1. BIOTIC INTERACTIONS Three Categories of interactions
Predation
Competition
Symbioses
As a result organisms evolve (change):
develop to maximise the benefit of their interaction (minimise the disadvantage)
Intraspecific
Between individuals of the same species
Interspecific
Between individuals of different species

2. Density Dependence/ Independence
Density dependent – the severity of the effect increases as the population size increases.
Density independent – the severity of the effect is the same irrespective of the population density.

3. Density Dependent
Density Independent
Predation
Any abiotic factor e.g.
Food
Temperature
Water
Light
Disease pH
Space

5. PREDATION Predation is a force for natural selection
Selection pressure
Causes co-evolution of predator/prey
Predator gets faster, stronger, hunt co-operatively etc.
Prey gets faster, form herds, modify behaviour/ physical characteristics
Grazing is classified as a predation?!
Grazing promotes biodiversity by selectively reducing dominant (more frequently encountered) species
VIDEO

6. Predation Predators are adapted to enhance their success:
have highly evolved senses
sight – eagles/ cats
smell – anteaters, pigs
Infra red (rattlesnake), hearing – owls
echo location – bats, electrical – sharks, platypus
Predators can cooperate (lions, army ants, chimpanzees)
Allow exploitation of resources beyond the capability of a single individual of the species
Predators can also use:
mimicry - angler fish
camouflage - lion, preying mantis
Prey evolve to avoid predation

7. Avoiding Predation Prey can use: behavioural adaptations
hiding (fish on coral reefs)
running away (antelope from lion, seal from killer whale)
mobbing (kittiwake on gulls)
herding (musk ox)
distraction displays (plover broken wing, butterfly eyes on tail)
Active defence
fight back (water buffalo/ gnu mothers)
Camouflage (crypsis)
animal is coloured to merge into background
e.g. stonefish, chameleon, stick insect

8. Avoiding Predation Prey can use: Aposematic (warning) colouration
Animals advertise their toxicity
wasps & bees yellow & black
Mimicry – one organism resembles another
Batesian mimicry
a harmless species mimics a toxic one
Hoverfly looks like a wasp
need more wasps than hoverflies otherwise predators learn yellow & black is not toxic. (but see below)
Mullerian mimicry
two or more aposematically coloured species develop similar warning colouration
e.g. bees & wasps
warning signal is greatly reinforced by such large numbers showing the same warning

9. Avoiding Predation Mechanical & chemical defences
plants contain toxins, grow spines/ thorns
Animals secrete toxins/ bitter taste/ slimes (slugs, frogs), grow armour (pangolin), spines (hedgehog)

10. Predator Prey Interactions

11. Predator prey Interactions
Cyclical oscillations in predator population reflects cyclical oscillations in prey population
Carrying capacity = population which can be supported by the ecosystem
As snowshoe hare population increases
carrying capacity (lynx) of ecosystem increases - more food available
Lynx population increases
hare population eventually exceeds carrying capacity of the ecosystem (food, space run out)
population (hare) crashes
lynx population no longer has sufficient food resource
consequently lynx population crashes
Grass (hare food) population would peak BEFORE the hare population
FIRST in food chain peaks FIRST in cycle
NB the predator DOES NOT usually control prey population, it is a species’ food supply which controls its population size

12. Competition Resources are limited (e.g space, food, water)
The ability of organisms to gain resources will determine their success.
As the density of population increases competition becomes more severe
Some organisms are more effective at securing resources
Those are successful, survive and reproduce
Less successful organisms perish
Competition causes natural selection
Species change (evolve) to reduce competition

13. Competition
Intraspecific competition is more severe than interspecific because the same species compete directly for exactly the same resource.

14. Galapagos Finch- fortis
                                                  
Fortis eats seeds.
During drought big tough seeds are all that are available to eat
Big beaks make this easier
Prior to drought average beak was 10,68mm long and 9.42 mm deep
After a drought period, average beak length 11.07mm long and 9.96mm deep
Competition for food caused nearly 6% change in beak shape in one year.

15. Two types of Competition
Exploitation competition - occurs indirectly through a common, limiting resource, which acts as an intermediate. For example the use of the resource(s) depletes the amount available to others, or they compete for space.
e.g grey/ red squirrel food;
e.g.
Interference competition - occurs directly between individuals via aggression etc. when the individuals interfere with foraging, survival, reproduction of others, or by directly preventing their physical establishment in a portion of the habitat.
e.g ant & Rattan & herbivores
e.g ant, acacia & giraffe
Private life of Plants- Living Together
8 min in Ant & Rattan
9.5 min in Ant Acacia & Giraffe

16. Niche
A niche is an organism’s position within an ecosystem described in terms of abiotic and biotic interactions:
abiotic interactions (i.e. mineral needs/ pH tolerance, moisture/temperature range)
The larger the range of physical conditions tolerated, the wider the niche and more widespread the organism is
biotic interactions (i.e. position in the food chain, diversity of food sources exploited, diversity of species which exploit it as a food source)
The greater diversity of these interactions the more widespread the organism
Within an ECOSYSTEM no two organisms can occupy the same niche

17. Competitive Exclusion Principle
Two organisms cannot coexist sharing the same niche in an ecosystem.
They will compete, one will be more successful and the second will become extinct.
Experimentally demonstrated using Paramecia species (Gause,)

18. B competes more strongly
A competes more strongly

19. B competes more strongly
A competes more strongly

20. Fundamental & Realised Niche
The fundamental niche is the entire range of abiotic & biotic parameters an organism can survive within.
Fundamental niches can overlap
Realised niche is the actual range of parameters within which the species occurs.
Realised niche can be smaller than the fundamental niche
Realised niches cannot overlap
Species cannot share exactly the same resources
Competition would lead to the exclusion of one of the two species occupying the same niche
Adaptations of species is such that they are best suited to a subset of their fundamental niche parameters
e.g. barnacle zonation on the shore

21. Resource Partitioning
To reduce competition between organisms with overlapping niches, species adapt and diverge to become specialised for a smaller realised niche

25. Resource Partitioning
e.g. Cormorant/ Shag
Cormorant nests high on cliffs or broad ledges
Shag –nests on shallow ledges, low on cliffs
Cormorant – feeds on mixed diet no sand eels/ sprats
Shag – Eats mostly sand eels/ sprats

26. Importance of Niche overlap
Within a population some individuals are adapted to living at the extremes of the niche
i.e. they are adapted to conditions slightly different to those currently found in the ecosystem
such organisms will survive, albeit less successfully, in the overlap of niches
This variability within a population is vital for allowing a species to survive change
These weaker individuals may have traits ideally suited to the new conditions

27. Alien Species Realised niches cannot overlap
Indigenous species are adapted to exploit niches within their home ecosystem, and resist competition from other indigenous species
A new species (alien, exotic or introduced) may:
Prey on other species in the ecosystem, not adapted for defence against their predation
Compete more effectively for resources, ousting an indigenous species from a niche
Be immune from natural biological control mechanisms so grow unchecked
Introducing species, particularly to islands can cause grave harm to the established species (extinction)

28. Alien species prey on defenceless animals
Examples
Hawaiian Islands
Hawaii’s endemic moths destroyed by introduced parasitic wasps
Hawaii’s plants threatened by seed & fruit predation by rats
Hawaiian native snails threatened by introduced snails
Hebrides
Hedgehogs eat eggs of ground nesting birds

29. Alien species grow unchecked
Australia
Cacti are not native to Australia
Prickly pear (S. America) grows unchecked, not natural predator
Native plant species are ousted (no space)
1925, Cactoblastis (moth), lays its eggs specifically on the cactus and larvae burrow in causing bacterial infection
Good biological control

30. Alien species grow unchecked
Australia
Rabbit rapid reproduction & poor control by predators
Population explosions occur
Eat grass
Myxomatosis introduced as biological control in 1950’s
Similar explosions seen with mice

31. Alien species steal Niches
Example
Hawaiian Islands
Ants are not native to Hawaii
Their introduction has led to loss of endemic flightless fly which previously filled the niche
now occupied by ant

32. Resource Partitioning
e.g. Shore birds (beak length)
e.g herbivores on African plains (Giraffe, Elephant & Antelope)

33. Symbiosis Symbiosis = living together
Two species form a close relationship
They co-evolve to maximise the benefits from their interactions (parasitism only one species benefits)
Three types of symbioses:
Parasitism
Commensalism
Mutualism

34. Parasitism
The symbiont (the parasite) benefits, the host (parasitised) loses
Two forms of parasitism:
Ectoparasite – live externally on the host
e.g. ticks & fleas, leeches,
Endoparasite – live inside the host
e.g. malaria, tapeworm, hookworm,
most gut bacteria are not parasites

35. Parasite transmission
Transmission is:
vertical (mother to baby – HIV, rubella)
horizontal (amongst members of species)
direct close contact – cold, measles
sexual contact – HIV, syphilis
indirect contact – polio, cholera (through water)
vector contact – malaria, sleeping sickness
Parasites develop ingenuous strategies to transfer between host
Often complex multistage , multihost life cycles involved

36. Pinworm Human gut parasite
Eggs transferred into mouth (oro-faecal transmission)
Develop and grow in small intestine
Warm, moist, good food supply
Once mature females fill with eggs
Migrate to anal region
In evening/sleep, migrate out of anus, lay eggs perianally (around anus)
Secretion causes irritation/ redness of perianal region (pruritus ani)
Host scratches irritation
Poor hygiene allows transfer of egg into mouth

37. Important aspects of host- parasite interactions
Parasites adapt to improve effectiveness of parasitism
Obligate parasites – must live as a parasite
Facultative parasites – can live as parasites when host is alive, but switch to saprophytes once host dies
Hosts adapt to counter parasitism
immune system
preening behaviour
plants produce defensive chemicals, galls develop to seal off parasite from rest of host
Escalation of “war” leads to specificity in host/ parasite relationships
e.g. smallpox virus, fleas

38. Commensalism A biotic interaction between two species
one species benefits, the other is UNAFFECTED
Difficult to find clear examples
Lichen on a tree is possibly one case
Where carriage is provided e.g. hermit crab & anemone, energy is expended in transporting the anemone,
But hermit crab appears to benefit because it actively replaces the anemone when removed – likely mutualism
In the nitrogen cycle, Nitrobacter depends on Nitrosomonas for its nitrite
The two species otherwise live entirely independently in the soil

39. Mutualism A biotic interaction in which both species gain benefit
Ant & acacia
Ant – gains secure home, food supply
Acacia – gains protection from predation
Coral & Algae
Coral – gains carbohydrate from photosynthesis
Algae – protection and mineral nutrients
Mycorrhizae & plants
Mycorrhiza – gains photosynthetic product
Plant – improved mineral and water absorption
Ruminant herbivore & bacteria
Ruminant - gets its food digested
Bacteria – gains protection, warmth, moisture & food
Lichen
Fungus – photosynthetic products
Algae – gains water, minerals and structural support
Rhizobium and legumes
Rhizobium – gains photosynthetic product
Plant – gains nitrate for protein synthesis

40. More on Rhizobium
Rhizobium responsible for N fixation in nodules on roots of legumes
Nodules form as a result of interaction between bacteria and root hair cells
90% of fixed nitrogen passes to plant
plant gives carbohydrate to bacteroids
Enzyme involved is NITROGENASE
Rhizobium produces NITROGENASE
However nitrogenase is poisoned by OXYGEN
The PLANT produces a protein which binds the oxygen and prevents NITROGENASE being poisoned
leghaemoglobin traps oxygen

41. Cost, Benefits & Consequences
INTERACTION Effect on Population Density
Predation
Parasitism
Commensalism
Mutualism
Competition
Predator increases, prey decreases
Parasite increases, host decreases
Commensal increases, host density is unaffected
Both species in mutualism increase
Both species in competition decrease

42. Effect of External factors
Quantitatively, the outcome of a species interaction is determined by:
Biotic factors e.g. disease, food availability
Abiotic factors e.g. temperature, water availability
If there is a pre-existing stress, negative interactions are more damaging.
Humans further complicate the interaction by using medicines, fertilisers, pesticides & herbicides to alter the consequences of species interaction between ourselves and our crops

43. Coral Bleaching Coral is dying in a number of areas around the world
bleaching – when coral dies it turns white
death is due to loss of algal mutualism
this due to increase in sea temperatures (1ºC)

44. Competitive Exclusion
In closed conditions
Competition between two species will lead to the exclusion of one of the species
The triumphant species will ultimately depend on the conditions within the system
In real ecosystems, competition may lead to the exclusion of a species through most of its range
Local conditions may allow pockets of reduced density to survive, because they are better suited to these local conditions
Should conditions change to favour the outcompeted species these pockets are sources from which the species can migrate and colonise its former range

45. Essay
Compare parasitic, commensalistic and mutualistic interactions, using neamed examples. (15)
Parasitism:
Definition (1)
Ecto/endo (1) +1
Obligate/ facultative (1) +1
Effect on host/ parasite (energy) (1)
Evolutionary pressures (1)
Life cycle vs host (1) +1
Max. 7
Commenalism:
Definition (1)
Examples (1)
Diffiulty relating clear examples (1)
Benefits analysis (energy) (1)
Max. 3

46. Keystone species
A keystone species is one whose removal will have an extremely detrimental effect on the community
e.g. The removal of sea otter from californian kelp forest