Chapter 17: Community Structure

Question 1

Ecological Hierarchy?

Answer 1

1. Individual
2. Population: group of individuals of the same species that occupy a given area
3. Community; assemblage of species that occupy a given area, interacting directly or indirectly

Question 2

The biological structure of a community is?

Answer 2

• the mix of species (number and relative abundance)

- some communities have a few more common species while others have a wide variety of species

Question 3

Species Diversity:

- Species richness?

Answer 3

• number of species

Question 4

Species Diversity:

- species evenness?

Answer 4

• how individuals are apportioned among the species

Question 5

Species Diversity:

- relative abundance of species?

Answer 5

of individuals of species A/ total # of individuals of alls species

Question 6

Species Diversity:
- community with some individuals of many species is ____ than one with few species.
ex?

Answer 6

• more diverse
  ex: 100 individuals and 10 species
  Maximum diversity: 10 of each species
  Lowest diversity: 91 of one species and 1 of each of the other species
  **lowest diversity: you have a 91% chance of identifying it

Question 7

If diversity is very high you have a better chance of ___ environmental changes, impacts of pollution, disease etc

Answer 7

• standing /tolerating
• lots of species interactions
• if low diversity = more likely to be affected

Question 8

Indices of Diversity:

- many diversity indices used to quantify and compare diversity. They tend to differ in?

Answer 8

• their weighting of evenness and species richness

Question 9

Indices of Diversity:

- which index did we use for the forest lab?

Answer 9

• Shannon- seiner index

Question 10

Indices of Diversity:

- aside from Shannon-weiner index, there are other indices that are also based on ??

Answer 10

proportional abundance of species ex Simpson’s

Question 11

Simpson’s index?

Answer 11

• number of times we would have to take pairs of individuals at random to find a sprit of the same species. Inverse of Simpson’s dominance index

Question 12

Simpson’s index:

- equation?

Answer 12

D= summation(niIN)^2

D= dominance (opposite of diversity is dominance. If you have high diversity you have low dominance)

• summation= summation of all species
• ni= number of individual species i
• IN= total number of individuals of all species

Question 13

Simpson’s index:

- As D increases??

Answer 13

• as D increases(greater chance of finding pairs of same species), diversity decreases

Question 14

Simpson’s index:

- Simpson’s reciprocal index??

Answer 14

= 1/D ranges from 1 to species richness

*less sensitive than other indices to speceis richness s

Question 15

Shannon-Weiner Index?

Answer 15

• measures degree of uncertainty. If diversity is high, certainty of picking a particular species at random is low

Question 16

Shannon-Weiner Index:

- first step in calculation?

Answer 16

• calculate relative abundance of each species:

- pi= ni/N

Question 17

Shannon-Weiner Index

- after calculating relative abundance of each species what is then computed?

Answer 17

• Shannon index (H)

H= -summation(pi)(lnPi)

• summation: summation of all species
• ln= log base e
• pi= proportion of individual species i
• how diverse are they in terms of the proportion of each individual species…picking two at random what is the chance they are the same
• if each species was even the huber would be higher therefore greater uncertainty

Question 18

Why is quantifying biological diversity within a community a necessary step in assessing the impact of human activities?

Answer 18

• better way of comparing sites vs descriptive means
• helps us examine our impact in areas
• repeatable

Question 19

Dominance?

Answer 19

• single or few species that predominate in a community

Question 20

Dominance’s relationship with diversity?

Answer 20

dominance is converse of diversity

Question 21

Dominance is usually measured by?

Answer 21

• abundance but may also be biomass

* In forest lab: dominance is measured as basal area: total basal area of tree species/area sampled.

Question 22

Keystone species?

Answer 22

• dominance is only one measure of effect go a species on community
• they function in unique manner. Effect disproportionate to abundance
• • a dominant species has an effect on its ecosystem that is proportionate to its abundance (t
• community importance ( the change in a community or ecosystem trait per unit change in abundance of a species)
• **keystone species have an impact much greater than their biomass
  graph: total impact of a species (y) and proportional biomass (x)

Question 23

Ecologists often focus on what when examining structure of communities?

Answer 23

• feeding relationships

Question 24

Two models of feeding relationship?

Answer 24

1. Food chain: descriptive diagram eg grass->grasshopper-> sparrow -> hawk
   * *very simplified..
2. Food web: made up of numbers food chains, highly interwoven with linkages representing a wide variety of species interactions
   * mor realistic
   * *predation and herbivory are the two most important interactions

Question 25

Trophic levels?

Answer 25

- are feeding groups 1. autotrophs (primary producers like plants) 2. heterotrophs ( secondary producers: herbivores, carnivores and omnivores) aka cannot fix carbon..consume things that can

Question 26

Trophic levels: | - guilds?

Answer 26

- sometimes divided into groups of species that use a common resource in a similar way ex: nectar-feeding bird

Question 27

Trophic levels: | - Functional type?

Answer 27

- a broader grouping based on function in community; feeding start food category shredders dead leaves colloectors fine organic filter feeders particles in water column miners buried particles

Question 28

Physical structure of communities?

Answer 28

- abiotic factors: depth and water flow in river ex | - biotic factors such as the spatial arrangements of organisms ex vegetation n forest

Question 29

Vertical Stratification of Communities?

Answer 29

- most communities have a distinctive vertical structure - On land determined largely by lang life form - In lake, layers determined by light penetration * more complex habits have more species

Question 30

Zonation?

Answer 30

pattern of spatial variation in community structure - common to all environments - generally occurs along with physical gradients * ex salt marsh * demonstrates abiotic attributes of an environment really set the stage.

Question 31

Explain changes in species composition of forest stands along topographic gradient in Virginia via at the bottom of ahill

Answer 31

changes in species composition in trees as you go down the hill top to the water physical gradient? amount of water lower area probably have a lot of flooding top you probably get really dry soil moisture in summer and flooding during other times of the year what do the trees have to be able to do down there? tolerate flooding…..you get specialists that can do well down there…as you move up the hill its not that these trees cannot tolerate the dryer condition its that they cannot out compete the other species in more fertile environments

Question 32

Boundaries between communities?

Answer 32

- difficult to define if transition gradually - communities often distinguished based on species assemblages that are characteristic of different physical environments - indices of community can be used to compare communities e.g. Jaccard's coefficient

Question 33

Comparison of diversity indices does not tell you if there are ?

Answer 33

- the same species in two communities. Can use a similarity index?

Question 34

Jaccard's coefficient?

Answer 34

- 1= total species overlap - 0 = no overlap - a= number of species in community - B= number in community 2 Formula: Cj= j/(a+b-j) * just using species diversity tells you nothing about the composition * *does not use this form according the instagram

Question 35

Why do both similarity and diversity indices? What do they tell you that are different?

Answer 35

-because diversity indexes only tell us relative diversity, species richness, evenness and abundance but similarity tells us the composition and how similar or dissimilar they are diversity does not tell you just what species are there most people present both in papers

Question 36

If you use more than one diversity index, can you directly compare your numbers for two different diversity indices?

Answer 36

if you were to use simpsons and shannon it would be meaningless -you couldn't …you would essentially be comparing to different summaries of the data which wouldn't make sense point of these is to compare between sites