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Populations and Ecosystems (Plants in Relationship to Their Habitats…
Populations and Ecosystems
Concepts
Ecology
The study of organisms in relationship to all aspects of their surrounings
An individual plant never exists in isolation in a habitat
There are other individuals of the same species and together they constitute a population
A population of plants can sustain a population of pollinators
All of the populations together constitute a community
When considered along with the physical, nonliving environment it is an ecosystem
Populations are rarely stable
Change is much more common
Plants in Relationship to Their Habitats
The set of conditions in which an organism completes its life cycle
Habitat
Pollinators are critically important aspects of the habitat for the plant species they pollinate
Aspects of the habitat that definitely affect a plant constitute its operational habitat
Whereas all components, whether with known effect or not, are its habitat
Two types of habitat components
Abiotic
Nonliving and are physical phenomena
Climate
Critically important to all organisms
Soil
Formed by the breakdown of rock
1 more item...
Distinct soil with 3 layers or horizons
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Latitude
Contributes many factors to the abiotic environment
Altitude
Disturbances such as fires, floods, and avalanches
Affect the biotic factors directly
Biotic
Living factors
The plant itself
Other plant species
Species of animals
Fungi
Protists
Prokaryotes
Niche
Each species is assumed to be adapted to s particular set of conditions
Ecotypes
Long before the various subpopulations could be called subspecies, they would be called ecotypes
Commensal relationships
In which one species benefits and the other is unaffected
Predation
A relationship in which one species benefits and the other is harmed
Herbivores
Animals that eat plants
The process is called herbivory
More precisely delimited as browsing or grazing
Fungi and bacteria
Described as being pathogenic
The Structure of Populations
Limiting factor
The growth of any organism depends on the availability of many factors such as water, light, and various nutrients
The rate of the organism's growth is limited by whichever factor is in short supply
Applies to all aspects of a plant's interaction with its habitat
Any factor of the ecosystem can act as a limiting factor
Random distribution
Used whenever there is no obvious identifiable pattern to the position of individuals
Has no predictive value
Clumped distributions
Are those in which the spacing between plants in either small or large, but rarely average
Uniform distributions
The types that occur in orchards and tree plantations
All are evenly placed from their neighbors
Age distribution
Is the manner in which a population responds to various factors in its habitat
Demography
The relative proportions of young, middle-aged, and old individuals
Two factors that affect the possible rate of 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
Is the number of offspring produced by an individual that actually live long enough to reproduce under ideal conditions
r- and K- Selection
r-selected species
Typically are annuals or small shrubby perennials because the disturbed habitat gradually changes back into a crowded one that is no longer suitable for the pioneer r species.
K-selected species
Many long-lived conifers such as redwoods, Douglas firs, and bristle-cone are good examples
The Structure of the Ecosystem
Physiognomic structure
The physical size and shape of the organisms and their distribution in relation to each other and to the physical environment
Temporal Structure
The changes that an ecosystem undergoes with time
Species composition
Refers to the number and diversity of species that coexist in an ecosystem
And depends on whether the climate is mild or stressful, the soil is rich or poor, and the species' tolerance ranges are broad or narrow.
Trophic levels
Feeding levels
Autotrophs
Primary producers
Herbivores
Primary consumers
Carnivores
Secondary consumer
Decomposers
Fungi and bacteria break down the remains of all types of organisms
Energy flow and carbon flow
Energy and carbon compounds move from one trophic level to the next
