EPHM7110 Chap.1 Ecosystems and the Levels of Biological Organisation
Ecosystems and the Levels of Biological Organisation
Biodiversity is held at three levels, not one
The course opens with biodiversity described as the variety of organisms, and it is careful to say that the variety sits at three levels at once: ecosystems, species and genes. That variety maintains the balance of the system because every component occupies its own niche, its own role. Holding the three levels apart matters more than it first appears.
A site can keep its species list intact while losing most of its genetic variation and one of its two habitat types, and a summary that counts species alone will record no change at all.
A ladder where each rung buys a new kind of statement
The organisation ladder runs from the atom, the smallest unit of an element that still shows the element's properties, through the molecule and the cell, The smallest unit that is itself alive and does the work of living, to the organism, one individual living being.
Above the organism the gains stop being chemical and become ecological. A population adds a defined space, a community adds other species, an ecosystem adds the non living environment of matter and energy, and the biosphere is everywhere in the air, water and soil that life reaches.
A finding is only as strong as the rung it belongs to.
The species rung is stricter than it looks
Members of one species breed only with each other, and four features are used to decide: shape, colour, behaviour and the genes that distinguish one species from every other.
Three of those four are visible in the field and the fourth usually is not, which is the practical reason field surveys under count species that look alike, and the reason risk assessment keeps a category for taxa with insufficient data.
Where the physical system enters, and why rate matters
An ecosystem is A community taken together with the matter and energy of the place it occupies, and the consequence the course draws is precise.
Every species in a community carries adaptations suited to that particular physical environment. Should those conditions move, the species change with them and in their relationships, and extinction follows once the shift outruns the pace at which useful traits can spread.
The danger is located in the rate of change rather than in its direction, which is why a shift of a given size can be survivable over ten thousand years and lethal over fifty.
What this chapter covers
- 01
Biodiversity at three levels: ecosystems, species and genes
- 02
The niche as a role, and why every component has one
- 03
The organisation ladder from atom to biosphere
- 04
Four features used to separate one species from another
- 05
The ecosystem rung, where matter and energy join the community
- 06
Rate of change, adaptation and the point at which extinction follows
- 07
Atmosphere, hydrosphere and lithosphere as the earth's life support systems
- 08
Solar energy, cycling of matter and gravity as the three sustaining factors
Put four field notes on the rung each one can support
- 3Place the first two notes and say what each rung licenses.
- 3Place the third and fourth notes.
- 2Name the note that could explain the other three, and why.
Key terms
- Biodiversity
- The variety of organisms, held at three levels at once: ecosystems, species and genes.
- Niche
- The role a component plays in maintaining the balance of the system it belongs to.
- Species
- A single kind of living thing whose members resemble one another in appearance, behaviour, chemistry and genetic make up and can breed together.
- Population
- All the members of one species inside a stated area.
- Community
- Populations of different species living in one place and potentially interacting with each other.
- Ecosystem
- Several species living together and trading matter and energy with the non living surroundings they share.
- Biosphere
- Everywhere in the planet's air, water and soil that life reaches, taken as the sum of all ecosystems.
- Lithosphere
- The earth's crust and upper mantle, about one hundred kilometres thick, in oceanic and continental forms.
Ecosystems and the Levels of Biological Organisation FAQ
Why does the course insist on three levels of biodiversity rather than a species count?
Because a place can hold every one of its recorded organisms and still be losing the thing that keeps it working. Genetic variation inside a small remnant shrinks without any name disappearing from a list, and one of two habitat types can be filled or drained while the checklist stays identical.
Counting names measures the level that is easiest to observe and slowest to respond, so a report built on it will register a loss years after the loss began.
What is actually added when you move from a community to an ecosystem?
Matter and energy. Up to that point everything under discussion is alive, and the statements available are about who eats whom and who lives alongside whom. Adding the physical surroundings lets you ask why any of them is present at all, because soil, water, temperature and light set what the living part can do.
It is also the step that makes a single physical change capable of explaining several biological observations at once.
Does a fast environmental change threaten a species more than a large one?
On the reasoning this course uses, speed is what makes a change dangerous. Adaptation accumulates slowly across generations, so a shift of any magnitude can be absorbed if there is time for suitable traits to spread. Extinction is described as what happens when conditions move faster than that process, which means the same amount of warming or drying may be survivable over ten thousand years and fatal over fifty.
Exam move
Draw the ladder from memory and put one real observation from a place you know beside each rung. Then check the two rungs you left empty, because those are the levels your evidence about that place does not reach. Finish by writing, in one sentence, what you would have to measure to fill them.
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