Year 12 Biology

Diversity and change

Ecosystems change –Abiotic factors may vary – eg light, water, temperature, salinity, tidesThese 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 (1st 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

• Damschanges 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

http://www.micro.utexas.edu/courses/levin/bio304/ecosystems/ecology.html

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

http://www.scienceclarified.com/Sp-Th/Succession.html

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 ecosystemsCriteria Natural Agricultural Urban

Inputs Low – 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

Outputs Low – 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

High (usually 5+)

High

High

Low

Low – 1 -2 crops

Low (1- 2)

Low

Low - moderate

Very low

Very low

Low (1- 2)

Low

Low - none

Effects on neighbouring ecosystems

Low High – feral species, algal blooms, erosion, salinity, biological magnification

High – feral species, pollution, greenhouse, desertification, ozone depletion, algal blooms

Comparing natural, urban & agricultural ecosystems

Biotic

Biotic

Biotic

Abiotic

Abiotic

Abiotic

Natural ecosystem

AgriculturalUrban

HeatHeat

HeatSolar energy

Chemical energy Chemical energy

Recycling

Matter Matter

Feed, fertiliserpesticides

Seed, stock

Less recycling Very little recycling

Produce

Waste, produce

Heat, electricity

Wastes

Raw material,manufactured goods

Rubbish, seweragemanufactured goods