Ecology Chapter: Succession in Communities

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Questions and Answers

What is primary succession and how does it differ from secondary succession?

Primary succession occurs on bare substrate without any initial soil, while secondary succession happens after a disturbance that leaves the soil intact.

Describe the stages of primary succession, starting from bare rock.

The stages of primary succession include: 1) lichens and mosses colonizing bare rock, 2) soil formation, 3) appearance of small annual plants, 4) establishment of herbs and grasses, and finally 5) colonization by shrubs and trees.

How does a climax community differ from earlier successional stages?

A climax community is a stable, long-lasting ecosystem that is primarily determined by climate, whereas earlier successional stages are characterized by more dynamic changes in species composition.

What role do 'K' and 'r' selection strategies play in ecological succession?

'K' selection favors species like elephants that have low population growth and high competitive ability, while 'r' selection supports species like frogs that have high growth rates and many offspring. Signup and view all the answers

What is a chronosequence and how is it useful in studying successional changes?

A chronosequence is a sequence of communities or ecosystems that differ in age, allowing researchers to study changes in species diversity and composition over time. Signup and view all the answers

Explain the significance of Glacier Bay in understanding ecological succession.

Glacier Bay provides a model for studying primary succession, showcasing changes in species composition and ecosystem structure over time as glaciers retreat. Signup and view all the answers

What is the difference in time required for primary versus secondary succession, and why?

Primary succession typically requires over 100 years, while secondary succession often takes less than 100 years due to the presence of existing soil and seed sources. Signup and view all the answers

How can the process of wildlife succession influence changes in an ecosystem?

Wildlife succession occurs as organisms modify their environment, making it suitable for other species, thereby facilitating further ecological development. Signup and view all the answers

What key ecosystem processes are changed during succession?

Succession changes include increases in biomass, primary production, respiration, and nutrient retention. Signup and view all the answers

Design an experiment to study nutrient retention by plants after forest clear-cutting.

Measure nutrient levels in a river before and after clear-cutting to compare nutrient retention in different stages of succession. Signup and view all the answers

How did the application of herbicide affect nutrient retention in the Hubbard Brook study?

Herbicide application reduced regrowth, leading to increased nutrient losses; stopping its application allowed succession to decrease losses. Signup and view all the answers

What is the role of facilitation in ecological succession?

Facilitation involves early colonists modifying the environment, making it suitable for later species to thrive. Signup and view all the answers

Explain the concept of inhibition in community succession.

Inhibition occurs when early colonizers make the environment less suitable for subsequent species, hindering their establishment. Signup and view all the answers

What were the findings of Morris and Wood regarding primary succession on volcanic substrates?

They found a complex blend of facilitation, tolerance, and inhibition influences on early succession after the Mt. St. Helens eruption. Signup and view all the answers

What factors influence rapid succession in stream communities like Sycamore Creek?

Factors include low and intermittent flow, flash floods, and the ability of invertebrates to find refuge during disturbances. Signup and view all the answers

How does human intervention produce a lawn, and what does this imply about its naturalness?

Lawn maintenance involves planting seeds, mowing, applying herbicides, and irrigating; this complexity indicates that lawns are artificial systems. Signup and view all the answers

Describe the changes in species diversity during ecological succession.

Succession leads to increases in species diversity and changes in species composition over time. Signup and view all the answers

What are the mechanisms that drive ecological succession?

The primary mechanisms include facilitation, tolerance, inhibition, and random colonization. Signup and view all the answers

Study Notes

Succession: Progressive Change in Communities

Succession describes the progressive changes in the biotic community following a disturbance.
Climax community: A stable, long-lasting community primarily determined by climate.
Primary succession: Occurs on newly exposed geological substrates (e.g., bare rock, newly formed land). It begins with a total lack of organisms. This process takes significantly longer than secondary succession, often exceeding 100 years.
- Sequence typically involves: bare rock, lichen/moss colonization, formation of soft substrate, development of soil, appearance of small annual plants, herbs/grasses, shrubs, shade-tolerant trees.
Secondary succession: Occurs following disturbances that do not destroy the soil. This process generally takes less than 100 years.
- Key characteristic: Existing community is disturbed/destroyed, but soil remains intact, retaining nutrients. Reestablishment of the previous ecosystem is often quicker than primary succession.
Mount St. Helens: An example demonstrating the extended timeframe of primary succession, taking over a century for a stable plant community to re-establish itself.

Wildlife Succession

K-selected species: Characteristics include large body size, high competitive ability, low population growth rate, slow development, iteroparity (multiple reproductive events), few, large offspring. Ex: Elephant
r-selected species: Characteristics include small body size, low competitive ability, high population growth rate, rapid development, semelparity (single reproductive event), many, small offspring. Ex: Frogs
Successional changes in wildlife: Species activities alter environments, creating conditions suitable for other species.

Studying Successional Changes

Chronosequence: A sequence of sites at different successional stages, useful for understanding patterns over time. Glacier Bay and Hawaiian islands are good locations for this study.
Paleoecology: Studying past ecosystems to understand how they changed over time, often used in conjunction with chronosequences.

Ecosystem Changes During Succession

Ecosystem structure Changes significantly during succession.
Components affected:
- Soil depth & horizon development increases
- Organic content, moisture, and nitrogen (N) concentrations increase.
Ecosystem processes Changes:
- Biomass increases
- Primary production increases
- Respiration increases
- Nutrient retention increases

Mechanisms of Succession

Clements: Proposed a deterministic view, where succession proceeds towards a predetermined climax.
Facilitation: Early colonists modify the environment, making it suitable for later species. Species replacement occurs due to facilitating colonizers.
Tolerance: Early colonists have minimal impact on later species. Any species can initiate succession, and climax is achieved in an orderly fashion.
Inhibition: Early colonists make the environment less favorable to other species. Species replacement is hindered by preceding ones.
Connell & Slayter: Introduced the concepts of tolerance, inhibition, and facilitation.
Lawton (1987): Emphasized the role of random colonization in some successional processes.
Primary Succession on Volcanic Substrate (Mt. St. Helens): Demonstrates a complex interaction of facilitation, tolerance, and inhibition.

Application of Succession: Human Impact

Lawns: Represent an example of human-induced artificial systems that constantly oppose natural succession.
Management practices: Frequent mowing, herbicide use, irrigation and pesticides are used to control species diversity to maintain a desired appearance.

Marine, Stream & Lake Succession

Marine Succession: Changes in species composition in marine environments over time.
Stream Communities: Rapid changes in diversity/composition of algae and invertebrates observed in stream ecosystems, subject to flash floods.
Shallow lakes: Lakes becoming shallower, warmer over time due to organic matter buildup.

Take-Home Message

Succession alters species diversity and composition.
Ecosystem changes during succession: increased biomass, primary production, respiration and nutrient retention.
Key mechanisms driving succession: facilitation, tolerance and inhibition.

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Description

Explore the fascinating processes of succession in ecological communities, including primary and secondary succession. Learn about how biotic communities evolve following disturbances and what characterizes climax communities and the changes leading to them. Test your understanding of these crucial ecological concepts.