6.3.2 Flashcards
Why can exponential population growth not be sustained indefinitely?
Due to limiting factors such as the availability of food which will prevent it rising above the carrying capacity
What is a limiting factor?
Environmental resource or constraint that limits population growth
If growth of a population is plotted on a graph?
Creates a population growth curve - sigmoid population curve
Phase 1 of graph?
Slow growth - Small numbers of individuals that are initially present reproduce increasing the total population ; as birth rate is higher than death rate, population increases in size
Also slow increase due to ACCLIMATISATION
Phase 2 of graph?
Rapid growth (exponential) - number of breeding individuals increases and thus the total population multiplies exponentially (no constraints act to limit the population at this point)
Phase 3
Stable Phase - further population growth is prevented by external constraints. POPULATION SIZE DOES FLUCTUATE but overall it’s size remains stable ; birth rates = death rates
What can fluctuations in phase 3 be accounted for?
Presence of predators
Exponential growth curve?
Size of the population doubles each time a fixed period elapses
How is it best to draw an exponential growth curve?
On a logarithmic scale with the y axis increasing each time by a set factor (often by *10 - on calculator) ; this gives a linear/proportional line
X-AXIS/TIME is LINEAR
When is there a period of exponential growth?
Conditions are ideal and maximum growth rate is achieved
Examples of limiting factors?
Competition between the organisms for resources, build up of the toxic by-products of metabolism or disease
What are the types of limiting factors?
Abiotic factors - non-living factors include temperature, light, pH, the availability of water or oxygen and humidity
Biotic factors - predators, disease and competition
What is carrying capacity?
Maximum population size than an environment can support ; population size remains stable as the number of births and deaths are approximately equal
What is another biotic factor that affects population size?
Migration
Types of migration
Immigration and Emigration
Immigration
Movement of individual organisms into a particular area increasing population size ; often migrate annually to reproduce, dramatically increasing
Emigration
Movement of individual organisms away from a particular area to decrease its population size ; away from areas of high population density or poor habitat
Density independent factors?
Have an effect on the whole population regardless of its size ; these can dramatically change population size such as earthquakes, fires, volcanic eruptions and storms - in some cases they may remove whole populations of a species from a region
What has led to population explosion in humans?
Development of agriculture, industrial revolution and advances in medicine
Population growth formula?
(Population change during period/initial population) * 100
+ is population has grown
- population has decreased
What affects death rate in a population?
Age profile (elderly population = higher the death rate), quality of medical care, food availability/quality and the effects of natural disaster or war
What does the future size of a population depend on?
Number of women of children bearing age
What do organisms compete for?
Food, shelter, space and light
Competition?
Biotic (interactions of living organisms)
Interspecific : competition between different species
Intraspecific : competition betwene members of the same species
What does interspecific competition less to?
Different species competing for the same resource ; reduction of the resource available to both populations. As a result of less food, organisms will have less energy for growth and reproduction resulting in smaller populations than if only one of the species had been present
What else can happen with interspecific competition?
If two species of organisms are both competing for the same food source but one is better adapted, the less well adapted one is likely to be outcompeted ; if conditions ARE THE SAME then numbers will decline until it no longer exists in the habitat alongside the better adapted species
COMPETITIVE EXCLUSION PRINCIPLE
State definition of competitive exclusion principle?
Two species are competing for limited resources, the one that uses the resources more effectively will ultimately eliminate the other
Rey and red squirrels competition
In the 1870s - the grey squirrel, native of North America was introduced into the wild in the U.K. ) population increased rapidly in numbers and red squirrels reduced
Grey squirrel can eat a wider range of food and store more fat as it is larger ; increases chances of survival and thus ability to reproduce - increasing its population
INCREASING POPULATION OF GREY FURTHER REDUCES FOOD SUPPLY for red ; reducing their ability to survive and reproduce
Infraspecific competition
Members of same species compete for the same resource ; availability of resource determines population size and thus greater availability = greater population leading to fluctuations in the number of organisms present over time
Graph of intra specific competition
Looks like a flipped quadratic joined to a normal quadratic (pg 636)
Stage 1
Resource is plentiful so enough of that resource for all organisms to survive and reproduce, increasing population size
Stage 2
More individuals sharing food/space so resources now limited and thus not available for all organisms to survive (population decreases in size)
Stage 3
Less competition exists so again more organisms survive and reproduce resulting in population growth - a lot of same resources still available
Another major biotic factor?
Predation ; an organism kills and eats another organism - predation is a type of interspecific completion operating between prey and predator species
Evolution in predator prey relationships?
Predators have evolved to become highly efficient at capturing prey (speed/stealth) and likewise prey have evolved to avoid capture through camouflage, mimicry and defence mechanisms like spines ; HAVE HAD TO EVOLE TOGETHER IF NOT THEN ONE OF THE SPECIES MAY HAVE BECOME EXTINCT
How is predator prey relationship exploited?
By farmers ; use natural predators like ladybirds to destroy pest populations and prevent them damaging crops without the need to use pesticides
Predator prey interlinked?
As population of one changes it affects the other ; there are many fluctuations and they all essentially follow the same pattern of peaks and troughs after a time delay
Stage 1 P+P
Increase in prey population provides more food for the predators ; more survival and reproduction - results in an increase in the predator population
Stage 2
Predator population eats more prey - causing a decline in the prey population ; death rate > birth rate
Stage 3
Reduced prey population can no longer support the larger predator population ; intraspecific competition for food increased, resulting in a decrease in the size of the predator population
Stage 4
Reduced predator numbers results in less prey being killed so they increase and reproduce ; cycle begins again
What other factors influence predator prey relationships?
Availability of food plants of the prey or presence of other predators ; fluctuations may also result from seasonal changes in abiotic factors
Why should we conserve the environment?
For future generations to enjoy ; preserve the beauty of the natural world while also ensuring that the biodiversity of world ecosystems is not lost
Reasons for maintaining biodiversity?
Economics, preserving genetic variety and retaining species that might be useful to people
Conservation vs preservation
Often used interchangeably but they have different meanings
Conservation
Maintenance of biodiversity through human action or management ; this includes maintaining diversity between species, maintaining genetic diversity within a species and maintenance of habitats
What does conservation involve?
Management of ecosystems so that the natural resources in them can be used without running out ; sustainable development - the forest stewardship council ensures that forests are managed so that they provide a sustainable source of timber
What kind of management of forests are they aiming for?
Socially beneficial, environmentally appropriate and economically viable