Community Ecology is the study of interactions among all populations in a common environment. Species Interaction is a traditional approach to population interactions has been to consider the direct pair wise interactions. Two populations may or may not affect each other; if they do, the influence may be beneficial or adverse Types of Population Relationships: Interspecific interactions: Competition and Coexistence Predation Mutualism Commensalism Intraspecific Interactions Grasshoppers provide an animal example. Individual grasshoppers deprive their fellow conspecifics of food (exploitation competition). It is probably a major factor involved in the evolution of plumage patterns in birds. during intraspecific competition, animals will use whatever weapons are available to them and this makes it likely that the nature of the weapons determines the nature and location of patterns.

1. BIO104
LEC6
COMMUNITY

2. Community Ecology biosphere
ecosystem
community
population
organism

3. Community Ecology
 Community
 all the organisms that live together in a place
 Community Ecology
 study of interactions among all
populations in a common
environment
 Answers the Q:
 In what ways do populations
interact?

4. SPECIES INTERACTION:
The HEART of ECOLOGY

5. Definition of terms
Community – all the organisms that live
together in one place
Community ecology – study of interactions
among all populations in a common
environment.
Interspecific interactions – among individuals of
the different species.
Intraspecific interactions – among individuals of
the same species.

6. Species Interaction…
A traditional approach to population
interactions has been to consider the direct
pair wise interactions.
Two populations may or may not affect each
other; if they do, the influence may be
beneficial or adverse.

7. Designations:
(-)  detrimental effect
(+)  beneficial effect
(0)  no effect

8. Types of Population Relationships
Interspecific interactions:
– Competition and Coexistence
– Predation
– Mutualism
– Commensalism
How about:
– Amensalism?
– Altruism?

9. Intraspecific Interactions
– Grasshoppers provide an animal example. Individual
grasshoppers deprive their fellow conspecifics of food
(exploitation competition).
– It is probably a major factor involved in the evolution of
plumage patterns in birds.
during intraspecific competition, animals will use whatever
weapons are available to them and this makes it likely that the
nature of the weapons determines the nature and location of
patterns.

10. Direct Pairwise Interactions between 2 populations:
Competition and Coexistence
Predation
Mutualism
Commensalism
(Amensalism)

11. Competition
(-,-)
it can be interspecific or intraspecific
this takes place when each of two populations
affects the other adversely
both require the same resource/s that is/ are in
short supply.

12. Two Mechanisms of Competition
1.Exploitation competition
– organisms use up resources directly.
– Once used, the resource is no longer available for other
species.
– More common mechanism
2.Interference interaction
– one organism prevents other organisms from using the
resource.
– can occur, particularly where the resource is "patchy" -
only occurring in discrete patches - and thus able to be
defended.

13. Competition…
Territorial animals: some individuals actively prevent
others from exploiting a given resource.
Example: An elephant might be able to prevent other
animals from using a water hole, but would be unlikely
to be able to chase them away from a river with its long
banks.

14. 1.Scramble (resource) competition
Organisms compete for a limiting resource
Observed in invertebrates
No need for individuals to interact directly, as each
takes from a common resource
Each competitor affects all other competitors by
reducing the amount of resource available to others

15. Scramble (resource) competition: 2 types
Exploitative -- consumption of the same food item or abiotic
resource
Preemptive -- taking space on a surface needed for living
(rocks for mussels, land for plants, etc.)

16. 2. Contest (interference) competition
individuals harm each other by physical force
observed in vertebrates

17. What is Competitive Exclusion?
states that two species competing for the same limiting
resource in an area cannot coexist.
it is rare to find two very closely related species in the same
area.
one species or the other will be better at the competition and
will displace the other.
if they live in the same area, they differ in the way they use
the resources often not in apparent way.
two species cannot share the same niche.
Niche – functional role of an organism in an ecosystem

18. Competitive Exclusion…
Example:
– a series of birds might feed in the same trees for the same
insects. However, each species might forage only on a
particular part of the tree - such as the top, the bottom,
the inner branches, etc.
– In this way they reduce the competition and are able to
co-exist.
nuthatch (works its way UP the trunk) and the brown creeper
(forages Down the trunk).

19. Florida's native anole, the Green Anole (Anolis carolinensis, left) is a direct
competitor with the introduced Brown Anole (Anolis sagrei, right).
where the two are found together, the Green Anoles are more common on the
vegetation and higher up, while the Brown Anoles tend to occupy the ground and
the tree trunks.

20. Competitive Exclusion…
One trick that some organisms use to reduce
competition within the species is to partition the
habitat between the young and the adults.
– Example:
Caterpillars feed on plants while butterflies only sip nectar
tadpoles live in the water feeding on algae while the adult frogs
are carnivorous

21. Butterflies get nectar from the flower of the plant
while caterpillars feed on the plant itself (mostly on
leaves).

22. Competition...Lotka-Volterra model
4 results:
– species 1 extinct,
– species 2 extinct,
– species 1 &2 extinct or
– species 1 & 2 coexist
Experiments on competition
- Gause on Sacccharomyces and Schizosaccharomyces
- Thomas Park on Tribolium comfusum and Tribolium
castaneum

23. Predation
(+,-)
This occurs when one population affects another
adversely but benefits itself from the interaction
A biological interaction where a predator (an
organism that is hunting) feeds on its prey, the
organism that is attacked.
the act of predation always results in the death of
the prey

25. Predation --- 3 Types:
Predator and prey
Parasitism
Herbivory

26. Predation  Predator & prey
a predator kills its prey and consumes part or all of the prey
organism
some predators kill large prey and chew it prior to eating it,
such as a lion, while others may eat their (usually much
smaller) prey whole .

27. Predation… Predator & Prey
Some predation entails venom which subdues a prey creature
before the predator ingests the prey by killing, which the box
jellyfish does, or disabling it, found in the behavior of the cone
shell.
In some cases the venom, as in rattlesnakes and some spiders,
contributes to the digestion of the prey item even before the
predator begins eating.
In other cases, the prey organism may die in the mouth or
digestive system of the predator. Baleen whales, for example,
eat millions of microscopic plankton at once and being broken
down well after entering the whale.
A predator serves a role, but they result in the death of the
prey.

29. Predation  Parasitism
(+,-)
is a type of symbiotic relationship between two different
organisms where one organism, the parasite, takes from the
host, sometimes for a prolonged time
essentially identical to predation except that the host is
usually not killed outright but is exploited over some period of
time.
“weak” form of predation
parasites don’t actually kill their victims, but they do cause
harm.

30. Classification of Parasites
(based on their interactions with their hosts and lifecycles)
ectoparasites (e.g. some mites) - those that live on its
surface.
epiparasite - is one that feeds on another parasite. This
relationship is also sometimes referred to as
hyperparasitism which may be exemplified by a protozoan
(the hyperparasite)
living in the digestive tract of a flea living on a
dog.
endoparasites (e.g. hookworms) - those that live inside the
host.
– can exist in 2 forms:
intercellular (inhabiting spaces in the host’s body)
intracellular (inhabiting cells in the host’s body)

31. What is a parasitoid?
an organism that spends a significant portion of its life history
attached to within a single host which it ultimately kills (often
consumes).
– term coined by O.M. Reuter

32. Parasitoid, an example:
Tachinid fly (Family Tachinidae)

33. All Tachinid flies have evolved different ways of infecting
their hosts:
Some stick eggs directly on the host
Some deposit eggs on foliage of host food plants to be ingested by
the host.
Some species lay their eggs their hosts, when hatch, those larvae
move towards their host and get into their body through the soft
part of the host skin.
Females of some other species that attack bugs and adult beetles
have piercing ovipositors that insert their eggs into the body of
their hosts
Some species, instead of laying eggs, they lay live larvae and apply
them onto the host using either one of the about methods.

34. Predation  Herbivory
– is a form of predation in which an organism, known as an
herbivore, consumes principally autotrophs such as plants,
algae and photosynthesizing bacteria
– however, it is generally restricted to animals eating plants
– herbivores form an important link in the food chain as
they consume plants in order to receive the carbohydrates
produced by a plant from photosynthesis.

35. Mutualism
(+,+)
interaction between individuals of
two different species where
individuals derive a fitness benefits,
for example, increased survivorship.
mostly observed in mutualistic
pollination systems.
Ex. Male euglossine bees
– visit flowers for floral fragrance

36. Mutualism…
Dispersal systems
Ex. Calvaria major in Mauritius (left)
– cannot propagate unless seeds eaten by dodo (right)

37. Mutualism
Protection system
Ex. Ants and aphids
– Aphids secrete honeydew which is being eaten by the ants while
ants protect aphids from predators

38. Commensalism
(+,0)
The norm in a community
One population benefits
while the other is
unaffected
Phoresy: association
involves passive and more-
temporary transport of one
organism by the other
Ex. Anemones on hermit
crab shells

39. A small frog seems to be hiding in the middle of the
water lily waiting for its prey to be ambushed.

40. Amensalism
(-,0)
said to occur when one population is affected adversely by
another but the second is unaffected.
this is not a type of symbiosis since it does not exhibit an
intimate relationship among organisms involved
this usually this occurs when one organism exudes a chemical
compound as part of its normal metabolism that is
detrimental to another organism

41. Amensalism…
Allelopathy - the inhibition of growth of a plant due
to biomolecules released by another.
– Examples:
Common bread mold, penicillium secrete penicillin (0), a chemical
that kills bacteria (-).
the black walnut tree (Juglans nigra), which secrete juglone, a
chemical that harms or kills some species of neighboring plants,
from its roots

42. Altruism?

43. ALTRUISM
1. Loving others as oneself.
2. promotes the survival chances of others at a cost to ones own.
3. Self-sacrifice for the benefit of others
–Auguste Comte coined the word altruisme
Zoology. Instinctive
behavior that is detrimental
to the individual but favors
the survival or spread of
that individual's genes, as
by benefiting its relatives.

44. wolves and wild dogs bring meat back to members of the pack that were
not present at the kill

45. sacrificing one’s chances of reproducing

46. vampire bats regurgitate blood to those that
were not able to hunt
Buddy system
(Wilkinson,G.)

47. male Golden orb-weaving spiders self-destruct after
mating while still intact to the female

48. The altruistic gene causes an organism to behave in a way which
reduces its own fitness but boosts the fitness of its relatives
— who have a greater than average chance of carrying the
gene themselves.

49. overall effect :increase the number of copies of the altruistic
gene found in the next generation, and thus the incidence
of the altruistic behavior itself.

50. When thinking about Community Ecology
 Keep in mind:
 the Food Pyramid (The Trophic Levels)
 the Biogeochemical Cycles

52. that’s all for now, GUYS…