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Chapter 25: Populations and Ecosystems (The Structure of Ecosystems…
Chapter 25: Populations and Ecosystems
Plants in Relationship to Their Habitats
Biotic Components of the Habitat
Other Plant Species
Competition
Disadvantageous interaction
Mutualism
Beneficial interaction for both organisms
Niche
Competitive Exclusion
Whichever species is less adapted is excluded from the ecosystem by superior competitors
Organisms Other Than Plants
Herbivores
Process is called herbivory
Browsing - eating twigs and leaves of shrubs - deer, giraffes
Animals that eat plants
Grazing
Eating herbs - sheep, cattle
Predation
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Food source or some other form of resource
Is a relationship in which one species benefits and the other is harmed
Pathogenic
Many interrelationships between plants and fungi or bacteria are harmful to the plant, but the fungi and bacteria are described as being pathogenic
Commensal Relationships
Common between plants and animals
One species benefits and the other is unaffected
The Plant Itself
Habitat modification may be beneficial, detrimental, or neutral to the continued success of that species in its own habitat
The plant itself, just by being in a habitat, modifies the habitat and is a part of it
Abiotic Components of the Habitat
Soil Factors
Initially, the resulting soil is thin and virtually identical to the parent rock in its chemical composition
Pioneers - first plants that invade a new soil
Are formed by breakdown of rock
A horizon is uppermost and is sometimes called the zone of leaching
B horizon is the next layer - zone of deposition
C horizon - Below that layer - composed mostly of parent rock and rock fragments
Latitude and Altitude
Latitude - the angular distance north or south from the equator of a point on the earth's surface, measured on the meridian of the point.
Altitude - the height of anything above a given planetary reference plane, especially above sea level on earth.
Climate
The growing season of an area is often determined by the date of the last severe, killing frost in the spring and the first killing frost of autumn
Tolerance range - between the low and high extremes
Critically important for all organisms
Disturbances
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Way to prevent flooding
Disturbances are phenomena such as fires, landslides, snow avalanches, and floods
Habitat
Habitat is the set of conditions in which an organism completes its life cycle
Operational Habitat
Aspects of the habitat that definitely affect a plant constitute its operational habitat, whereas all component, whether with known effect for not, are its habitat
Ex) Redwood forests in California
The Structure of Populations
Age Distribution: Demography
Demography - the relative proportions of young, middle-aged, and old individuals
Two Factors Affect the Possible Rate of Population Growth
Intrinsic Rate of Natural Increase (Biotic Potential): is the number of offspring produced by an individual that actually live along enough to reproduce under ideal conditions
Generation time: the length of time from the birth of one individual until the birth of its first offspring
The manner in which a population responds by various factors in its habitat is affected partly by its age distribution
Carrying Capacity: the number of individuals in each population that can live in a particular ecosystem is limited
r- and K- Selection
r-Selection
Typically are annuals or small shrubby perennials
A disturbance usually produces r conditions
K-Selection
Douglas firs, and bristle-cone pines
Where a population is close to its carrying capacity
Conditions in a crowded habitat
As the population increases, theoretically it goes through a young phase in which numbers of individuals are low and resources are plentiful
Population growth is limited by the
Species' own biotic potential - r
Geographic Distribution
Local Geographic Distribution
Clumped Distribution
Are those in which the spacing between plants is either small or large, but rarely average
Uniform Distribution
Are the types that occur in orchards and tree plantations: all individuals are evenly spaced from their neighbors
Random Distribution
Is used whenever there is no obvious, identifiable pattern to the position of individuals
Boundaries of the Geographic Range
Limiting Factor
Limits growth
Limits distribution
Limits abudance
Of an organism or population
Soil factors
Often produce abrupt boundaries for the geographic ranges of populations
The ability of a plant species to spread throughout a geographic area is a result of its adaptations to the abiotic and biotic components of that area
The Structure of Ecosystems
Species Composition
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The presence of a large number of species actually creates more niches
Refers to the number and diversity of species that coexist in an ecosystem
It depends on whether the
Climate is mild or stressful
The species' tolerance ranges are broad or narrow
The soil is rich or poor
Trophic Levels
Each ecosystem contains some members, autotrophs, that bring energy into the system
Primary Producers
Autotrophs are known as primary producers
They are the first step of any food web
Trophic levels are basically feeding levels
Primary Consumers
Sometimes called secondary producers
Energy and nutrient supply (food) for the herbivors
Decomposers
Fungi
Bacteria
Break down the remains of all types of organisms
Temporal Structure
The time span can be as short as a day or can encompass seasons or decades
The changes that an ecosystem undergoes with time constitute its temporal structure
Four of the most commonly mentioned structures are the physiognomic structures, temporal structure, species diversity, and trophic levels
Physiognomic Structure
Trees, shrubs, and herbs are the three most useful categories
The physical size and shape of the organisms and their distribution in relation to each other and to the physical environment
