BIOLOGY 403:
PRINCIPLES OF ECOLOGY
(Communities, Succession, Biomes)
COMMUNITIES
• DEFINITION
a community is a unit composed of two or more
interacting species in a given area
• Communities have boundaries in space and time.
• How many communities are there on the earth?
One ???
Millions ???
• Ecotone
zone between communities where composition
very rapidly changes from that typical of one
community to that typical of the other
ECOTONE
• A ‘pressure’ zone
(an intermediate / intergrading area)
• May be narrow or wide
• May have larger flora / fauna than
adjacent communities --- WHY ???
• May have species unique to it
EMERGING CHARACTERISTICS
IN COMMUNITIES
• Dominant (= Keystone) Species / Subordinant
Species
• Stratification (= Layering)
• Phenology (rhythmic seasonal patterns)
• Succession
a non-cyclic process in which species /
communities in a particular area are replaced by
other species / communities over time (the ‘life
history’ of a community)
• Sociability --- the + or – affinity one species has
for another
ECOLOGICAL SUCCESSION (I)
ECOLOGICAL SUCCESSION (II)
ECOLOGICAL SUCCESSION (III)
ECOLOGICAL SUCCESSION (III)
• What causes it?
Organisms and the changes they create are
the driving force.
• Types of Succession
Primary
occurs on a primary bare area
Secondary
occurs on a secondary bare area
ECOLOGICAL SUCCESSION (IV)
• Sere - the whole sequence of communities in a
particular succession
(Xerosere, Mesosere, Hydrosere)
OFTEN: X  M  H
• Pioneer (species of community)
the first species to invade an area
• Seral (species or community)
those which occupy intermediate positions in a
succession (early, mid, late, etc.)
• Climax (species or community)
those occupying the final position in a succession
(Monoclimax or Polyclimax ?????)
CLIMAX COMMUNITIES (I)
• DEFINITION:
dynamic steady state community whose
characteristics are determined by the
characteristics of its habitat / environment
• Primary Climax
do not depend on recurrent disturbances by fire or
animals to maintain floristic / faunal composition
Climatic Climax --- on normal soils, with average
topography, and thus only the macroclimatic
conditions are controlling it.
Edaphic Climax --- develops differently from what one
expects for the macroclimatic conditions due to an
unusual soil
Topographic Climax --- develops differently from
others in the same region due to a distinctive
microclimate
CLIMAX COMMUNITIES (II)
• Disclimax
all climaxes that maintain their floral / faunal
composition only as a result of persistent
disturbances of the same kind, frequency and
intensity
- Fire
NJ Pine Barrens
Some Grasslands
- Zootic
Some Grasslands
TRENDS DURING SUCCESSION (I)
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Stage in Ecosystem Development
Attribute
Young
Mature
-------------------------------------------------------------------------------Biomass
low
high
Trophic Relationships
simple
complex
Food Chains
short, grazing
long, detritus
Food Webs
simple
complex
Stratification
less
more
Species Diversity
low
high
Niche Specialization
broad
narrow
Feeding Relations
general
specialized
Life Cycles
short, simple
long, complex
Population Control
Mechanisms
physical
biological
TRENDS DURING SUCCESSION (II)
Stage in Ecosystem Development
Attribute
Young
Mature
-------------------------------------------------------------------------------• Fluctuations
greater
lesser
• Stability
low
high
• Potential Yield to
Humans
high
low
• Net Community
Production
higher
lower (0 ??)
• Community Respiration
lower
higher
• Community P / R Ratio
P>R
P=R
PHYSIOGNOMIC TYPES OF
VEGETATION (I)
• Physiognamy --- landscape appearance due to
occupying vegetation type(s)
• Forest --- tall trees covering the area densely and
uniformly (needle-leaved, broadleaved evergreen,
broadleaved deciduous; OPEN vs. CLOSED)
• Woodland when trees are of a lower stature
• Gallery forest or woodland --- in a strip along
stream courses (subdivided as in forest)
PHYSIOGNOMIC TYPES OF
VEGETATION (II)
• Savanna --- singly scattered trees or shrubs over a
more continuous phase of low vegetation
• Groveland --- clusters of trees or shrubs scattered
over a more continuous phase of low vegetation
• Parkland --- ‘islands’ of low vegetation (the
PARKS) interspersed in a more continuous phase
of forest
PHYSIOGNOMIC TYPES OF
VEGETATION (III)
• Scrub (Shrub) area covered by lower growing
woody vegetation (subdivided as in forest)
• Grassland --- herbs are the dominant vegetation
– Steppe --- xerophytic herblands (usually dominated by
narrow- leaved grasses)
– Meadow --- Mesophytic herblands (usually dominated
by broader-leaved grasses and forbs)
• Shrub-Steppe --- mixture of low shrubs and
grasses sharing dominance in an arid area
BIOMES
• DEFINITION
• a large area, on land, characterized by certain
dominant climax plant species
• why characterized by the plants instead of
animals????????
• The major Biomes
• see class handout for their names and the
conditions causing them
TEMPERATURE, MOISTURE
AND BIOMES
BIOMES OF THE WORLD
LATITUDE, ALTITUDE & BIOMES
N. & S. AMERICAN BIOMES
DESERTS OF THE WORLD
GRASSLANDS AND THEIR ORGANISMS