Year 12 Biology

Diversity and change Ecosystems change – Abiotic factors may vary – eg light, water, temperature, salinity, tides These may vary cyclically eg day/night; monthly, seasonally, over longer periods, or catastrophically (eg fire, flood, volcanic eruption, ice age, etc) Biotic factors may vary – Numbers of Producers Prey species (1 st order consumers) Predators (high order consumers)

Everything in an ecosystem is linked A change in one factor can lead to changes in other factors – domino effect eg decreased rainfall  decrease in vegetation  decrease in herbivores (prey species)  decrease in predators eg removal of predators (hunting or biomagnification)  increase prey species (plague)  decrease vegetation  decrease in herbivores due to no food Key species a species whose removal negatively affects an entire ecosystem eg otters in kelp forests – when hunted to extinction, sea urchin numbers increased so much that they destroyed the kelp  decrease in the other species depending on kelp for food or shelter

Changes in ecosystems - water Dams  changes distribution of populations in ecosystems – can get animals accumulating around dams  over grazing near the water source; loss of original ecosystem in flooded area Presence of bores  lowers water table; increases number of animals around bore  over grazing near the water source Tailing dams  kills wildlife that tries to use it as water Removing water for human use  lowers amount of water in river/streams eg Murray  not enough water to maintain ecosystem Filling in wetlands  destroys ecosystem; loss of habitat for migrating birds; damage to neighbouring ecosystems as wetlands act as filters to remove pollutants and excess nutrients

Changes in ecosystems - clearing Loss of trees  loss of habitat & nesting places as well as the following Loss of topsoil  (= erosion) loss of fertility  decreased producers  decreased biomass in the whole ecosystem Rise of water table  water logging in low lying areas, increased soil salinity as salts are brought up with the water Increased soil salinity  loss of fertility  decreased producers  decreased biomass in the whole ecosystem Increased water salinity  loss of fertility  decreased producers  decreased biomass in the whole ecosystem; poisoning of consumers, loss of aquatic life

Changes in ecosystems – climate change Climate change  changes in temperature, rainfall & humidity – also affects water availability Increased temperature  increased water loss  higher water needs; may cause death of organisms if temperature too high; rising sea levels (thermal expansion of water) and melting of glaciers and polar icecaps may also impact on ecosystems Decreased rainfall  reduced water availability  decreased biomass (less plants  less animals) Reduced water table  dries out seasonal water sources (eg swamps, small creeks) and cave systems, less water  decreased biomass (less plants  less animals) Change in seasons  organisms may not be able to find enough food to survive & raise offspring eg birds breed as light levels change, insects breed as temperature rises

Changes in ecosystems -agriculture Farming  agricultural practices include Monoculture  presence of only one species in the crop, decreases biodiversity, encourages population explosions or plagues of pest species eg mice, locusts, in the long term reduces soil fertility Killing insects (eg pesticides)  disrupts ecosystems by destroying food source of higher order species (eg owls, wattle birds); can lead to ecological magnification Loss of dead/decaying matter  loss of fertility, loss of decomposers  soil problems  reduction in producers  reduction in consumers Fertilisers  chemical poisoning of plants or animals (eg high phosphate fertilisers kill many native trees; run-off into rivers can cause eutrophication (algal blooms)

Changes in ecosystems – human interference Human presence  disrupts ecosystems in many ways including: Loss of predators  removal of predators (sg spiders, wolves) can lead to population explosions of prey species Introduction of new carnivore  eg foxes, cats, dogs  loss of native wildlife Introduction of new herbivore  eg rabbit, sheep, may out- compete natives  loss of native species; may cause over grazing as no native predators  erosion Introduction of new producer  eg brambles, prickly pear, may out compete natives (as often not edible to consumers)  loss of native plant and animal species (now not enough food for them); aquatic plants eg duckweed may block rivers

Succession Succession change in an ecosystem over time as organisms change the abiotic features (eg soil, humidity) so it becomes more suitable for other organisms to survive Colonisers hardy organisms that first invade an area and establish themselves. They must be able to cope with harsh conditions eg no soil, low soil fertility, salinity, low humidity, etc Climax community final community. This is the most diverse and stable, and usually consists of forest

Primary succession Occurs when the soil is totally destroyed or absent, or extremely infertile, organisms must invade from neighbouring ecosystems eg after a volcanic eruption, a glacier retreats or at the beach

Secondary succession Occurs when a disruption occurs that kills organisms, but the soil remains relatively fertile, organisms may still survive or seeds may still be present eg after a fire, clearing or logging, abandoned land

Measures of stability Stability ability to cope with change. The more stable an ecosystem, the better it can cope. Stable systems usually have high biodiversity, complexity and recycling Biodiversity number of species present. The greater the number, the higher the biodiversity Complexity how many relationships can be seen, size of food web. The more complex the ecosystem the larger the food web, and the more relationships that can be seen Recycling amount of matter that is lost from the system. The greater the recycling, the less matter is lost to other ecosystem

Types of ecosystem Natural – relatively unaffected by humans eg forest, reserves, parks Agricultural – farming ecosystems Urban – human ecosystems eg towns and cities Aquatic – ecosystems in water eg rivers, seas Terrestrial –ecosystems found on land eg forests, deserts

Different ecosystems CriteriaNaturalAgriculturalUrban InputsLow – energy, water & nutrients Migratory animals or flow from rivers or leeching from soil High – energy & matter (+ possibly water – irrigation) Stock & seedlings, fertilizers & pesticides High – energy, water & matter Raw materials and goods OutputsLow – energy, water & nutrients Migratory animals or flow from rivers or leeching from soil High – energy & matter Crops & animal products & wastes High – energy & matter Wastes & sewerage, manufactured goods Ecological complexity Biodiversity Trophic levels Stability Recycling of matter High High (usually 5+) High Low Low – 1 -2 crops Low (1- 2) Low Low - moderate Very low Low (1- 2) Low Low - none Effects on neighbouring ecosystems LowHigh – feral species, algal blooms, erosion, salinity, biological magnification High – feral species, pollution, greenhouse, desertification, ozone depletion, algal blooms

Comparing natural, urban & agricultural ecosystems Biotic Abiotic Natural ecosystem Agricultural Urban Heat Solar energy Chemical energy Recycling Matter Feed, fertiliser pesticides Seed, stock Less recycling Very little recycling Produce Waste, produce Heat, electricity Wastes Raw material, manufactured goods Rubbish, sewerage manufactured goods