Community Interactions (Sec 3.3 pg 68-73)

Each species has a special role that it plays within the ecosystem. A niche is the overall role of an organism in the community, including the range of abiotic and biotic factors the organism requires and can tolerate.

No two species can occupy the same niche (Fig. 1 p No two species can occupy the same niche (Fig.1 p.68), but many species compete over the same limited common resources.

There are two main types of competition: Inter-specific competition = when two different species compete for the same resources.

There are two main types of competition: Intra-specific competition = when organisms of the same species compete for the same resources.

Some adaptations that allow species to reduce competition include: Resource partitioning = when two competing organisms use the same resource but at different times, in a different way, or in a different place.

Some adaptations that allow species to reduce competition include: Adaptive radiation = when a single species develops a way to become specialized at exploiting smaller parts of the niche (one species becomes many). For example, one species of bird that eats nuts and fruit could evolve into two species of bird – one a specialized nut-eater, the other a specialized fruit-eater.

When foreign species (also called ‘introduced’ or ‘alien’ species) move into an area they may be able to out-compete native species for a particular niche, fill a niche that was not previously filled, or put pressure on native species to adapt in new ways or go extinct.

Humans have introduced many foreign species to new environments (often unintentionally), and some have had devastating effects (e.g. scotch broom). See Fig.3,4,5,6,7 p.69&70. Introduced foreign species can dramatically reduce local biodiversity.

Newly cleared land is always colonized by new plant communities. The gradual change in the types of plants that represent the structure of a community is called ecological succession.

After land is cleared, pioneer species are first to colonize a new environment. The pioneer species change the environment in a way that allows other plants to colonize, and these other plants eventually out-compete the pioneer species

Ecological succession generally takes place in two ways: Primary succession = occurs in lifeless, barren areas (e.g. rock). First producers to move into the area are mosses, lichens, etc. They help to break down the rock and trap tiny pieces of wind-blown soil to form new soil. Grasses and small shrubs begin to grow. Left undisturbed, the community will eventually develop in to a stable ecosystem known as a climax community. Please note primary succession can also occur in aquatic environments (Fig.9 pg.71).

Ecological succession generally takes place in two ways: Secondary succession = begins in areas that already have soil. There may have been a disturbance (fire, flood, forest harvesting). The community will go through different stages of dominant plant types (grasses/shrubs → fast-growing sun-loving trees → slower-growing shade-tolerant trees) until it reaches the climax community.

Succession Video: http://www.youtube.com/watch?v=k03vxRYsJ4Y