Biodiversity, Species Interactions, And
Population Control
Species Interaction

Species Interact in 5 ways
1) Interpecific competition occurs when two
or more species interact to gain access to
the same limited resource
Species Interaction

Predation occurs when a member of one
species (the predator) feeds directly on all or
part of a member of another species (the prey)
Species Interaction

Parasitism occurs when one org. (parasite)
feeds on another org. (host) usually by living
on or in the host
Species Interaction

Mutualism an interaction that benefits both sps
by providing each w/ food, shelter, or some
other resource
Species Interaction

Commensalism an interaction that benefits
one sp but has little, if any effect on the other
Interspecific competition
Sp compete with one another for certain
resources
1) Limited Resource such as food, can
result in comp.
2) Each sp plays a role in its ecosystem,
called its Ecological Niche
3) If a sp is competing w/ another sp for a
part. Resource, then their niches
overlap; ↑Overlap = ↑Competition

Interspecific competition

Some Sp evolve ways to share
resources
1) Resource partitioning occurs when sp
competing for similar scarce resource
evolve specialized traits that allow them to
use shared resources at diff times, in diff
ways, or in diff places
2) An example of resource partitioning is
seen when specialized feeding niches of
bird sp evolve (pg. 81)
Predation
Most consumer species feed on live
organisms of other sp
 Predator feeds on prey = predator-prey
relationship
A) Predators can capture their prey by:

Pursuit and ambush
Camouflage to hide and ambush
Attack with chemical warfare
Herbivores can walk, swim or fly up to plants
they feed on
5) http://www.youtube.com/watch?v=1rp167WqVo
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Predation
B) Prey have Evolved ways to avoid
predators
 Ability to run, swim and fly quickly and a highly
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developed sense of sight or smell that alerts
them to the presence of predators
Camouflage
Chemical warfare
Bad-tasting, bad smelling, toxic, or stinging prey
with warning coloration
Engage behavioral strategies
Avoidance adaptations
Mimicry
Predation

Avoidance adaptations
 Ex: protective shells – turtles, thick bark
 Spines - Porcupines
 Thorns - Cacti
 Detaching limbs - lizards
Predation
C) Interactions b/t predator and prey sp can drive
each other’s evolution
 Coevolution occurs when 2 different sp interact over
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a long period of time; changes in the gene pool of
one sp can lead to changes in the gene pool of the
other
Some bats and moths have coevolved
Predators help control prey pop
Predators easily catch the young, sick, old & week
prey leaving indiv that tend to survive longer leading
these indiv. To reproduce
Prey develop mechanisms to avoid capture;
predators must overcome those mechanisms in
order to survive
Parasitism
Feed off other sp by living on or in them
 Can live inside or outside; can live in
single or multiple hosts
 Usually much smaller than its host
(prey) and rarely kills its host
 Tapeworms and some other parasites
can transfer disease-causing
microorganisms to their host

Mutualism
Both sp benefit.
 When 2 sp behave in ways that benefit
both by providing each with food,
shelter, or some other resource.
 Birds that ride on backs of large
animals, like African buffalo remove
pests in a mutualistic relationship
 Clown fish & sea anemones

commensalism
One sp benefits and other is not harmed
 Epiphytes (orchids) are plants that
attach themselves to the trunks or
branches of large trees for access to
sunlight; use tree as anchor w/o harming
it

Growth Limits of Populations

Populations can grow, shrink or remain
stable
 Population change = (births + Immigration) –
(deaths + emigration)
 Population size may vary in cycles based on
births, deaths, immigration, and emigration
Growth Limits of populations

Species have different reproductive
patterns
 Have many, usually small, offspring and give
them little if any parental care or protection
 Some have few, usually large, offspring and
give a lot of parental care or protection
No Population can grow
indefinitely
 Limiting factors such as light, water, space,
nutrients, predators, diseases, or
competitors keep pop size from
uncontrollable expansion
 Pop crashes are more likely when the org
cannot move easily to other locations
 J-curve, S-curve
 Regardless, limited resources and
competition limit growth
Environmental Resistances
Env. Resistance = combo of all factors
that act to limit the growth of pop.
 Largely determines the carrying capacity
(k) = the max pop. of a given sp that a
part. habitat can sustain indefinitely
 Growth rate ↓ as pop. Size nears k b/c
resources start to swindle

Exponential growth
Starts slowly but then accelerates as the
pop ↑ bc the base size of the pop is ↑
 Pop has few if any limitations
 Grows at a fixed rate
 J-Shaped

Population Crash
Not a smooth transition btw exponential
and logistic growth
 Pop use up their resources & temporarily
overshoot/exceed K
 Due to reproductive time lag = the period
needed for birth rate to fall & death rate to
increase in response to resource
overconsumption
 Pop suffers unless excess ind. Switch to a
new resource or move to an area w/ new
resources

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K is not fixed and is influenced by:
 Seasons
 Weather/climate/env. conditions
 Presence or absence of predators
 Scarcity of competitors
Logistic Growth
S-shaped curve
 Growth rate decreases as pop becomes
larger & faces env. Resistance
 Over time, pop stabilizes at or near k

Growth limits of Populations

Humans are not exempt from nature’s
pop controls
 Ireland recorded about 1 million human
deaths and 3 million emigrants associated
with the 1845 potato crop destruction
 During the 14th century, the bubonic plague
killed at least 25 million people
 Between 1981 and 2007, AIDS killed more
than 27 million people and continues to
claim another 2 million lives each year
Ecological Succession
The gradual change in sp composition in
a given area; Communities and
ecosystems change over time
 Two types: Primary & Secondary

Primary Succession
involves the gradual establishment of
biotic communities in lifeless areas
where there is no soil in terrestrial
ecosystem or no bottom sediment in an
aquatic ecosystem
 Usually takes 100s-1000s of yrs bc of
need to build up nutrient levels

Secondary Succession
Occurs with a series of communities or
ecosystems w/ different sp develop in
places containing soil or bottom
sediment
 Ecosystem has been disturbed,
removed or destroyed
 Abandoned farmland; burned or cut
forests; heavily polluted streams.
 Soil is present so new veg can begin to
germinate w/in a few wks.

Secondary/Primary succession
Both are impt natural services that
increase biodiversity = increased
sustainability
 Both are types of natural ecological
restoration

Ecological Succession

Succession does not follow a
predictable path
1) The Traditional View holds that succession
proceeds in an orderly sequence along an
expected path until a certain stable type of
climax community occupies an area
2) The Current View reflects the ongoing
struggle by different sp for enough light,
water, nutrients, food, and space; state of
continual disturbance & change; cant
predict course of succession
Limits of Change
1)
2)
Inertia (persistence) – the ability of a
living system, such as a grassland or
forest, to survive moderate
disturbances
Resilience – the ability of a living
system to be restored through
secondary succession after a more
severe disturbance
Save the Rainforest!!!