Topic 27 -Community Dynamics

Question 1

succession

Answer 1

change in community structure (at a specific location) through time

change in species composition and population dynamics

b and d of species change in response to environmental conditions
leads to shifting patterns of species dominance and diversity

Question 2

succession involves a pattern of species…

Answer 2

colonization and extirpation from a specific region -with species displacing other species from a community over time

Question 3

early successional species (“pioneer” or “colonizing”) are the

Answer 3

first to colonize an area

r-selected life history traits -high growth rate, smaller size, short-lived, high rates of population growth, high degree of dispersal (colonization)

can often survive under extreme abiotic conditions but are poor competitors

Question 4

Late successional species (“climax” species) replace

Answer 4

early successional species in a community over time

k-selected life history traits -slower growth rate, larger size, long-lived, low rates of population growth, low degree of dispersal (colonization)

generally better competitors (outcompete early species, extirpation) but could not colonize because they cannot survive under extreme abiotic conditions

Question 5

our understanding of succession is mainly based on

Answer 5

plant communities

Question 6

Primary succession

Answer 6

process occurs at a site not previously occupied by a community ex. rock cliffs, sand dunes

Question 7

Secondary succession

Answer 7

process occurs on a site previously occupied by a community after a disturbance

Question 8

disturbance

Answer 8

any process that results in the removal (either partial or complete) of the existing community ex natural fire, windstorm, flood, cold, drought etc

Question 9

Disturbance event

Answer 9

relatively discrete event that disrupts community structure and function

Question 10

Disturbance regime

Answer 10

pattern of disturbance events that characterize a landscape over a longer period of time

Question 11

Disturbance intensity

Answer 11

proportion of a species population that the disturbance kills or eliminates

Question 12

Disturbance scale

Answer 12

spatial extent of the impact of the disturbance relative to the size of the affected landscape

Question 13

disturbance frequency

Answer 13

mean number of disturbances that occur within a particular time interval

Question 14

small-scale disturbance creates

Answer 14

a gap -provides access to physical space for colonization by new individuals (often enhances diversity by increasing environmental heterogeneity)

ex wind storm leading to death of tree

Question 15

Large-scale disturbance reduces or eliminates local populations which

Answer 15

significantly modifies physical environment leading to a secondary succession ex fire

Question 16

succession is driven by the processes of species colonization and extirpation, explain

Answer 16

colonization increases species richness
extirpation decreases species richness

diversity peaks during middle stages -after arrival of later species but before replacement of early species

Question 17

without disturbances

Answer 17

later species will replace early species -diversity declines

Question 18

with high disturbances

Answer 18

succession is kept at early stages -low diversity

Question 19

with intermediate disturbances

Answer 19

colonization is maintained and competitive replacement (extirpation) is minimal

Question 20

intermediate diversity hypothesis

Answer 20

pattern of high diversity at intermediate frequencies of disturbance

Question 21

Human disturbances have

Answer 21

a more profound and long lasting impact on communities than natural disturbances

Question 22

human activities involve

Answer 22

continuous management of communities

completely remove natural communities and replace with cropland, pastures, paved highways/cities etc.

Question 23

Traditional view of communities

Answer 23

communities are in a state of equilibrium or a state of balance (climax state) -unless seriously disturbed

Question 24

reality of communities

Answer 24

most communities often have a certain level of disturbance occurring normally all the time

Question 25

current view of communities

Answer 25

communities are generally in a state of recovery from disturbance (not usually in climax state)