Sustainability Interdependance Key Area 8 Threats to biodiversity

Sustainability & Interdependance Key Area 8 Threats to biodiversity

Learning Intentions By the end of this topic you should be able to: Define the term ‘exploitation’. Describe how it is possible for populations to recover from exploitation and the impact this would have on genetic diversity. Explain ‘the bottleneck effect’ in relation to evolutionary responses brought about by environmental change, particularly in small populations. Define habitat loss and habitat fragmentation. Outline the impact of habitat fragmentation on species richness with reference to degradation at the edges of the habitat fragments. Describe how to remedy widespread habitat fragmentation using habitat corridors. Define introduced (non-native) species as those that humans have moved either intentionally or accidentally to new geographic locations.

Exploitation

Exploitation Humans make use of many different species to gain useful products like raw materials, food, drugs… This is known as exploitation

Overexploitation of a species occurs when humans remove and use up individuals faster than the species can reproduce. Eg: Overharvesting Eg: Overfishing

Overexploitation With overeploitation, populations can be reduced to a low level but may still recover. Some species have a naturally low genetic diversity in their population and yet remain viable Eg: Overharvesting Eg: Overfishing

Recovery There have been certain legislations passed to help species recover from overexploitation: �Catches have to stay within fixed quotas �Limits to the number of boats, length of time spent at sea and areas permitted for fishing

Bottleneck events

Bottleneck event An event that can wipe out a significant proportion of the population in an unselective way is known as a bottleneck event Examples: Fire Flood Earthquakes

Bottleneck effect A bottleneck event can cause a bottleneck effect If the surviving population is small, genetic variation can be lost. This could decrease the chance of adapting to environmental change.

Bottleneck effect The surviving population can have: �Less genetic variation. This could decrease the chance of adapting to environmental change �Allele frequencies that are different from the original population (increase for some alleles, decrease for others) This loss of diversity means that reproduction among members could be genetically similar to inbreeding. This results in poorer rates of reproduction and so the population may become extinct.

Bottleneck effect - Cheetahs are an example of a species which have experienced a population bottleneck. Scientists have speculated that roughly 10, 000 years ago, as the last ice age drew to a close, large numbers of cheetahs died out leaving very small populations in Asia and Africa. All the cheetahs now living are descended from this handful of individuals

Bottleneck effect - Cheetahs In most species, related individuals share about 80 per cent of the same genes. With cheetahs, this figure rises to approximately 99 percent. This genetic inbreeding in cheetahs has led to: • low survival rates; • greater susceptibility to disease; • poor reproductive rates.

Habitat Loss

Habitat loss An animal's habitat includes feeding sites, breeding grounds, burrowing sites and hunting areas. Human activities can split up such areas, causing animals to lose both their natural habitat and the ability to move between regions of an ecosystem

Habitat loss Fragmentation is the forming of several habitats whose surface area is less than the original habitat. Habitat fragments suffer degradation at the edges which decreases the size further

Habitat loss Smaller fragments can only support small populations – and smaller populations will be more vulnerable to extinction. More isolated fragments and smaller fragments exhibit a lower species diversity Edge species : Species adapted to the habitat edge will increase in number due to fragmentation and eventually may need to invade the interior habitats. This will be done at the expense of interior species and so may reduce biodiversity.

How it is caused? Fragmentation has resulted from human activities such as clearing of forests for: �Agriculture �Housing �Hydroelectric dams �Motorways

Solution Fragmentation can lead to fragments of tiny ‘islands’ of natural forest isolated from one another by farmland, housing, motorways…Habitat corridors are narrow strips of quality habitat that can link otherwise isolated habitats. This allows members of a species to mate, feed and recolonise habitats after local extinctions.

The corridors allow movement of animals between fragments increasing access to food and choice of mates. This may lead to recolonization of small fragments after local extinctions Solution

Introduced, Naturalised & Invasive Species

Introduced, naturalised & invasive species Foreign species can be introduced to the UK Or new geographical locations) accidently or intentionally. These become introduced species in new locations Introduced species become naturalised species if they become established within the wild communities These become invasive species if they spread rapidly and eliminate native species therefore reducing species diversity

Invasive Species Invasive species can spread rapidly and prey on native species, out-compete them for resources or hybridise with them. This is because the introduced species have no natural competitors, pathogens, parasites or predators in this new ecosystem. VS

Red Squirrel vs Grey Squirrel The grey squirrels were introduced to the UK in the late 1800 s. Since then, they have caused a dramatic reduction in red squirrel numbers due to their ability to outcompete them for food and nesting sites. Grey squirrels also carry a disease which kills red squirrels but does not affect the grey squirrels.

Other examples Mink arrived from N. America - they were released into the wild and compete with otters for food. Rhododendron were brought from Asia/S. Europe. Their thick growth restricts growth of other plants.