Chapter 16- change in communities

• change in the species composition of communities over time
• results in a variety of abiotic and biotic agents of change
• species interaction, abiotic conditions, and catastrophic disturbances

abiotic event that physically injures or kills some individuals and creates opportunities for other individuals to grow or reproduce

abiotic factor reduces the growth or reproduction of individuals and creates opportunities for other individuals

• extremely intense and infrequent event cause change to entire community
• weak but frequent disturbances like tree fall cause patches of available resources, mosaic

stable end point in which community experiences little change until a particular intense disturbance sends community back into earlier stage

• colonization of habitats that are devoid of life
• very slow
• 1st colonizers tend to be species capable of withstanding great physiological stress and transform habitat in ways that benefit further growth and developement (nitrogen-fixing plants)

• reestablishment of community in which most, not all, organisms or organic constituents have been destroyed
• faster- fires, hurricanes, logging

earliest species modify enviroment in ways that ultimately benefit later species but hinder own continued dominance, leads to climax community composed of species that no longer facilitate other species are displaced only by disturbance

assume early species modify environment, in neutral ways that neither benefit or inhibit later species, early species grow and reproduce quickly, later species persist b/c tolerate environment or biological stress that would hinder early successional species

early succession modify environment in way that would hinder later successional species , supression is broken only when stress or disturbance decreases abundance of inhibitory species

newly exposed habitat dominanted by few species

• second community about 30 years after exposure
• named after small shrubs- nitrogen fixation
• species richness increases
• spruce seedlings have low survival rate and low germination due to increase in seed predators

• after about 50 years
• third community
• shade and seed preadtors low overall germination and survival rate

• 100 years
• mature Sitka spruce forest
• diverse array of lichen, low shrubs, and herbs
• increase in soil organic matter and soil moisture

cases in which different communities develope in same area under similar environmental conditions

• a community that returns to original state after some perturbation
• multiple stable stages occur

inability to shift back to original community type even when original conditions are restored

shifts in communities to alternative states, caused by removal or addition of strong interactors that maintain one community type over another