Lecture: Chapter 17-18 Community Structure and Factors of Influence

Question 1

Communities

Answer 1

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

Question 2

Synergistic

Answer 2

The interactions are synergistic; they make communities into something more than the sum of their parts

Question 3

What are communities?

Answer 3

In practical terms, ecologists usually define communities based on physical or biological characteristics.

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

Biological: all the species associated with a kelp forest, a freshwater bog, or a coral reef

Question 4

Taxonomic affinity

Answer 4

All bird species in a community

Question 5

Guild

Answer 5

Group of species that use the same resources

Question 6

Functional group

Answer 6

species that function in similar ways, but do not necessarily use the same resources

Question 7

Species diversity and species composition are important discriptors of community structure

Answer 7

Community structure is the set of characteristics that shape communities

Question 8

Species richness

Answer 8

the number of species in a community

Question 9

Species evenness

Answer 9

Relative abundances of species comapred with one another. how many individuals belong to each species - are they distributed fairly equally or rather unequally

Question 10

Species diversity

Answer 10

Combines species richness and species evenness

Question 11

Shannon index

Answer 11

H = -E(pi)(ln(pi))

Question 12

Species diversity (and biodiversity) are often used more broadly to mean the number of species in a community

define biodiversity

Answer 12

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

• species diversity
• genetic variation
• habitat variation (spatial heterogeneity)

Question 13

Rank abundance curves

Answer 13

Plot the proportional abundance of each species (pi) relative to the others in rank order

Question 14

Species accumulation curves

Answer 14

species richness is plotted as a function of the total number of individuals that have been counted

Question 15

Species composition

Answer 15

identity of species in a community

Question 16

Two communities could have identical species diversity values, but have completely different species.

Answer 16

The identity of species is critical to understanding community strucutre

Question 17

Dominant species or foundation species

Answer 17

Have large effects on other species, and thus species diversity, by virtue of their considerable abundance or biomass

Question 18

Keystone species

Answer 18

Strong effects because of their roles in the community. Disproportionate impact on the community relative to their abundance or biomass

Question 19

Keystone predators

Answer 19

predators that often function as keystone species within communities

Question 20

Food webs

Answer 20

Conceptual models of the trophic interactions within communities. Organize species and describe interactions based on trophic or energetic interactions

Question 21

Trophic Levels

Answer 21

Primary producers: plants and algae
Primary consumers: herbivores
Secondary consumers: carnivores
Tertiary consumers: carnivores

Question 22

control of energy flow - bottom-up

Answer 22

The bottom-up view: the abundance of organisms at a trophic level is determined by the trophic level below it

Question 23

control of energy flow - top-down

Answer 23

The top-down view: Energy flow is governed by predator consumption rates at the highest trophic lvel, which influences multiple trophic levels below them. HSS (Hairston, smith, slobodkin) hypothesis. “The world is greeen’

Question 24

Trophic cascade

Answer 24

Change at one trophic level results in alternating responses of trophic levels below.

Mediated by “trophic” relations - feeding

Question 25

How are communities characterized?

Answer 25

By complex networks of direct and indirect interactions that vary in strength and direction

Question 26

Direct interactions

Answer 26

occur between two species (e.g. competition, predation)

Question 27

indirect interactions

Answer 27

Occur when the relationship between two species is mediated by a third (or more) species

Question 28

trophic cascade

Answer 28

a carnivore eats an herbivore (a direct negative effect on the herbivore)

the decrease in herbivore abundance has a positive effect on a primary producer

Question 29

The keystone predator effect

Answer 29

A predator witha species prefernece

selectively removes competitive dominant species

allows other species that would be excluded by the dominant competitor to persist

Question 30

species richness

Answer 30

differs among communities due to variation in regional species pools, abiotic conditions and species interactions

Question 31

resource partioning

Answer 31

among the species in a community reduces compeition and increases species richness.

Competing species coexist by using resources in different ways/