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Populations and Ecosystems (Plants in Relationship to Their Habitats…
Populations and Ecosystems
Plants in Relationship to Their Habitats
Habitat= set of conditions in which an organism completes its life cycle
Operational habitat= aspects of the habitat that definitely affect a plant
Abiotic Components of the Habitat
Climate
Temperature
Rainfall
Relative humidity
Wind
Soil Factors
Pioneers=first plant to invade soil, very harsh
A Horizon= zone of leaching
B Horizon= zone of deposition
C Horizon= Parent rock and rock fragments
Latitude and Altitude
Day length and seasonal variation
Altitude variations
Disturbance
Phenomena that produce a significant, often radical, change in an ecosystem quickly
Fires, landslides, snow, avalanches, and floods
Biotic Components of the Habitat
The Plant Itself
Individuals modify the environment by virtue of their presence and subsequent interactions with ecosystem
Other Plant Species
Mutualism
Competition
Competitive exclusion
Niche
Ecotypes
Transplant experiments
Common Garden
Organisms Other Than Plants
Plants and Animals have many relationships
Commensal Relationships
Predation
Herbivory
Pathogenic Relationships
The Structure of Populations
Geographic Distribution
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Boundaries of the Geographic Range
Limiting Factor
The factor which most directly determines the health of a plant
Oxygen in photosynthesis
Water
Local Geographic Distribution
Three types of local distribution
Random distribution
Clumped distributions
Uniform distributions
Age Distribution: Demography
Relative proportions of young, middle-aged, and old individuals
Two factors affect rate of population growth
Generation time= length of time from the birth of one individual until the birth of its offspring
Biotic potential/Intrinsic rate of natural increase
Number of offspring produced by an individual
Represented in population equations as r
Measured under ideal conditions
Carrying capacity
K
Number of individuals that can realistically live in an ecosystem
r- and K-Selection
r-Selection
A disturbance usually produces r-conditions
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r-selected species are usually annuals or small shruby perennials
bc the disturbed habitat gradually changes back into a crowded one that is no longer suitable for the pioneer r species
K-selection
K-selected species face intense competition from other plant species
Adaptations that increase the ability to use scarce resources are beneficial
The Structure of Ecosystems
Physiognomic Structure
The physical size and shape of the organisms and their distributions in relation to each other and to the physical environment
Trees, shrubs, and herbs are the three most useful categories
Life Forms of Raunkiaer
Temporal Structure
The changes that an ecosystem undergoes with time
Time span can be as short as a day or can encompass decades
Seasonal changes
Species Composition
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Number and diversity of species that coexist in an ecosystem
Depends heavily on the climate
Depends on soil condition
Trophic Levels
Feeding levels
Primary producers
Autotrophs
First step of any food web
Energy and nutrient supply for herbivores
Primary consumers
Herbivores
Eat the primary producers
Prayed on by
Secondary Consumers
Carnivores
Decomposers
Fungi/Bacteria
Recycle valuable materials, i.e; nitrogen, sulfur cycle
Photosynthesis accounts for virtually all energy input
Energy Flow
Carbon Flow
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