Community structureThe following organisms form part of a community

A community is a group of

populations (producers,

consumers and decomposers)

living together in a habitat

Predator-prey

relationships

Competition1. Intraspecific competition: the competition between organisms of the same species depending on the same resources like food, space, shelter, water and access to mates.2. Interspecific competition: the competition between organisms of different species depending on the same resources e.g. light, space, water, shelter, food

Competition: Intraspecific competition

Intraspecific competition: males compete for territory.

Interspecific competition:

In the African savanna, hyenas

and vultures compete with

one another for the flesh of dead animals such as

the dead elephant

pictured here.

Interspecific competitionLion and hyenas fighting for the same food

resources

Jackal and a hyena fighting for the same food source

Specialisation for specific modes of lifeWhen two similar species co-exist, they will start to specialize in their habitats and feeding habits and undergo character displacement to reduce the severity of interspecific competition.This is demonstrated by Galapagos finches described by Charles Darwin. The ancestral bird from the mainland of Ecuador had an intermediate-sized beak to consume insects and seeds of all sizes. Notice, however, how the break size has changed, to reflect specialization in feeding habits. (In fact, there is one finch, the woodpecker finch, which uses a twig as a tool to dig out insects from holes in trees.)

Specialisation of the Galapagos finches

1. Competitive exclusion: the competition in which one of the two competing species is much more successful that the other such that the successful species survives and the other species disappears.2. Resource partitioning: The kind of competition situation in which competing species coexist in the same habitat since they use the resources slightly differently

Paramecium aurelia and P. caudatum: In a classic study in the 1930’s, Gauss cultured P. aurelia and P. caudatum both alone and together in culture tubes. When grown separately, the populations grew to a fairly predictable density. However, when grown together, P. caudatum always lost and eventually went extinct.

Resource partitioning amongst plantsDifferent species of plants in the same habitat will compete for the same resources like light, water, mineral salts, etc. Different species of plants grow to different heights or have roots that are different lengths so they divide the resources, accessing them in slightly different ways

Resource partitioning: co-existing shore birds

Symbiosis: The close association of two organisms such that one or both benefit form the association

Parasitism: a relationship in which one of the species benefits and the other is harmed by the relationship

Mutualism: The symbiotic relationship in which both of the species benefit form the association

Commensalism: Two species living together where one species benefits and the other neither benefits nor suffers disadvantage

Parasitism: malaria mosquito sucking human blood

Life cycle of the malaria mosquito

Parasitism: Ticks feeding on animals or humans

A tick bite can cause tick bite fever in humans

Parasitism: swimming habits may influence parasitic infections

Life cycle of the bilharzia

parasite

World distribution of bilharzia

Sanitation may

influence parasitic

infections

Parasitism: cholera

One species is harmed in a parasitic relationship –some scientists regard it as predataion since the host may be killed

The spreading of

cholera from

Zimbabwe

Platyhelminthes: taenia solium/tapeworm

Tapeworm with hooks with which it attach to the wall of the small intestine

With its long, narrow shape the tapeworm is well adapted to attach to the small intestine of the human

Life cycle of a tapeworm

Mutualism: oxpeckers on a giraffe. The oxpecker gets food form the giraffe and the giraffe benefits

by getting rid of its parasites

Mutualism: Lichens is an organism made up of fungi and algae. The fungus provides the external structure of the lichen and provides the algae wit a protected place to live. Algae photosynthesise and provide the fungus with food.

Mutualism: Bees collect pollen and nectar from flowers, flowers are

pollinated in the process

Some bees pollen collect in a packet around their legs

Mutualism: Ants get nectar from the Acacia tree as well as shelter in specialised swollen thorns. Ants defend the tree against herbivorous and wood boring insects.

Commensalism: The egret catch insects which are disturbed by the activity of a large animal. The herbivore are neither helped nor harmed by the egret

Commensalism: Remora fish swim next to sharks or attach to them. It gets protection and scraps of leftover food from the shark. The shark isneither helped nor harmed by the remora fish

Human influence on community structure

The elephant herd in the Kruger National Park increased from 8, 000 to 12,500 in 2008 and to 19 000 in 2009. The elephant population is increasing by 7% per year, and might reach 20 000 by 2012. This large herd cannot be sustained since adult elephants consume 130 kg food a day and they live for 55 – 65 years. On 25 February 2008 the SA Government finally concluded it would have to lift a 17 year-old moratorium on the culling of the native elephant to cope with its booming population. Minister van Schalkwyk announced that killing of excess animals would only be allowed once all other options (translocation and contraception) had been ruled out. Minister van Schalkwyk said:”Our simple reality is that elephant population density has risen so mulch in some southern African countries that there is concern about impacts on the landscape, the viability of other species and the livelihoods and safety of people living within elephant ranges.”

Extinct: a species of plant or animals that does not exist any more as all the individuals have died.Biodiversity: the variety of different kinds of living organisms (species0 that exist on earth.

The aesthetic value placed on South Africa’s

biodiversity.Discuss the values placed

on “large and fury’ animals compared to “small and

slimy” animals1. Which of these animals will attract most tourists?

‘Small and slimy” can

be very interesting.

COMMUNITY CHANGE OVER TIME: ECOLOGICAL SUCCESSION

1. Primary succession: the sequence of organisms that occupy a new habitat.2. Pioneer plant: a plant that can colonise bare soil and that is part of the community that forms the first stage in the

process of succession3. Secondary succession: the sequence of organisms that occupy a disturbed habitat or when an established

community has been disturbed in a catastrophic manner.4. Climax community: the final stage in the process of succession that refers to a mature community of plants that will

remain stable with few, if any, changes over time

Succession

Primary succession begins in areas consisting of bare, lifeless substrate such as rocks or a car path. Organisms gradually move into the area and begin to change its nature,

Secondary succession occurs when a established community has been disturbed in a catastrophic manner, e.g. after a veld fire or a flood. In the disturbance all the vegetation is destroyed, but all or some of the soil remains. The same process occurs as in primary succession, but as there is soil for grasses and small plants to grow in, these plants form the pioneer communities.

Pioneer plants

Lichens are pioneer plants as they are the first organisms to colonise a bare area. Acidic secretions from the lichens help to break down the hard surface of the rocks and slowly bits of soil accumulate, mosses may grow on these small pockets of soil, enriching the quality and quantity of the soil with the organic material that they add to it. As time passes and the soil becomes richer and deeper, other plants like grasses and small herbaceous plants become established in the larger pockets of soil , small animals may also move into an area when these plants become established.

An example of primary succession

Pioneer grass on a sand dune

Climax community

Random sampling: a sample that is not deliberately selected but is selected by chance. This means that any area being sampled or any individual in a population being sampled has an equal probability of being selected