Factors affecting the variety of species in an ecosystem

1. Factors affecting the variety of species in an ecosystem Chapter 7

2. Species & Biodiversity • Species: • - organisms similar enough to interbreed & produce fertile offspring • Biodiversity: • - total variation between all living things on earth • - includes variation within a species • - and between different species • About 1.75 million species studied • - (BUT 10-100 million could exist)

3. Habitat, Niche & Adaptation • Habitat • - where an organism lives within an ecosystem • Niche • - the role a species plays within a community • To succeed, organisms must be suited to their environment • - this often involves adaptation • - can be structural or behavioural

4. Adaptation & Distribution • An organisms adaptations will make it well, or poorly, suited to a habitat or niche • This will affect it’s distribution • The better it is suited, the more likely it will be found in that area • - Desert plants • - Mosquitoes • - Darwin’s Finches

5. Stable Ecosystem • Contains a wide variety of species • Including producers, consumers & decomposers • All members of the community are interdependent

6. Effects of grazing on species variety • Grassland has many varieties of grass • Some are sturdy, others more delicate • - rabbits are unselective grazers • - they keep the sturdy grasses in check • - but if rabbits are removed, sturdy grasses drive out the delicate grasses • - variety of grass is reduced • Sheep select to eat the sturdy grasses – help maintain biodiversity

7. Effect of pollution on species variety • Sulphur Dioxide (SO2) • Released by burning fossil fuels • Can damage plants & respiratory systems • - lichen have varying sensitivity to SO2 • - more SO2, less lichen survive • SO2 (and nitrogen oxides) can also dissolve in water (e.g. rainwater) • - this leads to acid rain • - this falls on, and lowers the pH of, seawater, freshwater & soil

8. Other pollution • Thermal • Power stations use river water as a coolant • Water returned to the river is much warmer • Increases temperature causes a decrease in oxygen levels • Causes a decrease in variety of fish species • Sewage • If untreated sewage leaks into rivers, bacteria feed on it • They use up the oxygen in the water • Only a few freshwater species can survive in low oxygen • Most will die – decrease in species diversity

9. Effects of human activity – habitat destruction • Humans dominate the world ecosystem • Deforestation • Clearing of natural forest, without replacement • - CO2 levels increase • - soil becomes infertile • - flooding of low-lying areas • - river levels change, water becomes muddy • Desertification • - caused by over-use of land on the edge of a desert • - water levels drop, forests cleared, desert sands take over

10. Biodiversity in crisis • Life on earth has had many mass extinctions • Some species adapt to global changes, others don’t • Humans are causing extinctions to increases by 400 times • Many species wiped out by over-hunting & habitat destruction • There are also many endangered species

11. Disruption of food webs • Most food webs are finely balanced • If one organism in the web is lost, it can have a knock-on effect on others • If a food web is small, the effects are very severe • E.g. myxomatosis on rabbits • Larger webs have less severe effects

12. Importance of biodiversity • Aesthetics: • - natural beauty of the environment enriches life • Economics: • - Most species have 100’s/1000’s of genes • - These could potentially be used medicines, food, materials etc • - many potentially useful genes have yet to be discovered • Effect of selective breeding: • - increases weakness to environmental changes • - e.g. disease, global warming • - wild varieties could hold resistance to these changes

13. Importance of biodiversity – ctd. • Opportunists: • - cockroaches, rats, weeds often over-run destroyed habitats • - more destroyed habitats = more opportunists • The U.N has pledged to: • - conserve biodiversity • - use biodiversity sensibly, ensure it lasts • - share the benefits of biodiversity to all nations

14. Behavioural adaptations in animals • Animals detect an environmental stimulus using receptors • E.g. sense organs • Internal communication (e.g. nervous system) makes a response • Carried out by effectors (e.g. muscles) • Different species will respond differently • Their particular behaviour will help them to adapt to the environment

15. Competition between plants • Plants will compete for: • - light, water, soil nutrients • Plants of the same species will have the same requirements • - competition will be intense • - sown seeds need to be carefully spread • Plants of different species will have different requirements (less intense) • But, some species can dominate at the expense of others • E.g. conifer trees (pine trees)

16. Competition between animals • Animals compete for: • - food, water, shelter, mates etc. • Within a species - competing will be very intense • Territoriality • - competition for a territory (e.g. robin/grouse) • - territory contains enough food for an animal, it’s mate & it’s young • - territory is defended by social signals • - territory will be defended aggressively near the centre, less so at the edges • - ensures population is well spaced out

17. Competition between animals • Between different species • Many different species occupy the same niche/habitat • Squirrels: • - Grey squirrel has become dominant over red squirrel • - Grey competes more aggressively for food • Trout: • - rainbow trout has dominated brown trout • Reducing competition: • - some species come to a compromise, rather than compete • - e.g. green & common cormorant

18. Predator-prey interaction • Increased no. of prey, leads to increased predation • As the no. of prey then decreases, competition gets more intense • So, eventually, the predators no. drop • This allows no. of prey to increase again