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Transcript
Ecology (BIOL 250) Lecture 14: Succession and Stability Today’’s Outline Introduction Primary Succession Secondary Succession Disturbance Ecosystem Recovery Mechanisms of Succession Community and Ecosystem Stability Announcements Introduction Succession: Gradual change in plant and animal communities in an area following disturbance. – Primary succession on newly exposed geological substrates. – Secondary succession following disturbance that does not destroy soil. Climax Community: Late successional community that remains stable until disrupted by disturbance. Introduction Primary Succession at Glacier Bay Reiners et.al. studied changes in plant diversity during succession. – Total number of plant species increased with plot age. – Species richness increased rapidly in early years of succession and more slowly during later stages. Not all groups increased in density throughout succession. Primary Succession Primary Succession at Glacier Bay at Glacier Bay 1 Primary Succession Secondary Succession at Glacier Bay in Temperate Forests Chapin (1994) documented substantial changes in ecosystem structure during succession at Glacier Bay. – Total soil depth and depth of all major soil horizons show significant increase from pioneer community. Studies often find the number of woody plant species increases during secondary forest succession. – Other studies show increases in bird diversity across successional sequence closely paralleled increase in woody plant diversity. In addition, organic content, moisture, and N concentrations all increased. – Physical and biological systems are inseparable. Model of Ecosystem Recovery Model of Ecosystem Recovery Biomass Accumulation Model Reorganization (10-20 yrs) – Forest loses biomass and nutrients. Aggradation (100+ yrs) – Ecosystem reaches peak biomass. Transition – Biomass declines from peak. Steady-State – Biomass fluctuates around mean. Model of Ecosystem Recovery Models of Ecosystem Recovery Mechanisms of Succession Three Models – Facilitation – Tolerance – Inhibition Facilitation Proposes many species may attempt to colonize newly available space. – Only certain species will establish. Colonizers “Pioneer Species” modify environment so it becomes less suitable for themselves and more suitable for species of later successional stages. 2 Model of Ecosystem Recovery Successional Mechanisms Tolerance in Rocky Intertidal Zone Tolerance Initial stages of colonization are not limited to pioneer species. – Early successional species do not facilitate or inhibit later successional species. Inhibition Early occupants of an area modify the environment in a way that makes it less suitable for both early and late successional species. Sousa investigated mechanisms behind succession of algae and barnacles in intertidal boulder fields. – If the inhibition model is in effect what should happen? – If the inhibition model is in effect, early successional species should be more vulnerable to mortality. Why? – Early arrivals inhibit colonization by later arrivals. Successional Mechanisms in Primary Succession on Volcanic Substrate 1980 - Mt St. Helens, Washington erupted. – Disturbance set stage for succession. Avalanche debris, hot volcanic ash and pumice killed all plant life. Community and Ecosystem Stability Stability: Absence of change. Resistance: Ability to maintain structure and function in face of potential disturbance. Resilience: Ability to recover from disturbance. Community and Ecosystem Stability Community and Ecosystem Stability Park Grass Experiment Hertfordshire, England Park Grass Experiment – Studied effects of fertilizer treatments. Continued for 150 years. Silverton(1987) investigated ecosystem stability. Dodd (1995) showed that although community stability is present, populations of individual species can change substantially. – Stability depends on resolution an area is investigated at. – Used community composition variability as measure of stability. – Represented composition as proportion of community consisting of each plant form. 3