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Biomes are dynamic – they change as the Earth changes. This process is called succession. Ecosystem succession takes two forms, depending on the starting point. Organisms that thrive during the early stages of succession are called pioneer species. (e.g. Lichens) Lichens- composite organism that emerges from algae or cyanobacteria (or both) living among filaments of a fungus Algae/Cyanobacteria provide food through photosynthesis Fungus provides minerals, nutrients, and anchor to soil 1 2 Primary succession occurs when a new ecosystem develops where there was none before. A combination of wind, water, and pioneer species such as lichens break down rock into soil (facilitation). Once the soil has enough organic matter, small plants and shrubs can be supported. Over time, trees spout and become dominant. 3 Secondary succession occurs following the disruption of an existing ecosystem. Fire, flood, clear-cutting, etc. This form of ecological succession does not take as long. Soil is already in place, and pioneer species appear within days or weeks. 4 (a) Soon after fire (b) One year after fire Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics 1. The exposed moraine is colonized by pioneering plants including lichens, liverworts, mosses, fireweed, Dryas, willows, and cottonwood © 2011 Pearson Education, Inc. 1941 1907 1 Pioneer stage, with fireweed dominant 1860 Glacier Bay Alaska 1760 0 5 10 15 Kilometers 1 Pioneer stage, with fireweed dominant 2. Dryas dominates the plant community © 2011 Pearson Education, Inc. 1941 1907 2 Dryas stage 1 Pioneer stage, with fireweed dominant 1860 Glacier Bay Alaska 1760 0 5 10 15 Kilometers 2 Dryas stage 3. Alder invades and forms dense thickets © 2011 Pearson Education, Inc. 1941 1907 2 Dryas stage 1 Pioneer stage, with fireweed dominant 1860 0 5 10 15 Kilometers Glacier Bay Alaska 1760 3 Alder stage 3 Alder stage 4. Alder are overgrown by Sitka spruce, western hemlock, and mountain hemlock © 2011 Pearson Education, Inc. 1941 1907 2 Dryas stage 1 Pioneer stage, with fireweed dominant 1860 0 5 10 15 Kilometers Glacier Bay Alaska 1760 4 Spruce stage 3 Alder stage 4 Spruce stage Succession is the result of changes induced by the vegetation itself On the glacial moraines, vegetation lowers the soil pH and increases soil nitrogen content © 2011 Pearson Education, Inc. Soil nitrogen (g/m2) 60 50 40 30 20 10 0 Pioneer Dryas Alder Successional stage Spruce Today, only about 2% of Haiti’s original forest cover remains. Even this remains at risk, because most of the people depend on charcoal as a source of heat. The lack of forests has made the country much more susceptible to flooding, mudslides, and erosion. 21 Neighboring Dominican Republic, which gained its independence with much less strife, is the second largest economy in the Caribbean. 22 Haiti’s hopes for recovery hinge on its ability to speed the process of ecological succession – to encourage reforestation and find an alternative fuel to charcoal. 23 a) b) Discuss the expected changes in biodiversity as the stages of succession progress as shown in the diagram above Describe and explain THREE changes in abiotic conditions over time that lead to succession, as shown in the diagram above 24 c. For each of the following disturbances, discuss the immediate and long-term effects on ecosystem succession (i) A volcano erupts, covering a 10-squarekilometer portion of a mature forest with lava (ii) A 10-square-kilometer portion of a mature forest is clear-cut 25 Biodiversity increases (plants, animals, decomposers). Explanation of why biodiversity increases/changes are observed: • Some populations facilitate biodiversity/succession (by developing conditions more suitable for other species and/or developing conditions less suitable for their progeny). • Some populations inhibit biodiversity/succession (by developing conditions less suitable for other species and/or developing conditions more suitable for their progeny). • Increase in plant stratification (increased layering of plants; e.g., canopy, understory). • More niches/habitats formed (plants, animals, decomposers). • Pioneer plant species → dominants (more shade-tolerant plants emerge). • Increase in producer diversity brings about increase in consumer diversity. 26 Description of change in abiotic condition Explanation (why abiotic condition changes) Explanation (why it enhances succession) Increase in soil quality More detritus increases humus; decreased erosion because more plants hold soil Provides more anchoring for plants Improvement in soil quality Soil gains organic matter (humus) Provides more nutrients for plant growth More N available to ecosystem Caused by decomposition and/or by nitrogen fixation Favors plants with higher nitrogen needs More P available Caused by decomposition Favors plants with higher phosphorus needs Increase in water retained in soil Increased organic matter retains water; increased shading reduces evaporation More water is available for plants Decrease in pH of soil Acids released during decomposition lower pH Mobilizes cations facilitating mineral uptake (e.g. Fe++, Ca++); favors acid-tolerant plants Increase in pH of soil Soil gets more basic with increase in ammonia Favors plants with higher N requirement; alkaline tolerant plants Decrease in light availability Caused by shading Increased shading favors shade-tolerant species; inhibits shadeintolerant species Decrease in temperature Caused by shading Favors species that are not heat tolerant; inhibits plants needing higher temps Higher humidity Caused by more transpiration Facilitates transition from xerophytic to mesophytic 27 Volcano erupts Immediate- primary succession/ no soil Long term lava must be degraded by weathering, microbes, lichens, fungi to form soil Lots of light is available (phototrophic organisms will thrive when soil is present) Mature forest is clear-cut Immediate- secondary succession/ soil present All life is not destroyed Seed banks are present Different/ other habitats/ niches open/closed Long-term- loss of trees may lead to erosion and soil loss Lots of light is available Many smaller plants actually benefit 28