ch. 19: community succession Flashcards
succession
process by which species composition of community changes over time
- can take weeks, months, or hundreds of years
seral stage
each stage of community change during process of succession
pioneer species
earliest species to arrive at site
- usually have ability to disperse long distances and arrive quickly at a disturbed site
climax community
final seral stage in process of succession
- generally composed of group of organisms that dominate in a biome
2 ways to observe succession:
direct observations (easiest way), indirect observations
chronosequence
sequence of communities that exist over time at a location
- when direct observations is not possible
primary succession
development of communities in habitats devoid of plants and organic soil
- colonized by species that require no soil and can live on the surfaces of rocks and sand
- ex: sand dunes, lava flows, bare rock
secondary succession
development of communities in habitats that have been disturbed and include no plants but still have organic soil
- ex: abandoned agricultural fields
3 mechanisms of succession
facilitation, inhibition, and tolerance
facilitation
presence of 1 species ↑ probability that a 2nd species can become established
inhibition
1 species ↓ the probability that a 2nd species will become established
tolerance
probability that a species can become established depends on its dispersal ability and ability to persist under physical conditions
priority effect
arrival of 1 species at a site affects subsequent colonization of other species
transient climax community
climax community that is not persistent
- frequently disturbed sites = climax community can’t persist
- ex: small wetlands
fire-maintained climax community
successional stage that persists as final seral stage due to periodic fires
- Biomes in which fires occur at regular intervals favor the persistence of fire-tolerant species
grazer-maintained climax community
successional stage persist as final seral stage due to intense grazing
- Grazers consume the most palatable plants, leaving behind less palatable or better-defended species
- ex: plants won’t eat cheatgrass (inedible) AND cheatgrass is fire resistance, so cheatgrass = climax community
Frederick Clements view on biological communities:
- communities are stable, integrated, and orderly entities with a highly predictable composition
- communities develop by passing through a series of predictable stages dictated by extensive interactions among species and this development culminates in a stable final stage called a climax community
- Closed community
Henry Gleason believed that…
- a community found in a particular area is neither stable nor predictable
- it is largely a matter of chance whether a similar community develops in the same area after a disturbance occurs
- Open Community
Clements vs Gleason- who was more correct?
- Clements’s position was too extreme
- Gleason’s view is more correct
clement hypothesis
identical communities will always develop in identical environments
Gleason hypothesis
identical communities will not always develop in identical environments
disturbance definition
an event that removes some individuals or biomass from a community
disturbance always…
alters some aspect(s) of resource availability
impact of a disturbance is based on (3 things):
- type of disturbance
- frequency
- severity
6 types of disturbances
- fire
- windstorms
- floods
- deforestation
- disease epidemics
- herbivore outbreaks