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Chapter 25: Populations and Ecosystems (The Structure of Ecosystems…
Chapter 25: Populations and Ecosystems
Concept
population
individual plant never exist in isolation in a habitat
other individuals of the same species
together they constitute
community
all populations together constitute
population does not exist in isolation
numerous populations of other plant species
animals
fungi
protists
prokaryotes
ecosystem
along with the physical
nonliving environment
Plants in Relationship to Their Habitats
Abiotic Components of the habitat
climate
critically important to all organisms
most species are restricted to certain regions primarily
not live in climatic conditions outside
tolerance range
between the low and high extremes
soil factors
pioneers
first plants invade a new soil
must tolerate severe conditions
A horizon
uppermost
sometimes called zone of leaching
consists of little and debris
breaks down
C horizon
composed mostly of parent rock
rock fragments
B horizon
area where materials from the A horizon accumulate
latitude and altitude
latitude contributes
many factor to abiotic environment
higher latitudes
sun is only rarely overhead
only near midsummer
on mountain tops are similar
disturbance
phenomena
such as
fires
landslides
snow avalanches
floods
produce a significant
often radical change in ecosystem
Biotic Components of the Habitat
the plant itself
just by being in a habitat
modifies the habitat
beneficial
detrimental
neutral to the continued success of that species in it own habitat
part of it
other plant species
several individuals
either just one or several species
occur together
possibility for interaction
mutualism
basically beneficial for both organisms
if it disadvantageous
competition
competitive exclusion
whichever species is less adapted
from the ecosystem by superior competitors
transplant experiments
performed
plant from each site are transplanted to alternate site
plant from both sites may be grow together
common garden
organisms other than plants
commensal relationships
which one species benefits
other is unaffected
common between plant and animals
predation
relationship in which one species benefits
other is harmed
The Structure of Ecosystems
Physiognomic Structure
Physiognomic Structure
physical size
shape of organisms
distribution in relation to each other physical environment constitute
three most useful categories
trees
shrubs
herbs
Temporal Structure
changes an ecosystem undergoes with time constitute
time span can be as short as a day
can encompass seasons or decades
Species Composition
refers to the number
diversity of species that coexist in ecosystem
depends on whether the climate is mild or stressful
soil is rich or poor
species' tolerance range are broad or narrow
Trophic Levels
trophic levels
basically feeding levels
primary producers
autotrophs
first step of any food web
obvious reasons
primary consumers
called secondary producers
secondary consumers
herbivores are preyed on by carnivores
energy flow
energy and carbon compounds move to herbivore trophic level
plant eaten
carnivore trophic level
finally to the decomposers
carbon flow
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The Structure of Populations
Geographic Distribution
boundaries of the geographic range
limiting factor
described for photosynthesis
medium level of carbon dioxide
increasing the amount of light
increase in photosynthesis
local geographic distribution
random distribution
no obvious
identifiable pattern to the position of individuals
clumped distributions
spacing between plants is either small or large
rarely average
uniform distributions
types that occur in orchards
tree plantations
all individuals are evenly spaced from their neighbors
allelochemics
inhibition is allelopathy
zone can be established
at least theoretically
release from the plant of chemicals
Age Distribution: Demography
age distribution
demography
relative proportions of young
middle-aged
old individuals
two factors affect the possible rate
generation time
length of time from the birth of one individual
until birth it first offspring
affect the rapidity of population growth
annuals have a generation of 1 year or less
increase rapidly
intrinsic rate of natural increase or biotic potential
number of offspring produced by an individual that live long enough to reproduce under ideal conditions
carrying capacity
number of individuals in each population live in particular ecosystem is limited
symbolized by K
r- and K-Selection
r-selection
disturbance usually produces r conditions
r-selected species
typically are annuals
small shrubby perennials
disturbed habitat gradually changes back into crowed that on longer suitable for pioneer r species
k-selection
conditions in crowded habitat
population is close to carrying capacity
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select for phenotypes very different from those beneficial
k-selected species
redwoods
douglas firs
bristle-cone pines