Succession

Question 1

Biogeography -

Answer 1

spatial and temporal distribution of species, communities and ecosystems

Question 2

Definitions of succession

2 points

Answer 2

1. The directional and continuous pattern of
   colonisation and extinction on a site by species
   populations
2. Changes in species composition in a community over time, as a result of both abiotic and biotic
   factors

Question 3

Succession

5 points

Answer 3

1. A succession (or sere) is a directional process
2. Colonisation by pioneer species
3. Seral stages
4. Ecosystems become progressively more stable and protected from environmental disturbance
5. Culminates in a climax community

Question 4

Climax communities

2 points

Answer 4

1. at equilibrium for climate and substrate conditions, resources, biotic interactions
2. A plagioclimax community is the result of arrested and / or deflected succession (usually due to human activity, e.g. harvesting, conservation)

Question 5

Biotic effect of animals

3 points

Answer 5

1. Animals follow the succession among plants
2. Sometimes they may affect succession e.g. rabbits, elk
3. Biotic factors can also influence community change

Question 6

Ecosystem engineers

2 points

Answer 6

1. Ecosystem engineering species create, modify,
   or maintain physical habitat for themselves and
   other species
2. e.g. Beavers create new habitats by cutting down trees, using them to dam streams and create ponds and wetlands

Question 7

Life history (r or K selected)
4 points

Answer 7

1. Species populations may be r or K selected
2. r selected species reproduce rapidly

Have a high r value

typical of the early stages
of a succession

Fast population growth

Tolerate extreme conditions

3. K selected species reproduce more slowly

typical of the late stages of late stages of succession

Good competitors

4. Populations close to the carrying capacity (K) of the habitat

Question 8

Species richness

3 points

Answer 8

1. Species richness increases with successional age
2. Succession involves colonisation suggesting the
   early stages are not saturated with species
3. Not always the case -

Multiple pioneer species may be replaced by dominant competitors

e.g. heather (Calluna vulgaris) in heath habitats

Question 9

6 Types of succession

Answer 9

1. Allogenic
2. Autogenic
3. Degradation
4. Primary succession
5. Secondary succession
6. Cyclic succession

Question 10

Allogenic

1 point and e.g.

Answer 10

1. 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

Question 11

Autogenic

1 point 2 e.g.

Answer 11

1. 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

Question 12

Degradative

2 ponts and e.g.

Answer 12

1. sequence of decomposition of organic matter by heterotrophic species associated with e.g. faeces, fallen trees, animal corpses
2. 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

Question 13

Primary succession

Answer 13

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.

Question 14

Secondary succession

2 points and e.g.

Answer 14

1. occurs after most but not
   all organisms in a community are destroyed
2. Secondary succession occurs on partly or
   completely denuded areas which previously
   supported a biological community

e.g. following
a fire / hurricane / flood. Soil remains.

Question 15

Cyclic succession

2 points

Answer 15

1. Cyclic succession is the dynamic creation and recolonisation of gaps in a spatial and temporal mosiac of disturbance, e.g. wave action, tree falls
2. 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

Question 16

Models of succession

Ecosystem view of succession including properties and processes

Answer 16

Energy, biogeochemical processes, life history, selection pressure (r- and K-selection), abundance, and community structure change over time

Question 17

Models of succession

Three mechanisms that drive succession, leading to three models

Answer 17

1. Facilitation
2. Tolerance
3. inhibition

Question 18

Models of succession

Three mechanisms that drive succession, leading to three models

Facilitation

Answer 18

1. Initial (pioneer) species alter habitat to make it more favourable for later species
2. Subsequent species enhance conditions and resources facilitating the establishment of later species at each stage

Question 19

Models of succession

Three mechanisms that drive succession, leading to three models

Tolerance

Answer 19

1. Early species neither help nor hinder later species
2. Succession based on tolerance to changing conditions
3. Late successional species may invade the initial stages of colonisation
4. Succession involves reduced abundance of species originally present rather than an invasion
   by later species facilitated by specific pioneers

Question 20

Models of succession

Three mechanisms that drive succession, leading to three models

inhibition

Answer 20

1. Competition within and between stages
2. Succession works on a first come first served basis – species that happen to arrive first become established
3. Stochastic dispersal and recruitment allows potential for different successional trajectories resulting in alternative climax communities
4. Earlier species actively inhibit the establishment of later species
5. Succession proceeds as individuals die and their space is occupied by later species

Question 21

Zonation

2 points

Answer 21

1. Zonation of plant and animal communities may reflect successional stages,
   e. g. sand dunes, salt marsh, lake - bog - forest
2. However, spatial zonation may only be the result of differential adaptation to environmental gradients and not temporal succession,
   e. g. mountains, rocky shores

Question 22

Observable change

5 points

Answer 22

1. Difficult to observe changes that occur over long periods of time (longer than the life of a scientist, tree, database system or research grant)
2. Very few examples of observable evolution or succession
3. Long term data sets are an important resource
4. Succession stages viewed as snap shots in time
5. Dateable relative to recorded disturbance event