Chapter 19: Community Dynamics

Question 1

What is succession?

Answer 1

• gradual and seemingly directional change in community structure over time
• sequence of species replacements that occurs after habitat has been opened up for colonization
• shifting pattern of species dominance and diversity (birth and death rates cause this)

Question 2

What is community dynamics?

Answer 2

• the changing pattern within the community of its structure
• changing structure over time is community dynamics
• succession is HOW that occurs

Question 3

Explain the colonization of concrete blocks in intertidal zone Sousa study with respect to succession!

Answer 3

• intertidal zone in Cali
• noted that if you were to look at rocky intertidal areas action of waves will move rocks and turn them over stripping algae off them. Over time the algae comes back and colonizes. The author looked at the colonization..which species come first..who competes etc
• they monitored algae succession on the blocks over time
• they noted early, mid and late succession of the algae.
• they found a general pattern of colonization and extinction. Basically species like Ulva (green algae) come in early succession and take over but they don’t compete well so they decrease as others come in. The late colonizers were the better competitors (Gigartina canaliculata)
• *done over two years

Question 4

Explain the characteristics you would expect to see in initial or early successional species (pioneer species)! What type of species would these be classified as?

Answer 4

• fast growing, high reproductive rates, high mortality rates, small size, high degree of dispersal
• R Species

Question 5

Explain the characteristics you would expect to see in late successional species. Also, what type of species would these be classified as?

Answer 5

• low rates of dispersal, s;ow growth rate, larger in size, longer lived, produce fewer offspring, nurture them, out compete other species such as the early successional ones
• K Species

Question 6

What is primary succession?

Answer 6

• it occurs on a site previously unoccupied by a community
• aka an area that nothing ha lived on before
  ex: newly exposed surface

Question 7

Explain the coastal sand dune example for primary succession!

Answer 7

• costal sand dune is created by the action of waves washing up sand and creating a new substrate..succession occurs over time..beach grass colonizes it which stabilizes the area. Aft this k-sekected secures ca come in and colonize the area since it has been stabilized by the r-selected species.

Question 8

Explain the changes in wood species at Glacier Bay with respect to primary succession!

Answer 8

• When a glacier melts it isn’t just water..it is filled with silt
• silt builds up creating a new substrate that organisms can live on
• glacier use to cover the whole area and over the past 200 years it has been retreating exposing new areas that a variety of species can now come in
• over time 550500 years after the retreat we have seen alders, willow and cotton wood that are colonizers come in and stabilize the area making it more habitat for other species….
• after this spruce have now come in (no longer just shrubs). They can grow and start shading shrub species which will die off. They make the area better for hemlock since they are shade tolerant and can grow under the spruce
• now the spruce cannot live bc hemlock shades them out and they cannot tolerate it …fucking hemlock - what a douche

Question 9

What is secondary succession?

Answer 9

• succession that occurs on a previously occupied site following a disturbance
• the amount and composition of surviving community influence successional dynamics

Question 10

Explain the secondary succession example with respect to the salt marsh and ice scrapping!

Answer 10

• ice scrapping the salt marsh will wipe out life. Then secondary succession occurs. If there is still some of the older k-selected species they can stay and the pioneer species that come in may not be the same as if it was primary succession

Question 11

Explain the secondary succession example about a cleared forest!
(fyi theres a fucking ton on this)

Answer 11

• the forest was deforested and turned into a field which was then abandoned. During the first year the field was filled with annual crab grass which took over. By next spring, horse weed took over the field from crab grass . During that second summer other plants cam in such as white aster and rag weed. By the third summer there was broom sedge which is a perennial bunch grass and it coloized the area which out competed the earlier pioneers. Around this same time pine seedlings began to invade. Within 5-10 years the trees were taller enough to shade out the broom hedge since they grow quite quickly
• over time the hardwoods come in (lat successional species..slowly growing ) - they start slowly and build up. As the pine builds up they start to decline via competition with the hardwoods as they get big enough because there is not enough room for all the seedlings. Over time the hardwoods will out compete the pines. As the pine seedlings reach maturity they will die out because the hardwoods have shaded out the forest flower and the seedlings cannot grow anymore.

Question 12

What are the three models of succession?

Answer 12

• Facilitation
• tolerance
• inhibition

Question 13

Explain the facilitation model of succession( aka establishment, recruitment, replacement, continuation and long-term/steady state)!

Answer 13

• Disturbance opens space
• Establishment: only certain early succession species can establish themselves
• Effect go early occupants on Recruitment: environment becomes less suitable for early succession and more suitable for late succession species
• Replacement: Early succession species facilitate later succession species. In time the earlier species are eliminated
• Continuation: continues until the resident species no longer facilitate other species

Question 14

Explain the tolerance model of succession aka establishment, recruitment, replacement, continuation and long-term/steady state)!

Answer 14

• Disturbance opens a space
• Establishment: any that are able to survive there as adults can establish themselves
• Effect go early occupants on Recruitment: environment becomes less suitable for early species, little or no effect on late species
• Replacement: Juveniles of later species invade despite early species. In time, earlier species are eliminated
• Continuation: continues until now species exist that can invade and grow in the presence of residents

Question 15

Explain the inhibition model of succession aka establishment, recruitment, replacement, continuation and long-term/steady state)!

Answer 15

• disturbance opens up space
• Establishment: any that are able to survive there as adults can establish themselves
• Effects of early occupants on Recruitment: environment becomes less suitable for recruitment of both early and late successional species
• Replacement: earlier colonists exclude, suppress or inhibit subsequent colonists
• *no continuation period**

Question 16

With respect to facilitation, tolerance and inhibition secondary successional models whats going on long term/steady state wise after the process has occurred?

Answer 16

further invasion and / or growth can occur only when a resident individual is damaged or killed, releasing space
*aka more disturbance is needed

Question 17

What are the two classes of environmental condition changes ?

Answer 17

• Autogenic

- Allogenic

Question 18

Explain the autogenic environmental condition change class.

Answer 18

• result of organisms within the community
• basically the direct result of the presence and activities of organisms within that community. Driven by what is there.
  ex: vertical profile of light in a forest…forest floor is limited by what ca liver there because the forest is filtering out light thereby limiting exposure down there

Question 19

Explain the allogenic environmental condition change class.

Answer 19

• due to long term changes in physical environment
• basically the feature of the physical environment such as nutrients, moisture, wind stress etc physical stressors that are not related to other species living there
  ex: decline of average temperature with increasing elevation

Question 20

Explain the secondary succession example involving the dominance shift of overstay and understory tree species during secondary succession in North Carolina.

Answer 20

• not all plant species respond the same way to variations in light exposure
• as the oak-hickory trees establish themselves they shoot up as the pine trees die off. Seedlings and saplings grow quite quick and do well in shade but one that shade is wiped out the trees themselves do much better
• successional results from changes in relative environment tolerance and competition of species is an example of allogenic change. Species change bc of the shade
• in addition to changes in species dominance, patterns of species diversity changes
• species diversity will increase into the late herbaceous stage
• later successional species eventually replace early ones and species diversity declines
• peaks right between the herb and shrub stage
• at that transition: going from one stage where you have lots of herbs you are now getting shrubs establishing themselves…best of both worlds..but as the shrubs grow up they shade out the herbs causing them to die off; therefore, highest diversity is in between the two when you have both successional stages present
• as succession goes along you have differences in your species diversity

Question 21

Succession can/cannot result in changes in diversity

Answer 21

CAN

Question 22

Succession and Diversity:

- explain the graph of changes in diversity during secondary succession in a oak-pine forest in NY.

Answer 22

• rate of displacement is influenced by species growth rates involved in the succession
• slow growth rates= displacement, also moves more slowly bc they grow slowly they are not outcompeting the species as fast. Have species diversity reading higher and longer
• late succession species grow faster = lower species diversity over time

Question 23

Disturbances reset the clock for succession. If disturbance frequency is high what happens to later successional species?

Answer 23

• they will not be able to colonize = low diversity

Question 24

What is the intermediate disturbance hypothesis?

Answer 24

• at an intermediate frequency of disturbance, colonization occurs but competitive displacement is held to minimum
• pattern of high diversity at intermediate disturbance is called the intermediate disturbance hypothesis (mixture of late and early succession species)

Question 25

Explain the study by Sousa on degrees of disturbance and species diversity of algae on intertidal boulders. Does it support the intermediate disturbance hypothesis?

Answer 25

- at intertidal zone: concrete blocks are examined to look at colonization of algae, change of early to mid to late successional stages - with low disturbance when the concrete blocks are rolled over we have an average of 1-3 species present - intermediate disturbance level most boulders have between 2-4 species..diversity has increased from low to medium disturbance - high disturbance: most of the time you only have one species present - IT SUPPORTS IT YO

Question 26

Allogenic changes in community structure. Explain this.

Answer 26

- due to changes in environment - scales of days to millennia ( changes in the physical environment can be a long process aka) - if you have short changes in physical environment you may not really see successional changes, you need them to occur over the entire life span - shifts in physical conditions at periods longer than lifespan likely to result in successional changes

Question 27

Allogenic changes in community structure.Examples?

Answer 27

1. seasonal changes result in phytoplankton succession in lakes.Succession happens in fall turnover as water on top is cooled down and moved to bottom it brings up bottom water filled with nutrients which can make a plankton bloom 2. sediment deposition results inc change from marsh to forest

Question 28

Geological time scale ??

Answer 28

- changes in species distributions since the last ice age would be an example of this - ice sheet that covered most of Canada at least...it has over 10 thousand years decreased to a smalls upset of where it actually occurs - successional changes have happened in all of these regions, colonizing and making them more habitable - as temp changes you have different communities living in the areas and as the temp rises that ice sheath moves further north !