The ecological carrying capacity or of an ecosystem is the maximum growth limit of a biological population that the environment can support in a given period, without negative effects on that population or on the environment. This maximum threshold size of individuals of a population that the environment can support depends on the available resources such as water, food, space, among others.
When the ecosystem carrying capacity is exceeded or exceeded, individuals are forced to one of these three alternatives: change their habits, migrate to an area with a greater amount of resources or decrease the size of the population with the death of many individuals.
No population can have unlimited growth, since resources are finite and limited. Regarding the human species in particular, it is estimated that the planet Earth can support about 10 billion individuals.
However, humanity grows exponentially and generates negative effects on the environment, mainly due to industrial activities that involve its degradation, that is, the impact on the environmental functional integrity.
Factors determining load capacity
Size of a population
The size of a population depends on four variables: number of births, number of deaths, number of immigrants, and number of emigrants.
Increases in the size of a population occur with the births of individuals and with the immigration or arrival of individuals from outside environments. The size of the population decreases with deaths and with the emigration or departure of individuals to other environments.
In such a way that the following equality can be established:
Change in population = (births + immigration) – (deaths + emigration)
Growth capacity or biotic potential
The growth capacity (or biotic potential) determines the variation in the population. The intrinsic growth rate of a population is the rate at which the population would grow if the available resources were unlimited.
High population growth rates involve early reproduction, short intervals between generations, a long reproductive life, and high progeny at each reproduction.
As an illustrative example of a high population growth rate, we can cite the house fly, a species with a surprising capacity for growth.
In theory, in 13 months the descendants of a fly would reach 5.6 billion individuals and in a few years they could cover the entire surface of the planet; but the reality is that every population has a size limit on its growth.
Because there are limiting factors such as the amount of water, available light, nutrients, physical space, competitors, and predators, a population has a growth limit.
All the limiting factors for the growth of a population make up the so-called environmental resistance. The growth capacity of a population and environmental resistance are the determining factors of the carrying capacity.
Forms of population growth
If the environment offers many resources to a population, it is capable of growing at high rates, that is, rapidly. With the rapid growth of the population, resources decrease and become limited; then the growth rate experiences decline and leveling or adjustment.
A population for which the environment offers few limitations, grows exponentially at a fixed rate of 1 to 2% per year. This exponential growth begins slowly and increases rapidly over time; In this case, a graph of the number of individuals versus time produces a J-shaped curve.
The so-called logistic growth presents a first stage of exponential growth, which is followed by a stage with a slow, not abrupt, fluctuating decrease in growth until a leveling out of the population size is reached.
The decrease or slowdown in growth occurs when the population faces environmental resistance and is approaching the carrying capacity of the environment.
Populations that show logistic growth, after leveling out their growth, experience fluctuations with respect to the ecological carrying capacity.
The graph of the number of individuals versus time, in the case of logistic growth, has an approximate form of S.
¿ What happens when the capacity of an ambient and is surpassed?
When a population exceeds the amount of resources available in the environment, many individuals die, thereby reducing the number of individuals and balancing the amount of resources available per individual.
Another alternative for the survival of the population is a change of habits to use resources other than those that have been exhausted. A third alternative is the emigration or movement of individuals to other environments that have more resources.
As illustrative examples we can analyze some particular cases.
Populations consume resources and temporarily exceed or exceed the environmental carrying capacity.
These cases occur when there is a delay in reproduction; the period in which the birth rate must decrease and the mortality rate must increase (in response to the accelerated consumption of resources) is very long.
In this case, a collapse or drop in the population occurs. However, if the population has the adaptive capacity to exploit other available resources or if the surplus number of individuals can migrate to another environment that offers more resources, the collapse does not occur.
Populations exceed the environmental carrying capacity permanently.
This case occurs when the population exceeds and causes damage to the carrying capacity, and the habitat is no longer capable of sustaining the high number of individuals that it originally supported.
The overgrazing can deplete areas where grass grows and leave extensions free land for the growth of other plants competitive, that does not consume livestock. In this case, the environment has reduced its carrying capacity for livestock.
The human species with the dominant economic development model today is exceeding the environmental carrying capacity.
This economic model of excessive production and consumption in developed countries requires the use of environmental resources at very high rates, higher than their natural replacement.
Natural resources are finite and economic development raised in this way, assumes unlimited growth, which is impossible. Not only does the human population grow over time, but the resources of the environment are used unevenly, mostly and intensively by the populations of developed countries.
Some authors claim that the development of science and technology will save humanity from collapse. Others predict that humanity as a species is not exempt from reaching the limits that the environment always imposes on all populations.
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