Succession

Question 1

Succession definitions

Answer 1

• Succession refers to the way in which communities change over time as a consequence of local colonization and extinction
  1. Primary succession - change in an environment that is initially devoid of life and usually lacks soil e.g lava flows, ash fields, exposed moraine
  2. Secondary succession - Community establishment and a change after a disturbance event, vegetation damaged but some plants and soil remain after the disturbance

Question 2

How do communities change through time?

Answer 2

• Driven by environmental changes - abiotic conditions (abiotic changes e.g ocean acidification)
• Through biotic interactions (competition etc)
• In response to disturbance - abiotic or biotic (e.g. loss of keystone species) (e.g. tsunami, oil spill, eruption)

Question 3

What is the simple model of succession?

Answer 3

No life - Pioneer stage - intermediate stage - climax stage
No life to pioneer is primary succession
Rest is secondary succession

Question 4

The development of theory of succession

Answer 4

• Henry Cowles (1869-1939): built on previous ideas from Europe and published important papers that established principles of succession
• Worked on a dune system on the shores of Lake Michigan
• Found out that the area he was studying was a climax community of mixed oak woodland

Question 5

Ecosystem engineer and Chronosequence definition?

Answer 5

• A species that influence its community by creating or modifying the abiotic environment
• Chronosequence: A series of spatially distinct sites of varying ages that are assumed to represent a temporal sequence of vegetation - Space for time substitution

Question 6

Clements and Gleason’s Theory of Succession

Answer 6

• Core idea: communities changing through time, driven by interactions between species and between species and their environments
• Two opposing ideas on mechanisms driving succession.
  1. Clements idea - Super-organisms where groups of species worked together as a community towards a deterministic end - succession was predictable
  2. Gleason’s idea - rejected super-organisms’ idea and said that communities were random product of the environment - non-deterministic

Question 7

Clements’s Theory of Succession (1916)

Answer 7

• Succession deterministic and orderly sequence of serial stages that ended in climax community
  Each stage composed of a group of species viewed as super-organisms that work together
• Work together to modify the environment until the distinct group is replaced by another distinct group stage

Question 8

Gleasons view of Succession

Answer 8

• Succession occurred as species responded individualistically to the changing abiotic environment
• Species do not arrive and disappear as a stage

Question 9

Connell and Slater (1977) - Facilitation Model

Answer 9

• Inspired by Clements - early colonisers modify the environment in ways which ultimately benefit later arriving species but hinder their own continued dominance

Question 10

Connell and Slater (1977) - Tolerance Model

Answer 10

• Colonisers change the enivroment but neutrally succession occurs because early succession species have life history strategies that allow them to colonise, grow and reproduce quickly - but once the site is colonised they are less competitive than late succession species

Question 11

Connell and Slater (1977) - Inhibition Model

Answer 11

• Colonisers change the environment, suppressing later succession species
• Succession only proceeds when stress/disturbance breaks the dominance of early succession species