1. Unit 1 The Biosphere
Populations
Interactions

2. 3 Properties of
Populations
• Population Size
• Population Density
• Population Dispersion

3. Population Size
• Population-groups of organisms that
belong to the same species and live in a
particular area at one time
• Population size-number of individuals a
population has
• Sometimes there are too many to count
so a sampling is used.
• Scientists count a number of organisms
in a certain area and multiply the area.

4. Population Density
• Population density-measures how
crowded a population is
• The number is always expressed
as the number of individuals per
unit of area or volume
• Some areas are densely populated
and others are sparsely populated

5. Population Dispersion
• Dispersion is the spatial distribution
of individuals within a population.
• There are three types of dispersion.
• Clumped dispersion occurs because
resources and living space is clumped
or because of behavior, herding
• Even dispersion is the result of social
behavior and organisms stay as far
away from each other as possible
• Random dispersion results from wind
distribution of seeds so plants usually
have a random dispersal

6. Types of Dispersion

7. Population Dynamics
• All populations are dynamic,
meaning they change in size and
composition over time.
• Birth rate-number of births over
time
• Death rate (mortality rate)-
number of deaths over time
• Life expectancy- how long on
average an individual is expected
to live

8. Age Structure
• Age structure-distribution of
individuals among different ages in
a population
• Different countries have different
age structures.
• We can use graphs to compare age
structure.

14. Population Growth Rate
• Growth rate- the amount by
which a population’s size
changes over time
• Immigration-individuals moving
into a population
• Emigration-individuals moving
out of a population

15. Exponential Growth Model
• Exponential Model- population
increases rapidly after only a few
generations; the larger the
population gets, the faster it grows
• Limiting factor-a factor that
restrains or stops the growth of a
population
• Limiting factors are available
resources, space, waste
accumulation, population density

17. Logistic Growth Model
• Logistic model-builds on the
exponential model but adds the
limiting factors.
• Carrying capacity (K)- the number
of individuals the environment can
support over a long period of time
• Once carrying capacity is reached,
the population remains constant

19. Population Regulation
• Density-independent factors-
weather, flood, fires; these reduce
the population regardless of size
• Density-dependent factors- food,
nesting sites, illness; these occur
as a result of population size

20. Perils of small populations-
Inbreeding
• The rapidly growing human
population has caused extreme
reductions in the populations of some
other species and subspecies.
• Fewer than 200 Siberian tigers
remain in the wild due to over
hunting and habitat destruction
• The California condor is down to 9
individuals.
• Fewer individuals means inbreeding
or mating with relatives.
• This mean the babies will be more
likely to have defects or diseases.

21. Predation
•Predator-captures, kills
and consumes another
individual
•Prey-is captured and
consumed for food

22. Predators, Prey and Natural
Selection
• A predator’s survival depends on
its ability to capture food, but a
prey’s survival depends on its
ability to avoid being captured.

23. Mimicry
• Deception is important in
antipredator defenses.
• In a defense called mimicry, a
harmless species resembles a
poisonous or distasteful species.
• The harmless mimic is protected
because it is often mistaken to
be its dangerous look-alike

24. MimicryMonarch
Viceroy

26. National Geographic’s Collection of Mimicry and Camouflage

37. Plant-Herbivore
Interactions
• Animals that eat plants are called
herbivores.
• Through natural selection, plants
have evolved adaptations that
protect them from being eaten.
• Physical defenses, such as sharp
thorns, spines, sticky hairs, and
tough leaves, can make a plant
more difficult to eat.

39. Plant-Herbivore Interactions
• Plants have also evolved a range of
chemical defenses.
• They synthesize chemicals from
products of their metabolism, called
secondary compounds, that are
poisonous, irritating, or bad tasting.
• Examples are the tobacco plant and
poison ivy and poison oak.
• Many medicines are derived from
secondary compounds.

40. Secondary
Compounds

41. Purple
Coneflower or
Echincaea.
Immune
system
Willow Tree
aspirin

42. Parasitism
• Parasitism- a species interaction that
resembles predation in that one individual
is harmed while the other benefits
• Parasite- feeds on another individual,
harming it
• Host-fed upon by another organism
• Ectoparasites-external, ticks, fleas, lice
• Endoparasites-internal, worms, protists

43. Ectoparasites

44. Endoparasites

45. Competition
• Competition results from niche overlap.
• Competition is the use of the same
limited resource by two or more
species.
• Competitive exclusion is when one
species is eliminated from a community
due to competition.
• One species uses a resource more
efficiently and has a reproductive
advantage over the other.
• Competition is the most intense
between similar species using the same
resources.

46. Mutualism and Commensalism
• Mutualism- a cooperative
relationship in which both
partners benefit
• Some mutualistic relationships
are so close that neither partner
could live without the other.
• Pollination is a major mutualistic
relationship that benefits the
world.

47. Mutualism and Commensalism
• Commensalism- a relationship
between organisms in which one
organism benefits and one
organism is unaffected.
• One example is birds eating
insects and lizards that are flushed
out by buffalo.
• The buffalo is not harmed and
does not benefit but the birds
clearly benefit from the buffalo.

48. Mutualism

49. CommensalismThese are mainly
commensalism but
could change to
mutualism if the
situation changes.

50. Commensalism

51. Mutualism

52. commensalism

53. Parasitism

54. Predation

55. Parasitism

56. mutualism

57. mutualism