ch 19 : community succession

Question 1

describe the nature of communities

Answer 1

communities are in a constant state of flux, yet the appearance and composition of communities seem to change little over time

Question 2

what do we need to know to predict how communities respond to environmental disturbances?

Answer 2

we must understand how species composition changes over time.

Question 3

the process by which the species composition of a community changes over time

Answer 3

succession

Question 4

each stage of community change during succession

Answer 4

seral stage

Question 5

the earliest species to arrive at a site; typically are able to disperse long distances and arrive quickly at disturbed sites

Answer 5

pioneer species

Question 6

the final seral stage in the process of succession; generally composed of organisms that dominate in a given biome

Answer 6

climax community

Question 7

how long does succession in a community take?

Answer 7

succession in a community can take weeks or months (e.g., succession of decomposers on a dead animal) or hundreds of years (e.g., succession of a forest).

Question 8

what is the clearest way to record succession in a community?

Answer 8

direct observation of changes

Question 9

what can we do if direct observation of succession is not possible?

Answer 9

scientists can use methods of indirect observation, such as a chronosequence

Question 10

a sequence of communities that exist over time at a given location

Answer 10

chronosequence

Question 11

t/f it’s not possible to look back in time by examining pollen preserved in layers of lake and pond sediments

Answer 11

false, it is possible

Question 12

how does examining pollen for the sake of observing succession work?

Answer 12

• flowering plants produce pollen grains with distinct sizes and shapes that travel through the air and land on a lake surface.
• the pollen grains sink and become preserved in layers of sediment at the bottom of the lake.
• researchers can take a sample that penetrates through many layers of mud on the lake bottom.

Question 13

when is carbon dating used

Answer 13

to identify the age of the pollen in each layer, and helps to determine the changes in plant species composition around the lake over hundreds or thousands of year

Question 14

the development of communities in habitats that are initially devoid of plants and organic soil, such as such dunes, lava flows, and bare rock

Answer 14

primary succession

Question 15

what do early colonizers do?

Answer 15

produce organic matter that helps in the creation of soil that generates more hospitable conditions for other species

Question 16

: the development of communities in disturbed habitats that contain no plants but still contain organic soil (e.g., plowed fields, forests uprooted by a hurricane)

Answer 16

secondary sucession

Question 17

the sequence of seral stages that a site passes on its way to a climax community can differ depending on what

Answer 17

its initial conditions

Question 18

why would similar sites pass through different seral stages?

Answer 18

similar sites can pass through different seral stages due to variation in historic abiotic conditions, soil fertility, and disturbances.

Question 19

what does the use of chronosequences assume?

Answer 19

• the use of chronosequences assumes that older and younger sites pass through similar seral stages.
• however, it is difficult or impossible to determine if sites did not differ in ways that affect succession.

Question 20

how do changes in the plant community affect the animal community?

Answer 20

changes in the plant community can change the habitats that are available to animals, which causes changes in the animal community.

Question 21

succession in intertidal communities can occur rapidly after what?

Answer 21

a disturbance due to the short generation time of dominant species

Question 22

why do streams undergo rapid succession?

Answer 22

because organisms can move downstream from sites that are less disturbed

Question 23

when do streams experience disturbance?

Answer 23

streams can experience disturbance when heavy rainfall increases the volume and speed of water, causing sand and rocks to tumble downstream and wipe out most plants, animals, and algae

Question 24

most models of pond / lake succession suggest slow transformation

Answer 24

1. after a lake or pond is created, the edge of the water body is initially colonized by plants
2. the plants expand laterally across open water and begin accumulating dead plant matter (i.e., peat)
3. plants continue to expand and the peat layer becomes thicker
4. peat layer eventually fills the basin

Question 25

research suggests a different model: a lake may undergo hundreds of years with little succession, with brief episodes of rapid change.

Answer 25

1. an open lake or pond experiences a drought of one or more decades and the water level falls.
2. plants colonize the newly exposed lake sediments.
3. as the drought ends, the lake fills and living plants detach from lake sediments and float on the lake’s surface.
4. peat sediments eventually fill the basin.

Question 26

what happens to species richness after a disturbance

Answer 26

species richness is at or near zero

Question 27

what happens to species richness during succession?

Answer 27

species richness increases rapidly at first, followed by a plateau and a small decline

Question 28

a mechanism in which one species increases the probability that a second species can become established

Answer 28

facilitation

Question 29

a mechanism in which one species decreases the probability that a second species will become established (e.g., by competition, predation, or parasitism)

Answer 29

inhibition

Question 30

early in succession, inhibition can prevent ???

Answer 30

prevent movement toward a climax community

Question 31

late in succession, inhibition can prevent ???

Answer 31

prevent pioneer species from colonizing and surviving

Question 32

when the arrival of species at a site affects the colonization of other species; often occurs through inhibition

Answer 32

priority effect

Question 33

a mechanism of succession in which the probability that a species can become established depends on its dispersal ability and its ability to persist under the physical conditions of the environment

Answer 33

tolerance

Question 34

research indicates that the intertidal communities of southern California are dominated by the common acorn barnacle and a brown macroalgae species

Answer 34

review slides 40 and 41!!!

Question 35

why is climax an elusive concept?

Answer 35

• communities change in response to long-term climate changes
• human activity has prevented many communities from reaching a steady state
• disappearance of keystone consumers can change species composition
• introduction of invasive species

Question 36

changes in climax communities : what happens as succession occurs?

Answer 36

we typically observe changing environmental conditions and a progression from small to large life forms

Question 37

changes in climax communities : through the early stages, what happens?

Answer 37

through the early stage of climax communities changing, abiotic conditions alter rapidly BUT when the community contains the largest plants that it can support, the environment will change more slowly

Question 38

changes in climax communities : when environmental conditions are stable, what happens to the composition of plant species?

Answer 38

the composition of plant species in a community also becomes stable

Question 39

as one moves along environmental gradients, climax communities can also vary in ________

Answer 39

composition

Question 40

a climax community that is not persistent; occurs when a site is frequently disturbed so a climax community cannot persist

Answer 40

transient climax communities

Question 41

a climax community that develops in an ephemeral habitat, e.g. seasonal ponds

Answer 41

transient climax

Question 42

a repeating sequence of stages of succession, none of which by itself is stable, but together represent a persistent pattern

Answer 42

cyclic climax

Question 43

what is considered a gap in a climax community?

Answer 43

small-scale disturbances in an area with a climax community can allow the growth of species that are not considered climax species

Question 44

what do biomes in which fire occur at regular intervals favor?

Answer 44

biomes in which fires occur at regular intervals favor the persistence of fire-tolerant species

Question 45

a successional stage that persists as the final seral stage due to periodic fires

Answer 45

fire maintained climax community

Question 46

when a successional stage persists as the final seral stage due to intense grazing

Answer 46

grazer maintained climax community

Question 47

what do grazers usually consume?

Answer 47

grazers preferentially consume the most palatable plants, leaving behind less palatable or better-defended species