Ch19 Ecological Succession and Community Development.docx

6 Pages

Course Code
Spencer Barrett

This preview shows pages 1 and half of page 2. Sign up to view the full 6 pages of the document.
BIO120H © Lis| Page 1011 chapter 19: ECOLOGICAL SUCCESSION AND COMMUNITY DEVELOPMENT  Krakatau island (Indonesia) exploded on Aug. 27, 1883  all life was obliterated  it was a great chance for scientists to study the development of biological communities on a newly formed, raw terrain of volcanic ash  nearest sources of colonists were from Sumatra and Java (40 km away)  sea-dispersed plants were first to show up (made up 10 out of 24 species by 1886)  wind-dispersed grasses and ferns – seeds and spores could be blown across ocean  wind-dispersed tree species arrived; closed forest developed across the island by 1920s  pioneering species were pushed to marginal habitats or disappeared  birds and bats were attracted to the trees (fruit-eating species)  brought seeds of animal-dispersed trees and shrubs  animal-dispersed outnumber sea- and wind-dispersed plants now  island fragments are constantly changing due to continuing eruptions  island will continue to change  communities exist in a state of continuous flux, but indiv. are replaced by their own kind  disturbance: an event that causes rapid or marked change in a population or community, often thought of as displacing an ecological system from its equilibrium  after a habitat is disturbed, pioneering species adapted to disturbed habitats are successively replaced by other species as the community attains its former structure and composition  species successively replace one another in the process of succession  succession: a sequence of changes in the species composition of a community initiated by a disturbance, progresses to a stable state  climax community: the ultimate association of species achieved after succession  the end point of a successional sequence, or sere; a community that has reached a steady state under a particular set of environmental conditions  Frederic E. Clements THE CONCEPT OF THE SERE INCLUDES ALL THE STAGES OF SUCCESSIONAL CHANGE  any new habitat attracts colonizers (adapted to be good pioneers)  rates of succession slow as slower-growing plants appear  transition from abandoned field to mature forest takes only one of several successional sequences that may lead to similar climax communities w/in a given biome  sere: a series of stages of community change in a successional sequence leading toward a stable state  although initial stages of the sere depend on the beginning habitat, with time, seres converge on similar climax communities  seres have been classified into 2 types according to origin Primary Succession  primary succession: succession in a newly formed or exposed habitat devoid of life  ex. natural conversion of ponds in north-temperate and boreal climates to dry lands  deep ponds (kettle holes) left by glaciers and those formed by beaver dams undergo bog succession  rooted aquatic plants establish at the edge of the pond  some species of sedges form mats on the water surface and eventually cover pond BIO120H © Li| Page 22011  produces a firm layer of vege.  “quaking bog”  detritus produced by sedge mat accumulates at pond bottom (anaerobic, thus no microbial decomposition occurs down there)  as a bog accumulates sediments and detritus, sphagnum moss and shrubs establish along edges  add to development of a soil  black spruce and larch  birch, maple, fir  over thousands of years, aquatic habitat becomes terrestrial as organic detritus accumulates and soil rises above water table Secondary Succession  ssecondary succession succession in a habitat that has been disturbed, but in which some aspects of the community remain  even when reseeding initiates a secondary sere, the type of disturbance and size of gap it creates influences the first species to establish  disturbance and recovery occur quickly in marine habitats  marine invertebrates have inversely related colonizing and competitive abilities  created bare patches  on rock occupied by sessile invertebrates and;  filled in quickly by tunicates and sponges (highly successful competitors)  gap size didn’t influence succession  bryozoans and polychaete larvae attempted to colonize but were overgrown  on artificial hard surfaces, ex. ceramic tiles, placed in sand away from colonists  gap size had huge effect on pattern of colonization  tunicates and sponges don’t disperse well, thus, didn’t Michael Keough colonize them (influence of gap  bryozoans and polychaetes had chance size/isolation on  larger gaps = larger targets – colonized by T & S succession in  smaller gaps – colonized by B & P (once established, can marine habitats) prevent the colonization of T & S)  B & P are disturbance-adapted species ecologists in the field  weed a.k.a. ruderals: an organism, generally having strong powers of dispersal, that is capable of living in highly disturbed habitats  colonize open patches quickly  mature and produce offspring at an earlier age  eliminated by slowly colonizing superior competitors  require frequent disturbances to stay in sys.  size of gap also influences whether predators & herbivores will be active there  some feed in large gaps – easy to find  others are vulnerable to predation and need the cover of intact habitat, from whose edges they venture to feed – graze small gaps and gap edges than the centre of large gaps BIO120H © Li| Page 32011 The Climax Community  succession leads to the climax community (ultimate expression of community dvlpmt)  each sere develop under a particular set of envmtal conditions, but all progress toward similar climax states  Clements believed that climate alone determined the nature of the local climax and that diff. climax states were discrete, recognizable, and separate from one another (closed community)  communities are more commonly viewed as open sys. today  alternative “climax” communities are possible, resulting from factors ex. intensity of a disturbance, size of the gap it produces, physical conditions during early succession  continuum index: the scale of an environmental gradient based on changes in physical characteristics or community composition along that gradient SUCCESSION ENSUES AS COLONISTS ALTER ENVIRONMENTAL CONDITIONS  a species’ presence in a sere is determined by: 1. how it readily invades a newly formed/ disturbed habitat 2. how it responds to changes that occur in the envmt over the course of succession  those that disperse and grow rapidly dominate the early stages of a sere  they sometimes modify envmts that allow later-stage species to become established o ex. herbs shad soil to help it retain moisture  others inhibit others into a sere by competing more effectively or by direct interfrnc.  Joseph Connell and R.R. O. Slatyerlassified the processes governing the course of succession into 3 categories: facilitation, inhibition, tolerance  describes the effect of one species on the prob. of a second becoming established and whether that effect is +ve, -ve, or neutral  facilitation: a process by which one species increases the probability of another species becoming established, particularly during early succession  ex. alder trees harbour N-fixing bacteria in roots which provide soil w/ N, facilitates N-limited plants i.e. spruce, which eventually replace them 
More Less
Unlock Document

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.