[19.6] succession
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what is succession?
a long term process whereby plant communities in an ecosystem are gradually replaced by a series of changes
what happens in each stage of succession?
new species colonise the area and these may change the environment
how might a species change its environment during succession?
• make it less suitable for existing species. new species may out-compete the existing one so take over a given area • more suitable for other species with different adaptations. this species may be out-competed by the better adapted new species
what adaptations do typical pioneer species have that allow it to establish quickly?
• large quantities of wind-dispersed seeds / spores • rapid germination of seeds • fast reproduction rate
what adaptations do typical pioneer species have that allow it to be self-sufficient?
• photosynthetic • nitrogen-fixing from atmosphere • tolerance to extreme conditions and harsh abiotic factors so it can survive where other species cannot
what is a sere?
what each stage of succession is known as
1st stage of succession
• low number of species and individuals • pioneer species colonise an inhospitable environment (eg. algae, lichen, mosses) • adapted to surve harsh abiotic factors
2nd stage of succession
• environmental conditions alter due to presence of pioneer species • environment becomes less hostile eg. shelter for germination, new habitats for animals
3rd stage of succession
• pioneer species are outcompeted by newcomers • new community further changes conditions, until they are in turn outcompeted • eveutally climax commnity is reached • balance of species stablises • gradual blending of one community into the next
what is a climax community
a community of animals and plants with much biodiversity and few species replacing those established, which stays stable over a long period of time
what common features emerge during succession? (8)
• harshness of abiotic conditions ⭣ • soil factors (eg. depth, stability, water content) ⭡ • number and variety of habitats and niches ⭡ • species richness ⭡ • biodiversity ⭡ then ⭣ • complexity of food webs ⭡ • total ecosystem biomass ⭡ • overall ecosystem stability ⭡
what is secondary succession?
• when land has already been sustained or life is suddenly altered so an ecosystem returns to its climax community in the same way but more rapidly • some of the species in the climax community may be different
why is secondary succession quicker than primary succession?
• seeds often remain alive in soil • influx of animals and plants through dispersal and migration from the surrounding area
what impact can humans have on factors can interrupt succession and prevent the development of a climax community or destroy an established climax community? (7)
• grazing • agriculture • ploughing • deforestation • pollution • climate change • management for conservation
what impact can natural events have on factors can interrupt succession and prevent the development of a climax community or destroy an established climax community? (4)
• flood • fire • drought • disease