EDNS212 | Ecosystems | Dr L Molefe
Ecosystem Structure &
Interactions
Ecosystem
§
§
It is a community (i.e., populations of different species) together with the nonliving environment.
q
In short, it is all the organisms living in a community, as well as the abiotic
factors with which they interact.
q
An example: The community of Artic fox, Caribou, Snow geese, plants (e.g.,
grass & shrubs) and their non-living environment (e.g., river water and soil).
(see next slide)
Ecosystems range from a microcosm (e.g., an aquarium [or even a cow dung]) to
a large area (e.g., lake or forest).
EDNS212 | Ecosystems | Dr L Molefe
Snow geese population
Shrubs & grass
Caribou population
Soil
River Water
The Working Ecosystem
A Community & Non-Living Environment
Herbivory
Rock with lichens
Predation
Arctic fox
Components of Ecosystem
§
§
These are abiotic (non-living components) and biotic (living components).
q
Both biotic and abiotic factors influence species distribution. For example:
• Dispersal (spread) and interactions among organisms also affect
where species live (see red kangaroo slide).
• Normally, climate (e.g., temperature) and other factors (e.g., seedling
predation by rodents, insects, etc.) affect the distribution of the saguaros
(see next slide 3).
Ecologists ask questions about where species occur and why species occur
where they do (see next slide).
EDNS212 | Ecosystems | Dr L Molefe
Ecologists ask questions about where species occur and why species occur where they do
Kangaroos/km2
0–0.1
0.1–1
1–5
5–10
10–20
> 20
Area Z
What could have influenced concentration of Kangaroos here instead of Area Z?
Freezing temperatures strongly limit
where saguaros are found. Other
abiotic and biotic factors are also
important
Components of Ecosystem
§
These are abiotic (non-living components) and biotic (living components).
q
Both biotic and abiotic factors influence species distribution. For example:
• Normally, climate (e.g., temperature & precipitation) and other factors
(e.g., light & nutrients) affect the distribution of the tiny frog (next slide)
and plants (see next slide 2).
EDNS212 | Ecosystems | Dr L Molefe
Effect of Climate
A closer look at an organism’s interaction with other organisms and the
physical environment
§
Two or more organisms’ interaction: At the ecosystem level, each organism
interacts continuously with other organisms. (see slide about the working
ecosystem)
q
These interactions may be:
• beneficial (e.g., Symbiotic relationship between bees & flowers) or
• harmful (e.g., Predation - Fox & Goose chicks [see next slide]; Parasitic
- Wasp & Dodder and Batrachochitrium dendrobatidis [see next slide 2]),
• to one or both of the organisms.
§
Organisms’ interaction with their environment: Organisms also interact
continuously with the physical factors in their environment and the environment is
affected by the organisms living there.
EDNS212 | Ecosystems | Dr L Molefe
The Working Ecosystem
A Community & Non-Living Environment
Arctic fox
Predation
Snow goose chicks
Fungi Kingdom
Plant Kingdom
Parasitic Dodder
Animal Kingdom
Merciless Wasps
Abiotic Factors
Organisms’ existence on this planet is driven by their need to survive and
reproduce. Abiotic factors affect their distribution
§
Such abiotic factors include (see next slide):
① Temperature
② Water
③ Oxygen
④ Salinity
⑤ Sunlight
⑥ Rocks and Soil
§
Most abiotic factors vary in space and time.
EDNS212 | Ecosystems | Dr L Molefe
Artic temperature & sunlight
Type of soil
Oxygen
Water salinity
River Water
Rock with lichens
Polar bear’s small and round ears
Thick layer of fur
Which abiotic factors are illustrated
On this slide?
Salamander with external gills
Thick layer of fat under skin
Temperature
§
Environmental temperature is an important factor in the distribution of
organisms because of its effects on biological processes.
q
Cells may freeze and rupture below 0°C, while most proteins denature
above 45°C.
q
Many organisms (plants and animals; see previous slide) have specific
characteristics to help them adapt to areas of extreme temperatures. For
instance, thick layer of fur and fat for insulation against the cold and for
energy storage. Small ears to reduce heat loss.
EDNS212 | Ecosystems | Dr L Molefe
Oxygen
§
§
Furthermore, certain organisms must adapt to areas of dissolved oxygen (see
salamander on salamander & polar bear slide).
They may use external gills for short-range exchange of nutrients, gases and
wastes (through diffusion) between blood and water.
EDNS212 | Ecosystems | Dr L Molefe
Which abiotic factor is illustrated below?
Organ Pipe Cacti
Xerophytes
Spines: Modified
leaves
(for protection
EDNS212
| Ecosystems
| Dr L Molefe and what?)
Spongy bones in the nose are for?
Abiotic factors
Which abiotic factor is
illustrated on the right?
Camel
Which abiotic factor is illustrated here?
“Jubilee” – A natural phenomenon that occurs sporadically on the shores of Mobile Bay. It coincides with an adaptation by
certain marine animals (e.g., small flatfish & crabs) to get more oxygen.
Water And Oxygen
§
§
§
Water availability in habitats is another important factor in species distribution.
Desert organisms exhibit adaptations for water conservation.
q For example, Cactus has small waxy leaves that reduce water loss. (See
xerophyte slide).
q For example, Camels can:
• Survive for an entire week without water (drink 32 gallons of water at
once).
• They hardly sweat.
• Their spongy nose bones absorb any excess moisture (they breathe out
dry air) (See camel slide).
Water affects oxygen availability as oxygen diffuses slowly in water. (see “Jubilee”
slide)
q
Oxygen concentrations can be low in deep oceans and deep lakes.
EDNS212 | Ecosystems | Dr L Molefe
Which abiotic factor is illustrated below?
Salmon breeding in Freshwater gravel nests
White mangrove leaf with excreted salt.
Maturity in ocean
Which abiotic factor is illustrated below?
Flamingos in the Bolivian largest salt flat in the world
What is the source of pink colour on Flamingos (click)?
Salinity
§
§
§
Salt concentration affects the water balance of organisms through osmosis.
Most aquatic organisms are restricted to either freshwater or saltwater habitats.
q Euryhaline animals: Salmon are able to migrate between freshwater and
ocean. (See previous slide 2)
q The flamingos have glands that allow them to excrete excess salts from their
nostrils (like Albatross; see next slide). They prefers shallow, salty, like
salinas that they frequent in greater numbers in winter. (see previous slide)
Few terrestrial organisms are adapted to high-salinity habitats.
q White mangrove (Avicennia marina): A halophyte that excretes excess salt
through its leaves. (See previous slide 2)
EDNS212 | Ecosystems | Dr L Molefe
Albatross
Vein
Nasal salt
gland
Artery
Secretory cell
of transport
epithelium
Lumen of
secretory
tubule
Ducts
Nasal gland
Nostril with salt
secretions
(a) Location of nasal glands
in a marine bird
Salt
ions
Capillary
Secretory tubule
Transport
epithelium
(b) Secretory
tubules
Blood flow
Salt secretion
(c) Countercurrent
exchange
Key
Salt movement
Blood flow
Central duct
EDNS212 | Ecosystems | Dr L Molefe
Epiphytic Orchid
Which abiotic factor is illustrated here?
Sunlight
§
§
§
§
Light intensity and quality (wavelength) affect photosynthesis.
Green plants distribution is likely to be more extensive in areas with higher light
intensity. NOTE: shading by leaves makes competition for light intense on the
forest floor. Thus, some plants have become epiphytic (e.g., orchid as
epiphyte). (See the previous slide)
Water absorbs light; as a result, in aquatic environments, most photosynthesis
occurs near the surface (limnetic zone occupied by phytoplankton; see next
slide).
In deserts, high light levels increase temperature and can stress plants and
animals.
EDNS212 | Ecosystems | Dr L Molefe
EDNS212 | Ecosystems | Dr L Molefe
Which abiotic factor is illustrated below?
Soil
Rocks And Soil
Many characteristics of soil limit
the distribution of plants and
thus the animals that feed on
them.
Slope
pH: Most organisms live in nearly neutral environment (pH 6-7.5). Acidic
conditions are favourable to plants such as pineapple and maize.
Coconuts grow well in alkaline condition.
Slope/gradient: May not be suitable for plants because it affects the rate
of water flow. (See above)
Above the tree line, freezing temperatures, moisture deficits and strong winds restrict the growth and survival of
trees
Which abiotic factors are illustrated here?
other
What ecological interactions are missing in this list?
Biotic Component Of
Ecosystems
Did you know that
working ecosystems
involve a lot of
interactions (see next
two slides) and
processes?
Today some authors (e.g.,
Campbell et al., 2021)
classify interactions
between species into 3
categories, namely
competition,
exploitation and
positive interactions.
The Working Ecosystem
Herbivory
Predation
Predation and/or competition
Competition
Algal cell
Fungal
hyphae
Symbiosis
Facilitation
The Working Ecosystem
Biotic Factors
§
§
Many key biotic factors involve interactions between individuals. (see the 3
previous slides)
interspecific interactions: Ecologists call relationships between species in a
community interspecific interactions. These include:
① Competition
② Predation
③ Herbivory (e.g., sea urchins can limit the distribution of seaweeds; see
next slide)
④ Symbiosis (types are parasitism, mutualism, and commensalism)
⑤ Facilitation
EDNS212 | Ecosystems | Dr L Molefe
Sea Urchin & Kelp Forest
Interactions in ecosystems
What is the other possible
interaction illustrated in the figure?
What biotic & abiotic factors
caused the even curve (see the
arrow) instead of an upward
curve?
What type of interspecific interaction is shown here?
Competition
§
§
Interspecific competition occurs when species (members on their own species
or other species; see next slide) compete for a resource in short supply, such as
food, light, space and mates.
Strong interspecific competition can lead to competitive exclusion, resource
partitioning (RP) and character displacement (CD).
q
Some scientists argue that the last two phenomena (RP & CD) provide
indirect evidence that interspecific competition probably fostered the
evolution of:
• Behaviour
• structures
• ecological differences
q
that enable species avoid it (i.e., interspecific competition).
EDNS212 | Ecosystems | Dr L Molefe
Competition Among Same & Different Species
ABOVE: Increase in Dholes (wild dogs) resulted in
increase in competition over resources (e.g., Deer as food)
ABOVE: Hyenas in competition with lions over
resources
150
100
50
Eric V. Grave/Science Source
Relative
population size
No two species
indefinitely occupy the
same niche in a
community (e.g., G.F.
Gause’s experiment in
which P. Aurelia
outcompeted P.
Caudatum)
200
B. P. aurelia alone
200
150
100
50
C. Mixed culture
Relative
population size
Competitive
exclusion principle
Michael Abbey/Science Source
Relative
population size
A. P. caudatum alone
200
150
100
50
0
2
4
6
8
10 12 14 16 18 20 22 24
Days
Two species
of paramecium
Competition
§
The competitive exclusion principle states that two species competing for the
same limiting resources cannot coexist in the same place. For them to coexist,
resource partitioning is important.
q Resource partitioning is differentiation of ecological niches, enabling similar
species to coexist in a community. (See next slide)
• An ecological niche: An organism’s ecological role. Thus, the total of a
species’ use of biotic and abiotic resources is called the species’
ecological niche.
EDNS212 | Ecosystems | Dr L Molefe
Spatial partitioning of niches
Cape May warbler
Blackburnian
warbler
Resource Partitioning in
Animals
In this case, at least half of
foraging time is spent in
each warbler designated
area of a spruce tree (i.e., its
niche)
Camel
Bay-breasted warbler
Yellow-rumped
(Myrtle) warbler
Black-throated
green warbler
Spatial partitioning of niches
Resource Partitioning in
Plants
In this case, plants reduce
level of competition by
partitioning resources (i.e.,
water & nutrients collected
at different depths).
Camel
Character displacement
Unlike the allopatric species
(geographically separate), the
sympatric type (overlapping
geographically) have varying beak
depths that favour eating differentsized seeds, hence coexistence
without competition.
Camel
Competition
§
An ecological niche: An organism’s ecological role. Thus, the total of a species’
use of biotic and abiotic resources is called the species’ ecological niche.
q Ecologically similar species can coexist in a community if there are one or
more significant differences in their niches. (See previous slide 2)
q Can removal of competition reveal the fundamental (real) niche of an
organism? (See next slide)
EDNS212 | Ecosystems | Dr L Molefe
Can species niche be influenced by interspecific competition?
Yes (see the results of an experiment on 2 barnacles – Chthamalus and Balanus)
Control: No treatment.
Treatment 1: Remove Balanus. In
Treatment 2: Remove Chthamalus.
Chthamalus occupies only shallow
water and Balanus occupies only
deep water.
the absence of Balanus,
Chthamalus occupies both shallow
water and deep water.
In the absence of Chthamalus, Balanus
still occupies only deep water.
High tide
Chthamalus
Low tide
Balanus
Realized (potential)
niche
Fundamental
niche of
Chthamalus
Fundamental
niche of
Balanus
Fundamental (actual)
niche
Competition
§
§
Resource partitioning is differentiation of ecological niches, enabling similar
species to coexist in a community.
The common spiny mouse and the golden spiny mouse show temporal
partitioning of their niches.
q Both species are normally nocturnal (active during the night).
q Where they coexist, the golden spiny mouse becomes diurnal (active
during the day).
EDNS212 | Ecosystems | Dr L Molefe
Temporal partitioning of niches
The Diurnal Golden Spiny Mouse
(Acomys russatus)
Predation
§
§
§
§
Predation: It is the consumption of one species (prey) by another (predator).
Note. Some people argue that herbivory can be considered as (herbivorous)
predation. Do you agree?
Some feeding adaptations of predators are:
q
Claws and/or teeth (e.g., lions, honey badger, etc.).
q
Fangs that inject poison (e.g., spiders & snakes).
q
Stingers (e.g., bees, jellyfish, etc.).
Prey display various defensive adaptations: Behavioral defenses include
hiding, fleeing, forming herds or schools, *self-defense (e.g., *Cobra, now as
prey), and alarm calls.
EDNS212 | Ecosystems | Dr L Molefe
Honey Badger Against Reptiles
Predation
Morphological & Physiological Defense Adaptation
§
Animals also have morphological and physiological defence adaptations. For
example:
q
Camouflage (cryptic colouration) makes prey (e.g., grasshoppers) or even
predators themselves (e.g., spiders) difficult to spot and, hence survive. (see
the next two slides)
• Camouflage & survival formed the basis for Thayer’s (1909) (American
painter & Life Scientist) theories (click) about evolution and colour, which
made him famous.
q
Do you think Thayer missed what was also important in ecosystem
interactions – colour in sexual selection? (see the third slide)
EDNS212 | Ecosystems | Dr L Molefe
Katydids
(long-horned grasshopper)
It resembles insect-damaged leaves
(camouflage).
Thus, it survives as it doesn’t attract
the attention of predators.
Note. Also included are other preys
that are camouflaged..
Camel
Camouflage And Survival
(Prey)
What is the predator here?
And the prey is?
What adaptations enabled the predator successfully prey on its prey to survive?
Camouflage And Survival
(Predator)
The great Frigate
bird
(pictured)
Males inflate their
red-coloured throat
pouches to attract
females
Survival And Reproduction
The importance of colour in sexual reproduction
§
Thayer (1909) argued that camouflage (protective colouration)
had been an essential factor (for survival) in evolution. He was
praised for this view.
§
Thayer, however, missed the importance of colour in sexual
selection, that is, colour’s importance in evolution in relation to
attracting mates (click) for reproduction.
Survival And Reproduction
What do you think Thayer missed about colour that was also important
in human being interactions?
What else (apart from colour) is important (see previous & next slides)?
Survival And Reproduction
The importance of colour in sexual reproduction in plants
§
Do you know why angiosperms are the most successful terrestrial plants?
q
q
Flower colour: Did you know that bees find blue, purple (pictured) and yellow flowers most appealing
(see Gardeners.com., 2017)?
Flower morphology: Did you know that flat or shallow blossoms, such as daisies (pictured), zinnias,
asters and Queen Anne's lace, attract the largest variety of bees (Gardeners.com., 2017)?
EDNS212 | Ecosystems | Dr L Molefe
Predation
Mechanical and Chemical Defense Adaptations
§
§
Mechanical and chemical defences protect species such as porcupines and
skunks. (see [a] and [b] on next slide)
Animals with effective chemical defence often exhibit bright warning colouration,
called aposematic colouration. (see [c] on next slide)
q
Predators are particularly cautious in dealing with prey that display
such colouration.
EDNS212 | Ecosystems | Dr L Molefe
(a) Mechanical
defence
Porcupine
(b) Chemical
defence
Skunk
Quills released on contact
Nauseating thiols odour & memorable colour
(c) Aposematic colouration:
warning colouration
(d) Cryptic
colouration:
camouflage
Poison dart frog with alkaloid toxins in skin glands
(e) Batesian mimicry:
A harmless species
mimics a harmful
one.
Green parrot snake
(venomous)
(f) Müllerian mimicry:
Two unpalatable
Yellow
species mimic
jacket wasp
each other.
Cuckoo bee
Hawkmoth larva
EDNS212 | Ecosystems | Dr L Molefe
Canyon tree frog
Predation
Mimicry (imitation)
§
§
In some cases, a prey species may gain significant protection by mimicking the
appearance of another species.
Examples:
q
In Batesian mimicry (after English Life Scientist), a palatable or harmless
species mimics an unpalatable or harmful model. (see next slide)
q
In Müllerian mimicry (after German Zoologist), two or more unpalatable
species resemble each other. They are already distasteful. Thus, their
colour is an added advantage that makes common potential predators
avoid both (see next slide 2)
EDNS212 | Ecosystems | Dr L Molefe
A harmless scarlet king snake looks so much like a venomous coral
snake (below) that predators may avoid.
Hawk moth larvae (left above) behaves like a
venomous green parrot snake: It hisses & moves
its head like the snake.
Müllerian mimicry in action
Is mimicry (click) more than just a defense mechanism?
When attacked
by damselfish
It can also imitate a crab
to feed on it
Defense against
visual predators
Startle Response by certain butterflies and moths
This mechanism is used when camouflage fails.
The moth (left) normally flashes eyespots on its wings (confused by predators as an owl [right]),
startling the predator, and giving the moth a chance to make its escape.
Is this behaviour by the owl an example of startle defense?
Herbivory
Mechanical and Chemical Defense Adaptations
§
§
Herbivory refers to an interaction in which an herbivore eats parts of a plant or
alga.
Herbivory has led to the evolution of:
q
Plant mechanical defences. For example, Cactus spines.
q
Plant chemical defences. For example, Milkweed death-causing alkaloids &
cardiac glycosides, and the skunk-like scent of skunk cabbage flowers.
q
Adaptations by herbivores. For example, monarch caterpillar. (See the next
3 slides)
EDNS212 | Ecosystems | Dr L Molefe
Skunk Cabbage
Did you know that:
§
The scent of skunk cabbage may be enough to keep herbivores away?
§
It is primarily pollinated by various types of flies? Why is it visited by bees, beetles and other
insects?
§
It is one of just a few plants that exhibit thermogenesis (the ability to metabolically generate heat, by
cyanide-resistant cellular respiration)?
§
It was used medicinally by Native Americans and in the 19th century was listed in the U.S.
Pharmacopoeia as the drug “dracontium” for the treatment of respiratory diseases, nervous disorders,
rheumatism, and dropsy.
Spines: Mechanical defense
Chemical Defense
Milkweeds produce alkaloids and cardiac glycosides that are poisonous to all animals except, for instance,
monarch caterpillars
Male
Female
Adaptation by herbivores
Monarch caterpillars can tolerate milkweed toxins. Their tissues accumulate the toxins, making them poisonous
too. Their colour normally warns predators.
§
The two interactions involve the consumption of organisms.
§
Food for thought
It is believed that “Herbivory is a form of predation in which the prey
organism is a plant” (Khan Academy, n.d.; emphasis added). Do you agree?
Can plants (click) be predators (click)?
EDNS212 | Ecosystems | Dr L Molefe
Symbiosis
In a symbiotic relationship, two or more species live in direct and intimate contact
with one another. Such a relationship can either be mutualistic, parasitic or be
referred to as commensalism
Parasitism
In parasitism, one organism (i.e., the parasite) derives nourishment from another
organism (i.e., its host), which is harmed in the process.
§ Parasites that live within the body of their host are called endoparasites. (e.g.,
Tapeworm, Jewel wasp larva [see next slide], etc.)
§ Parasites that live on the external surface of a host are ectoparasites. (e.g.,
ticks [see next slide 2], mosquitoes, Jewel wasps, etc.).
EDNS212 | Ecosystems | Dr L Molefe
Parasitoid jewel wasp (Ampulex compressa)
An adult wasp stings a cockroach into the head to
manipulate the cockroach behaviour.
Parasitism 1: The wasp then cuts the cockroach’s
antennae to drink hemolymph, and then leads the stung
cockroach into a nest to lay an egg on its cuticle.
Parasitism 2: The hatching larva feeds on the cockroach and pupates inside its
abdomen. It then emerges roughly 30 days later.
: Parasitism
: Parasitism
Brood parasitism
A cowbird chick with its foster parent. A female cowbird minimizes her cost of parental care by laying her eggs
in the nests of other bird species
A. Ticks sucking blood from a finch
B. Dodder (Cuscuta): Roots that extend from the leafless golden stems withdraw water and nutrients from
another plant
What type of interspecific interaction is illustrated here?
What type of interspecific interaction is illustrated here?
Why?
Why?
: Mutualism - Obligate
q Mutualistic symbiosis (mutualism) is an interspecific interaction that
benefits both species.
§
Mutualism can be:
q Obligate, where one species cannot survive without the other.
• Example: Persian violet flowers (PVF) and bumblebees.
• Only bumblebees can feed on pollen from PVF. In return, their buzz
pollination helps PVF get exclusive pollination.
• Example: Mycorrhizae – a mutualistic association between fungi and
roots of plants.
• Mycorrhizal fungi supply plants with essential minerals (e.g.,
phosphorus) from soil; plant supplies fungi with organic molecules
produced by photosynthesis.
EDNS212 | Ecosystems | Dr L Molefe
: Mutualism - Facultative
q Mutualism is an interspecific interaction that benefits both species.
§
Mutualism can be:
q Facultative, where both species can survive alone.
• Example: Crocodile & Egyptian plover.
• The bird feeds on small pieces of meat stuck between crocodile’s teeth.
• Example: Flowers and bees.
• The bees feed on nectar and the flowers get pollinated.
EDNS212 | Ecosystems | Dr L Molefe
: Mutualism - Defensive
Ants *remove fungal spores
Ants *attack herbivores on acacia tree
Ants feed on acacia tree *nectar
Area *cleared by ants around an acacia tree
Hollow thorns that *house stinging ants of the genus Pseudomyrmex
Defensive mutualism between acacia trees and ants
: Commensalism
In commensalism, one species benefits and the other is neither harmed nor
helped
§
Commensal interactions are hard to document in nature because any close
association likely affects both species.
q
Example: Finches and trees - trees provide protection against predators and
floods. (see next slide)
q
Example: Orchids and trees - they need trees to grow higher to get more
sunlight essential for photosynthesis. (see next slide)
q
Example: White egrets and buffalo - insects driven by grazing buffalo are
eaten by these birds. (next slide 2)
EDNS212 | Ecosystems | Dr L Molefe
Orchid As Epiphyte
Symbiosis: Commensalism
Weaver finches building nest on a tree
Egrets occasionally feed on ticks & warn of approaching predators
Is this commensalism?
: Commensalism
§
§
It is an interaction in which one species has positive effects on another species
without direct and intimate contact.
q
For example, the black rush (Juncus gerardii) makes the soil more
hospitable for other plant species.
Food for thought
It is believed that commensalism is a specific type of facilitation (Munguia et
al., 2009). Do you agree?
EDNS212 | Ecosystems | Dr L Molefe
Facilitation
The black rush makes the soil more hospitable
for other plant species.
It helps in *salt balance in salt marshes.
Also helps in *oxygen balance in salt marshes with its underground tissues.
Seaside sparrows & rice rats also *nest in it
Number of plant species
8
6
4
2
0
EDBS220
- Structure
Of Ecosystems Salt marsh with the black rush (Juncus
gerardii)
(above)
Ecosystems|Communities|LM
EDNS212
| Ecosystems
| Dr L Molefe
Molefe
Leonard M Molefe
With
Juncus
Without
Juncus
Barley within clumps of Laretia acaulis
Chickweed within clumps of Laretia acaulis
Facilitation
Laretia acaulis also display facilitation interaction. It increases survival rate of certain nearby plants.
How many interspecific interactions are illustrated in the figure?
Name Them.
Predator
Ignore
the fly
Prey
Flower