Control & Regulation

Control & Regulation Regulation & Monitoring of Populations Mr G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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 G Davidson

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. G Davidson

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 G Davidson

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. G Davidson

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: G Davidson

Prey Predator Numbers of Population Time Factors influencing change G Davidson

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 G Davidson

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. G Davidson

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 G Davidson

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. G Davidson

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. G Davidson

Indicator Species • Phytoplankton, microscopic, oceanic plants acts as the first link in the marine food chains. • They convert much CO2 into O2 during photosynthesis and could possibly make a big difference to the greenhouse effect. G Davidson

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. G Davidson

Control & Regulation