Populations and Sustainability
(a) explain the significance of limiting factors in determining the final size of a population
Population size is a balance between death rate and rate of reproduction. A habitat cannot support a population larger than its carrying capacity because of the limiting factors, which place a limit on population size. The limiting factors may include food, water, light, oxygen, shelter, predators,parasites, intensity of competition within and between species etc.
(b) explain the meaning of the term carrying capacity
(c) describe predator-prey relationships and their possible effects on the population sizes of both the predator and the prey
Predators are animals that hunt other animals (prey). Predation can act as a limiting factor on a prey’s population size.
- More predators = more prey eaten.
- Prey population decreases = less food for predators.
- Fewer predators survive = predator population decreases.
- Fewer prey now eaten = prey population increases.
- More prey = predator numbers increase and the cycle begins again.
(d) explain, with examples, the terms interspecific and intraspecific competition
Competition occurs when resources(like food or water) are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources. As the intensity of competition increases, the rate ofreproduction decreases (fewer organisms have enough organisms to reproduce), whilst the death rate increases (fewer organisms have enough resource to survive). There are two types of competition:
- Intraspecific competition- competition between individuals of the same species for the same resources, e.g. male deer locking horns when competing for mates.
- Interspecific competition- competition between individuals of different species for the same resources, e.g. cheetahs and lions competing for the same prey.
In 1934, GeorgyiFrantsevitchGause grew two species of Paramecium, both separately and together. When together, there was competition for food, with Paramecium aurelia obtaining more food effectively than Parameciumcaudatum, resulting in Paramecium caudatum dying out and the numbers for Paramecium aurelia increasing, eventually becoming the only species remaining.
Gause concluded that more overlap between two species’ niches would result in more intense competition. If two species have exactly the same niche, one would be out-competed by the other and would die out or become extinct in that habitat – competitive exclusion principle – used to explain why particular species only grow in particular places.
However, other observations and experiments suggest that extinction is not necessarily certainly going to happen:
- Interspecific competition could result in one population being smaller than the other, with both population sizes remaining relatively constant.
- Important to realise that in the laboratory, it’s easy to exclude the effects of other variables, so the habitat of the two species remains very stable. In the wild, however, a wide range of variablesmay act as limitingfactors for the growth of different populations – variables may change on a daily basis or even over the course of a year. For example, experiments on competition between flour beetles Triboliumconfusum and Triboliumcastaneum initially confirmed the competitive exclusion principle – the castaneum population size increased, whilst T. confusum died out – but even a small change in thetemperature could change the outcome so that T. confusum survived instead.
(e) distinguish between the terms conservation and preservation
(g) explain that conservation is a dynamic process involving management and reclamation
Conservation is the maintenance of biodiversity, including diversity between species, genetic diversity withinspecies, and maintenance of a variety of habitats and ecosystems.Conservation is a dynamic process involving management and reclamation.
Unfortunately, a steadily increasing human population can threaten biodiversity through:
- Over-exploitation of wild populations for food (e.g. cod in the North Sea), for sport (e.g. sharks) and for commerce (e.g. pearls collected from saltwater oysters and freshwater clams): species are harvestedfaster than they can replenish
- Habitat destruction and fragmentation as a result of more intensive agricultural practices, increased pollution, or widespread building.
- Introduction of species to an ecosystem by humans, deliberately or accidentally. These may out-compete native species, which may become extinct.
Conservation can involve establishing protected areas such as National Parks or Sites of Special Scientific Interest. It can also involve giving legal protection to endangered species, or conserving them ex-situ in zoos or botanic gardens. However, maintaining biodiversity in dynamic ecosystems requires careful management.
Some management strategies include:
- Raise carrying capacity by providing more food.
- Move individuals to enlarge populations.
- Fencing to restrict dispersal of individuals.
- Control predation and poachers.
- Vaccinate individuals against disease.
- Preserve habitats by preventing pollution/disruption, or intervene to restrict the progress of succession, e.g. coppicing, mowing, grazing.
Preservation is the protection of ecosystems, as yet unused by humans, leaving it untouched so it is kept exactly as it is.
(f) explain how the management of an ecosystem can provide resources in a sustainable way, with reference to timber production in a temperate country
With human population getting larger and expanding exponentially, it is putting pressure on our resources. More intensive methods need to be used to exploit our environment for resources, however such methods can disrupt or destroy ecosystems, reduce biodiversity or deplete resources. One situation is the potential conflict between our need for resources and conservation is in wood and timber production.
(h) discuss the economic, social and ethical reasons for conservation of biological resources
(i) outline, with examples, the effects of human activities on the animal and plant populations in the Galapagos Islands
