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Populations and Ecosystems (Plants in Relationship to Their Habitats…
Populations and Ecosystems
Plants in Relationship to Their Habitats
Abiotic Components of the Habitat
nonliving and are physical phenomena
climate, soil, latitude, altitude, etc.
Climate
temperature, rainfall, humidity & winds
critically important to all organisms
tolerance range
Between the low & high extremes
Soil factors
Soils are formed by breakdown of rock
pioneers
first plants that invade a new soil
must tolerate severe conditions
A horizon
uppermost; zone of leaching
consists of litter & debris
B horizon
zone of deposition
area where materials from the A horizon accumulate
contains humus and clay
C horizon
composed mostly of parent rock & rock fragments
Latitude & Altitude
higher latitudes to either the north or south
summer days become longer, as do winter nights
Above the Arctic and Antarctic Circles
mid-summer days are 24 hours long
as are mid-winter nights
At intermediate &higher latitudes
day length is an excellent indicator of season
Disturbance
phenomena; fires, landslides, snow avalanches, floods
produce a radical change in an ecosystem
affect biotic factors directly
little/no impact on abiotic factors
Biotic Components of the Habitat
The plant itself
An individual itself, modifies the habitat
Other plant species
When several individuals, of either just one or several species,
occur together, the possibility for interaction is created
mutualism
interaction is beneficial for both organisms
competition
disadvantageous
competitive exclusion
Whichever species is less adapted is
excluded from the ecosystem by superior competitors
Organisms Other Than Plants
Commensal relationships
one species benefits & the other is unaffected
predation
one species benefits and the other is harmed
herbivores
animals that eat plants
Habitat:
set of conditions which an organism completes its life cycle
Operational habitat
Aspects of the habitat that definitely affect a plant
The Structure of Populations
Geographic Distribution
Boundaries of the Geographic Range
limiting factor
all aspects of a plant’s interaction w/ its habitat
plant species spread throughout a geographic area
result of its adaptations to the abiotic & biotic components of that area
Local Geographic Distribution
random distribution
no obvious, identifiable pattern to the position of individuals
Clumped distributions
spacing between plants is small or large; rarely average
Uniform distributions
occur in orchards & tree plantations
Age Distribution: Demography
demography
relative proportions of young, middle-aged & old individuals
generation time
length of time from the birth of one individual
until the birth of its first offspring
affects the rapidity of population growth
intrinsic rate of natural increase
the # of offspring produced by an individual
that live long enough to reproduce under ideal conditions
r- and K- Selection
r selection
disturbance usually produces these
k selection
almost every possible site is filled
k selected species:
redwoods, Douglas firs, bristle-cone pines
The Structure of Ecosystems
Physiognomic Structure
physical size & shape of the organisms
their distribution in relation to each other
and to the physical environment
Trees, shrubs, and herbs
3 most useful categories
life forms
defined by C. Raunkiaer
in 1934
Temporal Structure
changes that an ecosystem undergoes with time
time span can be
as short as a day
can encompass seasons or decades
Species Composition
the number and diversity of species
that coexist in an ecosystem
Trophic Levels
feeding levels
Each ecosystem contains
some members, autotrophs, that bring energy into the system
autotrophs are known as
primary producers
first step of any food web
herbivores are known as
primary consumers
or secondary producers
carnivores are known as
secondary consumers
decomposers
fungi & bacteria
break down the remains of all types of organisms
Concepts
Ecology:
study of organisms in relationship
to all aspects of their surroundings
Population
individuals of same species & together they constitute a pop.
Community
All of the populations together
Ecosystem
when considered along w/ the physical, nonliving environment
