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Species
Interaction
1
Species Interact in Five Major Ways
• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism
2
Interspecific Competition
• Occurs when members of two or
more species interact to gain
access to the same limited
resources such as food, light, or
space
3
Predation
• Occurs when a member of one
species (the predator) feeds
directly on all or part of a
member of another species (the
prey)
4
Parasitism
• Occurs when one organism (the
parasite) feeds on the body of, or
the energy used by another
organism (the host), usually by
living on or in the host
5
Mutualism
• Is an interaction that benefits
both species by providing each
with food, shelter, or some other
resource.
6
Commensalism
• Is an interaction that benefits one
species but has little, if any, effect
on the other.
7
These interaction:
• have significant effects on the
resource use and population sizes
of the species in an ecosystem.
• also influence the abilities of the
interacting species to survive and
reproduce, thus serve as agents of
natural selection
8
Competition
• The most common interaction
• The niches of two species overlap
when they are competing for the
same resources.
9
Competitive exclusion principle
• Two species can’t occupy exactly
the same ecological niche for very
long.
10
If one species can take over the largest share
of one or more key resources, the other
competing species must:
• Migrate to another area (if possible)
• Shift its feeding habits or behavior through
natural selection
• Suffer a sharp population decline
• Become extinct in that area
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PREDATION
12
Predators
• Herbivores
• Carnivores
• Omnivores
13
Methods to capture preys
• Herbivores: just walk, swim, fly
• Carnivores:
–pursuit,
–ambush,
–camouflage,
–chemical warfare
14
Prey Adaptations
• Avoid detection
– camouflage, mimics,
– diurnal/nocturnal
15
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19
Prey Adaptations
• Avoid detection
– camouflage, mimics,
– diurnal/nocturnal
• Avoid capture
– flee
– resist
– escape
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Prey Adaptations
• Avoid detection
– camouflage, mimics,
– diurnal/nocturnal
• Avoid capture
– Protective shells
– Thick bark
– Spines and thorns
– Chemical warfare
24
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• At the individual level, members
of the predator species benefit
and members of the pray species
are harmed.
• At the population level, predation
plays a role in evolution by
natural selection.
26
Coevolution
• Evolution in which two or more
species interact and exert selective
pressures on each other that can
lead each species to undergo
adaptations.
• Ex. Predator-prey, parasite-host
27
Symbiosis:
Mutualists,
Commensalists
and Parasites
28
Parasitism
• Occurs when one species (the
parasite) feeds on the body of, or the
energy used by, another organism
(the host), usually by living on or in
the host.
• The parasite benefits and the host is
harmed but not immediately killed
29
Parasitism
• Parasite usually is smaller than
host
• Live on
• Live in
• Little contact
30
Mutualism
DEFINITION:
An interaction between two
individuals of different species
that benefits both partners in this
interaction
31
Pollination
• Animals visit flowers to collect nectar
and incidentally carry pollen from one
flower to another
• Animals get food and the plant get a
pollination service
32
Yucca and Yucca Moth
• Yucca’s only
pollinator is the
yucca moth. Hence
entirely dependent
on it for dispersal.
• Yucca moth
caterpillar’s only
food is yucca seeds.
• Yucca moth lives in
yucca and receives
shelter from plant.
33
Lichen (Fungi-Algae)
• Symbiotic relationship of algae and
fungae…results in very different
growth formas with and without
symbiont.
• What are the benefits to the fungus?
34
Commensalists
• Benefit from the
host at almost no
cost to the host
• Birds nesting in
trees
• Eyelash mite and
humans
• Sharks and remora
35
To avoid or reduce Competition
• Some species develop adaptations
that allow them to reduce or
avoid competition with other
species for resources. In other
words, some species evolve to
reduce niche overlap.
36
Resource Partitioning
• Process of dividing up resources
in an ecosystem so that species
with similar needs (overlapping
ecological niches) use the same
scarce resources at different
times, in different ways, or in
different places.
37
Population Growth
• No population can continue to
grow indefinitely because of
limitations on resources and
because of competition among
species for those resources.
38
Populations Have Certain
Characteristics
• Populations differ in
–Distribution
–Numbers
–Age structure
–Density
39
Population dynamics
• Is a study of how these
characteristics of populations
change in response to changes in
environment conditions.
40
Changes in population
characteristics due to:
–Temperature
–Presence of disease organisms or
harmful chemicals
–Resource availability
–Arrival or disappearance of
competing species
41
Most Populations Live Together
in Clumps or Patches
• Population distribution
–Clumping (Ex. Wolf packs, desert
vegetation around springs,…)
–Uniform dispersion ( Ex.Creosote
bushes in a dessert)
–Random dispersion (Ex.
Dandelions)
42
Why clumping?
– Species tend to cluster where resources
are available
– Groups have a better chance of finding
clumped resources
– Protects some animals from predators
– Packs allow some to get prey
– Temporary groups for mating and
caring for young
43
•The living world is
mostly clumpy and
patchy
44
Populations Can Grow,
Shrink, or Remain Stable
• Population size governed by
– Births
– Deaths
– Immigration
– Emigration
• Population change =
(births + immigration) – (deaths + emigration)
45
Age structure
–Pre-reproductive age
–Reproductive age
–Post-reproductive age
• The size of a population with a
fairly even distribution among
these three age groups tends to
remain stable.
46
No Population Can Grow Indefinitely:
J-Curves and S-Curves
• Biotic potential: capacity for population growth under ideal
conditions.
– Low
– High
• Intrinsic rate of increase (r): is the rate at which the
population of a species would grow if it had unlimited
resources.
• Individuals in populations with high r
– Reproduce early in life
– Have short generation times
– Can reproduce many times
47
– Have many offspring each time they reproduce
No Population Can Grow Indefinitely:
J-Curves and S-Curves
• Size of populations limited by
–Light
–Water
–Space
–Nutrients
–Exposure to too many competitors,
predators or infectious diseases
48
• Environmental resistance: Is the combination of all
factors that act to limit the growth of a population.
• Carrying capacity (K): The maximum population of
a given species that a particular habitat can sustain
indefinitely without being degraded.
• The growth rate of a population decreases as its size
nears the carrying capacity of its environment.
49
Exponential or geometric growth
• Exponential growth: starts slowly
but then accelerates as the
population increases, because the
base size of the population is
increasing (J-shaped growth
curve)
50
Logistic growth
• Involves rapid exponential
population growth followed by a
steady decrease in population
growth until the population size
levels off.
51
Why logistic growth?
• This slowdown occurs as the
population encounters
environmental resistance from
declining resources and other
environmental factors and
approaches the carrying capacity
of its environment.
52
• After leveling off, a population
fluctuates slightly above and
below the carrying capacity.
• The size of such population may
also change as the carrying
capacity does.
• Read page 110
53
When a Population Exceeds Its Habitat’s Carrying
Capacity, Its Population Can Crash
• Carrying capacity: not fixed
• Reproductive time lag may lead to overshoot
– Dieback (crash)
• Damage may reduce area’s carrying capacity
54
Reproductive Patterns
• r-selected species:
– Have many, usually small, offspring
– Little or no parental care or protection
– Massive losses of offspring.
– Ex. Algae, bacteria, rodents, frogs,..
– Tend to be opportunists
55
Reproductive Patterns
• k- selected species:
– Tend to reproduce later in live
– Have a small number of offspring with fairly
long life spans
– For k-selected mammals, the offspring
develop inside their mothers, are born fairly
large, mature slowly and are cared
– They do well in competitive conditions
56
Genetic Diversity and small
populations
• Several genetic factors can play a role in
the loss of genetic diversity and the
survival of small, isolated populations.
– Founder effect
– Demographic bottleneck
– Genetic drift
– Inbreeding
57
Founder effect
• Can occur when a few individuals in
a population colonize a new habitat
that is geographically isolated from
other members of the population. In
such a cases, limited genetic diversity
may threaten the survival of the
colonizing population
58
Demographic bottleneck
• It occurs when only a few individuals
in a population survive a catastrophe
such as a fire. Lack of genetic
diversity may limit the ability of
these individuals to rebuild the
population (increase in the frequency
of harmful genetic deseases)
59
Genetic drift
• It involves random changes in the
gene frequencies in a population
that can lead to unequal
reproductive success. The
founder effect is one cause of
genetic drift.
60
Inbreeding
• It occurs when individuals in a
small population mate with one
another.
• This can occur when a population
passes through a demographic
bottleneck
61
Minimum viable population size
• Conservation biologists use these
concepts to estimate the minimum
viable population size or rare and
endangered species: the number
of individuals such populations
need for long-term survival.
62
Density-dependent population controls
• Population density is the number of
individuals in a population found in a
particular area or volume.
• Density-dependent population controls
– Predation
– Parasitism
– Infectious disease
– Competition for resources (mates, food,
sunlight,…)
63
Density independent
• Some factors (mostly abiotic) that
can kill members of a population
are density independent.
• Ex. Severe freeze, flood, pollution,
fire,…
64
Several Different Types of Population
Change Occur in Nature
• Stable
• Irruptive
• Cyclic fluctuations, boom-and-bust cycles
– Top-down population regulation
– Bottom-up population regulation
• Irregular
65
Humans Are Not Exempt from
Nature’s Population Controls
• Ireland
– Potato crop in 1845
• Bubonic plague
– Fourteenth century
• AIDS
– Global epidemic
66
Ecological
Processes
67
Ecological Succession
Primary and Secondary Succession
gradual & fairly predictable change in species
composition with time
•some species colonize & become more
abundant;
•other species decline or even disappear.
68
Primary Succession
• Involves the gradual
establishment of biotic
communities in lifeless areas
where there is no soil in a
terrestrial ecosystem or no
bottom sediment in an aquatic
ecosystem.
69
Secondary Succession
• A series of communities or
ecosystems with different species
develop in places containing soil
or bottom sediment
70
Primary Succession
• Bare rock weathers release nutrients for soil
formation.
• The slow process of soil formation begins when early
successional plant species or pioneer arrive and
attach themselves to inhospitable patches of rock.
Such as lichens, mosses,..
• After hundreds to thousands of years, the soil may be
deep and fertile enough to store the moisture and
nutrients needed to support the growth of
midsuccessional plant species, such as herbs,
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grasses,..
Primary Succession
• Late successional plant species
(mostly trees) that can tolerate
shade are going to replace the
midsuccessional plant species.
72
Secondary Succesion
• Candidates for secondary
succession include abandoned
farmland, burned or cut forests,
heavily polluted streams, and
land that has been flooded.
73
Succession Doesn’t Follow a
Predictable Path
• Traditional view
– Balance of nature and a climax community
• Current view
– Ever-changing mosaic of patches of
vegetation
– Mature late-successional ecosystems
• State of continual disturbance and change
74
Living Systems Are Sustained
through Constant Change
• Inertia, persistence
– Ability of a living system to survive moderate
disturbances
• Resilience
– Ability of a living system to be restored through
secondary succession after a moderate disturbance
• Tipping point
75
Ecological Succession
Gradual changing environment in
favor of new / different species /
communities
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Primary
Succession
Glacier
Retreat
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Disturbance
Event that disrupts an ecosystem or community;
• Natural disturbance
•tree falls, fires, hurricanes, tornadoes, droughts,
& floods
• Human–caused disturbance
•deforestation, erosion, overgrazing, plowing,
pollution,mining
• Disturbance can initiate primary and/or secondary
succession
81
Ecological Stability
Carrying Capacity – maximum number of
individuals the environment can support
82
Ecological Stability - Stress
1. Drop in Primary Productivity
2. Increased Nutrient Losses
3. Decline or extinction of indicator
species
4. Increased populations of insect
pests or disease organisms
5. Decline in Species diversity
6. Presence of Contaminants
83
Which law directed the Secretary of the
Interior to review every roadless area of
5,000 or more acres and every roadless
island within National Wildlife Refuge and
National Park Systems?
A. Endangered Species Act
B. Wilderness Act
C. Lacey Act
D. National Park Act
E. Wild and Scenic Rivers Act
84
What are keystone species?
A. existing in such small numbers that it is in
danger of becoming extinct
B. introduced to an environment where it is not
native, and that has since become a nuisance
C. likely to become an endangered species within
the foreseeable future throughout all or a
significant portion of its range
D. serve as early warnings of damage to a
community
E. presence and role within an ecosystem has a
disproportionate effect on other organisms within
the system
85
Who did Roosevelt appoint to head
the newly created US Forest
Service to protect and manage the
world’s forests?
A. E.O. Wilson
B. Aldo Leopold
C. Robert MacArthur
D. Stephen Mather
E. Gifford Pinchot
86
Mutualism benefits:
A) one of the organisms & hurts
the other
B) neither of the organisms
C) both of the organisms
D) benefits one & doesn’t hurt the
other
E) only one of the organisms
87
Commensalism:
A) benefits only one of the organisms
B) benefits both organisms
C) benefits one, doesn’t harm the other
D) benefits neither of the organisms
88
Biodiversity:
A) decreases with speciation and
extinction
B) decreases with speciation and
increases with extinction
C) increases with speciation and
extinction
D) increases with speciation and
decreases with extinction
89
What is not a pre-zygotic barriers?
A) behavioral isolation
B) habitat isolation
C) mechanical isolation
D) hybrid isolation
90
Which of the following does
species richness not depend on?
A) rate of immigration
B) island size
C) distance from mainland
D) types of species
91
Which is a species on which the
persistence of a large number of other
species in the ecosystem depends?
A) r-strategists
B) k-strategists
C) nonnative
D) keystone
92
What is not characteristic of a
k-strategists?
A) long life
B) bigger bodies
C) produce a lot of offspring
D) produce late in life
93
What is not a predator
adaptation?
A) prey detection
B) prey capture
C) eating prey
D) avoid detection
E) mass numbers
94
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