Species interactions Use pictures to construct species webs

for different ecosystems

Desert Mangrove Coral reef Arctic ocean and pack ice

Types of species interaction Predator prey Grazing Intra-specific competition Inter-specific competition Decomposer organisms Host parasite Host pathogen Commensalisms Symbionts

Predator prey relationships The classic ecological explanation of

these is that predator populations are controlled by the availability of prey.

This is fair in natural ecosystems but must be qualified.

In unnatural ecosystems prey may have no refuges and be completely consumed before the predators starve to death

Natural vs managed ecosystemsNatural lowland river in England

River straightened for drainage

The rich variety of habitat structure in this river allows prey species to evade predators. In the drainage ditch the prey fish have nowhere to hide and the predator can catch and eat them all.

Farming Farming maintains unnaturally high

concentrations of prey/host species This is why farmed animals are very

vulnerable to natural predators and disease

Predator prey relationships Read the text then answer these questions 1. Name three distinct types of predator prey

relationships. 2. Which predator prey relationship did Volterra

observe and what did it show? 3. Why were ecologists able to model snowshoe

rabbit-canadian lynx populations over such an extensive time period?

4. Why do you think the predatory protozoan was able to annhiliate the Paramecium in laboratory cultures?

Predator prey relationships 5. What do you understand by spatial

heterogeneity? 6. Why, after achieving such dramatic

reductions in prickly pear numbers could the moth not fully eradicate it from Australia?

7. Both moth and prickly pear live in central America – how come the prickly pear is so common here!?

8. How does a keystone predator act to maintain species diversity?

Cattle as key stone predators

0 cows 1 cow 2 cows 3 cows 4 cows 5 cows

5 27 26 14 12 6

Grazing density / hectare Plant species /m2

Summarise the impact of cattle grazing on species biodiversity in the habitat. In what ways may the cattle grazing activity improve species diversity?

Intraspecific competition Competition between members of the

same species within a population. Darwen thought about elephants. Darwin calculated that in elephants,

which are among the slowest breeding land mammals, if all of the potential young of a single female survived and reproduced at the same rate, after 750 years the descendants of this single mother could number 19,000,000!

There are not 19million elephantsWhy not? Competition for food and resources Too many elephants and they would eat all the food.

Then they would starve. Why is this so important? All species are under constant pressure due to

intraspecific competition. Only the fittest can survive! This is called survival of the fittest Any that have extra benefit from a better gene will be

sure to survive. This can lead to an increase of that gene in the population.

This is the basis of evolution.

Interspecific competition Competition between species This can lead to one species dominating –

think of the rocky shores Under natural conditions this is reduced

allowing several species to coexist. This is because each species has a different

niche Or one species is prevented from dominating But change the environment and this balance

can be lost

Interspecific competition in immigrant species

Around the world different often related species occupy the same niche

Red and Grey squirrels

Grey squirrels were introduced to Britain and have nearly replaced the native redThey have done this because they can make better use of available food, are bolder and more willing to forage on the ground and are immune to a disease they carry

Similar species Many similar species do coexist How? By avoiding inter-specific competition Strategies Different food Different tolerances to environmental factors Different abilities to avoid predators Different breeding requirements Different requirements of light, temperature,

shade etc.

Research Look at an assemblage of similar species

found in a geographical area Explain how they coexist Produce a power point to show how they

reduce inter-specific competition.

E.g. antelopes on the african savanah

Decomposers Many organisms eat solely dead and

decaying material These organisms are fundamental in all

ecosystems Some are very specific only occupying

rotting material at specific stages of its decomposition

The White backed woodpecker feeds only on invertebrates of decaying wood.

Invertebrates There are more than 1700 different

invertebrate species in Britain and Ireland which are dependent on decaying wood in order to complete their life cycles

Many are rare due to the lack of old and rotting trees. We have little natural woodland!

Important decomposers Carrion eating birds Flies and their larvae Beetle species Worms Fungi Bacteria

Closer relationships Some species relationships are

physically much closer than predator and prey.

Some benefit both species, others only one species whilst in others one species is harmed.

These relationships are referred to as symbiosis, especially if both species benefit

Almost nothing on earth exists without symbiosis

We have a symbiotic relationship with our gut bacteria.

Symbiosis Both species benefit from close association May be endo-symbionts with one species living

within the tissue of another E.g nitrifying bacteria in the root nodules of

leguminous plants, algae living inside reef building corals.

Others are ecto-symbionts where one lives on the other: e.g. gut bacteria or lice on the skin or barnacles on whales

Mutual symbionts include such things as cleaner fish and shrimps and the fish they service.

Commensalism Means literally feed at the same table. This is a loose association of species.

Usually one species benefits whilst the other is neutral.

Cattle egrets and Cattle. The animals stir up and attract insects that the egrets feed on. The cows are unaffected.

Mutualism Both species interact in a way which is

beneficial to both. Examples include the bacteria in the guts of

cattle that help digest grass or in the guts of termites that help digest wood

Insects and birds pollinating flowers – nectar is produced to encourage this mutualism

Oxpeckers removing ticks from large grazing animals

Cleaner fish and shrimps.

Obligate mutualism Two species are unable to survive

without the other Most orchids require a fungal mycorrhizal

association with their roots to be able to grow.

Parasitism One organism benefits, one is harmed.

Disease causing organisms are all parasites

Klepto parasitism one animal steals another’s food:

The frigate bird:

Ectoparasitism Ticks suck blood

Gut parasites – technically ectoparasites

Tapeworm Roundworms (nematodes)

Endoparasites Found in the body tissue e,g flukes

Research a parasitic disease Learning focus: writing extended essays Task: Identify a parasitic disease caused by a

multicellular or single cell organisms not including virus or bacteria

Describe the life cycle of the disease causing organisms

Identify the symptoms, incidence, and mortality of the diseases.

Describe treatment and outcomes. Describe control measures

Include references

Marks Parasite Disease Treatment and control

Structure1 mark for each

1 Named Named A treatment or control measure

Sentences correctly punctuated

2 Described Symptoms briefly described

Both Paragraphs used

3 Life cycle described

Incidence, seriousness short and long-term outcomes, percentage morbidity explained

General description of control measure/ treatment

Subheadings

4 Transmission between stages explained

Both Referenced

5 Thorough description

Success evaluated.

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