55-communities

Question 1

Community

Answer 1

A group of species living together in the same place and time

• vary in size and scope
  - can be small/contained or cover a large geographic area

Question 2

Biologists use subsets to organize communities based on…

Answer 2

• taxonomy (similar species)
• guilds (use similar resources)
• functional group (perform similar tasks)

*trophic structure (food webs)

Question 3

Trophic levels

Answer 3

-Contain species which have a similar way of interacting & obtaining energy
-depicted in food webs
Primary producer —> primary consumer —> secondary consumer —> tertiary & higher consumers
*detrivores/decomposers & scavenges

Question 4

Interaction webs

Answer 4

-include non-trophic interactions such as competition and positive interactions (more realistic)

Question 5

Species composition

Answer 5

Kinds of species

Question 6

Species diversity

Answer 6

• combines species richness (# of species) & species evenness (relative abundance)
• Shannon diversity index

H = -(sum of s) [pi x ln(pi)] i = 1

   - s= #of species
   - pi= relative abundance
   - H=Shannon index value  - the higher H, the higher species diversity of the community

Question 7

Community membership depends on 3 factors…

Answer 7

1) species supply
- regional species pool and dispersal ability
2) abiotic conditions
- physical and chemical environmental conditions
3) biotic conditions
- species interactions

Question 8

Species supply

Answer 8

• regional species pools provide upper limits on # of species that can live within communities
• first step to community membership is the species being present at the regional level with the ability to disperse to the community

Question 9

Abiotic conditions

Answer 9

• “abiotic filters” restrict species that are physiologically incapable of serving in the community
• physical environment can be significant barrier for non-native species
• community membership can change with environmental conditions

Question 10

Biotic conditions

Answer 10

-species must be able to live with the other species in the community
(Obtain food, survive without being eaten, cope with competition)

-resident species ca promote or restrict species membership

Question 11

Biotic resistance

Answer 11

The ability of resident species to exclude or slow the population growth of non-native species

Question 12

Direct interactions

Answer 12

Occurs between two species

Question 13

Indirect interactions

Answer 13

When the direct interactions between two species re mediated by a 3rd

• often occur via trophic interactions
• can be traced to a trophic level several away from where it is seen

Question 14

trophic cascade

Answer 14

When the rate of consumption at one trophic level results in a change in species abundance at lower trophic levels

Question 15

Interaction strength

Answer 15

-the affect one species has on the abundance of another species

• can be measured experimentally by removing the “interactor” species, and observing what happens to the target species
  
  • positive interaction if target species declines
  • negative interaction if target species increases
  • no interaction if no change in target species

Question 16

Resource-mediated coexistence

Answer 16

When competition among species i mediate by factors that affect the dominant species’s ability to acquire resources

Question 17

Intermediate disturbance hypothesis

Answer 17

Describes how varying degrees of disturbances (abiotic process that kills or injures individuals) affect species diversity

  - high diversity with intermediate disturbance levels 
  - low diversity with high or low disturbance levels

Question 18

Keystone species

Answer 18

• have strong effects in community; not because of size or abundance, but because of the role they play
• mostly act by creating trophic cascades

Question 19

Foundation species

Answer 19

• have large effect on community because of their size and abundance
• Trees

Question 20

Ecosystem engineering species

Answer 20

• create, modify, or maintain a physical habitat fo themselves and other species
• don’t necessarily have great size or abundance

Question 21

Succession

Answer 21

How a community changes in species composition over time

-result of biotic and abiotic factors

Question 22

Disturbance

Answer 22

An abiotic event that physically or chemically injuries or kills individuals
- creates opportunities for other individuals to grow and reproduce

Question 23

Stress

Answer 23

When some abiotic factor reduces growth, reproduction, and/or survival of some individuals

Question 24

Climax community

Answer 24

Stable assemblage of species that experience little change until an intense disturbance wipes out the community

Question 25

Primary succession

Answer 25

-result of a disturbance killing all of the organisms in a community
-sometimes caused by glaciers, landslides, volcanic activity and floods
-slow because early arrivals must deal with extreme conditions
(Pioneer species/early successional species)

Question 26

Secondary succession

Answer 26

The reestablishment of a community when most, but not all organisms have been destroyed

• more common
• progresses more rapidly

Question 27

Alternative states

Answer 27

The different community assemblages that could develop at the same location under similar environmental conditions

Question 28

Hysteresis

Answer 28

When the community is unable to shift back to its initial state, even if original conditions are restored

Question 29

Stability

Answer 29

The communities resistance to disturbance

-communities with more species are generally more stable, ie. use resources efficiently