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Communities and Succession Communities and Succession A community consists of all the plants and animals that occupy a particular area. The individual populations within a community interact with each other. The community is a constantly changing and dynamic unit, which passes through a number of stages from its origin to its climax. The transition from one stage to the next is called succession. nothing Climax community Have you ever seen something like this? How does it happen? This is bare rock. Nothing lives here. Why? •Exposed. •No soil. •Absorbs and reflects heat. •Dry. •No nutrients. How does succession work? A bare patch of ground will not stay bare. It will rapidly be colonized by a variety of plants. A recently cleared patch of ground The same ground 2 years later, How Does Succession Work? There are 2 types of succession: PRIMARY- Plants grow where NO PLANTS HAVE GROWN BEFORE. SECONDARY- Plants grow where there has been a previous population. These will have been destroyed, eg: by fire The 1st species to colonise are called PIONEER SPECIES. The “ultimate” species to colonise are called the CLIMAX COMMUNITY. Sand dune succession. The pioneer species is marram grass. Pioneer species Pioneer species are often 'opportunist' species which are able to rapidly exploit a sudden new opening in ground plant cover. They must be able to grow quickly. They are usually short-lived. EXAMPLE: Mosses They are low growing, carpeting the ground and with little height. They then provide a microhabitat equivalent to a miniature forest for a variety of invertebrates such as mites and spiders. The moss also acts like a sponge when wet, in some cases providing a semiaquatic microhabitat. Task • In pairs, come up with a list of features that pioneer species may have, which would help them to colonise inhospitable environments Features of Pioneer Species • Production of a lot of wind-dispersed seeds to easily reach isolated areas • Rapid germination of seeds • The ability to photosynthesise • The ability to fix nitrogen from the atmosphere • Tolerance to extreme conditions Looking again at our example…. Bare Ground No plant competition for light, space, nutrients or water. Soil mobile and liable to erosion and loss. A more extreme surface microclimate because the bare soil both absorbs and reflects heat more than soil covered in vegetation. A drier environment because there is no plant cover to hold moisture above ground and little humus to hold it in the soil. Lower nutrient levels in the soil. Two Years Later Intense plant competition for space and other resources. Soil bound by roots and plant cover. The plant cover provides a certain amount of ground insulation from extremes of temperature. There are now also a variety of microclimates within the vegetation. Plant cover and increasing humus levels help to retain water. The nutrient levels in the soil will have increased. Bare Ground No plant competition for light, space, nutrients or water. Soil mobile and liable to erosion and loss. A more extreme surface microclimate because the bare soil both absorbs and reflects heat more than soil covered in vegetation. A drier environment because there is no plant cover to hold moisture above ground and little humus to hold it in the soil. Lower nutrient levels in the soil. Two Years Later Intense plant competition for space and other resources. Soil bound by roots and plant cover. The plant cover provides a certain amount of ground insulation from extremes of temperature. There are now also a variety of microclimates within the vegetation. Plant cover and increasing humus levels help to retain water. The nutrient levels in the soil will have increased. Stages of Plant Succession Each stage of succession changes the abiotic environment and makes it less hostile For example: • Colonisers (lichens): when they die, they release nutrients. This changes the abiotic environment by creating soil. • Mosses, then Ferns: rock is continually eroded, as these die organic matter increases, building up soil • Small flowering plants, shrubs then trees establish Over time… • Undisturbed, an area will pass through a number of further different successional stages, each with its own characteristic mix of species. • Each new community will be better adapted to the changed environment which has been provided by the previous community. •Eventually, a climax or 'final' community is reached. At this point, the succession will not go any further. However, this does not imply that there will be no further change. Climax Community • The organisms that make up the final stage of ecological succession • A balanced equilibrium • In the UK, this is deciduous woodland Animal Succession • Animal species present depend on the plant species found in the area • For example, mosses and grasses provide food and habitats for insects and worms. These can then support secondary consumers. Infographic on succession to include: Definition of succession • • Stages of succession (illustrated with an example) • Comparison of the 2 different types of succession • Features of pioneer species • Description of the way each stage of succession affects the environment to suit the plants of the following stage. Questions. 1. What kind of problems would a pioneer species encounter? 2. Describe the kind of adaptations you might expect to see in a pioneer species in order to overcome these challenges. 3. Explain the difference between primary and secondary succession. 4. Early stages of ecological succession contain short-lived plants which devote enormous amounts of energy producing seeds. More mature communities do not need to do this. Why?