Succession Flashcards
Biogeography -
spatial and temporal distribution of species, communities and ecosystems
Definitions of succession
2 points
- The directional and continuous pattern of
colonisation and extinction on a site by species
populations - Changes in species composition in a community over time, as a result of both abiotic and biotic
factors
Succession
5 points
- A succession (or sere) is a directional process
- Colonisation by pioneer species
- Seral stages
- Ecosystems become progressively more stable and protected from environmental disturbance
- Culminates in a climax community
Climax communities
2 points
- at equilibrium for climate and substrate conditions, resources, biotic interactions
- A plagioclimax community is the result of arrested and / or deflected succession (usually due to human activity, e.g. harvesting, conservation)
Biotic effect of animals
3 points
- Animals follow the succession among plants
- Sometimes they may affect succession e.g. rabbits, elk
- Biotic factors can also influence community change
Ecosystem engineers
2 points
- Ecosystem engineering species create, modify,
or maintain physical habitat for themselves and
other species - e.g. Beavers create new habitats by cutting down trees, using them to dam streams and create ponds and wetlands
Life history (r or K selected) 4 points
- Species populations may be r or K selected
- r selected species reproduce rapidly
Have a high r value
typical of the early stages
of a succession
Fast population growth
Tolerate extreme conditions
- K selected species reproduce more slowly
typical of the late stages of late stages of succession
Good competitors
- Populations close to the carrying capacity (K) of the habitat
Species richness
3 points
- Species richness increases with successional age
- Succession involves colonisation suggesting the
early stages are not saturated with species - Not always the case -
Multiple pioneer species may be replaced by dominant competitors
e.g. heather (Calluna vulgaris) in heath habitats
6 Types of succession
- Allogenic
- Autogenic
- Degradation
- Primary succession
- Secondary succession
- Cyclic succession
Allogenic
1 point and e.g.
- Serial replacement of species driven by changing external geophysical and chemical processes
e. g. silt deposition changing aquatic habitat to terrestrial habitat in salt marshes
Plant species show zonation above sea level
Silt deposition causes spatial succession
Autogenic
1 point 2 e.g.
- Driven by biological processes changing conditions and / or resources
e. g. alterations in soil conditions and shading as vegetation develops; community changes due to biotic interactions; sessile animals dying
e. g. Abandoned agricultural land
Degradative
2 ponts and e.g.
- sequence of decomposition of organic matter by heterotrophic species associated with e.g. faeces, fallen trees, animal corpses
- Resource is utilised successively by a number of species
Dung / leaf litter / wood / stored products
e.g. Volcanic lava / fire / retreat of ice sheets
Pioneer species - Early successional species facilitate entry of new species
Changes in soil conditions are crucial
Primary succession
occurs after a catastrophic
disturbance
Primary succession is the development of a biological community on newly formed or exposed substrate, where one did not previously exist
e.g. exposed till after glacier retreat; volcanic lava flows; coastal sand/silt deposits. Initially no soil.
Secondary succession
2 points and e.g.
- occurs after most but not
all organisms in a community are destroyed - Secondary succession occurs on partly or
completely denuded areas which previously
supported a biological community
e.g. following
a fire / hurricane / flood. Soil remains.
Cyclic succession
2 points
- Cyclic succession is the dynamic creation and recolonisation of gaps in a spatial and temporal mosiac of disturbance, e.g. wave action, tree falls
- Cyclic succession within a species
Heather (Calluna vulgaris) has 4 lifecycle stages
Pioneer phase (5 - 6 years) - seedling Building phase (6 - 15 years) - bush-like form Mature phase (15 - 25 years) - less vigorous Degenerate phase (> 30 years) - leading to death
Models of succession
Ecosystem view of succession including properties and processes
Energy, biogeochemical processes, life history, selection pressure (r- and K-selection), abundance, and community structure change over time
Models of succession
Three mechanisms that drive succession, leading to three models
- Facilitation
- Tolerance
- inhibition
Models of succession
Three mechanisms that drive succession, leading to three models
Facilitation
- Initial (pioneer) species alter habitat to make it more favourable for later species
- Subsequent species enhance conditions and resources facilitating the establishment of later species at each stage
Models of succession
Three mechanisms that drive succession, leading to three models
Tolerance
- Early species neither help nor hinder later species
- Succession based on tolerance to changing conditions
- Late successional species may invade the initial stages of colonisation
- Succession involves reduced abundance of species originally present rather than an invasion
by later species facilitated by specific pioneers
Models of succession
Three mechanisms that drive succession, leading to three models
inhibition
- Competition within and between stages
- Succession works on a first come first served basis – species that happen to arrive first become established
- Stochastic dispersal and recruitment allows potential for different successional trajectories resulting in alternative climax communities
- Earlier species actively inhibit the establishment of later species
- Succession proceeds as individuals die and their space is occupied by later species
Zonation
2 points
- Zonation of plant and animal communities may reflect successional stages,
e. g. sand dunes, salt marsh, lake - bog - forest - However, spatial zonation may only be the result of differential adaptation to environmental gradients and not temporal succession,
e. g. mountains, rocky shores
Observable change
5 points
- Difficult to observe changes that occur over long periods of time (longer than the life of a scientist, tree, database system or research grant)
- Very few examples of observable evolution or succession
- Long term data sets are an important resource
- Succession stages viewed as snap shots in time
- Dateable relative to recorded disturbance event
