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)

Stage in Ecosystem DevelopmentAttribute 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 DevelopmentAttribute Young Mature--------------------------------------------------------------------------------

• Fluctuations greater lesser

• Stability low high

• Potential Yield toHumans high low

• Net CommunityProduction 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