24.1 Population Size

The human population is increasing at a significant rate - what has the global population grown to in 2012, from 1 billion in 1800?

7 billion

What is the global population predicted to reach by the end of the century?

11 billion

Why can’t rapid population growth be sustained indefinitely?

limiting factors (e.g. availability of food) will prevent the population from rising above a certain level

Limiting factor?

environmental resource or constraint that limits population growth

A population growth curve?

the growth of a new organism over time plotted on a graph

A population growth curve: Phase 1?

a period of slow growth

A population growth curve: why is phase 1 a period of slow growth?

the small numbers of individuals that are initially present reproduce increasing the total population - as the birth rate is higher than the death rate, the population increases in size

A population growth curve: Phase 2?

a period of rapid growth

A population growth curve: why is Phase 2 a period of rapid growth?

as the number of breeding individuals increases, the total population multiples exponentially. No constraints act to limit the population explosion

A population growth curve: Phase 3?

a stable state

A population growth curve: Why is Phase 3 a stable state?

further population growth is prevented by external constraints - during this time the population fluctuates but overall its size remains relatively stable and birth rates and death rates are approximately equal

A population growth curve: Phase 3 - what can slight increases and decreases be due to?

fluctuations in limiting factors, such as the presence of predators

When is the maximum growth rate achieved in nature?

when a short period of exponential growth occurs when conditions are ideal

What do limiting factors do?

prevent further growth of a population and in some cases cause it to decline

The two types of limiting factors?

biotic and abiotic

5 examples of abiotic limiting factors?

light, pH of soil, the availability of water and oxygen, and humidity

3 examples of biotic limiting factors?

predators, disease and competition

Carrying capacity?

the maximum population size that an environment can support

Although individual years can show slight increases or decreases in population size, why does the overall population generally remain stable?

the number of births and deaths are approximately equal

Another important variable that affects population size?

Migration

Immigration?

the movement of individual organisms into a particular area increases population size

Emigration?

the movement of individual organisms away from a particular area decreases population size

Density independent factors?

factors that have an effect on the whole population regardless of its size - these can dramatically change population size

4 Examples of Density independent factors?

earthquakes, fires, volcanic eruptions, and storms

What can Density independent factors do in some cases?

can remove whole populations of a species from a region