Control & Regulation Regulation & Monitoring of Populations M r G D a v i d s o n

Saturday, May 09, 2015G Davidson2 Populations  A population is a group of individuals of the same species which makes up part of an ecosystem.  The number of individuals of the same species in a unit area/volume of habitat is called the population density.

Saturday, May 09, 2015G Davidson3 Population Stability  When an environment is colonised by a species, the population grows to the highest level supportable by the environment.  The limit is known as the carrying capacity.

Saturday, May 09, 2015G Davidson4 Population Stability  The population level is now relatively stable save short-term oscillations from generation to generation.  It is said to be in a state of dynamic equilibrium.

Saturday, May 09, 2015G Davidson5 Factors influencing change  Every species has a large reproductive potential, but population increase is restricted by environmental resistance, which consists of factors such as: –Food- Water –Space- Oxygen –Light- Shelter –Predation- Disease –Climate

Saturday, May 09, 2015G Davidson6 Factors influencing change  A density independent factor is one which affects population growth regardless of density, e.g. weather extremes, forest fire, flood, etc.  A density dependent factor is one which affects a population once it has grown to a certain size and density.

Saturday, May 09, 2015G Davidson7 Factors influencing change  Once a population reaches this level, it is inevitably affected by one such factor, e.g. –competition  starvation –build up of population’s toxic wastes –disease –predation

Saturday, May 09, 2015G Davidson8 Factors influencing change  Predator and prey populations are linked and balanced.  If conditions favour prey, their numbers will increase.  As a result, there will be more food for predators, whose numbers will also rise.  An increase in predator numbers will increase predation and therefore prey numbers will fall.

Saturday, May 09, 2015G Davidson9 Factors influencing change  Increased competition following this reduction in food will cause predator numbers to drop as some die of starvation.  This brings the population back to its original state.  Since there tends to be less predators than prey, population graphs of predator and prey numbers are usually very similar:

Saturday, May 09, 2015G Davidson10 Factors influencing change Time Numbers of Population Prey Predator

Saturday, May 09, 2015G Davidson11 Monitoring Populations  Many species of wild plants and animals are surveyed closely by scientists to monitor population numbers and affecting factors.  This data is needed for: –management of species which provide food or raw materials –pest control –pollution assessment –protection and conservation of endangered species

Saturday, May 09, 2015G Davidson12 Food Species  The maximum sustainable yield of a population is a measure of the maximum rate at which individuals can be removed without affecting the population’s future productivity.  This keeps populations in check, e.g. –fish – prevent over-fishing by quotas. –keep down red deer populations with cullings.

Saturday, May 09, 2015G Davidson13 Pests  Pests are species which threaten mankind’s health or economy.  They can include insects, fungi and vermin which spread disease and ruin crops.  Noted examples are: –green fly- pathogenic fungi –locusts- mosquitoes –brown rats

Saturday, May 09, 2015G Davidson14 Indicator Species  Environmental health can be assessed by examining certain indicator species.  Fresh water indicator species include mayfly and stonefly, which show that pollution is low.  Birds of prey are affected by over-use of pesticide sprays as toxic chemicals move up the food chain and accumulate in the bird’s diet.

Saturday, May 09, 2015G Davidson15 Indicator Species  If, however, water is polluted, it can be shown by the presence of rat-tailed maggots and sludgeworms.  On land, air pollution levels can be shown by lichens.  The presence of lichens indicates low air pollution.

Saturday, May 09, 2015G Davidson16 Indicator Species  Phytoplankton, microscopic, oceanic plants acts as the first link in the marine food chains.  They convert much CO 2 into O 2 during photosynthesis and could possibly make a big difference to the greenhouse effect.

Saturday, May 09, 2015G Davidson17 Endangered Species  Rare species may have values ranging from medicinal to aesthetical.  To prevent extinction, the areas in which some endangered species live in are converted into nature reserves.  Over-hunting, poaching, picking and harvesting are controlled or restricted to maintain species numbers.