Patterns and inter-relationships in communities

Species diversityComposition of a community

Inter-relationships of organismsPatterns in a communtiy

Communities and species diversity

• A community is all the populations in a defined habitat

– Some habitats are long terms eg a forest and some temporary eg a rotting log

• Three characteristics of communities:1. More different species mean a more stable

community. Called species diversity2. A few organisms will be in great numbers eg

grass on the savannah. Just because you are rare doesn’t mean you aren’t important

• 3 There are always more producers than there are consumers.

Communities in the world

• The planet is divided into zones

• Based on the amount of sunlight per square metre

• More energy arrives on the earth in the tropics which is why they have richer communities

• There are tropical zones, tundra zones, grassland zones

Composition of community

1. Producers – can make own foodphotosynthesisers use energy from sunlightchemosynthesisers use energy from chemical reactions. Eg bacteria in sulphur springs, nitrification bacteria

2. Consumersherbivorescarnivores

predators, scavengers, insectivorous plants, parasites

Decomposers

Inter-relationships of organisms

• There are two – Intra-specific relationships

• Within the same species– Either cooperative like courtship, protecting young,

hunting in packs– Aggressive like fighting for mates and territory, pecking

orders

– Inter-specific relationships• Between two different species

– There are lots of these!!

Mutualism

• Both partners benefit

• EG– Clover and rhizobium bacteria– Wrasse and larger fish– Cows and bacteria– lichen

Clover and rhizobium

lichen

Wrasse

Commensualism

• One species gains while the other is not affected– Remora fish live on sharks. When the shark

swims, the remora sticks itself to the shark. When the shark kills, the remora detaches, and eats the scraps. The remora then reattaches to the same shark or some other passing one…

Antibiosis

• One species is harmed and the other one is indifferent or unaffected– Penicillium is the best example. The fungus

kills off bacteria. We use the chemical penicillin to kill bacteria too.

– Blue-green algae produce a chemical to kill fish, and sometimes cattle. The algae aren’t affected by the chemicals

Penicillium mould

Exploitation

• One species benefits and the other is harmed– Herbivores eating plants– Carnivores eating other animals– Parasites live on their hosts

Nits, kooties, lice

Parasitoids

• These are parasites that have a free living stage – where they are not living on their hosts

Patterns in communities

THIS IS REALLY IMPORTANT TO KNOW!!

Succession

• This is the change in communities OVER TIME• Occurs where there is nothing living

– Happens after landslides, volcanic eruptions or floods

• Community passes through a series of stages till the land has a climax community, which is big trees replacing big trees – ie stability

• Climax community could be tussock – depends on the environment

• Primary succession– Area had no previous life– No seeds, no bugs, no nothing– Volcanic eruptions, retreating glacier

• Secondary succession– Community cleared by some disturbance that

leaves the soil intact– Fire?, landslide?, weedspray?

• Small succession– In dead things, until the energy is gone

1. First colonisers lichen. Rocks break down by frost action

2. Lichens die resulting in a build-up of humus. Other plants grow such as mosses then grasses and small ferns

3. Bracken increases the humus levels and roots start to break up small rocks. Small trees such as manuka grow, which provide a nursery for larger trees

4. Eventually large trees grow which are replaced by large trees when they die

Primary succession

Secondary succession

• Seeds in the soil seed bank germinate– Usually annuals first– Gradually perennial plants that are large will

out-compete smaller plants, and start to control the environment

Pond succession

Succession in front of glacier

Stratification

• Vertical layering, ie the change in communities over height

• Occurs in grass, forest, the oceans and soil

• Affects animals and plants

Stratification in a lake

Forest stratification

Forest stratification

Soil stratification

Rock stratification

Zonation

• This is change in communities over horizontal space

• Obvious on forest edges, water edges and anywhere there is a change in abiotic factors on the horizontal plane

• Plants and animals have different adaptations to fit the changing environments