Resumen Sas

Changes
Limiting factors and carrying capacity
Carrying capacity is the maximum number of organisms that an area or ecosystem can sustainably support over a long period of time.
Limiting factors include temperature and water availability. The main limiting climatic features are temperature and water availability. Every species has a tolerance range for any environmental factor.

TemperaturesMany aspects of temperature affect species. These include daily, monthly and annual extremes, and mean temperatures. Temperature may be limiting at different stages in the life cycle.
In most animals, temperature is a vital limiting factor. Cold-blooded animals can take advantage of sunny areas or warm rocks to heat their bodies. In hot deserts, animals are limited by excessive heat. To cope,some animals avoid the heat by burrowing, while others have physiological adaptations to tolerate high body temperatures.

Water
All plants and animals need water to survive. For plants, water stress may cause germination to fail, seedlings to die, and seed yield to be reduced. Water and temperature conditions vary around the world.

S- and J- curves
The S-curve has been recorded for there-establishment of vegetation after the eruption of Krakatau in 1883 and Mt St Helens eruption in 1980. The typical S-curve shows three stages:
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Exponential growth phase
In this phase, if there are no limiting factors, a population can double in size on a regular basis. The reasons for the exponential growth include:
Plentiful resources such as light, space and food.
Lack of competition fromother species.
Favorable abiotic factors such as temperature and rainfall.
Lack of predators or disease.
Transitional phase
In this phase, unlimited growth declines as the factors listed above begin to change. The causes of the slowdown include:
Increase in competition for resources because there are too many individuals in the population
Increase in predators attracted by the largepopulation (food supply)
Increase in rate of disease (and mortality) due to increased numbers of individuals living in a small area.
Plateau phase
Over time, as available space and resources decrease, birth rates decline. As the risk of disease increases, mortality rate rises. This slows population growth. The combination of fewer births and increased mortality reinforce the decline in populationincrease. The population plateaus.

Density-dependent and density-independent factors.
Density-depending factors
Some limiting factors are related to population density. As a population grows in size, the availability of food per individual decreases and this can lead to a reduced birth rate and an increased death rate. Predators may be attracted to areas of high prey population density; hencethe mortality rate may increase.
Other density-dependent factors include the sixe of the breeding population and size of territory, the greater the potential change that a species has for survival.

Density-independent factors
Density independent factors can operate alongside density-dependent factor. Density-independent factors are generally abiotic. The most important ones are extremes ofweather and long-term climate change. Others include geophysical events such as volcanic eruptions and tsunamis. Their impacts is to increase the death rate and reduce the birth rate, especially of smaller individuals.

Internal and external factors
Internal factors include density-dependent fertility or size of breeding territory, and external factors include predation or disease.
The ultimatecauses of population regulation are found in the environment: factors external to the population limit the rate at which individuals can reproduce and survive.
Four ways that human can cause population growth:
-Increase available resources
-Reduce competition
-Reduce pressure from predators
-Introduce animals to new areas

Four ways humans can cause population decline and extinction:...