Biotic Interactions

Biotic Interactions
This is the interaction between living things
Predator/prey relationships
Plant/herbivore relationships
Competition
Symbiosis

Abiotic Interactions
These are interactions that exist between the organisms and the environment :
- Temperature
- Light
- Pressure
- Salinity
- Water availability
- pH
- Nutrients
- Exposure to wind or waves

Density Independent Factors
These are factors which reduce the population numbers independently of the population density
The proportion that dies could be the same whether the population is dense or not - Forest Fire - Floods - Volcanic eruptions - Prolonged drought - Acid rain

Density Dependent Factors
These are all biotic interactions
These cause the population to decrease when the population is high and increase when the population is low
- Predation - Competition - Disease

Inter-specific and Intra-specific Interactions
These interactions are always involved in competition
INTER is competition between species e.g. GRAZING, PREDATION AND PARASITISM INTRA is competition within the species e.g. TERRITORIAL BEHAVIOUR, DOMINANCE, MATING, RESOURCES

Predation
In a predator/prey relationship both the species can benefit
Predators obtains food
Reduced numbers in prey means more resources for those individuals that are left
Both the predator and prey population is governed by one another, however the exact nature of this can differ

Predator-Prey Relationship
The pattern between the two can be grouped
into 4 types:
1) Stable coexistence : where both populations remain stable
2) Cyclical variations : regular increases and decreases occur in the populations
3) Erratic swings : large scale “blooms” can take place at an irregular time, due to unstable populations of prey or predator, where a small change in the environment can have a major effect on the animal.
4) Extinction : due to over hunting of prey

Predator-Prey Relationship
One of these 4 patterns will occur depending on a variety of factors:
The CARRYING CAPACITY of the habitat (the maximum number of individuals that can be supported by a particular ecosystem on a long term basis)
The PREY REPRODUCTION RATE
The PREDATOR REPRODUCTION RATE
The degree of FLEXIBILITY of the predator in it’s ability to respond to changes in the prey population

Flexibility of the Predator
If the prey increased, the predator would naturally eat more , but this only happens if the predator is not eating it’s maximum number of prey
If the increase in prey is long term, then there will be an increase in the predator offspring that survive from reproduction as there is more food available and therefore less competition for food

If the prey population becomes very large there are two possible fates of interaction:
STABLE COEXISTENCE :
Predators prevent prey from exceeding the carrying capacity
To do this predators must reproduce quickly compared to prey and to eat more when there are more prey
CYCLICAL VARIATIONS :
Here the predators are less responsive to fluctuations, due to slow reproductive rate or have reached a maximum level of feeding

Cycling
Cycling results due to time lags, which are the responses of the predator to the change in population numbers of the prey.
The prey increases, then in some time the predator population increases
As the predator population rises their prey population begins fall
The lack of food reduces predator number …………… and so on!

Case Study: Snowshoe Hare and the Canadian Lynx
The information on the populations of both animals appears to give the perfect predator/prey relationship in a cycling effect
However, there are many other factors to consider, proving only that an ecosystem is a complicated network of interactions

Predator/Prey Cycle

The Role of Predators in Maintaining Diversity in Ecosystems
When different species are competing for the same resources, one will succeed at the expense of another
The weaker species will be lost from the habitat [COMPETITIVE EXCLUSION]
If, however, predation reduces the numbers of strong competing species, the weaker species have more of a survival chance
This increases the DIVERSITY OF THE ECOSYSTEM . The more diverse an ecosystem the more stable it becomes, i.e. tends towards a climax community

Defences against predation
During the process of evolution, predators have evolved ways to make them more successful at catching their prey ( e.g. claws, fangs, poisons).
Similarly, prey organisms have evolved adaptations to help them avoid being caught or eaten by predators

Prey Defences
3 main adaptations:
Camoflage
- Crypsis
- Disruptive colouration
Warning Colouration
Mimicry

Camoflage
An adaptation in form , pattern , colour or behaviour which enables the animal to escape detection by predators by blending in with it’s surroundings
Two interrelated but logically distinct mechanisms for this are:
CRYPSIS : the ability of an organism to ‘blend in’ with it’s environment
DISRUPTIVE COLOURATION : allows an otherwise visible organism to remain indiscernible from the surrounding environment by ‘breaking up’ it’s outline

Cryptic Colouration
Blend into the background !
The animal's colours are a random sample of the background
Examples: peppered moths, chameleons

Disruptive Coloration
Disruptive patterns (spots/stripes/markings) break up an animal's outline
Forming a pattern that does not coincide with the contour and outline of the body makes it difficult for other animals to see it!

Warning or Aposematic Coloration
This is a form of coloration which discourages a predator from eating an organism
There is often a sting, poison, or painful bite associated to it.
Animals learn these colours by trial and error

Red, black and yellow are common colours and are called aposematic colours (meaning ‘away signal’)
Many individual share the same pattern [ convergent evolution ]
This prevents young from having to try many combinations to learn all of the animals not to eat
This convergent evolution is a form of mimicry

Batesian mimicry
Involves a palatable, unprotected species (the mimic) that closely resembles a dangerous, poisonous or protected species (the model) and therefore is similarly avoided by predators
The scarlet king snake on the left is the mimic, and the coral snake on the right is the poisonous one SCARLET KING SNAKE CORAL SNAKE "Red on yellow, kill a fellow. Red on black, won't hurt Jack."

Mullerian mimicry
Involves two unpalatable species that are mimics of each other with conspicuous warning coloration (aposematic coloration)

Grazing
Grazing is a form of INTERSPECIFIC INTERACTION
A ‘GRAZER’ = any species that moves from one ‘victim’ to another feeding on part of it without actually killing it outright e.g. grasshoppers that jump from plant to plant, chewing a portion of the leaves as they go
Grazers, like predators, can both INCREASE or DECREASE species diversity depending on the intensity of the feeding of the grazers and on the type of plant being grazed

As an ecosystem tends toward a climax community, the process can be stopped or diverted away from the natural succession
This can be unnatural by implementing agriculture OR naturally by grazing animals
Grazing animals favour grasses as these species are more vigorous competitors due to low growing points
Shrubs have meristems at the tips of shoots, which are easily eaten by grazers

Apical and Basal Meristems
Meristem = point of growth in a plant
Grasses have BASAL MERISTEMS (growing points under the soil)
Shrubs have APICAL MERISTEMS (growing points at the tips of shoots), which are easily eaten by grazers

Overgrazing
When overgrazing occurs, this prevents the build up of leaf litter
Leaf litter is important in starting bush fires by lightning. Bush fires remove the shrubs from the ecosystem, but grasses thrive as they have basal meristems
Therefore if an grassland is overgrazed, shrubs will become more dominant, thus again reducing diversity
Many shrubs are not palatable to grazers, therefore they move away from the habitat

Grassland Habitats
These habitats provide an area of land which has a huge diversity of organisms living in it
If you remove a grazing animal, e.g. rabbits in Britain, the whole diversity soon disappears as the area becomes a wooded community
Woods lack diversity of plants, which in turn effects animal diversity, thus species can be lost from the ecosystem
Woodland areas have a different soil type which is permanently changed after a wood has been there

Competition
Competition is where 2 or more organisms need the same resource , and the resource is limited
This does not always result in fighting or confrontation !
Where there is competition, one or both of the organisms will lack the resource
When the resource is required by different species, and there is a lack of the resource, then the two organism’s niche overlaps
If the resource is unlimited then the overlapping of their niche is not a problem. The GREATER the overlap in the niche the MORE CHANCE there is for competition

Interspecific vs Intraspecific competition
INTERSPECIFIC competition is competition between organisms of two different species
INTRASPECIFIC competition is competition between organisms of the same species
Interspecific competition is not as intense as intraspecific competition, due to organisms of the same species having the greatest overlap in niches

Exploitation and Interference Competition
All competitions between organisms can be grouped as EXPLOITATION or INTERFERENCE competition
EXPLOITATION is when all individuals have the equal access to the resource, but they differ in how fast or how efficiently they can exploit it
INTERFERENCE is when certain individuals are able to restrict or prevent access of others to the resource and so control the use of it

Exploitation Competition
There are two possible outcomes from this competition:
They will co-exist
One of the two will be excluded
In theory, if there is enough overlap in their requirements, one species will always have a slight advantage and will succeed at the expense of the other

Gause’s experiment with Paramecium The two species of Paramecium used by Gause grew well by themselves but P. caudium was out competed by P. aurelia when the two were grown together

Interference Competition
In this case on organism will often show AGGRESSION to prevent another organism sharing a resource, e.g. territorial behaviour of the robin. The territory contains just enough resources for the breeding pair
In plants, this can be seen in the ability for some to GROW QUICKLY and block the sunlight out for others e.g. by growing in a lateral manner

Fundamental Niche and Realised Niche
The FUNDAMENTAL NICHE is the theoretical niche containing all of the required resources for an idealistic life
This cannot exist as there a huge network of interactions with other species, and each species will try and exploit the resources
The actual resources which a population uses are its REALISED NICHE

Case Study of Barnacle populations
Semibalanus balanoides Habitat – low tide mark to the lowest high tide mark as they have little toleration to desiccation
Chthamalus stellatus Habitat – found in areas of rocks which may be exposed to air for long periods, as they can survive some period of desiccation

East Coast of Scotland

West Coast of Scotland

Resource Partitioning
Species that share the same habitat and have similar needs frequently use resources in somewhat different ways - so that they do not come into direct competition for at least part of the limiting resource
This is called RESOURCE PARTITIONING

The Competitive Exclusion Principle Early in the twentieth century, two mathematical biologists, A.J.Lotka and V. Volterra developed a model of population growth to predict the outcome of competition Their models suggest that two species cannot compete for the same limiting resource for long. Even a minute reproductive advantage leads to the replacement of one species by the other

The Damaging Effects of Exotic Species
The Rhododendron ponticum is a shrub which was introduced to Scotland
It is successful competitor in acidic soils, many soils in the Scottish Highlands are acidic
It creates a dense canopy of leaves, which shades smaller shrubs, and therefore is a good INTERFERING competitor
In its native habitat it has grazers as they have evolved together, however in Scotland the sheep and rabbits do not eat it

These invasive, non-native species are a major threat to the environment because they ...
can change an entire habitat, placing ecosystems at risk
crowd out or replace native species that are beneficial to a habitat
damage human enterprise, such as fisheries, costing the economy millions of dollars
Other examples:
The zebra mussel, accidentally brought to the United States from southern Russia, transforms aquatic habitats by filtering prodigious amounts of water (thereby lowering densities of planktonic organisms) and settling in dense masses over vast areas. At least thirty freshwater mussel species are threatened with extinction by the zebra mussel
[HANDOUT / RESEARCH]

The Importance of Survival for Weak Competitors
Species diversity is important to all ecosystems
The diversity provides flexibility when the environment changes
Therefore competitors change when the environment changes
A less competitive species survives as they can adapt its niche slightly, and therefore maintain a presence
They are a valuable reserve for an alternative ecosystem. Without an alternative, if the environment were to change then the stability of the environment would be in jeopardy

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Biotic Interactions

by musselburghgrammar

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Biotic Interactions Presentation Transcript