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Chapter 25: Populations and Ecosystems (Structure of Populations (Local…
Chapter 25: Populations and Ecosystems
Plants in Relation to Habitats
operational habitat:
aspects of habitat that affect a plant
habitat:
set of conditions in which an organism completes its life cycle
no plant is migratory, but portions of plant are
spores, pollen, fruits, seeds, etc move thru habitat
for migratory animals, summer/winter area & migration routes are all habitat components
Abiotic Components:
Climate: includes temp, rainfall, relative humidity, wind, etc
tolerance range:
range between high & low extremes that a plant grows
#affects species composition
avg. temp not as important as range of extremes
Soil Factors: soil varies in mineral composition and nutrients available
A
Horizon
uppermost soil layer, consists of litter & debris
B
Horizon
zone where material from
A
horizon accumulate
rich in nutrients & contains humus and clay
C
Horizon
composed mostly of parent rock & rock fragments
Latitude & Altitude: affects amount of sunlight/seasons the plant experiences
Disturbances: fire, landslides, avalanches, floods, etc.
Biotic Components:
Plant Itself: by existing in the habitat the plant modifies it
Other Plant Species: several species occurring together increases possibility for interaction
mutualism:
when interaction is positive for both organisms
competition:
interaction is negative, species use same resources
#allelopathy gives plants competitive advantage
competitive exclusion:
whichever species is less adapted is excluded from ecosystem by better adapted species
niche:
conditions that specific species is adapted to occupying
Structure of Populations
Geographic Distribution
limiting factor: one factor that determines health of plant
any factor can act as limiting factor
Local Geographic Distribution
random distribution: used whenever there is no obvious identifiable pattern in position of plants
clumped distribution: spacing between plants small or large, but not consistent
uniform distribution: all individuals evenly spaced from neighbors
allelopathy:
use of chemicals by one plant to inhibit nearby growth of other plants
allelochemics:
chemicals used in allelopathy
Demography
def: relative proportions of young, middle-aged, and old individuals
2 Factors
generation time:
length of time from the birth of one individual until the birth of its first offspring
biotic potential:
number of offspring produced by individual that live long enough to reproduce
does not equal the # of seeds produced
represented as
”r”
large # of healthy/viable seeds = large
r
/biotic potential
carrying capacity:
symbolized by
”K”
the # of individuals in each pop. that can live in particular ecosystem
r- and K-Selection
r-selection:
#more successful in less stable operational habitat
disturbance usually creates
r
conditions
r-selected species:
produce many small seeds at once
mature quickly
typically annuals/small shrubby perennials
K-selection:
K-selected species:
mature slowly
produce few larger seeds
face more competition from other plants
usually occurs in crowded habitat close to carrying capacity
Structure of Ecosystem
Physiognomic Structure
def: physical size/shape of organisms & distribution in relation to each other
3 Most Useful Categories
Trees
Shrubs
Herbs
system of
life forms
defined by C. Raunkiaer (1934)
geophytes:
places buds below ground
bulbs/rhizomes
phanerophytes:
winterizes buds
trees/vines
classified by means in which plant survives stressful seasons
Temporal Structure
def: changes that an ecosystem undergoes with time
can be as short as a day or decades long
seasons part of temporal structure
Species Composition
refers to number & diversity of species that coexist in ecosystem
depends on climate, soil quality, and species tolerance range
Trophic Levels
basically feeding levels, also called
trophic pyramid
primary producers:
bring energy into system (autotrophs)
primary consumers:
consume prim. producers (usually herbivores)
secondary consumers:
consume prim. consumers (usually carnivores)
decomposers:
break down remains of all trophic levels
energy flow:
flow of energy throughout trophic levels
only
10%
of energy consumed is passed to next level
carbon flow:
flow of carbon throughout trophic levels
