ECOSYSTEMS

What is ecology?

What is an Ecosystem?

All of Earth’s inhabitants are woven together into a complex web of relationships. Removing one species from an environment can have affects on the whole system.

Ecology is the study of the interactions of living organisms with one another and with their physical environment (soil, water, climate, etc.)

Habitat and community

The place where a particular population of a species lives is it’s habitat.

A habitat could be a saltwater marsh, an undersea reef, or a grassland, desert, forest or swamp area. Wherever a particular species finds it’s home is it’s habitat.

The many different species that live together in a habitat are called a community.

Many different species may live together in a desert habitat.

What is an ecosystem?

An ecosystem, or ecological system, consists of a community and all the physical aspects of it’s habitat; the living and nonliving parts (such as soil, water, and weather).

Biotic and abiotic factors

The physical nonliving aspects of a habitat (weather, soil, etc) are called abiotic factors.

The living organisms that make up the community of the habitat are called biotic factors.

Together, the biotic and abiotic factors create the ecosystem.

biodiversity

The variety of organisms, their genetic differences, and the communities and ecosystems in which they occur is termed biodiversity.

Imagine taking a square mile of a local forest, and cataloging every type of living organism from trees to plants to insects to animals. The total collection of all the living organisms in a habitat is it’s biodiversity.

The biodiversity of Australia’s Great Barrier Reef is enormous, numbering tens of thousands of species.

Macrocosm to microcosm: range of biotic life forms

Many types of organisms inhabit an ecosystem together and support each other in a web of complex relationships.

Life forms, biotic forms, in a woodland environment may include large animals such as deer and coyote and extend to smaller animals such as squirrels, chipmunks, birds, snakes and lizards.

Interactions of Organisms and their Environments

The living organisms extend down to the trees, grasses, and ferns on the forest floor.

Within the forest soil; insects, worms and even bacteria and microscopic eukaryotes are part of the biotic factors that make up the life of the ecosystem.

Large to microscopic, all living organisms are included.

Lichens and fungi

Many kinds of fungi and lichens grow on trees and rocks within a forest.

These fungi are important living members of the forest ecosystem as well playing an important role in helping break down living organisms after the organisms die.

Abiotic factors

If you were to remove all these living parts; the animals, fungi, insects, birds, reptiles, and forest plants; the nonliving items remaining; the rocks, soil, climate minerals, organic compounds, rain, sunlight, etc, would make up the abiotic factors of the ecosystem

Boundaries of an ecosystem

The physical boundaries of an ecosystem are not always obvious, and they depend on how an ecosystem is being studied.

For example, a scientist may consider a single rotting log on a forest floor if he or she is studying only the fungi and insects of the forest that live in logs.

Interactions of Organisms and their Environments

Often individual fields, forests, lakes or wetlands are studied as an isolated ecosystem.

Of course, no location is entirely separated or isolated. Even oceanic islands get occasional migrant visitors such as birds blown off course.

Succession, primary succession, and secondary succession

A regular procession of species replacement is called a succession.

Pioneer species are the first wave of life in a new habitat and are called the primary succession.

Succession that occurs where their have been areas of previous growth, such as abandon fields or forest clearings, are called secondary succession.

Process of succession

It was once thought that stages of succession were predictable and that succession always led to the same final community of organisms within any particular ecosystem.

Ecologists now realize that initial conditions and random chance play a role in the process of succession.

For example, if two species are in competition for food, a sudden change in climate may favor the success of one species over the other. For this reason, no two successions are alike.

Process of Succession

Glacier Bay:

A good example of a primary succession is a receding glacier because land is continually being exposed as the face of the glacier moves back.

The glacier that composes much of the head of Glacier Bay in Alaska has receded some 100 kilometers over the last 200 years.

The most recently exposed areas are piles of rocks and gravel that lack any usable nitrogen that is needed by plants to establish themselves.

Process of Succession

Glacier Bay: example of succession

The seeds and spores of the first pioneer species are carried in by the wind.

These include lichens, mosses, fireweed, willows, cottonwoods, and dryas ( a plant about a foot across).

At first, all these plants grow low to the ground, severely stunted in their growth by a lack of mineral nutrients.

Eventually the dryas crowd out the other plants.

Process of Succession

Glacier Bay: example of succession

After about 10 years, alder seeds blown in from distant sites take root.

Alder roots have nitrogen-fixing nodules so they are able to out-grow the dryas.

Dead leaves and branches from the alders gradually add more usable nitrogen to the soil. The added nitrogen allows cottonwoods and willows to invade and grow with increased numbers.

Process of Succession

Glacier Bay: example of succession

After about 30 years, dense thickets of alder, willow, and cottonwood shade and eventually kill off the dryas.

The pioneer species make life possible for the later species which push them out once conditions exist to let them flourish.

Process of Succession

Glacier Bay: example of succession

After 80 years after the glacier first exposes the land, Sitka spruce invades the thickets.

Spruce use the nitrogen released by the alders and eventually form a dense forest.

Process of Succession

Glacier Bay: example of succession

The spruce blocks the sunlight from the alders and eventually the alders die off.

After the spruce becomes established, hemlock trees began to grow. Hemlocks are very shade tolerant and have a root system that works well with spruce, sharing the nitrogen in the soil so both species grow well in tandem.

Process of Succession

Glacier Bay: example of Succession

This community of spruce and hemlock proves to be a very stable ecosystem from the perspective of human time scales.

This system is not permanent however. As the local climate changes, the forest ecosystem must change and adapt as well.