Chapter 25 Populations and Ecosystems
Concepts
Individuals never
exist in isolation
a habitat
instead
there are other individuals
makes up a population
often do not interact strongly
if dioecious or self-sterile
carries out successful sexual reproduction
individuals cannot
can sustain
a population of pollinators
can be more susceptible to
pathogens
catastrophes
predators
population does not exist
in isolation
but rather
coexists with other populations
constitutes a community
when put together with
physical, nonliving environment
make up a ecosystem
Plants in Relationship to Their Habitats
Abiotic Components of the Habitat
Climate
important to
all organisms
many organisms restricted to
certain climate regions
many components
temperature
rainfall
relative humidity
winds
extremes are important
determine what plants can
live in that region
examples
many
bromeliads
aroids
orchids
restricted to tropics
frost free habitats
many temperate trees
need subfreezing temperatures
to be vernalized and bloom
growing season determined by
last killing frost in spring
and
first killing frost of autumn
must be adequate for
sufficient photosynthesis
growth development
reproduction
seasonal extremes most important
tolerance range
range of extremes that
certain plant can survive in
Soil Factors
soils formed by
breakdown of rock
pioneers
first plants to
invade new soil
in most tolerate severe conditions
soil conditions
sandy
large particle size
most minerals still locked
in the rock matrix
little water holding capacity
associated with nitrogen-fixing prokaryotes
change soil significantly
soil profile
3 distinct horizons
A horizon
AKA zone of leaching
consists of
litter
debris
B horizon
AKA zone of deposition
was nutrients into
B horizon
materials accumulate
from A horizon
rich in nutrients
contains
clay
humus
C horizon
composed mostly of
parent rocks
rock fragments
Disturbance
phenomena
examples
fires
landslides
snow avalanches
floods
produce significant radical change
in an ecosystem
affect
biotic factors directly
usually eliminate
all or most plants
plants can become
fire resistant
caused by
frequent fires
Biotic Components of the Habitat
The Plant Itself
can modify habitat
can be
beneficial
detrimental
neutral
Examples
Beech/Oak trees
create dense canopies
helps seedlings grow faster
Other Plant Species
Individuals occurring together
create interaction
can cause
mutualism
both plants benefit
competition
disadvantageous for plants
plants compete for
same materials
such as
light
soil nutrients
water
attention of pollinators
seed dispersers
Competitive exclusion
whichever species is less adapted
is excluded from ecosystem
first theory
Second Theory
Species overlap in tolerance range
weaker species occupies partial niche
Geographic range
can be very extensive
creates ecotypes
same species but
different ways of competing
which species is weaker
can depend on
what type of severe weather
is occurring
Organisms Other than Plants
Animals Fungi and Prokaryotes
can have interrelationships with plants
Mutualism
example
Ants and acacias
ant gets
food
housing
acacias get
protection
from
predators
competition
Commensal Relationship
one benefits/negative effect
and
other is unaffected
example
birds nesting in trees
Predation
one benefits
and
the other is harmed
example
herbivory
browsing
eating
twigs and leaves
grazing
eating herbs
The Structure of Populations
Boundaries of the Geographic Range
Plants adaptions to biotic
and abiotic factors
determine the geographic range
limiting factor
determines health of the plant
Cross-link Description: Light can be a limiting factor and is very important for the plants health. This can be why plants compete for light by shading over other plants.
determined by environment
any factor of an ecosystem
examples
amount of sunlight
amount of water
amount of herbivores in area
dependence on animals for
pollination
seed dispersal
Local Geographic Distribution
3 types
Random Distribution
no obvious, evident pattern
no predictive value
seems to be most common
Clumped Distribution
spacing between plants is either
small
large
reasons
seeds fall
certain distance from plant
fruit eaten by animals
will deposit seeds
within certain area
Uniform Distribution
Examples
orchards
tree plantations
individuals evenly spaced
not common in
natural habitats
r- and K-selection
r-Selection
r conditions
produced by disturbance
flood
fire
good for
surviving individuals
seeds arriving via floods/winds
most find best habitats
r-selected species
typically
annuals
small shrubby perennials
at disadvantage when
habitat goes back to normal
killing temperatures
Cross-link Description: The plants that inhabit a soil after a disturbance are known as the pioneers. They are known to create better soil. But may be at a disadvantage when conditions become better.
K-Selection
Conditions
in a crowded habitat
population close to carrying capacity
K-selected species
select differing phenotypes
than those that are beneficial
in a disturbed habitat
Energy mostly goes to
antipredator defenses
Examples
redwoods
results in
slower
growth
reproduction
Douglas firs
bristle-cone pines
The Structure of Ecosystems
Physiognomic Structure
physical size and shape
of
the organisms
organisms distribution
in relation to
each other
physical environment
Life Forms
Therophytes
Geophytes
Hemicryptophytes
Chamaephytes
Phanerophytes
Underground buds
buds located above ground
annual life span
buds located at surface
buds located high above
Temporal Structure
changes that an ecosystem
undergoes with time
days
seasons
decades
Species Composition
refers to the
number and diversity
of species in
an ecosystem
depends on
climate type
soil quality
species tolerance range
Trophic Levels
basically feeding levels
primary producers
autotrophs
first step of food web
energy supplier for
Primary Consumers
prey on by
Secondary Consumers
Decomposers
break down
Cross-link Description: Species composition could be relatively low after a phenomena because the soil and climate would have changed. Thus the species adapted to the previous ecosystem could be in danger.
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