Transcript Predation & Competition

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
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.
Density Dependent
Density Independent
Predation
Any abiotic factor e.g.
Food
Temperature
Water
Light
Disease
pH
Space
PREDATION
• Predation is a force for natural selection
– Selection pressure
• Causes co-evolution of predator/prey
– Predator gets faster, stronger, hunt cooperatively 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
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
• camouflage
-
angler fish
lion, preying mantis
– Prey evolve to avoid predation
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
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
Avoiding Predation
– Mechanical & chemical defences
• plants contain toxins, grow spines/ thorns
• Animals secrete toxins/ bitter taste/ slimes
(slugs, frogs), grow armour (pangolin), spines
(hedgehog)
Predator Prey Interactions
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
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
Competition
• Intraspecific competition is more severe than
interspecific because the same species
compete directly for exactly the same
resource.
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.
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
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
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,)
B competes more strongly
A competes more strongly
B competes more strongly
A competes more strongly
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
Resource Partitioning
• To reduce competition between
organisms with overlapping niches,
species adapt and diverge to become
specialised for a smaller realised niche
Resource Partitioning
• 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
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
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)
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
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
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
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
Resource Partitioning
–e.g. Shore birds (beak length)
–e.g herbivores on African plains (Giraffe, Elephant &
Antelope)
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
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
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
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
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
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
Mutualism
• A biotic interaction in which both
species gain benefit
Mutualism
Species 1
Species 2
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
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
Cost, Benefits & Consequences
•INTERACTION Effect on Population Density
•Predation
Predator increases, prey decreases
•Parasitism
Parasite increases, host decreases
•Commensalism
Commensal increases, host density is unaffected
•Mutualism
•Competition
Both species in mutualism increase
Both species in competition decrease
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
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)
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
Essay
• Compare parasitic, commensalistic and

Parasitism:
Commenalism:
mutualistic
interactions, using neamed

Definition
(1)
examples.
(15)
Definition
(1)

Ecto/endo
(1)
Examples
(1)+1

Obligate/
Diffiultyfacultative
relating clear examples (1)
(1)+1

Effect
on host/
parasite
(energy) (1)
Benefits
analysis
(energy)
(1)
Evolutionary pressures
(1)
Life cycle vs host
Max.(1)
3 +1
Max. 7
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