Transcript Biodiversity, Species Interactions, and Population Control

BIODIVERSITY, SPECIES
INTERACTIONS, and
POPULATION CONTROL! 
How do Species Interact?
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5 major ways!
Interspecific Competition
Predation
Parasitism
Mutualism
Commensalism
Interactions help limit population size.
These interactions influence abilities of
interacting species to survive and
reproduce; thus serving as agents of
natural selection.
Competition
 Each species has a niche.(some
are generalists with broad niches,
others are specialists with narrow
niches)
 When niches overlap, competition
occurs. No two species can share
a niche for very long (competitive
exclusion principle)
PREDATORS!
 In predation, a member of one species
feeds directly upon all or part of another
living organism as part of a food web.
 Herbivores, carnivores, and omnivores are
predators. (Decomposers and detritovores
are not)
 See page 102 to read about how predators
catch prey and how prey tries to keep from
being eaten. Vivid reading!
PREY!!
PREDATOR!!
Read about Kelp! p. 104
PARASITISM! (Feeds on the
body or energy of another
organism)
MUTUALISM! Both Benefit!
Commensalism!Benefits one, but
doesn’t help or harm other. (bromeliads
and tree….whale and barnacle)
Reduce Competition by
Resource Partioning!
 Species competing for similar scarce
resources evolve specialized traits
that allow them to use shared
resources at different times, in
different ways, or in different places.
 Examples are warblers and honey
creepers.
We all live in the same tree!
But we eat different things in
different places in our tree!
Limits to Population
Growth!!
 Populations differ in factors such as distribution,
numbers, age structure, and density.
 Age structure(number of individuals in different
age groups)
 Density(number of individuals in a certain space)
 Population dynamics is a study of how these
characteristics of populations change in response
to environmental conditions.(Temperature,
presence of disease or harmful chemicals,
resource availability, and arrival or disappearance
of a competitor)
Snow bird to beach bunny! (NY to
FLA) (Mice leave when cat moves in)
CLUMPS and PATCHES
 Most populations live in clumps or patches.
(Desert vegetation near water, wolf packs,
fish schools, bird flocks, herds)
 Groups cluster where resources are
 Searching in groups is better than alone
 Groups protected more from predators
 Better hunting in packs
 Group together for mating and raising
young.
 The Living World is Clumpy and Patchy!!
We are happy! We Clump!
Uniform
Dispersion
Random
Dispersion
4 Variables Govern
Population Size!
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Births(come in)
Deaths(go out)
Immigration(move in)
Emigration(move out)
(Age structure is important in
determining if a population is likely to
grow or decrease. )
Biotic Potential
 Biotic potential is the
capacity for populations
to grow under ideal
conditions.
 Huge animals like
elephants and whales
have low biotic potential.
 Bacteria and insects
have high biotic potential
 The INTRINSIC RATE OF INCREASE (r) is the rate
at which the population of a species would grow if
it had unlimited resources.
 Populations with high (r) have individuals that
reproduce early, have short generation times,
reproduce many times, and have many offspring
each time they reproduce.(Example:Bacteria)
 No population can grow indefinitely because of
limiting factors such as light, water, space, and
food, or exposure to competitors, predators, or
disease. THERE ARE ALWAYS LIMITS TO
POPULATION GROWTH)
 Environmental Resistance is the combination of all
factors that act to limit population growth.
 Together, biotic potential and environmental
resistance determine 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.
Food and Space are getting
scarce  Carrying capacity
reached. Fewer fishes.
 EXPONENTIAL GROWTH: starts slowly,
accelerates quickly. (Few limitations on
growth. Many resources.) This is shown on
graph as a J-shaped curve.
 LOGISTIC GROWTH: involves rapid
exponential growth followed by a steady
decrease until population levels off.
(Dwindling resources) This is shown as an
S-shaped curve on a graph.
 Changes in the population of a keystone
species such as the southern sea otter or
the American alligator can alter the species
composition of an ecosystem.
 Example: Decline in sea otters caused a
decline in species dependent on them, such
as giant kelp. This reduced species
diversity in kelp forests and altered its
functional biodiversity by upsetting food
webs and reducing energy flows and
nutrient cycles.
I am endangered.  Read
about my plight on p. 110
I EAT SEA OTTERS!!
Parasites in my tummy
make sea otters sick!!
Moving on…..
 Sometimes a population
grows so fast that it doesn’t
transition from exponential
to logistic growth
smoothly….alas, it
temporarily OVERSHOOTS,
or exceeds the carrying
capacity of the
environment. (Caused by
reproductive time lag)
 Then the population suffers
a DIEBACK, or CRASH,
unless the excess
individuals move to new
resources or switch to new
resources.
REPRODUCTIVE
PATTERNS
 R-SELECTED SPECIES: species with a
capacity for a high rate of population
increase (r).
 Have many small offspring. Little parental
care.
 Big numbers of babies offset large losses.
Reproduce and disperse rapidly when
conditions are right.
 Opportunistic.
We take advantage!!
 K-SELECTED SPECIES: These are
competitor species.
 Reproduce later in life. Have fewer
offspring. Born larger. Cared for by parent.
 More competitive for resources.
 Follow logistic growth curve.
 Can be prone to extinction, especially if
heavily hunted.
We are “K-Select”
r-select
K-select
on the farm!!
Genetic Diversity in Small
Populations! It can be lost!
 Founder Effect: a few
individuals in a
population colonize a
new habitat that is
geographically
isolated from the rest
of the population.
 These foxes live in
isolated areas.
 Demographic
bottleneck: Only a few
individuals survive a
catastrophe. Lack of
genetic diversity may
limit their ability to
rebuild population. 
 Even if population
increases, lack of
genetic diversity may
lead to an increase of
genetic diseases.
 Genetic Drift: Random
changes in gene frequency
may lead to unequal
reproductive success.
 Some individuals may
breed more, so their genes
dominate. This could help
or hinder the population’s
survival.
 This is similar to founder
effect or bottleneck.
 Example: polydactyly in Old
Order Amish.
 Inbreeding: Occurs when individuals
in a small population mate with one
another.
 Can occur through bottleneck.
 Increases frequency of defective
genes.
 Example: Hapsburg royal family
POPULATION DENSITY
 Population Density: the number of individuals in a
population found in a certain area.
 Density-dependent population controls include
predation, parasitism, infectious disease, and
competition. These have a greater effect as
population density increases.
 Density-independent population controls are not
dependent on population density: severe freeze,
floods, hurricanes, fire, pollution, habitat
destruction.
4 Patterns of Variation in
Population Size
 STABLE: fluctuates
only slightly above
or below carrying
capacity.
 Example: tropical
rainforest species
 IRRUPTIVE:
explodes with a
high peak, then
crash! Gets stable
or goes low.
 Example:
Temperate climate
insects
 CYCLIC: cyclic
fluctuations or boom
and bust cycles.
 Examples: lemmings,
lynx and hare.
 Top-down regulation is
through predation.
 Bottom-up regulation
is by scarcity of
resources.
 IRREGULAR: No
recurring pattern.
Chaos,
catastrophe, severe
weather.
 Examples: Bubonic
plague, potato
famine, AIDS
YAY!! TECHNOLOGY!!
 Technological,
social, and other
cultural changes
have extended the
earth’s carrying
capacity for the
human species.
Read about the WhiteTailed Deer. pp.114-15