Population Flashcards
What is carrying capacity
This is the maximum population size that an environment can support
What is phase 1
This is a period of slow growth. The small number of individuals that are initially present reproduce increasing their total population. As the birth rate is higher than the death rate, the population increases in size
What is phase 2
A period of rapid growth. As the number of breeding individuals increases, the total population multiplies exponentially.
What is phase 3
This is a stable state. Further population growth is prevented by external constraints/limiting factors. During this time, the population size fluctuates, but overall its size remains relatively stable
What are limiting factors
Factors that prevent further growth of a population or in some cases, its decline.
Examples of limiting factors
Competition between the organisms for resources, the build-up of the toxic by-products of metabolism, or disease
What are abiotic factors and state examples
They are non living factors e.g. temperature, water, oxygen, pH, light, humidity
What are biotic factors and state examples
These are living factors e.g. predators, disease, competition
What is immigration
Movement of organisms into a particular area, increasing population size
What is emigration
Movement of organisms away from a particular area, decreasing population size
What are density independent factors
These are factors that have an effect on the population regardless of its size. E.g earthquakes, storms, volcanic eruptions, fires etc
What is interspecific competition
Competition between two or more different species
What is a predator
An organism that kills and eats another organism
What is the formula for population growth (%)
Population change during the period/ population at the start of the period x 100
What does it mean if the result is positive
The population has grown
What does it mean if the result is negative
The population has decreased
State factors that affect the birth rate of the human population
Economic conditions, cultural and religious backgrounds, social pressure
Factors affecting the death rate in a population
The age profile of the population, the quality of medical care, food availability and quality, the effects of natural disaster, or war
What does the future size of a population depend on
The number of women of child-bearing age
What is intraspecific competition
This is competition between members of the same species
What happens during interspecific competition
This occurs when two or more different species of an organism compete for the same resource. If both species compete for the same food source, there will usually be less available for organisms of each species. As a result of less food, organisms will have less energy for growth and reproduction, resulting in smaller population than if only one of the species had been present
What is the competitive exclusion principle
This is if conditions remain the same, the less well adapted species will decline in number until it can no longer exist in the habitat alongside the better adapted idea. This occurs when two species are competing for limited resources
What competition occurs between red and grey squirrels for food in the UK
It is an example of interspecific competition. Its population quickly increased in numbers and resulted in the native red squirrel disappearing from many areas. This is primarily because the grey squirrel can eat a wider range of food than the red squirrel and as it is larger it can store more fat. This increases its chances of survival and therefore its ability to reproduce thus increasing its population. An increasing population of grey squirrels further reduces food supply available to the red squirrels, reducing their ability to survive and reproduce.
How does availability of resources determine the population size
The greater the availability, the larger the population that can be supported. This results in fluctuations in the number of organisms present in a particular population over time.
Stage 1 of population growth
When a resource is plentiful in a habitat, all organisms have enough of the resource to survive and reproduce. This results in an increase in population size
Stage 2 of population growth
As a result of the increased population, there are many more individuals that share the food or space available. Resources are now limited, not enough is available for all organisms to survive. The population will decrease in size
Stage 3 of population growth
Less competition exists as smaller population means less organisms are competing for the same resources. This means more organisms survive and reproduce, resulting in population grow. The cycle of events will then repeat
Stage one of predator-prey relationship
An increase in the prey population provides more food for the predators, allowing more to survive and reproduce. This in turn results in an increase in the predator population
Stage 2 of predator-prey relationship
The increased predator population eats more prey organisms, causing a decline in the prey population. The death rate of the prey population is greater than its birth rate
Stage 3 of predator-prey relationship
The reduced prey population can no longer support the larger predator population. Intraspecific competition for food increases, resulting in a decrease in the size of the predator population
Stage 4 of predator-prey relationship
Reduced predator numbers results in less of the prey population being killed. More prey organisms can survive and reproduce increasing the prey population- the cycle begins again
