Lab 11 Marine Benthic Succession

Lab 11 Marine Benthic Succession - MARINE BENTHIC...

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MARINE BENTHIC SUCCESSION Lab 11 11-1 Reminders ! Calculator Memory Stick or Floppy Disk I. SUCCESSION Succession is a progressive, often predictable change in species composition (and abundance) in a community over time. With time, certain species may become rare or even disappear, while others increase in abundance. Primary succession begins when a previously uninhabited area becomes available for colonization. For example, primary succession occurs when retreating glaciers expose soil that has been sterile for thousands of years. On the island of Hawai’i, primary succession occurs on fresh lava from volcanic flows. Secondary succession follows the disturbance of a previously inhabited area. A forest fire or hurricane that damages a forest leads to secondary succession as a new set of plants initially begin to replace the fallen trees. Although these examples involve plants, the concept of succession also applies to animal communities. For example, temperate rocky intertidal zones are first colonized by fast growing algae, then barnacles, then slower growing algae, and then mussels. After the onset of succession, a community may go through a number of seral stages where different flora and fauna dominate. A sere is the sequence of communities encountered in a particular location over time. Eventually, a stage may be reached where community structure will remain relatively constant in the absence of a major disturbance. This “equilibrium” community state is called the climax community. The species composition of a climax community is dependent on the local environmental conditions (e.g., temperature, rainfall, and soil type). Other factors affecting the pattern of succession and composition of the climax community include the rate and sequence of colonization of different species. Figure 1. Simplified example of a successional sere involving three plant communities. The concept of a monotypic climax , in which there is a single climax community for a given environment, has given way to the more dynamic concept of the pattern-climax . The pattern- climax concept recognizes that most forests are comprised of a patchwork of climax communities and different seral stages (due to patches of disturbance). Some communities never reach a “climax” state and are maintained in a state of subclimax. This occurs in communities that are regularly disturbed. This disturbance can come in a variety of forms, such as herbivory, wind, fire, flood, drought, ice scour, or wave action. Mechanisms of Succession Three primary mechanisms have been proposed to act during succession: facilitation, inhibition, and tolerance (Connell & Slayter, 1977). In facilitation , early successional species modify the environment, making the environment more suitable for germination and growth of later successional species. For example, a nitrogen- fixing plant may add nitrogen to nutrient-poor soil, allowing nitrogen-loving plants to colonize. Facilitation is extremely important during the
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Lab 11 Marine Benthic Succession - MARINE BENTHIC...

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