Bozeman science succession Transition in the species composition of a biological community, often following ecological disturbance of the community; the establishment of a biological community in an area virtually barren of life Bozeman science succession

(a) Explain the meaning of the term primary succession. [2] starts with previously uncolonised area / bare ground / bare rock / AW; ref to pioneer species / named pioneer; series of recognisable, seres / stages; progresses to, climax / final equilibrium stage;

(b) Explain the role of pioneer plants in succession on a bare rock or sand dune. [3] stabilise environment; soil development / increase humus / organic material; change soil pH; hold more water; release more minerals or nutrients / increase N content or fix N / hold ions; form microhabitat / reduce exposure / provide shelter / reduce erosion;

The figure below shows a primary succession in a temperate climate. X represents an example of deflected succession. Suggest two ways in which deflected succession at X could be caused. [2] any two from following: grazing; burning; mowing / application of fertilizer / application of selective herbicide; exposure to wind; grass able to continue to grow (linked to a statement above);

(d) Explain how biomass changes during a primary succession. [2] increases; plants at later stages are large / plants in early stages are small; trees / shrubs. are woody, appear later in succession;

Features of pioneer species Early arrivals Can tolerate extreme conditions e.g. low nutrient levels Have very good means of dispersal, usually by wind Are not able to compete for resources e.g. light Are not influenced by or dependent on animal species May be able to fix nitrogen (e.g. legumes) and build up soil nutrients

Features of climax community species Are unable to tolerate great fluctuations in the water content of soil Are strongly influenced by other organisms e.g. competitors, herbivores, pollinators, seed-dispersal agents and soil micro-organisms Species found in the end point community Have large seeds (with a large energy store) so that seedlings can survive low light intensity Have a specialised niche e.g. as an epiphyte An epiphyte is a plant that normally grows on another plant for support. It is not parasitic, but uses the host plant for support only. Air plants, or epiphytes, complete part or all of their life cycle anchored or perched on another plant or structure rather than rooted in the soil. They obtain water and nutrients from dew, air moisture, rainwater and collected plant debris via adventitious (growing from the stem or leaf) and aerial roots. Epiphytes include many lichens and mosses, as well as 10% of all seed plants and ferns and over half the orchid species. This way of life isn't parasitic, in contrast to plants like mistletoe, which 'steals' nutrients from the host tree. Video on Epiphytes