Density-dependent limiting factor
n., plural: density-dependent limiting factors
[ˈdɛn.sə.ti dɪˈpɛndənt ˈlɪmɪtɪŋ ˈfæk.tɚ]
Definition: A limiting factor of a population wherein large, dense populations are more strongly affected than small, less crowded ones
Table of Contents
What Is A Density-Dependent Limiting Factor?
Density-dependent limiting factors are limiting factors, which, depending on population density, may limit or slow down the growth of a population. These factors are essential in regulating population growth and thereby help maintain ecological balance. These factors become more pronounced and impactful as the population density increases. They operate through various mechanisms including competition, predation/herbivory, disease transmission, territoriality/aggression, and migration/dispersal. They act on various interactions — be they intraspecific (within species) or interspecific (between species). Thus, density-dependent limiting factors play a crucial role in preventing resource depletion and shaping population dynamics while maintaining sustainable population sizes in an ecosystem.
To understand this further, let us first understand certain concepts fundamental to the definition of density-dependent limiting factors:
Limiting factors are factors or variables in an environment that has the capacity to limit the growth, distribution, or abundance of a population in an ecosystem. Conversely, factors that do not limit or restrict the growth, abundance, or distribution of populations or species are referred to as nonlimiting factors. These factors, though, do not necessarily mean they are never going to be perpetually available or are limitless. Food, water, habitat, and other essential resources may still be depleted but they are at an amount that exceeds the requirements of the population. Nonlimiting factors do not act as primary drivers of population growth but limiting factors do. So while there is ample food, any disturbance that leads to a significant decline in food availability can quickly become a factor of population growth — from nonlimiting to becoming limiting. Limiting factors may be classified into density-dependent and density-independent, based on whether they depend on population density or not.
Here is a table summarizing the differences between nonlimiting and limiting factors (Density-dependent vs Density-independent):
Table 1: Differences between Nonlimiting Factors and Limiting Factors (Density-dependent vs Density-independent)
|Features||Nonlimiting factors||Limiting Factors|
|Impact on Population Growth||Do not restrict or limit population growth, abundance, or distribution||Restrict or limit population growth, abundance, or distribution|
|Stronger impact as population density increases||Affect population growth regardless of population density|
|Resource Availability||Resources are ample or exceeding population requirements, thus, not limiting population growth||Limited availability of essential resources, such as food, water, or suitable habitat, thus, limiting population growth|
|As population density increases, resources become limited, leading to increased competition for those resources||Affect resource availability but the impact is not directly tied to population density|
|Influence on Population Regulation||Do not significantly impact population regulation and do not impose restrictions on population size or distribution||Have a crucial role in population regulation by influencing birth rates, death rates, and population size|
|Directly affecting birth rates, death rates, or reproductive success, help maintain population stability, and prevent exponential growth||Can impact population size but are not directly related to population regulation, may cause significant fluctuations (including population crashes)|
|Consequences of Scarcity||Not associated with resource scarcity or competition||Lead to scarcity or competition for resources, resulting in decreased fitness, reduced population growth, or increased mortality rates|
|Scarcity of resources due to population density can result in increased competition, reduced fitness, higher mortality rates, or decreased reproductive success||Scarcity caused by these factors can lead to resource limitations, but the consequences may not be directly linked to population density|
|Requirement for Optimal Conditions||Characterized by conditions that meet or exceed the requirements of the population and are not limiting in terms of growth or survival||Often associated with suboptimal or insufficient conditions that limit population growth|
|Often involve the availability of optimal conditions for growth and reproduction, which can be affected by population density.||Can impact populations regardless of optimal conditions, as their effects are not directly tied to population density|
|Dynamics in Population Response||Do not significantly influence population dynamics or impose long-term constraints on population growth||Can drive population fluctuations and regulate population size over time|
|These factors can lead to density-dependent population regulation, where population growth rates vary with changes in density. Birth rates may decrease, death rates may increase, or dispersal may occur when population density reaches certain thresholds.||These factors can cause population fluctuations or declines irrespective of population density, and their effects may not show density-dependent patterns.|
Population density refers to the number of individuals in a population within a defined area or volume. It measures how concentrated or crowded a space or area is in terms of population.
Watch this vid about density-dependent limiting factors:
A density-dependent limiting factor is a type of limiting factor in ecology. As a subset of limiting factors, this factor is projected to limit or control the growth or size of the population depending on that population’s density. This is in contrast to another type of limiting factor, called the density-independent limiting factor, which limits the population regardless of its density.
Density-dependent limiting factors would, therefore, control or slow down population growth as the population density increases. These factors are essential in regulating population growth and maintaining ecological balance.
Density-dependent limiting factors examples:
- Food and water supply – a large population would require a higher supply of food and water. A limited supply of available food and water would result in competition.
- Living space – for instance, the growth of plants is affected by competition for space. Less space could mean less sunlight and less photosynthesis.
- Predation – more prey animals could mean more predators, thus, increased predation
- Disease – the spread of disease is faster in a dense population than in small ones
What Are 5 Density-Dependent Limiting Factors?
Population growth is limited by density-dependent factors such as follows:
Predators and herbivores
In predator-prey interactions, an increasing population of prey could “attract” predators as hunting becomes easier in an area where the population density of prey is relatively high. The same goes for herbivore-plant interactions. Herbivores can locate and consume plants easier when the plant density is high. The presence of predators or herbivores is essential in keeping check the ecological balance as they tend to limit the abundance of prey and plant in an area. Without effective predation and herbivory, this could lead to high population densities, which could make a profound impact on the ecological balance, as they would tend to engage in competition.
Limited resources (food, water, space, mate)
Resource limitation refers to the availability of essential resources that are vital for survival, growth, and reproduction. As population density increases, there is a tendency that competition will also increase between or among species. This is particularly seen when limited resources such as food, water, and space are dwindling as the population increases. Limited access to these resources may restrict population growth and abundance.
Pathogens and parasites
The spread of disease is easier in highly populated areas than in areas with sparse populations. This is particularly evident when the disease is highly contagious. The transmission of the pathogen from one infected individual to another is easily facilitated when more individuals come in contact with each other or in close proximity. Parasites, as well, can easily find new hosts in denser populations. Thus, diseases and parasitism can be limiting factors, especially when outbreaks occur. The more individuals that are sick in a population, the higher the possibility of reduced reproductive success or decreased fitness of that population.
Territorial and aggressive inhabitants
Many species exhibit territorial behavior where they defend a specific area against other individuals or against other species. An area teeming with territorial or aggressive dwellers will likely exhibit resource partitioning. Individuals will occupy distinct territories that only the occupants would have access to their respective resources. Intruders will be restricted from accessing them especially when the inhabitants are aggressively territorial. They would readily engage in a “fight”, protecting what they “claim as theirs” to the very end. This exclusionary behavior helps control population size by preventing the influx of additional individuals into the area.
A question arises after food availability, predators, and disease are all considered: Are density-dependent limiting factors biotic or abiotic factors? Density-dependent limiting factors can include both biotic and abiotic factors. They encompass a range of mechanisms that regulate population size in response to changes in population density.
So while density-dependent limiting factors mentioned above are primarily biotic factors, abiotic factors can also serve as density-dependent limiting factors, influencing population size in a density-dependent manner.
Environmental factors, including abiotic conditions such as temperature, humidity, pH levels, light availability, and nutrient availability can influence population growth and distribution. Fluctuations (abrupt change) or extremes in these factors can limit population size and impact the ability of individuals to survive and reproduce.
Mechanisms Of Density-Dependent Limiting Factors
How do density-dependent factors work in limiting high population density? How do they regulate or control a growing population? Here are some ways. Note, however, that in nature, population regulation is a complex system that involves not only density-dependent factors. It also entails the plausible interactions of the density-independent limiting factors with the dependent limiting factors.
Depleting resources is a significant trigger in a system of regulatory factors. When the population grows, the demand for food, water, shelter, and mate also grows. More and more individuals will compete for depleting resources. Escalating competition leads to reduced access to resources, lower reproductive success, and increased mortality rates. One possible reason is that such scarcity can result in reduced access to nutrition, thereby, adversely affecting growth and their capacity for reproduction, combatting diseases, and survival.
Competition may occur from the same species or from another species:
To give an example, take a look at the graph below. Have you noticed how the number of eggs of roundworm Ascaris lumbricoides dropped as the number of worms increases? Based on the data, it appears that as the population of the parasite becomes denser, the fewer eggs there are, thus, the lower their fecundity. However, why this occurs still warrants sufficient scientific explanation. (Boundless – Biology LibreTexts, 2018)
Competition for resources can occur both within a species and between different species. Intraspecific competition, though, tends to be more intense, as individuals of the same species have similar resource requirements. This mechanism helps regulate density-dependent growth, preventing populations from exceeding the carrying capacity of their environment and maintaining a balance between available resources and population size.
Transmission and spread of diseases
Diseases and parasites are transmitted easily when the population density is high. They spread at a rather faster rate when their prospective hosts stay in crowded areas or when their vectors can transmit them to their new hosts with ease. Higher infection (or infestation) rates (outbreaks) especially in a dense population without insufficient access to nutrition or with reduced overall fitness tend to be accompanied by higher mortality rates as well.
As population density rises, predation also intensifies. Predators tend to hunt in places where there is a high prey density. Thus, the risk of encountering predators increases. Hunting activity is heightened as predators would have higher chances of finding and capturing their prey when their prey abounds in an area. The resulting increased predation pressure limits prey population size and growth rate.
Aggression and territoriality
As population density increases, the availability of suitable territories decreases, leading to increased competition and aggression between individuals. This density-dependent regulation mechanism can result in limited access to resources, reduced reproductive success, and population regulation. In crowded conditions, individuals may have smaller territories, leading to heightened aggression, intraspecific competition, and increased mortality rates due to fights or injuries.
Migration and dispersal
In some cases, population density may lead to migration patterns and dispersal behavior. As noted earlier, as the population increases, the competition for available resources intensifies. Some species tend to seek new habitats or resources so as to alleviate competition and reduce density-dependent pressures. Thus, some of them would acquire new habitats or a new ecological niche. Migration and dispersal can help maintain population balance and prevent overcrowding in certain areas.
The role of density-dependent limiting factors in regulating and maintaining ecological stability is vital to the resiliency of an ecosystem. Therefore, understanding how they carry out such a role is important to researchers wanting to gain more insight into population dynamics, predict population responses to changing environments, and formulate conservation and management strategies for possible implementation.
Did you know that density-dependent limiting factors can lead to a phenomenon known as ‘population cycles’?
In certain species, particularly those involved in predator-prey relationships, population sizes can fluctuate dramatically in synchronized patterns over time. For example, the population of snowshoe hares and their main predator, the lynx, in the boreal forests of North America exhibit cyclic fluctuations. When hare populations are abundant, lynx populations thrive due to an ample food supply. However, as lynx populations increase, they exert intense predation pressure on the hares, leading to a decline in hare numbers.
As the hare population declines, the reduced food availability causes the lynx population to decrease as well. With fewer predators, the hare population begins to recover, restarting the cycle.
These population cycles can span several years, with the predator and prey populations rising and falling in sync, demonstrating the intricate interplay of density-dependent limiting factors in regulating populations.
These population cycles serve as a fascinating example of how density-dependent factors, such as predation and resource availability, can drive oscillations in population sizes, creating dynamic and ever-changing ecological systems.
Take the Density-Dependent Limiting Factor – Biology Quiz!
- Boundless – Biology LibreTexts. (2018). 45.2C: Retrieved https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/45%3A_Population_and_Community_Ecology/45.02%3A_Environmental_Limits_to_Population_Growth/45.2C%3A_Density-Dependent_and_Density-Independent_Population_Regulation#:~:text=Density%2Ddependent%20regulation,-In%20population%20ecology&text=Most%20density%2Ddependent%20factors%2C%20which,as%20those%20caused%20by%20parasites.
- Dynamics of Density-dependent limiting pfactors in appaernt competion:
- Holt, R. D. (1977). Predation, apparent competition, and the structure of prey communities. Theoretical Population Biology, 12(2), 197-229. doi: 10.1016/0040-5809(77)90042-9
- Evolutionary implications of density-dependent limiting factors on species interactions:
- Thompson, J. N. (1999). The evolution of species interactions. Science, 284(5423), 2116-2118. doi: 10.1126/science.284.5423.2116
- A comprehensive overview of ecological principles, including density-dependent limiting factors:
- Krebs, C. J. (2009). Ecology: The Experimental Analysis of Distribution and Abundance. Benjamin Cummings.
- Disease Transmission::
- Anderson, R. M., & May, R. M. (1979). Population biology of infectious diseases: Part I. Nature, 280(5721), 361-367. doi: 10.1038/280361a0
- Predator-Prey Dynamics:
- Murdoch, W. W., Briggs, C. J., & Nisbet, R. M. (2003). Consumer-Resource Dynamics. Princeton University Press.
- Mechanisms of Density-Dependent Limiting Factors:
- 1. Begon, M., Townsend, C. R., & Harper, J. L. (2006). Ecology: From individuals to ecosystems. Blackwell Publishing.
- 2. Anderson, R. M., & May, R. M. (1992). Infectious diseases of humans: Dynamics and control. Oxford University Press.
- 3. Amarasekare, P. (2008). Interactions between local dynamics and dispersal: Insights from single-species models. Theoretical Population Biology, 74(2), 291-322. doi: 10.1016/j.tpb.2008.07.002
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