1.Disturbance and Succession
Equilibrium theory: ecosystems are stable environments in which the biotic interactions among species determine the structure of the communities present.
Ecological succession: transition between biotic communities to some theoretical “climax” state.
Primary- no previous biotic community
Secondary- previously occupied by a community
Aquatic- transition from pond or lake to terrestrial community
Disturbances are non-equilibrium events.
Mosses invade an area and provide a place for soil to accumulate.
Larger plants germinate in the new soil layer resulting in additional soil formation.
Eventually shrubs and trees will invade the area.
Loss or modification of habitat.
Creates opportunities for other species.
Drives increases in biodiversity by initiating succession of communities.
Greater biodiversity increases an ecosystem resilience to disturbance.
6.The Forth Principle of Ecosystem Sustainability
Ecosystems show resilience during a disturbance; they bounce back from adversity.
7.Resilience Mechanisms:Forest Fire Example
Nutrient release to soil.
Regrowth by remnant roots and seeds.
Invasions from neighboring undisturbed ecosystems (biodiversity benefits).
Rapid restoration of energy flow and nutrient cycling.
8.Fifth Principle of Ecosystem Sustainability
Ecosystems depend on biodiversity.
Esthetic and morals
9.Assignment #5Witness Secondary Succession
Secondary succession can be easily demonstrated if you begin this week and check the site periodically over the next month.
Find a location where plants are currently growing, either with a low plant biodiversity (monoculture) or high plant biodiversity (naturalized field).
Stake out a small area (one foot square) and count the number of different plant species in your plot and note which are dominant, rare or intermediate in number.
Next scrape all the plants from the area. The bare soil should be surrounded by plants that have not been removed. Every few days the area should be watered if needed.
Periodically (at least once per week) record any changes to your area. Within a short period of time plants should return to the bare area, demonstrating the first sequence in secondary succession.
How many species are growing? Compare your results with those of a classmate with either a lower or higher initial plant biodiversity? Write a paragraph on the comparison and include what you think explains differences.
Increased population growth:
Increasing our biotic potential.
Decreased our environmental resistance.
Contributed to the degradation of ecosystems:
Eliminate natural predators
Alter abiotic factors
Misunderstand the role of fire
Have we exceeded the carrying capacity?
11.Implications For Humans
Protecting and managing the natural environment to maintain the goods and services vital to human economy and survival.
Establishing a balance between our own species and the rest of the biosphere.
Adaptive Ecosystem Management: an approach that accepts uncertainty of our knowledge base and flexible to change as new information is gathered.
12.Exam #1 Results
Average = 76.5% = C+/B-
F ≤ 52%; D 53%-64%; C range 65%-76%; B range 77%-88%; A range 89%-100%