population ecology

1. CH-13,ORGANISMS
AND POPULATION POPULATION
ECOLOGY

5. Exponential growth
When resource in the
habitat is unlimited,each
species has the ability
release fully its innate
potential to grow in
number,Darwin observed
while developing his theory
of natural selection then
the population grows in an
exponential or geometric
fashion
 rise in population =r [ ln 𝑁] 𝑁𝑜
𝑁𝑡
= rt
r=b-d ln 𝑁 t – ln No = rt
at high birth rate and ln
𝑁𝑡
𝑁𝑜
= rt
at low mortality rate
𝑁𝑡
𝑁𝑜
=𝑒 𝑟𝑡
 r- max therefore , Nt =No 𝑒 𝑟𝑡
Growth rate =
𝑑𝑁
𝑑𝑡
= rN as r is max, it is an
 Therefore,
𝑑𝑁
𝑑𝑡
= rN exponential growth equation
 or,
1
𝑁
ⅆ𝑁= r ⅆ𝑡
 integrating both sides

𝑁𝑜
𝑁𝑡 1
𝑁
ⅆ𝑁 = r 0
𝑡
ⅆ𝑡

6. loge Nt = loge N0 + loge ert = loge N0 + rt
This equation indicates that loge N changes linearly in time; that is, a semilog plot of loge
N against t gives a straight line with a slope of r and a y-intercept of loge N0.
Setting N0 equal to 1 (i.e., a population initiated with a single organism), after one
generation, T, the number of organisms in the population is equal to the net reproductive
rate of that individual, or R0 . Substituting these values in the above equation:
loge R0 = loge 1 + rT
Since log 1 is zero, this equation reduces to loge R0 = rT or r = loge R0/T.
Another useful population parameter closely related to the net reproductive rate and the
intrinsic rate of increase is the so-called finite rate of increase, λ, defined as the rate of
increase per individual per unit time. The finite rate of increase λ is measured in the
same time units as the instantaneous rate of increase, and
r = loge λ or λ = er
In a population without age structure, l is thus identical with R0 [T equal to 1 in above
equations].

7. Exponential growth in Escherichia coli

8. Logistic growth
 A population growing in a
habitat with limited resources
show initially a lag phase
followed by phases of
acceleration and deceleration
and finally an asymptote,
when the population reaches
carrying capacity.
 In nature, a given habitat has
enough resources to support a
maximum possible number
beyond which no further
growth is possible this limit is
what we call CARRYING
CAPACITY(K) for that species
in that habitat


10. 196
200
204
208
212
216
220
224
228
232
236
240
196
200
204
208 208 208 208 208 208 208 208 208
188
192
196
200
204
208
212
216
220
224
228
232
236
240
244
10 20 30 40 50 60 70 80 90 100 110 120
No.ofindividuals
Time(in years)
Population growth curves
EXPONENTIAL GROWTH CURVE LOGISTIC GROWTH CURVE
EXPONENTIAL GROWTH CURVE
LOGISTIC GROWTH CURVE
CARRYING CAPACITY(K)=208
INDIVIDUAL

11. Reindeer population in saint paul island
(demonstrating K & interspecific competition )

12. SIGNIFICANCE OF K & SURVIVAL OF THE
FITTEST
 When there is limited resources and population grows there exist a struggle for
survival. Darwin was convinced that interspecific competition is a potent force in
organic evolution.
 IF COMPETITION OCCURS 2 POSSIBILTIES MAY EXIST
 COMPETITIVE EXCLUSION-: It was explained by the scientist GAUSE. And gave
“Gausian competitive exclusion principle.”
 RESOURCE PARTIONING

13. Gause principle & experiment
 Gause's competitive exclusion principle, or sometimes called--Gause's Law, states
that “Two closely related species competing for the same resource cannot
coexist indefinitely and the competitively inferior one will be eliminated
eventually by the superior one” .

 He placed Paramecium caudatum and Paramecium aurelia together in a test tube
with the same food supply. P. aurelia grew faster than P. caudatum and when grown
together, P. aurelia outmultiplied and eliminated P. caudatum. In nature, species
tend to have niches that are very specific and this reduces direct competition
allowing for more species to survive. For instance, in one tree, there may be seed
eating birds, fruit eating birds, birds feeding at the top, middle or bottom of the
tree. All of these niches reduce competition. Gause realized that a direct
competition between two different species cannot go on forever and one will
eventually perish.

14. GAUSE EXPERIMENT
0
50
100
150
200
2 4 6 8 10 12 14
AxisTitle
Axis Title
When cultured separately
paramoecium aurelia paramoecium caudatum
0
20
40
60
80
100
120
140
160
2 4 6 8 10 12 14 16
When cultured together
paramoecium aurelia paramoecium caudatum

16. A North Atlantic right whale with solitary
calf. Whale reproduction follows a K-
selection strategy, with few offspring,
long gestation, long parental care, and a
long period until sexual maturity
A litter of mice with their mother. The
reproduction of mice follows an r-
selection strategy, with many offspring,
short gestation, less parental care, and a
short time until sexual maturity.

17. Survivor ship curve
 Type I survivorship curves are characterized by
high age-specific survival probability in early
and middle life, followed by a rapid decline in
survival in later life. They are typical of species
that produce few offspring but care for them
well, including humans and many other large
mammals.
 Type II curves are an intermediate between
Types I and III, where roughly constant mortality
rate/survival probability is experienced
regardless of age. Some birds and some lizards
follow this pattern.
 In Type III curves, the greatest mortality (lowest
age-specific survival) is experienced early in
life, with relatively low rates of death (high
probability of survival) for those surviving this
bottleneck. This type of curve is characteristic
of species that produce a large number of
offspring (see r/K selection theory). This
includes most marine invertebrates. For
example, oysters produce millions of eggs, but
most larvae die from predation or other causes;
those that survive long enough to produce a
hard shell live relatively long.

18. RESOURCE PARTIONING
 It refers to the phenomenon in which species facing competition might evolve
mechanisms that promote coexistence rather than exclusion. Mac Arthur showed
that five closely related species of warblers living on the same tree were able to
avoid competition and coexist due to behavioural differences in their foraging
activities
 Implications of resource portioning -:
1. Specialisation of morphology and behavior for different foods,such as the beeks of
birds which may be modified for picking up of insects , drilling holes,cracking nuts ,
tearing flesh and so on;
2. Verticle sepration(stratification) such as canopy dwellers and forest floor dwellers;
3. Horizontal sepration,such as the occupation of different micro habitat.
However , despite a tendency for each species its own particular niche , some direct
competition between species for available resources will still occur.

24.  Members of different population often interact in different ways with the
environment in which they live. These interactions between the two or several
species on based on three factors –
1. Nature of food and mode of obtaining it.
2. Kind of space to needed as shelter.
3. Habitat such as aggregation and breeding
 There are mainly 3 types of interactions among the biotic community .
1. Negative (antagonistic/detrimental) interaction ,one species is harm while the
other is benefitted harmed and remain unaffected.
2. Positive(beneficial) interaction ,one species benefitted
3. Neutral interaction ,neither species is harmed nor benefitted

25.  NEUTRALISM(0 0)
 PREDATION(+ -)
 PARASITISM(+ -)
 AMENSALISM(- 0)
 COMMENSALISM(+ 0)
 COMPETITION
a) DIRECT(- -)
b) INDIRECT(- -)
 PROTOCOOPERATION(+ +)
 MUTUALISM(+ +)

26. NEUTRALISM
 It is an interaction in which a species is not affected by
the presence of other species in its niche . This lack of
interaction is known as neutralism
 Eg – shrew , rabbit and rats inhabits the grassland but
none takes the other’s food. Shrew takes insects ,rats
feed on seeds and rabbits eat grasses.

27. PREDATION
 ROLE OF PREDATOR
a) predators keep pray population under control. This is called
biological control.
b) Predators also keep in maintaining species diversity in a
community, by reducing the intensity of competition among
prey species
c) Besides acting as ‘conduits’ for energy transfer across trophic
level , predators play other important role. In absence of
predator species, prey species could achieve very high
population densities and lead to ecosystem instability
 When certain exotic species are introduced in to a
geographical area ,they become invasive and start spreading
fast because the invaded land does not have its natural
predator.
 If a predator is too efficient and over exploits its prey, then
the prey might become extinct and following it, the predator
will also become extinct due to lack of food.

28. BIOLOGICAL CONTROL BY CANE
TOAD ON CANE BEETLE IN
AUSTRALIA

29. GAMBUSIA AFFINIS AND
MOSQUITO LARVA

30.  THE PREY DEFENCE MECHANISMS
a) CAMOUFLAGE: It is the ability of an organism to blend
with their surroundings or background
EXAMPLES
 METACHROSIS IN CHAMELEON
 GRASSHOPPER(ARACTIA RECTIFOLIA)
 PRAYING MANTIS(MANTIS RELIGIOSA){USES IN PREDATION}
 STICK INSECT
 LEAF INSECT
 DEAD LEAF BUTTERFLY(PHYLLOCRANIA PARADOXA) CANNOT
BE DISTINGUISHED UNLESS AND UNTIL THEY SHOW
MOVEMENT

32. GRASSHOPPER(ARACTIA RECTIFOLIA)

33. PRAYING MANTIS(MANTIS RELIGIOSA){USES
IN PREDATION}

34. Stick insect

35. Leaf insect

36. DEAD LEAF BUTTERFLY(PHYLLOCRANIA PARADOXA) CANNOT BE
DISTINGUISHED UNLESS AND UNTIL THEY SHOW MOVEMENT

38. WARNING COLOURATION
Concealing from and colouration enables a species to avoid its natural predator . The
brightly coloured and highly poisonous dart frogs (Phyllobates bicolour, Dendrobates
pumillo) of the tropical rain forest of south America are easily recognized and avoided
by predators

39. b) MIMICRY: It is the resemblance of one species with
another in order to obtain advantage, especially ,against
predation .the species which is imitated is called MODEL.
While the animal which imitates is known as mimic or
mimetic. Model is either ferocious or distasteful to
predator
 BATESIAN MIMICRY: In this mimicry the mimic is
defenseless .it has however resemblance to the
dangerous or unpalatable mode so that so that predator
usually does not prey upon it e.g.- viceroy butterfly
mimics monarch butterfly
 MULLERIAN MIMICRY: in this mimicry there is the
resemblance to two animal species both ferocious/
unpalatable e.g.- bumble bee , honey bee ,yellow jacket
and paper wasp

40. BATESIAN MIMICRY

41. MULLERIAN MIMICRY

42.  The monarch butterfly is highly distasteful to its
predator because of special chemical present in its body
which is acquired by the butterfly by feeding on a
poisonous weed in its caterpillar stage
 Some plants have thorns or spines for defense
mechanism e.g. cactus and acacia
 Some plants produce highly poisonous chemicals like
cardiac glycosides ,nicotine , caffeine , quinine ,
strychnine opium etc.

44. COMPETITION
COMPETION
INTERSPECIFIC
INTRASPECIFIC

45.  The competition occurs due to limited resources between
closely related species
 Some totally unrelated species could also compete for the
same resource e.g. in some shallow south American lakes
visiting flamingoes and resident fishes compete for the
zooplanktons
 In interspecific competition the feeding efficiency of one
species might be reduced due to the interfering and inhibitory
presence of other species. Although the resources are
abundant
 For example, after the introduction of goats in Galapagos
islands , the Abingdon tortoise became extinct within a
decade due to greater browsing efficiency of the goats
 COMPETITIVE RELEASE refers to the phenomenon of a species
whose distribution is restricted to a small geographical area
because of the presence of a competitively superior species is
found to expand to distributional range directionally range
dramatically when the competing species is experimentally
removed

47.  CONNEL’S ELEGANT FIELD EXPERIMENT
Connell’s elegant field experiments showed that on the rocky sea coasts of Scotland,
the larger and competitively superior barnacle Balanus dominates the intertidal area,
and excludes the smaller barnacle Chathamalus from that zone

48. PARASITISM
 Parasitic mode of life ensures free lodging and meals.
 Some parasites are host-specific (one parasite has a single host) in such a way
that both host and parasite tend to co-evolve.
 Parasitic adaptation
a) Loss of unnecessary sense organs.
b) Presence of adhesive organs or suckers to cling on to the host.
c) Loss of digestive system.
d) High reproductive capacity
 Parasites having one or more intermediate host or vectors to facilitate
parasitisation of its primary host.
 Liver fluke has two intermediate hosts (snail and a fish) to complete its live
cycle.
 Effects on the host:
1. Parasite always harms the host.
2. They reduce the survival, growth and reproduction of the host.
3. Reduce its population density.
4. They make the host more vulnerable to the predators, by making it physically
weak.

49.  Ectoparasite: feeds on the external surface of the
host.
 Lice on human
 Ticks on dog
 Marine fish infested with copepods
 Cuscuta parasitic plant grow on hedge plants.

54. Endoparasites: are those that live inside the host body at different sites.
 Life cycle is more complex.
 Morphological and anatomical features are greatly simplified.
 Highly developed reproductive system.
 E.g.
1. Taenia solium(pork tape worm)
2. Schistosoma(fluke)
3. Plamodium (malarial parasite)

58. Brood parasitism:
 Special type of parasitism found in birds.
 The parasitic birds lay its eggs in the nest of its host and
let the host incubate them.
 The egg of the host is very similar with the egg of the
host.
 Cuckoo lays eggs in the nest of the crow.

59. COMMENSALISM
 This is the interaction in which one species benefits and
the other is neither benefited nor harmed.
EXAMPLES
 Orchids growing as an epiphyte on a mango branch.
 Clown fish living among tentacles of sea anemone.
 Barnacles on back of whales.
 Cattle Egret and grazing cattle

64. AMENSALISM
 Amensalism is referred as the interaction between two
different species ,in which one is harmed and other is
neither harmed nor benefitted
 E.g. , the mould penicillium secrete penicillin which
kills bacteria but the mould is unaffected

65. MUTUALISM
 Mutualism is referred to as the interspecific interaction in which both the
interacting species are benefited
 Some examples of mutualism
a. LICHENS represent close association between fungus and photosynthetic algae or
cyanobacteria where the fungus helps in absorption of nutrients and provide
protection while algae or cyanobacteria prepress the food

66. b) MYCORRHIZAE are close mutual association between fungi and roots of higher
plants , where fungi helps the plant for absorption of nutrients while the plant
provides food for fungus

67.  Plant need help from animals for pollination and dispersal of seeds . In return ,
plant provide nectar pollen and fruits from pollinators.
 E.g.- Blastophaga (wasp) uses the fruit not only as an oviposition site but uses the
developing seeds within fruit for nourishment . The wasp pollinates the fig
inflorescence . While searching for suitable egg –laying site in return fig provides
the wasp some seeds for nourishment

68.  Mediterranean orchid Ophrys employs ‘sexual deceit’ to
get pollinated by the species of bee . One petal of this
flower bears an uncanny resembelence to the female bee
in size ,colours and marking
 The male bee is attracted to what It perceives s a female
and pseudocopulate with the flower . During the process ,
the pollen is dusted from the flower. When the small bee
pseudocopulates with another flower , it transfers pollen
to it and pollinates another flower