Name
Ecology 2/12
Per.
Disturbance and Succession KEY
PART 1: DISTURBANCE
• Read Ch. 19 (p.378-385) in Elements of Ecology.
1. Define disturbance.
A disruption to community structure and function.
2. List and briefly describe three characteristics of disturbances.
CHARACTERISTIC
DESCRIPTION
intensity
amount of life (biomass) killed or eliminated by disturbances
scale
area affected by disturbance
frequency
how often disturbances occur over a given time
3. Consider the two scenarios described below and determine which disturbance has greater intensity
frequency and scale.
-
Disturbance A: A large tree in a tropical rain forest falls due to seasonal winds.
-
Disturbance B: A large forest fire burns throughout Point Reyes National Seashore.
INTENSITY
SCALE
FREQUENCY
Disturbance B
Disturbance B
Disturbance A
4. Describe the types of disturbances that create gaps, and how gaps affect ecosystems.
Gaps are small-scale disturbances that provide opportunities for existing species to thrive
5. List and describe at least 5 major sources of disturbance.
Wind – force strong enough to down trees
Water – force strong enough to move rocks and boulders
Fire – condition which significantly alters abiotic and biotic factors
Overgrazing – defoliation of plant matter due to uncontrolled herbivory
Volcanic eruptions – creating new rock in place of pre-existing communities
6. Explain why disturbances are important to ecological communities.
Disturbances allow for regeneration and/or colonization of species
PART 2: POPULATION GROWTH AND SUCCESSION.
•
Read Ch 10 (p. 195-197) and Ch. 12 (p. 228-229) of Elements of Ecology.
1. Define the following terms related to population growth.
TERM
carrying capacity (K)
limiting factor
r-strategist
K-strategist
DEFINITION
maximum number of individuals of a given population the environment can
sustain
low resource availability which causes population growth to slow, stop or
decline
colonizers, pioneer species; generally small, short-lived species with high
reproductive rates and lots of offspring; generalists
climax species; large, long-lived species; efficient competitors with slow
growth, low reproductive rates and few offspring; specialists
2. Discuss the conditions in which r-strategies are most successful. Explain why they are most successful in
these conditions.
r-strategists are most effective following disturbances where resources are plentiful and competition is low
3. Discuss the conditions in which K-strategies are most successful. Explain why they are most successful in
these conditions.
K-strategists are most effective once populations are well-established and resources are limited and
competition is high
• Read Ch 13 (p. 256-260).
4. Define ecological succession.
A change in community structure and composition over time.
5. Study Figure 13.9 on p.257. Describe each of the figures a-f. Incorporate the following terms in your
descriptions: disturbance, secondary succession, pioneer species, climax, r-strategists, K-strategists.
STAGE OF
FIGURE
DESCRIPTION
SUCCESSION
a. and d.
(1940's)
early
some disturbance due to grazing and development
b. and e.
(1960's)
mid
pioneer species (r-strategists) begin being established
evidence of secondary succession present
c.
(1970's)
later
density of K-strategists increasing as community nears climax
f.
(1990's)
climax
stable end community established most populations at/around carrying capacity
6. Explain why primary succession is not used your descriptions above.
Primary succession only occurs when new land is formed.
• Read Ch. 17 (pp. 343-345).
7. Discuss how succession affects species diversity over time.
Diversity changes over time dependent on growth rates of populations, frequency of disturbance, and stage
of succession