Factors affecting the variety of species in an ecosystem Chapter 7

Species & Biodiversity - living 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)

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

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

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

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 grasses is reduced Sheep select to eat the sturdy grasses – help maintain biodiversity

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

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

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

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

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

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

Importance of biodiversity 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

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

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)

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

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

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