There are four variables which govern changes in population size. Biotic Potential Populations vary in their capacity to grow. The maximum rate at which a population can increase when resources are unlimited and environmental conditions are ideal is termed the population's biotic potential. Each species will have a different biotic potential due to variations in the species' reproductive span how long an individual is capable of reproducing the frequency of reproduction how often an individual can reproduce "litter size" how many offspring are born each time survival rate how many offspring survive to reproductive age There are always limits to population growth in nature.
Populations cannot grow exponentially indefinitely. Exploding populations always reach a size limit imposed by the shortage of one or more factors such as water, space, and nutrients or by adverse conditions such as disease, drought and temperature extremes. The factors which act jointly to limit a population's growth are termed the environmental resistance. The interplay of biotic potential and density-dependent environmental resistance keeps a population in balance.
Carrying Capacity For a given region, carrying capacity is the maximum number of individuals of a given species that an area's resources can sustain indefinitely without significantly depleting or degrading those resources. What causes logistic growth? What is logistic growth in ecology? What is the logistic model of population growth? What limits logistic growth?
What is carrying capacity? How do you find the carrying capacity of a population growing logistically? The picture below shows an example of a carrying capacity graph Figure 1.
Here, the carrying capacity symbol: K for a biological species is marked by the red dotted horizontal line to describe the number of organisms that the environment can support sustainably for a given time. Notice that it coincides with the stable equilibrium , which refers to the population size that has reached a steady-state as it aligns with the carrying capacity. The growth is depicted as S-shaped a characteristic of a logistic growth. The S-shape logistic growth forms when the growth rate is slow at first lag phase and next speeds up exponential phase.
Then, the rate slows down again as the population size reaches carrying capacity. In the real world, though, population size tends to rise and dip in oscillations from the carrying capacity rather than a flat line as depicted in the graph. To calculate for the carrying capacity K , the equation for the change of population size can be used for deriving a formula for K Ref.
A sample worksheet of carrying capacity and population biology can be found here. A population may grow at a faster rate and follow a J-shaped curve.
When the birth rate surpasses the death rate of the species, this results in exponential growth. However, this trend soon changes as resources become limited.
The growth rate slows down. Soon, it reaches a stable equilibrium where biomass in the given area seems unchanged over a certain period of time. At this point, the death rate appears to be compensated by the birth rate within a population. This means the per capita birth rate equals the per capita death rate. By contrast, when deaths appear to outgrow births, this indicates that the carrying capacity has been exceeded.
This is a case of overshoot. The population may go below the carrying capacity. This can occur, for instance, during disease and parasitic outbreaks. Several factors affect the carrying capacity of an ecosystem. With better public health, nutrition, physical infrastructure and public safety we live much longer. Today, in the United States, Europe, Japan, much of Latin America, even parts of India, fertility rates are below replacement, ie the average number of children born per woman is below two.
Much of the rest of the world will likely follow suit over the next few decades. As a result, most demographers project that the human population will peak, and then begin a slow decline, in some cases before the end of this century. As many now acknowledge, our social biology might not function like protozoa, but capitalism does.
It cannot survive without endless growth of material consumption. T here is no particularly well-established basis for this claim and plenty of evidence to the contrary. The long-term trend in market economies has been towards slower and less resource-intensive growth.
Growth in per-capita consumption rises dramatically as people transition from rural agrarian economies to modern industrial economies. But then it tails off. Today, western Europe and the US struggle to maintain 2 per cent annual growth. The composition of affluent economies changes as well. Manufacturing once accounted for 20 per cent or more of economic output and employment in most developed economies. Today, it is as low as 10 per cent in some, with the vast majority of economic output coming from knowledge and service sectors with significantly lower material and energy intensities.
For decades, each increment of economic growth in developed economies has brought lower resource and energy use than the last. Few of us need or want to consume more than 3, calories or so a day or live in a 5,square-foot house.
Many Americans prefer to drive SUVs but there is little interest in hauling the kids to soccer practice in a semi-truck. Our appetites for material goods might be prodigious but there is a limit to them. But this view is deeply ahistorical, assuming carrying capacity to be static.
0コメント