6.3.2 Populations- Summary notes

Populations

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• The limiting factors which determine the carrying capacity, that is the maximum population size that can be supported by the environment include: food, water, light, oxygen, nesting sites, shelter, parasites and predators. Competition between organisms takes place in a case where a particular resource is limited supply.

• Predator-prey relationships give rise to a fluctuating population size of predators and prey. This is because, as the predator population grows, more prey is consumed thus meaning that prey population decreases to a point where there isn’t a sufficient amount of prey to feed the predator population. As a result of that, there are fewer predators thus increasing the chance of survival of prey, thus causing the prey population to increase in size. This in turn means that the predator population can grow again, thus restarting the cycle.

• There are two types of competition between organisms; interspecific competition which is the competition between individuals of different species and intraspecific competition between individuals of the same species.

• Conservation serves to maintain or increase the biodiversity within a particular habitat by allowing a sustainable use of the resources whereas preservation serves to maintain the biodiversity levels and the habitat intact by minimising the effects of human activities on the particular habitat.

• There are many economic, social and ethical reasons for conservation. For instance, many species provide a source of food and medicine, and are important for processes such as pollination of crops as well as for maintaining a good quality of water as well as tourism. Social reasons include conservation for aesthetic reasons and recreation whereas ethical reasons include the right to survive.

The management of an ecosystem can provide resources in a sustainable way, for example:

• Coppicing – cutting down of trees close to the ground to encourage new growth, effective as stumps have good root systems

• Selective felling – the harvesting/removal of largest, mature trees, as well as diseased ones to enable other trees to grow, trees which are removed are replaced with seeds

• Pollarding is a form of coppicing where the trees are cut higher up, to prevent deer from eating the new shoots

• Efficient production where most of the tree is used to minimise wastage

• A good example of the effects of human activities on animal and plant populations is the Galapagos Islands. Due to an increase in tourism, the demand for resources such as water and energy has increased dramatically in the Galapagos Islands. As a result of that, amount of waste and pollution increased. This has led to an increase in waste and pollution as well as overfishing, thus causing sea cucumbers to become threatened. Moreover, many non-native species have been introduced, which outcompete the native species. There are several conservation projects in the Galapagos Islands which serve to minimise those effects, such as goat culling to eliminate non-native species, thus in turn increasing vegetation. Moreover, the population of giant tortoises has been depleted as they have been eaten by humans. To increase the population size of giant tortoises, they are now bred in captivity.

Many ecosystems in the world need management to protect the species and habitats. This can be done in many ways including:

• Controlling number of tourists/visitors

• Involvement of local communities

• Education of local communities

• Active management of vegetation

• Control of the introduction of species