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
intermediate disturbance hypothesis
biodiversity is highest when disturbances are not rare or frequent (disturbances occur at an intermediate rate)
- low disturbance = exclusion
- high disturbance = only tolerant survive
ecological succession
recovery of communities after a severe disturbance
- transformation of communities over time
ways of chronosequencing
- pollen in lake/pond sediments
- fossils
- carbon dating
primary succession
development of communities in habitats that are initially devoid of plants and organic soil, such as dunes, lava flows, and bare rock
- ONLY on ROCK
- must start from “scratch”
- where no plant has gone before
primary succession are colonized by…
species that require no soil and can live on rocks
- early colonizers produce organic matter to create soil (more hospitable for other species)
- ex: algae, lichen, mosses
Secondary succession
- development of communities in disturbed habitats that contain no plants but still contain organic soil
- specific sequence of species that appears over time is the successional
pathway - ex: plowed fields, forests harmed by hurricane, etc.
terrestrial succession
sequence of seral stages that a site passes on its way to a climax community can differ depending on the initial conditions.
Similar sites can pass through different ___ stages due to variation in ____________.
- seral stages
- variation in historic abiotic conditions, soil fertility, and disturbances
chronosequence assumes that…
older and younger sites pass through similar serial stages
- this assumption is not always met
The best approach to analyzing succession is to use a combination of methods, including….
chronosequence’s, pollen records, and long- term studies of single sites
animal succession
Changes in the plant community can change the habitats that are available to animals
- causes changes in the animal community
succession of intertidal communities
succession in intertidal communities can occur rapidly after a disturbance due to short generation time of dominant species
why can intertidal communities recover rapidly?
after a disturbance, the populations will experience rapid succession, due to short generation time of dominant species
stream succession
rapid succesion; organisms move downstream (away from more disturbed sites)
- quicker moving streams do not have submerged vegetation
type of extreme disturbance streams can face
heavy rainfall
- increases volume and speed of water
- causes sand and rocks to move downstream (killing/wiping out plants, animals, and algae downstream)
heterotrophic river
respiration > photosynthesis
autotrophic river
photosynthesis > respiration
rivers always start as…and usually end as…
start: heterotrophic
- initially not large amounts of photosynthesis/plant life
end: autotrophic
- longer life = erosion and mud; less submerged vegetation (no light) = less photosynthesis
lake/pond succession occurs at…
slow transformation rates
most lakes are…
oligotrophic (nutrient-poor)
- little submerged vegetation
mesotrophic
lake w/ more nutrients than oligotrophic
- some submerged vegetation
eutrophic lake
lots of nutrients (fish die-off from bacteria digesting algae and lack of CO2)
- LOTS of nitrogen and phosphorous
- LOTS of submerged vegetation
lake succession: model 2: years w/ little succession, w/ episodes of rapid change
- drought (dries up)
- new plants colonize bottom of lake (from bottom up)
- as drought ends, lake fills and plants detach from bottom
- sediments eventually fill basic and plants float to surface
Succession does NOT always produce…
a single climax community.
in early stages of succession, abiotic conditions are…
rapidly altered
- once a community contains the largest plants it can support, changes will occur more slowly
When environmental conditions are stable, the composition of plant species in a community…
also becomes stable
-the species in a climax community can continue to change.
When environmental conditions are stable, the species in a climax community can….
continue to change
as one moves along an environmental gradient, composition of ___ can ____
composition of climax communities can vary
Except for oceans, most aquatic systems are…
considered temporary (NOT climax community)
- all receive inputs of soil particles and organic matter from surrounding land
routine lake succession (model 1)
gradual filling of shallow bodies of water
- roots/stems accumulate below water
Small-scale disturbances in an area with a climax community can allow growth of…
species that are not considered climax species
- ex: break in tree canopy (climax tree species die); lots of plants colonize to try and get sunlight (competition for sunlight)
Climax Community Characteristics
- Maintain species diversity for extended time
- Multiple specialized ecological niches
- High level of organism interactions
- Nutrients recycled & biomass levels remain constant
The only thing differentiating a climax community from a successional community is…
time scale
After a disturbance occurs, a succession of species and communities…
replaces the individuals that were lost
The composition of a community is primarily a function of…
climate and history
Jaccard’s index measures…
how similar 2 communities are
Jaccard’s index equation:
J = X / (A+B+X)
- X = # of species in BOTH communities
- A = # of species in ONLY community (A)
- B = # of species in ONLY community (B)
Jaccard’s index range:
0–>1
- 0 = no species in common
- 1 = identical species composition
succession depends on…
the ecosystem
- habitat
- environment
- climate
