Changing Ecosystems Flashcards
3.2.16 Explain the concept of ecological succession (refer to pioneer and climax communities and series)
Explain the concept of ecological succession.
Ecological succession is the process by which the mix of species and habitat in an area changes over time. It can result from:
1. seasonal factors (e.g. rainfall, temperature changes)
2. sudden natural events (e.g. bushfires, cyclones, floods)
3. human activities (e.g land clearing for agriculture and housing)
3.2.16 Explain the concept of ecological succession (refer to pioneer and climax communities and series)
How does ecological succession begin?
Over time a series of intermediate communities form - each one is called a sere. The first sere of succession is called a pioneer community. Pioneer species are opportunists that:
-photosynthesise
-tolerate extreme conditions (extreme sunlight, high winds, salinity)
- have symbiotic relationships with bacteria that fix nitrogen from the air as soil may not be present
- are r-strategists
- have a shirt life cycle
-produce rapidly and have many offsprings (rapid germination of plants)
3.2.16 Explain the concept of ecological succession (refer to pioneer and climax communities and series)
Explain pioneer species.
Pioneer species are hardy species that are the first to colonize barren environments or previously biodiverse steady-state ecosystems that have been disrupted, such as by wildfire. The colonisation of pinoeer species is usually initiated by the dispersal of spores or seedy of hardy autotrophs by the wind or bird droppings. These pioneers survive in areas where limiting factors often include very high intensity, low-water holding capacity of teh substarte due to a lack of organic matter. Some lichens grow on rocks without soil, so may be among the first of life forms, and break down the rocks into soil for plants. Lichens, a mix of fungi and algae,usually colonise bare rock. They produce an acid that can erode the rock. Temperature changes then cause expansion and contraction, creating cracks and fragments. As the lichens age, bacteria breaks down the licheninto organic matter that begins to collect in rock cracks to initiate the formation of soil.
What are the stages that follow the pioneer stage?
The pioneer stage is replaced by a eries of intermediate seres. Each sere replaces the previous one until a final stable community (the climax community) is formed.
The bare rock is colonised by pioneer species such as moss.
Decomposition creates a layer of topsoil. Grasses grow and displace the pioneer species. More nutrients in soil allows for shrub growth. Increase in soil depth allows for the growth of trees.
3.2.17 Differentiate between the two main modes of succession: primary and secondary
Primary succession
-starts with bare rock
-slower than secondary succession
-no soil
-starts with hardy autotrophs (pioneer species)
-never had a community living in it
-new lava rock or volcanic eruption that forms a new island
Secoondary succession
-the ‘second’ time the area has been colonised
-faster than primary sucession
-soil already present
-other species already present
-occurs when dominant species of a plant community is removed and the area is left to natural interactions
- forest after destruction from a cyclone
Secondary succession is…
Secondary succession is the secondary ecological succession of a plant’s life. As opposed to the first, primary succession, secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane, etc.) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil. The factors that control the increase in abundance of a species during succession may be determined mainly by seed production and dispersal. It is usually faster than primary succession as soil is already present, and seeds, roots, and the underground vegetative organs of plants may still survive in the soil.
Primary succession is…
In primary succession pioneer species like lichen, algae and fungi as well as abiotic factors like wind and water start to “normalise” the habitat or in other words start to develop soil and other important mechanisms for greater diversity to flourish. Primary succession begins on rock formations, such as volcanoes or mountains, or in a place with no organisms or soil. Primary succession leads to conditions nearer optimum for vascular plant growth; pedogenesis or the formation of soil, and the increased amount of shade are the most important processes.
These pioneer lichen, algae, and fungi are then dominated and often replaced by plants better that are better adapted to less harsh conditions, these plants include vascular plants like grasses and some shrubs that are able to live in thin soils that are often mineral-based. Water and nutrient levels increase with the amount of succession exhibited. Small and large trees begin to grow, and the community reaches an equilibrium or balance. This results in a climax community (ecological community in which populations of plants or animals remain stable and exist in balance with each other and their environment.).
3.2.21 Predict the impact of human activity on the reduction of biodiversity and on the magnitude, duration and speed of ecosystem change.
What are the five human activities that cause significant ecological change?
-Habitat destruction and fragmentation
-Introduction of foreign species
- Overexplotation of resources
- Planting of monocultures
-Pollution
3.2.21 Predict the impact of human activity on the reduction of biodiversity and on the magnitude, duration and speed of ecosystem change.
Magnitude, duration, and speed of change
Magnitude relates to the size of the impact. Some activities may have a small impact such as recreation in a part, while others have a larger impact (mining coal and clearing forests).
Duration relates to how long the activity will impact the ecosystem. Some activities may have a short duartion.
Speed relates to how quickly the change to the ecosystem will occur. Will the activity take a long time to have a significant impact or is it causing rapid change?
