Chapter 16: The Nature of Communities

Question 1

Communities

Answer 1

groups of interacting species that occur together at the same place and time

Question 2

What are communities defined by (Physical Characteristics)?

Answer 2

Ex: all species in a sand dune, mountain stream, or desert

Question 3

What are communities define by (Biological Characteristics)?

Answer 3

Ex: all the species associated with a kelp forest or a coral reef; implies importance of abundant species

Question 4

What is an arbitrary way of defining a community?

Answer 4

Based on the questions they are posing

Question 5

What can community subsets be defined by?

Answer 5

-Taxonomic affinity
-Guild
-Functional Group

Question 6

Guild

Answer 6

a group of species that use the same resources

Question 7

Functional Group

Answer 7

species that function in similar ways

Question 8

What do food webs organize?

Answer 8

Organize species based on trophic or energetic interactions

Question 9

Trophic Levels

Answer 9

-Primary producers: autotrophs
-Primary Consumers: herbivores
-Secondary Consumers: carnivores
-Tertiary Consumers: carnivores

Question 10

Interaction Webs

Answer 10

more accurately describe both trophic (vertical) and non-trophic (horizontal) interactions

Question 11

Negatives of Food Webs

Answer 11

-tell little about strength of interactions or their importance in the community
-species can span multiple trophic levels
-rarely include important elements such as symbionts and detritivores
-Dont include nontrophic interactions

Question 12

Horizontal Interactions of a food web

Answer 12

competition and positive interactions

Question 13

Community Structure

Answer 13

-set of characteristics that shape communities
-provides basis for generating hypotheses and experiments to understand how communities work

Question 14

What is the most common measure of community structure?

Answer 14

species diversity

Question 15

What does species diversity combine?

Answer 15

-species richness (number of species)
-species evenness (relative abundance)

Question 16

Slide 22

Question 17

Biodiversity

Answer 17

describes diversity at multiple spatial scales, from genes to species to communities

Question 18

Implicit

Answer 18

interconnectedness of all the components

Question 19

Rank Abundance Curves

Answer 19

plot the proportional abundance of each species relative to others in rank order

Question 20

Species accumulation curves

Answer 20

-species richness plotted as a function of total number of individuals counted
-help determine when most or all of the species in a community have been observed

Question 21

Hughes et. al (2001)

Answer 21

-compared species accumulation curves for five different communities
-the communities varied greatly in amount of sampling effort needed to determine species richness
-temperate forest and tropical bird species were adequately represented before half the individuals were counted
-for tropical soil bacteria, more effort was needed to sample this extremely diverse community

Question 22

Importance of Spatial Scale in Hughes et al (2001)

Answer 22

-If tropical soil bacteria were sampled at the same scale as Costa Rica moths, the bacterial diversity would be immense in comparison
-the study highlights how little we know about community structure of rarely studied assemblages, such as microbial communities

Question 23

Species Composition

Answer 23

-identity of a species in a community
-two communities could have identical species diversity values but completely different species
-the density of species is critical to understanding community structure

Question 24

Direct interactions

Answer 24

occur between two species (competition, predation, facilitation)

Question 25

Indirect Interactions

Answer 25

relationship between two species is mediated by a third (or more) species; often discovered when species are removed to study direct interactions

Question 26

Trophic Cascade

Answer 26

rate of consumption at one trophic level results in change in species abundance or composition at lower trophic levels

Question 27

Trophic Facilitation

Answer 27

a consumer is indirectly facilitated by a positive interaction between its prey and another species

Question 28

Competitive Networks

Answer 28

interactions among multiple species in which every species has a negative effect on every other species. No one species dominates the interaction, allowing for coexistence

Question 29

Buss and Jackson (1979)

Answer 29

hypothesized that competitive networks allow coexistence of competitors and thus maintain species richness

Question 30

Interaction Strength

Answer 30

magnitude of the effect of one species on the abundance of another

Question 31

How is interaction strength measured?

Answer 31

measured by removing one species (interaction species) from the community and observing the effect on the other species (target species)

Question 32

Slide 49

Question 33

Interaction strength may depend on ____

Answer 33

environmental factors

Question 34

Menge et al. (1996)

Answer 34

-measured interaction strength of sea star predation on mussels in wave-exposed versus wave-protected areas
-Interaction strength was greater in protected areas. Pisaster was a less efficient predator in crashing waves

Question 35

Foundation Species

Answer 35

large or abundant species, such as trees, that provide food or habitat for other species

Question 36

Effects of foundation species

Answer 36

have large community wide effects, and thus species diversity, by virtue of their considerable abundance or biomass
-they may also be good competitors for space, nutrients, or light

Question 37

Ecosystem Engineers

Answer 37

create, modify, or maintain physical habitat for themselves and other species

Question 38

Keystone species

Answer 38

have strong effects because of their role in a community

Question 39

Effect of Keystone Species

Answer 39

their effect is large in proportion to their biomass or abundance

Question 40

Can keystone species also be ecosystem engineers?

Answer 40

Yes

Question 41

Ocean acidification

Answer 41

the oceans absorb atmospheric CO2, which reacts with seawater to lower pH

Question 42

Alsterberg et al. (2013)

Answer 42

studied algae and consumers in an estuarine community