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Transcript
Rhonda Alexander IC Science Robert E. Lee B.11.D describe how events and processes that occur during ecological succession can change populations and species diversity Succession Some of the organisms in an area are gradually replaced over time by new species. This succession is a result of the changes to the environment brought about by the organisms themselves. Through succession, the organisms tend to get bigger and more complex, as the biodiversity also rises. Pioneer species are those that first colonize bare soil or rock. They can withstand the harsh environment, and include lichens and mosses and Marram Grass on sand dunes. The process continues in stages until the climax community is reached, which will remain stable until the abiotic factors change. If succession is halted (e.g. by fire, flood or by Man’s actions – such as plowing), then a secondary succession will start. This is much faster than primary succession as there are many seeds in the soil from which new plants can grow, whilst animals readily colonize the area as soon as the plants appear. Ultimately, it does not matter very much what the starting point for succession is - rock, bog or pond - as eventually the climax community will be much the same, since the climate is the main influence on it. • Early Successional Communities • A succession (or sere) proceeds in seral stages, until the formation of a climax community, which is stable until further disturbance. • Early successional (or pioneer) communities are characterized by: Simple structure, with a small number of species interactions Broad niches Low species diversity Pioneer community, Hawaii • Climax Communities • In contrast to early successional communities, climax communities typically show: Complex structure, with a large number of species interactions Narrow niches High species diversity Climax community, Hawaii • • Hawaii: Local plants are able to rapidly recolonize barren areas Primary Succession When the starting point is an ABIOTIC environment • Volcano • Flood • Primary Succession ‣ Primary succession refers to colonization of a region where there is no pre-existing community. Examples include: Newly emerged coral atolls, volcanic islands Newly formed glacial moraines Islands where the previous community has been extinguished by a volcanic eruption ‣ A classical sequence of colonization begins with lichens, mosses, and liverworts, progresses to ferns, grasses, shrubs, and culminates in a climax community of mature forest. In reality, this scenario is rare • Secondary succession occurs where an existing community has been cleared by a disturbance that does not involve complete soil loss. • Such disturbance events include cyclone damage, forest fires and hillside slips.