Succession Various disturbances disrupt communities -abiotic: fire, volcano, retreat of glacier or water -biotic: e.g human activity (clearcutting, farming, etc...) New communities emerge after disturbances in a predictable sequence. This predictable change is called Succession. Succession happens because organisms cause changes in their surroundings that make the environment less suitable for themselves and more suitable for other organisms.

Details on Succession... Two Types: primary succession - sequence of events from barren area to stable ecosystem. Soil building is key component. E.g. barren rock -> soil with bacteria, moss, lichen -> shrubby plants -> large trees secondary succession - sequence of events from soil to stable ecosystem. Usually follows human activity that destroys a previous community (e.g. clearcutting). In each case succession starts with a few hardy invaders called pioneers. If undisturbed it continues until a diverse and relatively stable climax community forms

Primary Succession

Primary Succession in Hawaii

How does primary succession work? Pioneer species are first ones to grow E.g. Lichens can grow on barren rock, together with bacteria can generate organic material which later becomes soil. Early species often change conditions (e.g. making soil) that makes them more suitable for later successional stages. Entire process is a set of competitive replacements of one species by another. Does this jive with the Selfish Gene concept? Let’s look at an example...

Lake Michigan is receding… How does this image illustrate succession? No life on water’s edge - waves, sand Foredune - pioneer community, beach grass binds sand, supports insects Shrubs - inhibit grass by stealing light, improve soil quality by providing lots of plant material. Pine Woods - short stage because trees shade own seedlings and inhibit growth. Needles add to soil that supports… Hardwoods - own seedlings can grow in shade - reach equilibrium i.e. climax community

Aquatic Primary Succession Yosemite Valley meadows are an example of meadow succession Herbaceous growth brush Lodgepole pine vs. Red fir

Secondary Succession

Fire (secondary) succession at Yellowstone Pioneer herbs