A population is the amount of individuals of the same species that live in the same area at the same time. Since these trees are not the same species, they cannot be included in the same population; however, the singular species could have a population. For example, there can be a population of red oak trees or sugar maple trees.
Over an extended period of time, scientists are able to observe population growth and how environmental factors (such as food, water, space, predators, shelter, disease, etc.) affect carrying capacity, birth rate, and death rate. Scientists may also be able to observe the.
Area A most likely experienced more births than deaths over the first five years because of its exponential growth. Exponential growth, or a large boom in population, tends to happen when birth rates > death rates; therefore, it would make sense that area A experiences more births than deaths. c.
Demography is the study of how human populations change over time and space. It is a branch of human geography related to population geography, which is the examination of the spatial distribution of human populations. Geographers study how populations grow and migrate, how people are distributed around the world, ...
The areas most immediately affected by increased populations include forests (a fuel resource and a source of building material), fresh water supplies, and agricultural soils.
If a fertility rate for a given country is less than 2.1—the replacement level—the population of that country is in decline, unless there is significant immigration.
As countries move from an agricultural to an industrial economy, there is a major shift in population from rural to urban settings. The Industrial Revolution of the nineteenth century ushered in major technological developments and changes in labor practices, which encouraged migration from the farm to the city.
Additional large population centers exist in various countries with high urbanization. An example is the urbanized region between Boston and Washington, DC, which includes New York City, Philadelphia, Baltimore, and neighboring metropolitan areas, resulting in a region often called a megalopolis.
During the twentieth century, death rates due to disease and malnutrition decreased in nearly every corner of the globe. In developing countries with agricultural societies, however, birth rates remained high. Low death rates and high birth rates resulted in rapid population growth.
Providing food, energy, and materials for these additional humans will tax many countries of the world, and poverty, malnutrition, and disease are expected to increase in regions with poor sanitation, limited clean water, and lack of economic resources.
When a population reaches a high density, there are more individuals trying to use the same quantity of resources. This can lead to competition for food, water, shelter, mates, light, and other resources needed for survival and reproduction. Predation.
Waste accumulation. High population densities can lead to the accumulation of harmful waste products that kill individuals or impair reproduction, reducing the population’s growth. Photograph of a lemming. It is a small, chubby rodent that resembles a guinea pig.
For years, this population had cyclical oscillations in size, with a period—the length of a full cycle—of about four years. Ecologists found that the cycle could be explained by interactions between the lemming and four predators: the owl, fox, skua—a bird—and stoat. The owl, fox, and skua are opportunistic predators that can use various food sources and tend to eat lemmings only when they are abundant. The stoat, in contrast, eats pretty much only lemmings.
Density-dependent limiting factors tend to be biotic —living organism-related—as opposed to physical features of the environment. Some common examples of density-dependent limiting factors include: 1 Competition within the population. When a population reaches a high density, there are more individuals trying to use the same quantity of resources. This can lead to competition for food, water, shelter, mates, light, and other resources needed for survival and reproduction. 2 Predation. Higher-density populations may attract predators who wouldn’t bother with a sparser population. When these predators eat individuals from the population, they decrease its numbers but may increase their own. This can produce interesting, cyclical patterns, as we'll see below. 3 Disease and parasites. Disease is more likely to break out and result in deaths when more individuals are living together in the same place. Parasites are also more likely to spread under these conditions. 4 Waste accumulation. High population densities can lead to the accumulation of harmful waste products that kill individuals or impair reproduction, reducing the population’s growth.
Cyclical oscillations are repeating rises and drops in the size of the population over time. If we graphed population size over time for a population with cyclical oscillations, it would look roughly like the wave below—though probably not quite as tidy! Graph with population on the y axis and time on the x axis.
In many cases, oscillations are produced by interactions between populations of at least two different species. For instance, predation, parasite infection, and fluctuation in food availability have all been shown to drive oscillations. These density-dependent factors don't always create oscillations, however.
Density-independent factors affect per capita growth rate independent of population density. Examples include natural disasters like forest fires. Limiting factors of different kinds can interact in complex ways to produce various patterns of population growth.
The carrying capacity may be lowered by resource destruction and degradation during an overshoot period or extended through technological and social changes . An example of dieback occurred in Ireland after a fungus infection destroyed the potato crop in 1845.
A population gains individuals by birth and immigration and loses individuals by death and emigration. 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.
Reproductive lag time is the time required for the birth rate to decline and the death rate to increase in response to resource limits.
1.7% annual decline in rainforest acreage in Equador during the 1980's. The existence of 33,000 potential Superfund toxic contamination sites. Projected exhaustion of fossil fuels by the middle of the next century. Using groundwater in the U.S. 25% faster than aquifers are recharged.
For example 100 million vegetarians will have a significantly different environmental impact than 100 million meat-eaters. This can be demonstrated by comparing the affect on water supplies by both sub-populations. About 1000 tons of water are needed to produce 1 ton of grain.
About 1000 tons of water are needed to produce 1 ton of grain. Almost 40% of all grain is used in meat and poultry production. Add to this the amount of water that goes into the production of meat, and you can see that meat comsumption places more stress on global water supplies than grain consumption.
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.