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biology 301 > ch 18 : community structure > Flashcards

ch 18 : community structure Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

an assemblage of species that occur together in the same place

A

community

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2
Q

what were the two parts of the historical debate in community ecology? who were the important people involved?

A
  1. Superorganism / Holistic concept
    • (Frederick) Clements
  2. Individualistic concept
    -(Henry) Gleason
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3
Q

what was the holistic concept?

A

communities are a distinct ecological units or organizations having recognizable boundaries and whose structure and functioning are regulated by interaction among their component species

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4
Q

what did the holistic concept require?

A

requires that communities be DISCRETE entities and distinguishable from one another.

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5
Q

what was the individualistic concept?

A

a loose assemblage of species that can tolerate the conditions of a particular habitat

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6
Q

what did the individualistic concept not require?

A

distinct boundaries

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7
Q

how do we describe/characterize communities?

A
  • dominant species
  • environment/biomes
  • relationships
  • stability
  • control
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8
Q
  • riparian community - named for ???
  • deciduous hardwood forest community - named for ???
A
  • riparian community - named for environment
  • deciduous hardwood forest community - named for the behavior of the dominant tree species
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9
Q

distributions of species sets closely coincide and are separated from other sets of species

A

closed communities

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10
Q

species are independently distributed along environmental conditions

A

open communities

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11
Q

what do closed communities result in?

A

ecotones (regions of rapid replacement of species)

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12
Q

which are less common: open or closed communities? when?

A

closed communities are less common when there are gradual changes in environment–gradient

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13
Q

what is the continuum concept?

A

when species are distributed along a gradient

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14
Q

what were some conclusions that were made after Robert Whittaker surveyed the distributions of plant species in the Great Smoky Mountains?

A
  • different tree species appeared and disappeared at different elevations, corresponding to changes in moisture.
  • as environmental conditions change, plants will show a gradual and independent change in abundance
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15
Q

what might abrupt changes in species distributions be a result of?

A

however, abrupt changes in species distributions may be the result of abrupt changes in abiotic conditions (e.g., moving from lake to land), and do not necessarily suggest that species are interdependent.

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16
Q

the number of species in a community

A

species richness

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17
Q

the proportion of individuals in a community represented by each species

A

relative abundance

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18
Q

in a typical community, only a few species have _____________; most species have intermediate abundance; they follow a _____________

A

low or high abundance; log-normal distribution

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19
Q

a normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis

A

log-normal distribution

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20
Q

what can the species richness of a community be affected by?

A

the amount of available resources

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21
Q

how do ecologists understand the influence of resources?

A

ecologists have examined the relationship between productivity and species richness

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22
Q

across aquatic and terrestrial environments, the correlation between richness and productivity exhibits a wide range of patterns. what are the observed patterns?

A

U-shaped
negative
neutral
positive
hump-shaped correlations

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23
Q

across studies of vertebrates and invertebrates in aquatic and terrestrial systems, what is the most commonly observed relationship between diversity and productivity? what does it indicate?

A
  • a hump-shaped curve is the most commonly observed relationship between diversity and productivity.
  • this indicates that a site with medium productivity has a higher species richness than sites with either low or high productivity.
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24
Q

how is productivity manipulated in experiments?

A

adding nutrients (e.g., nitrogen) to an ecosystem

25
Q

what does added fertility do to the species richness of producers?

A

added fertility commonly causes a decline in the species richness of producers (e.g., plants and algae).

26
Q

communities with a higher diversity of habitats should offer what?

A

more potential niches (places to feed and breed) and a higher diversity of species

27
Q

a species that substantially affects the structure of communities, although species might not be particularly numerous

A

keystone species

28
Q

what would happen if there was the removal of keystone species?

A

removal of a keystone species can cause a community to collapse

29
Q

keystones species that affect communities by influencing the structure of a habitat

A

ecosystem engineers

30
Q

the hypothesis that more species are present in a community that experiences occasional disturbances than in a community with either frequent or rare disturbances

A

intermediate disturbance hypothesis

31
Q

what happens when disturbances are rare?

A

populations grow until resources are scarce, and competitively superior species become dominant

32
Q

what happens when disturbances are frequent?

A

habitats typically support a small number of species that are adapted to disturbances.

33
Q

what happens when disturbances occur at an intermediate frequency?

A

both types of species can persist

34
Q

a linear representation of how different species in a community feed on each other

A

food chain

35
Q

a complex and realistic representation of how species feed on each other in a community

A

food web

36
Q

what do the arrows in a food web indicate?

A

indicate consumption and the movement of energy and nutrients

37
Q

a level in a food chain or food web of an ecosystem

A

trophic level

38
Q

the autotrophs that convert light energy and CO2 into carbohydrates through photosynthesis

A

producers

39
Q

who forms the first trophic level of a food web?

A

producers

40
Q

a species that eats producers

A

primary consumers

41
Q

a species that eats primary consumers

A

secondary consumers

42
Q

species that eats secondary consumers

A

tertiary consumers

43
Q

a species that feeds at several trophic levels

A

omnivore

44
Q

within a given trophic level, a group of species that feeds on similar items (e.g., guilds of leaf eaters); members of the group are not necessarily related

A

guild

45
Q

what are the problems with trophic levels

A
  • informality of construction
  • lumping species into guilds or categories
  • ignore changing roles (catfish: detritivore/predator)
  • all links equal, although may vary in strength
46
Q

what are the general conclusions of trophic levels?

A
  • most are fairly short (average = 4 links in previous)
  • most are open (receive significant input from and export to adjoining systems)
47
Q

effect of structure on diversity?

A
  • predators can maintain high diversity
  • apparent competition
  • keystone species—one species that has a disproportionately high impact on a community
  • top predators—wolves (reintroduction to Yellowstone); otters—urchins and kelp
  • resource populations–krill
48
Q

how does control of communities work?

A

population regulation—effects on adjacent trophic levels

49
Q

what about more distant effects within communities?

A

trophic cascades—indirect effect of consumer-resource interactions on additional trophic levels

50
Q

what happens when one trophic level effects its adjacent level?

A

top-down vs bottom-up (consumer vs resource)
- can also lead to trophic cascades

51
Q

when the abundances of trophic groups are determined by the amount of energy available from producers

A

bottom-up control

52
Q

when the abundances of trophic groups are determined by the existence of predators at the top of the food web

A

top-down control

53
Q

top down control effects if food webs have 3 trophic levels

A

top-down control by predators would reduce the abundance of herbivores, leading to an increase in vegetation

54
Q

1960; what did researchers Hairston, Slobodkin, and Smith suggest?

A
  • suggested that since communities contain an abundance of vegetation, food webs must be controlled from the top down.
  • in fact, many communities are simultaneously controlled from the top down by predators and from the bottom up by resources.
55
Q

the ability of a community to maintain a particular structure.

A

community stability

56
Q

the amount a community changes when acted upon by a disturbance (e.g., addition or removal of a species)

A

community resistance

57
Q

the time it takes after a disturbance for a community to return to its original state.

A

community resilience

58
Q

________ may promote community stability
(**review slide 42)

A

diversity

biology 301 (6 decks)

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