Lecture 14 Succession

Question 1

What is ecological succession?

Answer 1

“the non-seasonal, directional and continuous pattern of colonization and extinction on a site by species populations”

the process by which the structure of a biological community evolves over time.

Question 2

what types of succession are there?

Answer 2

• primary v secondary

- allogenic v autogenic

Question 3

What evidence is available for the argument of succession?

Answer 3

• Current/direct observations through time (most grants available for 3-4yrs, impractical, disadvantage)
• Historical evidence i.e. maps, photographs
• preserved biological evidence - pollen seeds are good for this.
• chronosequences - describes a set of ecological sites that share similar attributes but represent different ages or Sequence of places that represent a sequence in time..

Question 4

Primary succession

Answer 4

“vegetation development on newly formed or exposed substrate”
pioneer species are lichens that will eventually after 100s of years will break down rock into soil bits and succession goes onnnnnn
e.g. glacial retreat, nothing can survive that
years and years of nothing

Question 5

Secondary succession

Answer 5

“replacement of pre-existing vegetation following a disturbance that disrupts the vegetation”

e. g. newly plowed field is secondary due to presence of soil & seeds still
e. g. after a fire or flood or natural disturbance, there will still be organisms

Question 6

allogenic succession

Answer 6

“vegetation change due to environmental conditions and environmental change” (driven by processes from outside community)

Question 7

autogenic succession

Answer 7

“vegetation change due to forces of biotic interactions and biotic modification of the environment” (driven by processes from within )

Question 8

what are mechanisms for succession? (3)

Answer 8

facilitation
inhibition
tolerance

Question 9

define in terms of succession facilitation

Answer 9

one or more species enable the establishment, growth or development of other species

Question 10

define in terms of succession inhibition

Answer 10

the prevention of establishment, maturation or growth of one species by existing species

Question 11

define in terms of succession tolerance

Answer 11

later species in the succession can grow to maturity despite the presence of early species and eventually outcompete early species when resources become scarce

Question 12

Explain the polyclimax theory

Answer 12

more than one climax vegetation can exist (“polyclimax”)
- determined by climate, soil, topography, disturbance regime, predation, and so on
(Tansley, 1935)

Question 13

Explain climax - pattern hypothesis

Answer 13

Whittaker (1975) came up with the climax-pattern hypothesis

• a continuum of climax types
• varying along environmental gradients
• not necessarily separable into discrete climaxes

Question 14

cyclic succession

Answer 14

in disturbed habitats, cyclical succession prevents climax succession communities. Occurs commonly on all scales of community (see patch gap)