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Ch. 25 Populations and Ecosystems (Concepts (habitat (set of conditions in…
Ch. 25 Populations and Ecosystems
Structure of Ecosystems
Physiognomic Structure
size, shape, and an organism's distribution
life forms
criteria is their means of surviving stress
ex.
therophytes
geophytes
hemicryptophytes
chamaephytes
ohanerophytes
Temporal Structure
changes an ecosystem undergoes with time constitute
can be as short as a day or encompass seasons or decades
Species Composition
number& diversity of species that coexist in an ecosystem
depends on
climate is mild or stressful
soil is rich or poor
species tolerance ranges are broad or narrow
Trophic Levels
feeding levels
primary producers
autotrophs
1st step of any food chain
energy & nutrient supply for primary consumers
primary consumers
herbivores
consumer primary producers
secondary consumers
carnivores
prey on primary consumers
decomposers
fungi and bacteria
break own remains of all types of organisms
energy & carbon flow
movement of energy & carbon compounds
from plants, to herbivores, to carnivores, to decomposers
Structure of Populations
Geographic Distribution
boundaries of the geographic range
limiting factor
factor that determines health of the plant
applies to plants interactions with its habitat
local geographic distribution
random distribution
no identifiable pattern
no predictive value
clumped distribution
spacing b/tween plants either small or large
rarely average
uniform distributions
occur in orchards & tree plantations
all evenly spaced
zones
prevents germination or growth of others
can be established by release of chemicals
allelochemicals
Age Distribution: Demography
age distribution
proportions of young, middle-aged, and old individuals
its demograhy
Two factors that affect rate of population growth
generation time
until the birth of its first offspring
affects rapidity of population growth
length of time from birth of one individual...
intrinsic rate of natural increase
or biotic potential
number of offspring produced by an individual
that live long enough to reproduce under ideal conditions
r- and K- selection
r- selection
annuals or small shrubby perennials
a disturbance produces r conditions
resources are then plentiful for the few plants that remain
K- selection
conditions in a crowded habitat
Douglas firs and bristle-cone pines
face intense competition from other plant species
Plants in Relationship to Their Habitats
Abiotic Components of the Habitat
Climate
tolerance range
ranges very greatly from species to species
components
temperature
rainfall
relative
humidity
winds
Soil Factors
pioneers
first plants that invade a new soil
must tolerate severe conditions
3 layers of horizons
A horizon
uppermost, zone of leaching
rainwater wash nutrients down to next layer
consists of litter and debri
B horizon
zone of deposition
area where materials from A horizon accumulate
C horizon
composes of parent rock and fragments
Latitude and Altitude
equator
all days are 12 hours long
no seasonal variation
plants cannot measure season by photoperiod
Artic & Antarctic Circle
mid summer days= 24 hours long
mid winter nights= 24 hours long
regions of high altitude= high latitude
Disturbance
ex.
fire
landslides
snow avalanches
floods
man-made ex.
insecticides
herbicides
hunting
habitat destruction
affect biotic factors
completely eliminating many or all individuals
alters species relationships in an ecosystem
Biotic Components of the Habitat
Other Plant Species
mutualism
interaction is beneficial for both organisms
competition
interaction that is disadvantageous
plants compete for
light
soil nutrients
water
attention of pollinators
competitive exclusion
whichever species is less adapted
is excluded from the ecosystem
niche
each species is adapted to a particular set of conditions
ecotypes
subspecies before they were named
Organisms Other Than Plants
commensal relationships
one species benefits, other is unaffected
predation
one species benefits, other is harmed
buffalo and plants
herbivores
animals that eats plants
herbivory
process of eating plants
browsing
eating twigs & leaves of shrubs
deer, giraffes
grazing
eating herbs
sheep, cattle
pathogenic
plants and fungi, bacteria
The Plant Itself
modifies the habitat
Habitat modification may be
beneficial
detrimental
neutral
Concepts
ecology
study of organisms in relationship to all aspects of their surroundings
population
a group of individuals of the same species
community
all of the populations together
ecosystem
physical, nonliving environment
habitat
set of conditions in which an organism completes its life cycle
operational habitat
