Chapter 25 Populations and Ecosystems
Population
an individual plant never exists in isolation in a habitat instead, there are other individuals of the same species
community
all populations together constitute
ecosystem
tied with community
adds to nonliving environment
population are rarely stable
buffalo were shot to make way for train tracks, and they would have eaten the grass removing fuel and then the forest fire wouldn't have occurred
Plants in Relationship to Their Habitats
habitat is the set of conditions in which an organism completes its life cycle
no plants are migratory but portions of plants are spores pollen fruits seeds and vegetative propaguales
small herbs would not effect large standing trees
opperational habitats
aspects of the habitat that definitely affect a plant
pollinators are critically important aspects of the habitat for the plant species that they pollinate and any disease organisms or predators that prey on those pollinators are also equally as important
herbs are necessary for the red woods in California
without the herbs there could not be fuel for the fires which then in turn allow seed germination
preventing forest fires impacted the growth of these trees
abiotic
nonliving and are the physical phenomena
climate, soil, latitude, altitude, and disturbances
biotic
components are living factors
the plant itself, other plant species and species of animals , fungi, protists, and prokaryotes
Abiotic Components of the habitat
Climate
critically important to all organisms most species are restricted to certain regions
components of climate include
temperature, rainfall, relative humidity, and winds
the average temperature if a habitat is not as important as its extremes
the lowest winter temperature and highest summer temperature
bromeliad, aroids, and orchids are restricted to frost free places
tolerance range
the high and low extremes
if there is top much water roots drown for lack of soil oxygen
soil Factors
pioneers
the first plants that invade a new soil
soil is formed by the breakdown of rock
soil is thin and virtually identical to the parent rock in its chemical composition
young soils are variable in the amounts of macronutrients and micronutrients they have available
nitrogen is not a significant component of any type of rock it is lacking in young soils
these plants must endure harsh conditions
the soil is usually sandy with large rock particles
little water holding conditions in these soils
many minerals are locked in the rock matrix
associated with nitrogen fixing prokaryotes
cyanobacteria and angiosperms with root nodules
horizon
roots reach through to bedrock breaking down soil
thick soil with distinct soil profile with three layers
(A) horizon is the uppermost and is sometimes called the zone of leaching contains litter and debris
(B) Horizon zone of deposition
water washes rain water into layer B
B is where materials from A horizon accumulate it is rich in nutrients and contains both humus and clay
(c) horizon composed of parent rock and rock fragments
Latitude and Altitude
contributes to the abiotic environment
at the equator all days are 12 hours long
at higher altitudes
no seasonal variation
plants cannot measure season by photoperiod
summer days are longer and so are winter nights
above the arctic and Antarctic circles
mid-summer days are 24 hours long same with nights
at intermediate and higher latitudes day length is an indicator of season
some species are sensitive to photoperiod
the amount of light energy that strikes a given area of earths surface varies with latitude
Disturbance
fires , landslides, snow, avalanches, and floods
affect biotic factors
causes a radical change in environment
fire is natural in dry ecosystems
lightning storms occur often without rainfall
plants and debris accumulate and then lightning strikes burning them clearing debris
plants have become fire resistant
some pine trees have a thick flame resistant bark, and the flames cannot hurt the vascular cambian
lower portions of trunk have no branches due to self pruning and then flames cannot reach them
this causes only small plants to be burned
Biotic Components of the Habitat
The plant itself
an individual just being in the habitat modifies the habitat and is a part of it
habitat modification may be beneficial, detrimental, or neural to the continued success of a species in its habitat
mature plants create a habitat that allows the success of its own species
aka beech and oak trees with a thick canopy
pine seedlings do not grow well in the shade of older pines
only disturbances can create open habitats needed for seedling pines #
Glaciers leave behind moraines
the soil is poor with no humus and few nutrients
pioneer species such as alder willow and fireweed colonize these exposed morines #
Other Plant Species
when several individuals of either just one or several species occur together the possibility for interaction is created
mutualism
interaction that is beneficial
competition
interaction among species that is disadvantageous
two populations that do not grow together
many plants compete with each other for light, soil, nutrients, water and attention of pollinators and seed dispersers
roots might grow and compete with other root systems
if a plant were allowed to grow by itself it would produce more gametes
competitive exclusion
whichever species is less adapted is excluded from the ecosystem
each species is adapted to their own niche
ecotypes
before divergent speciation
transplant experiments
these test ecotypes and if they exist
plants from a site are transplanted to an alternate site and then plants are grown together in a:
common garden
Organisms other than plants
frugivores
seed dispersal by fruit eating animals
benefits species as long as animal doesn't chew seeds and digest embryos
example of mutualism is the association of certain ants and acacias #
acacias are small trees with enlarged hollow throne at their leaf base
thorns are used as ready made homes for ants
acacias also produce nectar and their leaflet tips are modified into golden yellow food bodies
commensal relationships
one species benefits and the other is unaffected
predation
one species benefits and the other is unaffected
herbivores
plant eaters
browsing and grazing
Geographic Distribution
Boundaries of the Geography
limiting factor
most habitat components act on the plant simultaneously most are considered to be important at any given time and locality one factor alone determines the health of a plant
the concept of limiting factors applies to all aspects of a plants interaction with its habitat
Local geographic distribution
Random Distribution
clumped
not uniform
no obvious identifiable pattern to the position of individuals
Clumped Distribution
those in which the spacing between plants is either small or large but rarely average
seeds of a plant fall near plant, not in random places
if a bird eats fruit it will deposit the seeds in a clumped area
uniform distribution
types that occur in orchards and tree plantations all individuals are evenly spaced from their neighbors
not common in the wild
Allelochemics
chemicals released from plants to deter other plants
the inhibition of other plants is called allelopathy
Age Distribution: Demography
Two factors affect the possible rate of population growth generation time and inartistic rate of natural increase
Age distribution
manner in which a population responds to various factors in its habitat
its demography the relative proportions of young, middle aged, and old individuals
difficult to apply to plants
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 actually live long enough to reproduce under normal conditions
carrying capacity
the number of individuals in each population that can live in a particular ecosystem is limited
r- and K- Selection
r- selection
K- selection
disturbance usually profiles r conditions
fire or flood
r- related species
typically are annuals or small shrubbery
few defenses against predators
conditions in a crowded habitat where a population is close to its carrying capacity select for phenotypes very different from those that are beneficial in a disturbed habitat
in a disturbed habitat virtually all areas are good for seed germination and growth
its advantageous to live for a long time
K-selected species
douglas firs, bristle-cone pines
face intense competition from other plant species and therefor adaptions that increase the ability to use scare resources are beneficial
Temporal structure
the changes that an ecosystem undergoes with time constitute its temporal structure
can be as short as a day or can encompass seasons or decades
spring has a lot of renewed activity
spring brings fruits and mature seeds in summer
late summer and autumn
herbs die and trees develop resting buds
Physiognomic Structure
the physical size and shape of the organisms and their distribution in relation to each other and to the physical environment constitute the physiognomic structure
life forms
criterion for the classification was the means by which the plant survives stressful seasons such as by placing buds below ground
Species Composition refers to the number and diversity of species that coexist in an ecosystem and it depends on whether the climate is mild or stressful
Trophic Levels are feeding levels
Primary producers
autotrophs
Primary Consumers
first step in any food web
secondary producers
herbivores are preyed on by carnivores aka the secondary consumers
omnivores exist on both trophic levels
Decomposers are fungi and bacteria
energy flow and carbon flow
how energy is passed down
