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Ch25: Populations and Ecosystems, eco, Indv-Pop-Comm-Eco-Biome-Biosphere, …
Ch25: Populations and Ecosystems
Plants in Relationships to Their Habitats
Abiotic Components of the Habitat
Climate
temperature, rainfall, humidity, wind, etc
extreme temps are more important than average temps
(freezing winters/harsh summers)
Moisture levels range from arid deserts to swampy marshlands (
vast ranges
)
total precipitation isn't as important as seasonal extremes/timing of precipitation
Soil Factors
soils are formed by breakdown of rock
young soils are variable in the amount of macro/micronutrients available
young soils are nitrogen deficient
pioneers
: first plants to invade a new soil
often associated with nitrogen-fixing prokaryotes
must tolerate severe conditions
drastically change the soil- eventually creating a thick soil with a distinct soil profile (3 layers or horizons)
A horizon/zone of leaching
: uppermost layer consisting of litter/debris
B horizon/zone of deposition:
below the A horizon, accumulates the materials from the A horizon, humus and clay, rich in nutrients
C horizon
: below B horizon, parent rock/rock fragments
Latitude & Altitude
at the equator no seasonal variation in day length, plants can't measure season by
photoperiod
higher latitudes
: summer days and winter nights become longer
amount of light energy that strikes the earths surface varies with latitude
High altitude regions are similar to high latitude regions, high winds and poor soil, short growing reason, physiological drought is frequent, much/all of the year is cold
high altitude
: intense ultraviolet light, not fully shielded by ozone, oxygen, CO2, water vapor
Disturbance
fires, landslides, avalanches, floods
directly impact biotic factors, little/no impact on climate, lat/alt.
man-made: insecticides, herbicides, hunting, habitat destruction
Biotic Components of the Habitat
The Plant Itself
trees providing canopies, altering light levels
only disturbances can create the open habitats needed for pine seedlings
moraines: great mound of rubble, sand, and boulders left behind by glaciers retreating
pioneer plants colonize and enrich the soil
sitka spruce and hemlock become established
this creates low light for the pioneer plants and they eventually die off
Other Plant Species
mutualism
interactions between species that are beneficial for both organisms
competition
if the interaction/relationship is not beneficial then it's competition
competition for light, water, nutrients, attention from pollinators/seed dispersers
competitive exclusion
: (theory) in the result of competition, whichever species is less adaptive is excluded from the ecosystem by superior competitors
niche
: each species has a set of conditions that they're adapted to that no other species is adapted to use as efficiently
example: some plants like full sun and some like partial shade/low light
refers to aspects of the habitat that directly affect a species
range of seasonal rainfall, range of soil moisture/flooding, range of temperature, presence of appropriate pollinators, etc
Refer to page 704
alternative to competitive exclusion: refer to the
overlap zone
, two species can coexist but if either is removed then the other can take advantage of the overlap zone defined by competition, and can grow more effectively
long term result of competition should be species modification by natural selection
ecotypes: before subpopulations could be called subspecies, they were ecotypes
each specialized in response to ecosystem factors locally
Organisms other than Plants
animals, fungi, prokaryotes
interrelationships between plants and these organisms can be beneficial or detrimental
pollination? most instances are mutualistic
seed dispersal by fruit eating animals? mostly mutualistic
Commensal relationships
one species benefits and the other is unaffected
birds building nests in trees? mostly commensal
sticky fruits or seeds attaching to animal fur and getting dispersed? mostly commensal
Predation
one species benefits and the other is harmed
herbivory, browsing, grazing
many interrelationships between plants/fungi or plants/bacteria are harmful to the plant
the bacteria/fungi are mostly called pathogenic rather than predatory
microbial endophytes
Habitat
: set of conditions in which an org completes its life cycle
Migratory parts of plants
: spores, pollen, seeds, fruits, vegetative propagules
Operational Habitat
: aspects of the habitat that affect a plant
The Structure of Populations
r- and K-Selection
species own biotic potential: r.
when resources are plentiful and number of individuals is low
When resources are more scarce and an ecosystem is crowded, carrying capacity (K) of an ecosystem determines population growth
a disturbance usually produces r conditions
r-selected species are usually shrubby perennials or annuals
K-selected species example: long living conifers, grow in crowded and competition rich environments
Age Distribution: Demography
the relative proportions of young, middle-aged, and old individuals
mostly applied to animal populations, may be difficult to apply to plants
refers to reproduction rates and population growth
generation time
: the length of time from the birth of one individual until the birth of its first offspring
intrinsic rate of natural increase/biotic potential
: number of offspring produced by an individual that live long enough to reproduce under ideal conditions
carrying capacity
: number of individuals that can be supported by an ecosystem.
Represented by the number K.
Boundaries of the Geographic Range
at any given time and locality ONE factor determines the health of the plant:
limiting factor
plant species spreading depends on adaptations to abiotic and biotic components
could be light intensity, rainfall frequency, herbivores, etc
Local Geographic Distribution
small-scale, local distribution of individuals
three types of distribution
: random, clumped, uniform
random
: when there is no identifiable pattern to the position of individuals
clumped
: spacing between plants is small or large, but rarely average
uniform
: orchards/tree plantations, all individuals are evenly spaced from one another (not common in natural environments)
zones can be established by the release of chemicals from plants that inhibit other plants
the inhibitory chemicals:
allelochemics
. The inhibition:
allelopathy
.
Structure of Ecosystems
Physiognomic Structure
physical size and shape of organisms and their distributions in relation to each other and to the physical environment
Raunkiaer defined a system of life forms in 1934
classification relied on the means by which the plant survives in stressful seasons
Temporal Structure
the changes that an ecosystem undergoes with time
can be studied as a day, a year, months, decades, etc
ex: plants changing with the seasons
Species Composition
refers to the number and diversity of species that coexist in an ecosystem
depends on climate, soil, tolerance ranges
stressful climates with poor soil support a small number of species
Trophic Levels
dominant method: photosynthesis
accounts for virtually all energy input
feeding levels
algae and cyanobacteria carry about 1/3 of all photosynthesis worldwide
autotrophs are primary producers. Primary consumers (small herbivores), secondary consumers (carnivores), tertiary consumers (top carnivores).
decomposers: fungi and bacteria that break down the remains of all types of organisms
energy flow/carbon flow
: transfer of energy and carbon compounds up through the trophic levels beginning with the primary producers
Indv-Pop-Comm-Eco-Biome-Biosphere
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Niche
Two factors that affect rate of population growth
Physical
Time
Number/Diversity
Food Chain
