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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?
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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 (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 ControlMechanisms 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
