Transcript What determines where particular species live and how many of

Biotic Interactions in Ecosystems
AH Biology
Unit 2 Environmental Biology
The Five Laws of Ecology:
• Everything is connected to everything else.
• Everything has to go somewhere or there is no
such place as away.
• Everything is always changing.
• There is no such thing as a free lunch
• Everything has limits.
Everything is connected
Biotic and Abiotic Interactions
• Abiotic - Non living factors
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Temperature
Light intensity
Soil pH
Availability of water
Availability of minerals
• Biotic – living factors
– Competition
– Predation
– disease
Density dependent and density
independent factors
• Density dependent factors
– Effect increases of population density increases
– Population level off, then decrease
– Example - availability of food
• Density independent factors
– Effect independent of the size of the population
– Example – forest fire
Biotic Interactions
• Interspecific interactions
– Between individuals of different species
• Intraspecific interactions
– Between individuals of the same species
• Which type of interaction is more intense,
interspecific or intraspecific? Why?
Biotic Interactions
• Predation
• Grazing
• competition
predation
• Patterns of predator prey interaction
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Stable coexistence
Cyclical variations
Erratic swings
Extinction of prey species
• Important factors to consider
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Carrying capacity of the habitat
Reproduction rate of prey
Reproduction rate of predator
Degree of flexibility of predator to switch prey
Cyclical Variations
Exercise
• Convert the information in the table into a
graph to illustrate any patterns that may exist.
• Label and number the axes clearly
• Decide how to represent the populations of
hare and lynx on the same graph.
Population numbers in the lynx
and snowshoe hare
year
Population of hare
(thousands)
Population of Lynx
(thousands)
1845
12
22
1850
10
39
1855
63
6
1860
72
21
1865
139
3
1870
3
60
1875
62
4
1880
83
35
1885
120
63
1890
12
10
1895
70
40
1900
10
5
1905
68
43
1910
20
2
1915
60
23
Snowshoe hare and
lynx
Your graph should look something like this
Describe and explain the patterns shown by the graph
Role of Predators in maintaining
diversity
• By removing prey who are strong competitors,
weaker competitors can survive
• Reduce effect of competitive exclusion
• The ecosystem benefits from
– Increasing species diversity
– Increasing stability
– The ability to adapt to environmental change
• Examples where removing predators has
collapsed an ecosystem
– Otters and the sea kelp forests
Prey defenses to predators
Back
• Camouflage
• Warning (aposematic)colouration
– Red, black and yellow are aposematic colours
• Mimicry
– Batesian
– Mullerian
• Watch the video “predators and prey”
– Make notes on adaptations of prey to escape
from predators.
Grazing
• A grazer is defined as
– Any species that moves from one victim to
another, feeding on part of each victim
without actually killing it outright
• E.g. eating a shoot or a limb
• Can increase or decrease species
diversity depending on grazing pressure.
Grazing of Vegetation
Back
• Plant species with basal meristems can be
grazed without suffering mortality
• Plant species with aerial meristems can be
eliminated by grazing when the aerial part is
removed.
• Grassland is often referred to as a
plagioclimax, where a diversion deflected
succession off course to reach the natural
climax community e.g. fire, grazing, mowing
Competition
• Exploitation competition
– Consumer significantly reduces the resource
• Interference competition
– One species prevents individuals from another from using a
resource
• Competitive interactions can:
– Short term – variations in abundance and distribution
– Long term – evolutionary adaptations to improve
competitive ability
Styles” of Competition
• Exploitation competition
– occurs when individuals use the same limiting
resource or resources, thus depleting the amount
available to others.
• Interference competition
– occurs when individuals interfere with the foraging,
survival, or reproduction of others
– directly prevent their physical establishment in a
portion of a habitat.
Niche
• The sum of
– An organism’s adaptations
– The resources it needs
– The lifestyle to which it is fitted
• Gause’s principle of competitive exclusion
– Paramecium aurelia and P. caudatum Experiments
– Fundamental niche
– Realised niche
Principle of Competitive Exclusion
• When cultured together Paramecium aurelia has
a competitive advantage over P. caudatum for
gaining food.
Fundamental and Realised Niches
Introduction of “exotic species”
• Rhododendron ponticum - Scotland
– Dense canopy
– Leaves contain toxins
• Nile Perch – Lake Victoria
– Carnivourous fish eating species
• Rabbits and Prickly Pear cactus – Australia
• Hedgehogs – Outer Hebrides
• Rats – New Zealand
Importance of survival of weaker species
• Species diversity is essential
• If environmental conditions change,
– The dominant species may no longer be the best
adapted and die out
– This gives the weaker competitors who are better
adapted a chance to increase in number
• E.g. extinction of the dinosaur and the
emergence of mammals
Essay Question – 15 marks
Give an account of
interactions
between predators
and their prey
Symbiotic relationships
AH Biology
Unit 2 Environmental Biology
Learning Objectives
• Describe parasitism as beneficial to one species but
harming the other
• Explain the relationship between the host and the
parasite
• Describe modes of parasite transmission
• Describe commensalism as beneficial to one species,
leaving the other unaffected
• Explain commensalistic relationships
• Describe mutualism as beneficial to both species
• Explain mutualistic relationships
Symbiosis
• “the living together of two or more different
species of organism”
• 3 categories of symbiotic relationships
– Parasitism
– Commensalism
– Mutualism
Parasitism
• Relationship that is beneficial to the parasite
but is often damaging to the host species
• Ectoparasite
– External e.g. ticks, fleas and leeches
• Endoparasite
– Internal e.g. tapeworm, Trypanosoma, Plasmodium
• Obligate parasites
– Must live parasitically
• Facultative parasites
– Does not need to live parasitically
– E.g fungi can become saprotrophic if host dies
Parasite transmission
• Direct contact
• Production of resistant stages
• Use of vectors
– Trypanosoma and the tsetse fly
– Plasmodium falciparum and mosquito
Host-parasite evolution
• Development of a parasitic infestation is
countered by host (immune) reactions
• The parasite then further adapts
• Cyclical evolutionary war
– Increasing host specificity the longer the
relationship has existed
• Parasites may evolve to move from the host
to its predator
Commensalism
• Relationship is beneficial to one species
(commensal), the other species is unaffected by the
relationship
• Examples
– Egrets and grazing mammals
– Hitchhiking species (energetic consequences?)
– Clownfish and sea anemone
• It is hard to find strict examples of commensalism as it
is unlikely one species in a relationship will be
unaffected by the other
Mutualism
• Both organisms benefit from the interaction.
• Co-evolved mutualistic relationships
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Plants and micro-organisms
Protists and fungi (lichens)
Terrestrial plants and insects
Animals and protists
Animals and other animals
Interactions in coral reefs
• Evolution
– Development of inter connected structures, behaviours,
physiologies and biochemistries.
Essay Question
Compare parasitic,
commensalistic and
mutualistic interactions,
using named examples of
each.
The costs, benefits and
consequences of interactions
between species
AH Biology
Unit 2 Environmental Biology
Learning objectives
• Describe positive, negative and neutral interactions
between species
• Describe symbiosis as a relationship in which at least
one species gains a positive interaction
• Explain the effects of host health and environmental
factors in changing the balance in symbiotic
relationships.
• Explain the management of these effects by the
human species in promoting human, animal and plant
health and the quality of the host environment.
• Describe the tolerance and compensation mechanisms
for coping with variation in the environmental
conditions.
Interactions between species
Interaction
Effects on population density
Beneficial to one species (predator)
Predation
and detrimental to the other (prey)
Beneficial to one species (parasite)
Parasitism
and detrimental to the other (host)
One species benefits (the commensal)
Commensalism
while the other is largely unaffected
The interaction is beneficial to both
Mutualism
species
The interaction is detrimental to both
Competition
organisms
Host health and environmental
factors
• The delicate balance that is the consequence of
most symbiotic relationships is affected by both biotic
(host health) and external factors (environmental
conditions).
• Host health
– Healthy hosts are able to tolerate parasites presence
– Influenced and managed by the use of pesticides or drugs
that alter the balance of the parasitic relationship in favour
of host species.
• Environmental conditions
– E.g. coral bleaching
• Competition – negative interaction for both species
• Symbiosis – at least one species gains a positive
interaction
Interactions with the
environment
• All organisms must be able to make internal
adjustments in response to external changes
in conditions
– External – constant flux
– Internal – range that must not be exceeded.
• Organisms responses
– Resist or tolerate
– Regulation (homeostasis)
– Avoidance / migration
Behavioural responses
• Changes in an organism’s behaviour which
help them to survive changes in their
environment.
• Examples
– Desert mammals
• Nocturnal
• Live in burrows during day
– Hibernation or migration to avoid low
temperatures
Physiological responses
• Changes in a way an organism’s body
functions to enable it to survive in changing
circumstances.
• Organism can show a certain tolerance to its
environment
• Homeostasis
Essay question
Give an account of the
costs, benefits and
consequences of
interactions between
species, including human
involvement.