of population cycles consists of mathematical tools that yield qualitative and quantitative information about the characteristics of cycles, such as their amplitude or period. There are three broad types of cycle: transient cycles are a response to a perturbation of finite duration such as a fertility transition; externally driven cycles are triggered and sustained by a persistent external perturbation such as an economic cycle; internally driven cycles are maintained by interactions within the population such as a feedback between cohort size and cohort fertility. This article discusses the theory for these three types of cycles, dealing mainly with age-structured populations, although other aspects of population structure are mentioned.
How long are small mammals' population cycles?
They also are not easy to observe and thus demonstration of population trends depends on trapping data or cameras. Small mammal cycles tend to be 2–4 years in length. Krebs (2013) concludes that predation and social behavior are the most critical factors for understanding small mammal population fluctuations although winter food can influence survival ( Johnsen et al., 2017 ). Small mammal populations are amenable to manipulation and much work has been devoted to experimental fencing, feeding, and predator removal to elucidate mechanisms that could contribute to cyclic population dynamics, such as the importance of dispersal.
How does a large cohort affect childbearing?
The linkage between birthrates and adverse economic and social effects causes the emergence of ‘crowding mechanisms’ operating within three major social institutions: family, school, and labor market. The result of the ‘crowding mechanisms’ is that the appearance of social stress factors are quite different in large and small cohorts. A large cohort adapts in order to avoid deterioration of its living standard compared with that of its parents. One such adaptation is that family formation takes place later in life. Another is that a woman in such a situation finds herself compelled to combine labor force participation with childbearing, which reduces her natality. By means of such demographic adaptation the large cohort strives to maintain its economic status compared with that of its parents. For a small cohort the situation is again reversed. Its members have no need to make any demographic adaptation in order to preserve an economic status that is favorable from the outset.
Why are bank voles increasing?
Bottom-up regulation of food quantity and quality is probably the major driver of population increase in bank voles ( Tersago et al., 2009) and deer mice ( Calderon et al., 1999). Accordingly, results from field studies and modeling efforts mentioned above suggest that it might be sufficient to forecast the phase of the multiannual population cycle of rodent reservoir populations instead of hantavirus prevalence within reservoirs in order to predict human hantavirus infection risk - at least for the systems bank vole – PUUV and Peromyscus maniculatus – SNV. The sooner in trophic cascades the forecast can be made, the more useful the prediction will be because more lead-up time is achieved ( Mills et al., 2010 ).
Why should biodiversity programs be planned?
Thus, programs should be planned within a management framework to avoid simply gathering information without defined goals. The framework needs to be developed in the context of budget and resource levels to ensure program completion.
Why is each step calibrated periodically?
Each step is calibrated periodically to assure that the appropriate information feeds the next level, and the levels may overlap. Different managers are usually responsible for each component. Thus, the cyclical nature of the process is very important in validating the results of the separate steps.
Can a forecast predict human infection?
While basic forecast models yield useful results ( Glass et al., 2002; Tersago et al., 2009) that can be used for alerting high-risk groups and authorities, models that can predict local human infection risk are not available. This may be due to the large number of factors beyond climate and rodent food that matter for human infection risk be they related to climate (e.g., survival of hantavirus outside host, habitat features, human outdoor activity) or not (e.g., biodiversity, landscape). Some of these factors interact and the patchiness of virus distribution and potential effects of hantavirus infection on host demography and dynamics add further complexity.
How long are cyclic cycles?
The lengths of population cycles vary from 3 to 5 years in small mammals, 6 to 9 years for red grouse, and 8 to 11 years for snowshoe hares and forest Lepidoptera. Some have speculated that the periodicity of cycles is related to the number of generations a year and have proposed that this is scaled to body size, and rate of population increase for mammals [ 13 ]. A common characteristic of cyclic dynamics is an asymmetry such that the increase phase tends to be longer than the decline phase [ 7, 14, 15 ]. This could result if there are constraints on the potential magnitude of the rate of increase but not on the rate of decline. Variation in the degree and lengths of the increase and decline phases causes the amplitude and periodicity of the cycles to vary. One approach to discovering the processes underlying cycles is to compare cyclic and noncyclic populations.
Why are populations important to biodiversity?
Populations are the cornerstones of communities, ecosystems and the basic units of biodiversity because whether species are expanding or going extinct is determined by their population dynamics. To identify controlling factors, we need to determine the differences between increasing and declining populations.
What are the cyclic dynamics of tent caterpillars?
Cyclic populations of Western tent caterpillars in southwestern British Columbia show a pattern of a 15–20% reduction in fecundity beginning late in the population increase and into the population decline [ 34] ( figure 4 ). This could be a sublethal effect of infection by a nucleopolyhedrovirus [ 54 ]. Mortality from high levels of infection in peak populations and delayed recovery of fecundity are considered to be the drivers of cyclic dynamics in this species [ 34 ]. Infection by a protozoan reduced the fecundity of another cyclic Lepidoptera, the spruce needle miner, Epirzotia tedella [ 55 ]. Reduced fecundity or surrogates for fecundity such as moth size are characteristic of declining populations of other cyclic forest Lepidoptera [ 5, 21 ]. Models can be used to show that including reduced fecundity causes the simulated dynamics to be more realistic [ 56, 57 ].
What is the difference between a cyclic and noncyclic population of grouse?
Some evidence suggests that the differences between cyclic and noncyclic populations of grouse are related to the fragmentation of the habitat; populations on fragmented habitats are noncyclic [ 24 ].
How does a snowshoe hare affect its reproduction?
Changes in reproduction, particularly continued reduced fecundity or delayed reproduction into subsequent generations following peak populations, can greatly influence population dynamics [ 42 ]. For snowshoe hares, reproductive output is lower for several years before the peak density and through the population decline [ 43, 44] as females produce fewer than the maximum of four litters. This can reduce reproductive output by 50% (two versus four litters per year). Recent work has shown that this reduced reproduction is possibly caused by stress associated with predator avoidance [ 45 ]. This impact is carried over to subsequent generations perhaps through epigenetic changes in expression of stress regulatory genes [ 3 ]. For snowshoe hares, the length of the decline phase is related to the rate of population decline suggesting that high levels of predator risk associated with rapid population declines might cause stronger and longer lasting epigenetic influences [ 46 ].
What are the requirements for cyclic dynamics?
The requirements for cyclic dynamics are straightforward; a high reproductive rate to allow the population increase, density-related mortality to slow and stop the increase, and a prolonged negative condition to delay the recovery of the population [ 5 ]. Cyclic dynamics can occur if the density-dependent mortality mechanism is nonlinear [ 7] or over compensating [ 8 ]. If the density-dependent mortality is linear, a delayed process is required to produce cyclic dynamics [ 9 ]. This could be a carry over from reduced reproduction caused by stress or food limitation [ 5 ], deteriorating resource conditions [ 10 ], reduced quality of individuals with cross generational influences [ 11 ], or continued reduced survival from natural enemy attack into the decline such as a switch from specialist to generalist predators or parasitoids [ 12 ].
What is the first empirical demonstration of the predator-prey cycle?
The dynamics of lynx, Lynx canadensis, and snowshoe hares, Lepus americanus [ 1] ( figure 1 ), was the first empirical demonstration of the predator–prey cycles described in the classic models that Lotka and Volterra developed during the 1920s.
What are population fluctuations?
Population fluctuations are undoubtedly one of the most fascinating phenomena in ecology. Some of the earliest writings known to man describe outbreaks of pests, such as the fabled locust plagues in Egypt. Some species, such as the snowshoe hare or larch budmoth, cycle through changes in abundance as regular as clockwork.
What is a population dynamics textbook?
A sophisticated textbook covering various aspects of population dynamics , with particularly strong emphasis on integration of spatial with temporal population dynamics.
What causes population size to fluctuate?
Delayed density dependence can cause populations to fluctuate in size.
How does a population increase?
Population increases by a constant proportion at each point in time. When conditions are favorable, a population can increase exponentially for a limited time. Species such as the cattle egret colonize new regions by long-distance or jump dispersal events. Local populations then expand by short-distance dispersal events.
What happens to the extinction rate as patches get smaller?
As patches get smaller and more isolated, colonization decreases, and the extinction rate increases.
What is a metapopulation?
Metapopulations: For many species , suitable habitat exists as a series of spatially isolated patches, resulting in isolated populations. (So some of isolated populations may go extinct but the species continues to live on in other patches) Extinction and colonization of patches (Levins 1969, 1970):
What are the risks of extinction?
Population Extinction. The risk of extinction increases greatly in small populations. Fluctuations in growth rate, population size, and chance events can affect a population’s risk of extinction. The geometric growth equation can include random variation in the finite rate of increase (λ).
How often do rodent populations peak?
Populations of small rodents, such as lemmings and voles, typically reach a peak every 3–5 years. Delayed density dependence: Delays in the effect that density has on population size.
What is population fluctuation?
Population Fluctuation. In all populations, numbers rise and fall over time. Fluctuations can be erratic, or deviations from a growth pattern, e.g., the Tasmanian sheep population. Sometimes the number of individuals can increase rapidly, causing a population outbreak.
Introduction
Causes and Characteristics of Population Cycles
- The requirements for cyclic dynamics are straightforward; a high reproductive rate to allow the population increase, density-related mortality to slow and stop the increase, and a prolonged negative condition to delay the recovery of the population [5]. Cyclic dynamics can occur if the density-dependent mortality mechanism is nonlinear [7] or over ...
Comparing Cyclic and Noncyclic Populations
- One opportunity to compare cyclic and noncyclic populations is the North–South gradient in the amplitudes of voles and autumnal moth, Epirrita autumnata, cycles in Fennoscandia [12,16]. This is explained by generalist and nomadic predators being directly density dependent and stabilizing the vole populations in the south while specialist predators in northern regions such as the least …
Can Cyclic Dynamics Be Stopped?
- One way to test the causes of cyclic dynamics is to remove conditions thought to be responsible. This has proven to be difficult because manipulations must be done on large scales and over long time periods. In one attempt, spraying cyclic populations of Tussock moth late in the increase phase with a nucleopolyhedrovirus, a naturally occurring pathogen, elicited an early population d…
Changes in Mortality Versus Reproduction
- Changes in reproduction, particularly continued reduced fecundity or delayed reproduction into subsequent generations following peak populations, can greatly influence population dynamics [42]. For snowshoe hares, reproductive output is lower for several years before the peak density and through the population decline [43,44] as females produce fewer than the maximum of four …
A Lack of Genetic Differentiation: An Indicator of Dispersal in Cyclic Species
- A lack of both genetic differentiation and isolation by distance characterize cyclic forest Lepidoptera, voles and snowshoe hares (citations in [62]). An overview of northern cyclic species [63] concluded that density-dependent dispersal has a strong impact on the genetic structure of populations. This fits with the ‘founder/flush’ model with panmixia at high densities proposed to …
Amplitude and Periodicity
- As described above, the periodicity of cycles varies such that we talk about 3 to 5 year cycles of small mammals and 8 to 11 year cycles of forest Lepidoptera. In addition, as shown in the figures above, the amplitude of cycles varies among peaks. Predicting the density of the next peak and whether the cycle will be longer or shorter than average remains challenging. Ginzburg & Krebs […
Rejected Hypotheses
- (a) The Chitty or behavioural polymorphism hypothesis
In 1967, Dennis Chitty proposed that larger and more aggressive voles would be selected for in increasing and high densities, and smaller voles with delayed reproductive maturity in low densities [73]. The ‘Chitty Hypothesis’ predicted that variable selection would lead to a genetic s… - (b) The induced defense hypothesis
The ‘induced defense hypothesis' predicts that feeding damage causes plants to produce defensive compounds either directly or following a delay, and that these reduce the growth, reproduction or survival of the herbivore [75–78]. This hypothesis has been particularly widely st…
The Role of Models in Understanding Cyclic Dynamics
- A vast literature exists in which models have been used to explore the possibility of various mechanisms to create cyclic dynamics, e.g. [90], and the examples mentioned above. Although models can potentially identify what might cause cyclic dynamics, the simulated population trends are often unrealistic. Models seldom distinguish between multiple factors, and testable p…
Conclusion and The Future
- The main features of cyclic population dynamics for small mammals, snowshoe hares and forest Lepidoptera are summarized in table 1. It is surprising that these commonalities exist across these very different types of animals. Red grouse population cycles are more variable and do not fit into this general pattern as clearly (figure 2). A lingering question is, ‘how can low amplitude c…