UNIT-X ECOLOGY

1
UNIT-X ECOLOGY

• Chp.13-Organisms Populations

2
Organism Its Environment

• Change in seasons, annual variation in
  precipitation ( rain snow) results in formation
  of major biomes.
• Major biomes of India (a) Tropical rain forest
  (b) Deciduous forest (c) Desert (d) Sea coast.
• Regional and local variations in biomes lead to
  the formation of different habitats.

3
Major Abiotic factors

• TEMPERATURE
• Sub zero levels in polar areas and high altitudes
  to gt 500 C in tropical deserts.
• In thermal springs and deep sea hydrothermal
  vents gt 1000 C.
• Temperature effects the kinetics of enzymes.
• Eurythermal organisms that can tolerate a wide
  range of temperature.
• Stenothermal organisms restricted to a narrow
  range of temperature.

4

• WATER
• The productivity distribution of plants is
  heavily dependent on water.
• Euryhaline - organisms are tolerant of a wide
  range of salinities.
• Stenohaline organisms are restricted to a
  narrow range of salinities.

5

• LIGHT
• Photosynthesis.
• Flowering
• Animals use diurnal seasonal variations in
  light intensity and duration as cues for timing
  of foraging, reproductive and migratory
  activities.

6

• SOIL
• Nature and properties of soil depends on
• (i) Climate (ii) Weathering process
• (iii) Transported or sedimentary
• (iv) How soil development occurred
• Percolation water holding capacity is
  determined by soil composition, grain size and
  aggregation.
• Above factors along with pH, mineral composition
  and topography determine the vegetation and type
  of animals that can be supported.
• In aquatic environment sediment characterestics
  determine the type of benthic animals.

7
Responses to Abiotic factors
Conformers
Internal level
Regulaters
Partial regulaters
External level
8

• Homeostasis Organisms try to maintain the
  constancy of its internal environment.
• Regulate
• Organisms are able to maintain constant body
  temperature , osmotic concentration.
• Conform
• Organisms cannot maintain a constant internal
  environment.
• Body temperature and osmotic concentration
• changes with that of the ambient environment.

9

• Migrate
• Organisms move temporarily from the stressful
  habitat to a more hospitable area and return when
  stressful period is over.
• Suspend
• Bacteria , Fungi form thick walled spores to
  survive unfavourable conditions.
• Hibernation Winter sleep - eg. Bear
• Aestivation - Summer sleep eg. Fish
• Diapause Suspended development stage in
  zooplanktons

10
ADAPTATIONS

• Adaptation is an attribute of the organism that
  enables the organism to survive reproduce in
  its habitat.
• Desert plants have
• (i) thick cuticle on leaf surfaces.
• (ii) stomata arranged in deep pits.
• (iii) In Opuntia leaves are reduced to
• spines and photosynthesis is taken over
• by flattened stems.
• - Mammals from colder climates have shorter ears
  and limbs to minimise heat loss. ( Allens Rule )

11
Population attributes
Post reproductive
Reproductive
Pre reproductive
EXPANDING
12
Post reproductive
Reproductive
Pre reproductive
STABLE
13
Post reproductive
Reproductive
Pre reproductive
DECLINING
14
Population Growth

• Natality no. of births during a given period in
  the population.
• Mortality no. of deaths in the population
  during a given period.
• Immigration no. of individuals of the same
  species that have come into the habitat.
• Emigration no. of individuals who left the
  habitat.

15
IMMIGRATION
( I)

POPULATION
DENSITY
MORTALITY
-

NATALITY
(N)
(D)
(B)
-
EMIGRATION
(E)
16

• If N is the population density at time t then its
  density at time t1 is
• Nt1 Nt (B I ) (D E )
• Population density will increase if no. of
  births plus the no. of immigrants
• (BI) is more than the no. of deaths plus the no.
  of emigrants (DE).

17
GROWTH MODELS

• (i) Exponential growth
• When resources in the habitat are unlimited,
  population grows in an exponential or geometric
  fashion.
• If in a population of size N per capita birth
  rate is b and death rate is d then increase or
  decrease in N during a unit time period-
• dN/dt (b d ) N
• If b d r (intrinsic rate of natural
  increase)
• dN/dt rN
• It gives a J shaped growth curve

18

• Integral form of the exponential growth
  equation
• N t N0 e r t
• N t Population density after
• time t
• N0 Population density at time
• 0
• r intrinsic rate of natural
  increase
• e the base of natural logarithms
  (2.71828)

19

• (ii) Logistic growth
• A population growing in a habitat with
  limited resources show
• -a lag phase.
• -phases of acceleration
• deceleration.
• -an asymptote, when population
• density reaches the carrying capacity.
• - It results in a sigmoid curve.
• - This type of growth is called Verhulst Pearl
  Logistic Growth.

20
dN/dt rN
Population Density ( N )
K
dN/dt rN ( K N )
K
Time (t)
21
Population Interactions

• (i) PREDATION
• - act as conduits for energy transfer across
  trophic levels.
• - keep prey populations under control.
• Prey species could achieve very high
  population densities and cause ecosystem
  instability
• When exotic species are introduced in a
  geographical area, they spread very fast as
  invaded land does not have natural predators.
• Eg. Prickly pear cactus introduced in
  Australia in 1920 spread in millions of
  hectares. It was brought under control by
  introducing a cactus feeding moth.

22

• Predators help in maintaining species
  diversity in a community by reducing intensity of
  competition among competing prey species
• Pisaster ( Star fish ) in rocky intertidal
  American pacific coast when removed from an
  enclosed area leads to extinction of more than 10
  species of invertebrates.

23

• Prey species have evolved various defenses
• Camouflage- some insects frogs.
• Monarch butterfly is highly distasteful to
  predators ( bird ) due to a chemical acquired by
  it at caterpillar stage by feeding on a poisonous
  weed.
• Calotropis produces highly poisonous cardiac
  glycosides.

24

• ( ii ) COMPETITION
• occurs when closely related species compete
  for the same resource that is limiting but it is
  not true all the times
• In South American shallow lakes Flamingoes
  fishes compete for zooplanktons.
• Interfering inhibitory presence of a species
  reduces feeding efficiency of other species even
  if resources are abundant. (Interference
  Competition ).
• Definition
• Competition is a process in which fitness of
  one species (increase in r intrinsic rate of
  natural increase ) is lowered in presence of
  another species.
• Eg.- Abingdon tortoise in Galapagos island
  became extinct within a decade after goats were
  introduced on island due to greater browsing
  efficiency of goats.

25

• Competitive release
• A species whose distribution is restricted to a
  small geographical area due to a competitively
  superior species expands its range of
  distribution dramatically when competing species
  is experimentally removed.
• Eg. Connels elegant field experiments
• On rocky coasts of Scotland,competitively
• superior barnacle Balanus dominate and
  exclude smaller barnacle Chathmalus.
• Gauses competitive exclusion principle
• Two closely related species competing for
  the same resource cannot co-exist indefinitely
  and inferior one will be eliminated. ( If
  resources are limiting ).

26

• (iii) PARASITISM
• host- specific.
• Special adaptations loss of unnecessary sense
  organs , presence of adhesive organs or suckers ,
  loss of digestive system , high reproducing
  capacity.
• Complex life cycles
• - Liver fluke has two intermediate hosts a
  snail and a fish.
• - Malarial parasite needs mosquitoes as vector.
• - Ectoparasites and endoparasites.
• - Brood parasitism - birds

27

• (iv) COMMENSALISM
• One species benefits and other neither harmed
  nor benefited.
• Eg.- An orchid ( epiphyte ) on a mango branch.
• - A Cattle egret .
• - Sea anemone clown fish fish gets
  protection from predators.

28

• (v) MUTUALISM
• Benefit to both the interacting species.
• -Lichens fungus algae.
• -Mycorrhizae fungi roots of higher plants.
• A given Fig species is pollinated only by its
  partner Wasp species.
• Female wasp uses the fruit as an oviposition
  site feed its larvae on developing seeds.
• Mediterranean orchid Ophrys employs sexual
  deceit. One petal of its flower bears resemblance
  to the female of bee in size , colour, markings.
  The male bee pseudocopulates with the flower and
  dusted with pollen grains.