Sustainability

1. Important Definitions Carrying capacity: the maximum population size that can be maintained over a period of time in a particular habitat. Competition: happens when resources like food or water are not present in adequate amounts to satisfy needs of all the individuals who depend on those resources. Intraspecific competition: competition between individuals of the same species. Interspecific competition: competition between different species Gause’s Competitive Exclusion principle: if two species occupy the same niche when interspecific competition will result on one of the species being outcompeted and becoming extinct. Succession: the gradual directional change in an ecosystem over time through a number of stages ending in a stable climax community. Primary succession: begins with totally bare ground that contains no pre-existing life Secondary succession: takes place on ground that has already undergone succession – an area that has previously been colonised. Climax community: stable community that is established at the end of succession Deflected succession: when human activity prevents natural succession form occurring Plagioclimax: human activity stops succession before a climax community is reached. Pioneer plants: species that colonise previously uncolonised land leading to ecological succession Sustainable use: replacing or replanting whatever is removed form the environment so that harvesting can continue year after year indefinitely while maintaining a stable ecosystem Coppicing: cutting a tree trunk close to the ground to encourage new growth Pollarding: cutting a tree trunk higher up to encourage new growth whilst ensuring new shoots are not eaten by deer. Conservation: maintenance of biodiversity, including genetic diversity between species, genetic diversity within species and the maintenance of a variety of habitats and ecosystems Preservation: usually involves protecting areas of land, as yet unused by humans, in their untouched form. Sustainability

2. Population Growth 1. Lag phase: organisms are adjusting to the surrounding conditions. This may mean taking in water , cell expansion, activating specific genes and synthesising specific enzymes. Organisms are active but not reproducing, so the population remains fairly constant. 3. Stationary phase: Competition means that resources become limiting factors on growth. This is the carrying capacity of the habitat: birth rate equals death rate. Population 4. Death phase: A large population means that there are lots of waste products and increased disease. The death rate exceeds the birth rate and population declines. 2. Log phase: the population size doubles each generation because every individual has enough space and enough nutrients to reproduce. Time The carrying capacity of a habitat is the maximum population size that can be maintained over a period of time in that place. The habitat cannot support a larger population because of factors that limit the growth in population size. These are limiting factors and may include availability of food, water, light or shelter.

3. If resources are in short supply, there will be competition between organisms for that resource. Intraspecific competition is competition between individuals of the same species. Those individuals best adapted to obtaining food will survive and reproduce , and those that are less well adapted will die and fail to reproduce. This type of competition can lead to directional selection: the next generation will be better able to survive because they have evolved due to natural selection. Directional selection is a mode of natural selection in which a single phenotype is favoured. The advantageous characteristic increases in frequency . Interspecific competition takes place between different species. Interspecific competition can affect both the population size of a species and the distribution of a species in an ecosystem. Competition will be more intense if the 2 species have a similar niche – if they eat the same food for example.

4. Predator-prey relationships Predator-prey relations undergo cyclic fluctuations. The predator population peaks after the prey population peaks, but there are never as many predators as there are prey. • When there is a small predator population, there is less predation, so the prey birth rate exceeds the death rate and the prey population increases. • An increasing prey population means that more food is available to predators. The predator population will begin to increase. • As the predator population gets larger, more prey are eaten. The prey death rate exceeds the birth rate so the prey population size decreases. • With a reduced prey population, a large predator population cannot be sustained, so the predators begin to die off and the population size decreases.

5. Succession Succession is a natural directional change in a community of organisms over a period of time. It involves a number of stages called seres; one sere changes conditions to allow the next sere to be established. These changes may include increasing the depth of the soil or stabilising the soil. Succession leads to a climax community – a stable population in which all the potential niches have been filled. We can prevent succession occurring – this is deflected succession and leads to a plagioclimax. We do this by removing trees, burning, grazing cattle, moving lawns, ploughing fields and using herbicides and pesticides. Primary succession begins with a previously uncolonised area, with no pre-existing life. Secondary succession begins in an area that has already undergone succession and has previously been colonised. Sand Dune Succession… • Pioneer dune sere: Pioneer plants like sea rocket colonise the sand above the water mark. Pioneer plants often have adaptations to allow them to survive in harsh conditions – like a high tolerance to salt or long roots. • Yellow dune sere: Wind blown sand builds up around the base of these plants forming a mini sand dune. As plants die and decay, nutrients accumulate. The dune gets bigger and larger plants like sand couch grass colonise it. Sand couch grass has long underground stems that helps to stabilise the sand. • With more stability and more nutrients, Marram grass starts to grow. Marram grass has an extensive vertical root system that helps to stabilise the dune. The shoots trap sand as the dune gets larger. • The sand dune has built up humus and so other plants are able to colonise the dune. By the Grey dune sere, dunes have continuous plant cover, anchoring the dune on one place. • Leguminous plants with nitrogen fixing bacteria in their root nodules convert nitrogen to nitrates and with more nutrients available, an even more diverse range of species can grow. • The climax community is the woodland sere. The dominant species have excluded the competing species that are less well adapted. The vegetation is in a stable balance with the climate and soils of the area.

6. Sustainable Management: Timber production “Whatever is removed from the environment is replaced or replaced so that harvesting can continue year and year indefinitely while maintaining a stable ecosystem.” A standard tree is a tree that is not cut in rotational coppicing. They are left to grow to full size, and eventually, they are harvested when they are big enough to provide large timber. Coppicing is when a tree trunk is cut close to the ground to encourage new growth. Once cut, several new shoots grow from the cut surface and eventually mature into stems of quite narrow diameter. These can then be harvested and used for fencing, firewood or furniture. Pollarding is similar to coppicing but involves cutting the tree higher up to protect new shoots from deer. Rotational coppicing involves dividing a woodland into different sections. One section is cut each year, so that by the time we want to coppice the first section again, the new stems have grown and are ready to be harvested. Rotational coppicing increases the biodiversity of an area. Different areas of woodland at different points in the coppice cycle provide different types of habitat, so species diversity is maximised. Clear felling is when all of the trees in an area are cut down at once. This has many disadvantages: soil erosion can occur, resulting in reduced soil mineral levels. Habitats are destroyed on a large scale. Selective cutting provides a more sustainable alternative: only the largest and most valuable trees are removed so that habitats are mostly unaffected.

7. The Galapagos Islands • Threats to Biodiversity: • Population growth places huge demand on water, energy and sanitation services. More waste and pollution, increased building and conversion of land for agriculture have caused destruction of habitats. • Overfishing: fish species are harvested faster than they can replenish themselves. Depletion of sea cucumber populations has had a drastic impact on under water ecology. Sharks species around the islands have been depleted due to hunting for shark fin. • Giant tortoises were taken from the island because they could survive for a long time on ships before being killed to eat. 200,000 tortoises were taken in less than half a century. • Tourism is a rapidly growing industry and the increase in numbers has meant more pollution and more habitat destruction • Humans have introduced non-native species to the islands that have an impact on existing communities. How are ecologists working to manage and conserve the ecosystem? • Quarantine system: searching any arriving boats and tourists for foreign species • Use natural predators such as ladybirds to wipe out insects that were damaging native plant species • Culling of feral goats and pigs that were damaging the tortoise population • Galapagos marine reserve established ‘no take’ coastal zones , where no extraction of resources in allowed.

8. Exam-style questions • Explain, with reference to an example, what is meant by the term succession • Succession is a natural directional change in species composition in a n area over a period of time • Succession involves a number of clearly defined stages called seres • One sere changes the conditions to allow the next sere to be established • Succession leads to a climax community, in which the species in the community are in balance with the environmental conditions and all niches have been filled. The climax community will be dominated by the largest and most well adapted species. • Sand dunes are an example of where succession occurs. There are 4 seres in this example: embryo dune, yellow dune, grey dune and woodland. • Embryo dune is colonised by pioneer plants such as sea rocket that are tolerant to salt water and unstable sand. Wind-blown sand builds up around the base of these plants. As plants die and decay, nutrients accumulate. • Yellow dune: With more nutrients, grasses like sea-couch grass and marram grass can colonise. Their deep vertical root systems stabilise the sand and the taller grasses are able to trap more sand. The sand dune and nutrients build up. • Grey dune: other plants can now colonise the sand because the sand dune is fixed by roots and has accumulated humus. Species such as hare’s foot clover and bird’s foot trefoil are leguminous, meaning that the bacteria in their root nodules convert nitrogen to organic nitrates. • With more nitrates available, a diverse range of species can grow.

9. Exam-style questions • Using timber production as an example, explain how ecosystems can be managed in a sustainable way • Sustainable use involves replacing or replanting whatever is removed from the environment so that harvesting can continue year after year indefinitely • Coppicing can be used: deciduous trees are cut close to the ground. Once cut, several new shoots grow and mature into narrow stems that can then be used for fencing, furniture or firewood. • Pollarding involves cutting deciduous trees higher up to avoid deer eating new shoots • Rotational coppicing involves splitting a woodland area into sections. One section is cut each year until each section has been cut and then the cycle begins again. • Standard trees are not cut when rotational coppicing is employed: they are left to grow to their full size. • Different stages of the coppice cycle provide different habitats for organisms, encouraging biodiversity.

10. Exam-style questions • Discuss the reasons for conserving biodiversity • Ethical reasons: • Humans have a duty to preserve the natural world • The biodiversity was here when we were born so we have no right to destroy it • We are morally obliged to preserve biodiversity for future generations. • Economic reasons: • Money can be made from biodiversity from ecotourism • Species of plants produce valuable products such as hardwoods and oils • Natural environments are sources of potentially beneficial resources – many drugs are discovered in natural plant species. • Wild insect species are responsible for pollinating crop plants; without them harvest would fail and farmers would go out of business • Biological reasons: • Whole food webs can collapse on the loss of just one species; • Having lots of species means that there is a source of genetic diversity – each species contains unique genes and alleles. In the future, we may need to use these to genetically engineer plants that have useful properties like disease or drought resistance • Ecosystems recycle nutrients essential to human life – maintaining water quality, protecting soil and breaking down waste products. • Aesthetic reasons: • A biodiverse ecosystem looks better to humans • Make our lives more enriched and stimulating

11. Exam-style questions • Outline with examples the effects of human activities on the animal and plant populations in the Galapagos • Population growth places huge demand on water, energy and sanitation services. More waste and pollution, increased building and conversion of land for agriculture have caused destruction of habitats. • Overfishing: fish species are harvested faster than they can replenish themselves. Depletion of sea cucumber populations has had a drastic impact on under water ecology. Sharks species around the islands have been depleted due to hunting for shark fin. • Giant tortoises were taken from the island because they could survive for a long time on ships before being killed to eat. 200,000 tortoises were taken in less than half a century. • Tourism is a rapidly growing industry and the increase in numbers has meant more pollution and more habitat destruction • Humans have introduced non-native species to the islands that have an impact on existing communities.