Transcript BIOLOGY 154: ECOLOGY and ENVIRONMENTAL ISSUES

BIOLOGY 157:
LIFE SCIENCE: AN
ENVIRONMENTAL APPROACH
(Communities and Succession)
COMMUNITIES I
• DEFINITION:
a community is a unit composed of two or more
interacting species in a given area
• How many communities are there on the earth?
One ???
Hundreds ???
Thousands ???
Millions ???
It all depends on how you ‘define’ it.
COMMUNITIES II
• Community Diversity:
the number of species and strains in a community
• Community Complexity:
(= Ecological Diversity )
the number of trophic levels and how the species
are distributed among the trophic levels
• Communities have boundaries in space and time.
ECOTONES
• Ecotone
zone between communities where composition
very rapidly changes from that typical of one
community to that typical of the other
• Ecotones are ‘pressure’ or ‘tension’ zones
• Ecotones often have a greater biodiversity than
either of the adjacent communities
• Ecotones can be narrow or wide
• Ecotones and adjacent communities can shift over
time
ECOTONES (narrow)
ECOTONES (narrow)
EDGE EFFECT (I)
• Related to ecotones
• Size of the area and shape of the area interact
• Two areas of the same size may have very
different shapes and thus very different
amounts of ‘edge’.
• How does this affect species in those areas?
EDGE EFFECT (II)
COMMUNITY PRODUCTIVITY
EMERGING CHARACTERISTICS
IN COMMUNITIES
• Dominant (= Keystone) Species and
Subordinate Species (may not always be
related to abundance)
• Stratification (= Layering)
• Succession:
a non-cyclic process during which species /
communities in a particular area are replaced
by other species / communities over time
= the ‘life history’ of a community
ECOLOGICAL SUCCESSION (I)
ECOLOGICAL SUCCESSION (II)
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)
• Pioneer (species or 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
CLIMAX COMMUNITY (I)
• DEFINITION:
a steady state community whose characteristics are
determined by the characteristics of its habitat &
environment
• Primary Climax
does not depend on recurrent disturbances by fire or
animals to maintain floristic / faunal composition
Climatic Climax --- forms 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 COMMUNITY (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