Chapter 17: Change in Communities Flashcards
Communities are always ____
changing
What are the strongest forces behind community change?
human actions
What types of changes have happened to coral reefs in the Indian Ocean?
-Slow, subtle changes: gradual turnover of dominant species due to competition, predation, and disease
-Catastrophic Change: bleaching events and the 2004 tsunami
Succession
change in species composition in communities over time, resulting from both biotic and abiotic factors
Do abiotic factors vary?
Yes. Over daily, seasonal, decadal, and longer time scales
Disturbance
events that injure or kill some individuals and create opportunities for other individuals
Stress
abiotic factors that reduce growth, reproduction, or survival of individuals
Biotic agents of change
-species interactions can result in species replacements
-diseases can cause death or slow growth of a species
-ecosystem engineers or keystone species
____ and ____ factors often interact to produce community change
abiotic and biotic
What does succession involve due to abiotic and biotic agents of change?
colonization and extinction
Climax Stage
a stable end point that changes little
Primary Succession
colonization of habitats devoid of life
-can be very slow. initial conditions are very inhospitable
-the first colonizers tend to be stress-tolerant
Secondary Succession
reestablishment of a community in which some, but not all, organisms have been destroyed
-occurs after fires, storms, logging
-legacy of the preexisting species and their interactions with colonizing species play larger roles than in primary succession
Henry Cowles (1899)
studied succession on sand dunes along Lake Michigan
-he assumed that plant assemblages farthest from the lake’s edge were the oldest; the ones nearest the lake were the youngest, representing a time series of successional stages (a space for time substitution)
Climax Community
dominant species persist over many years and provide stability that can be maintained indefinitely
Are communities predictable or repeatable?
No
Connell and Slayter (1977)
reviewed the literature on succession and proposed three models
Facilitation Model
inspired by Clements-early species modify the environment in ways that benefit later species. The sequence of species facilitations leads to a climax community
Tolerance Model
assumes early species modify the environment in neutral ways that neither benefit nor inhibit later species
Inhibition Model
assumes early species modify conditions in negative ways that hinder later successional species
Pioneer Stage
dominated by lichens, mosses, horsetails, willows, and cottonwoods
Dryas Stage
at 30 years, dominated by the shrub Dryas, other tree species start to appear
Alder Stage
at 50 years, alder dominates
Spruce Stage
at 100 years, a mature Sitka spruce forest
