Chapter 16 Flashcards
Define community
Group of species inhabiting a given area and interacting (directly or indirectly)
The concept of a community is _____. What does this mean?
spatial. The species all live in a particular place with a defined boundary
What are the 3 specific attributes of a community?
-species richness & relative abundance
-physical structure (usually defined by plant forms)
-species interactions
Define relative abundance
The proportion of individuals of 1 species relative to the total number of individuals of all the species
What is the relative abundance equation?
What do the variables mean?
p = n/N
p - proportion of individuals of species x
n - number of individuals of species x
N - total number of individuals of all species
What is a rank abundance diagram?
It plots rank abundance (x) against relative abundance (y). Provides information on 2 features of community structure and diversity (species richess and evenness)
What is rank abundance?
The species rank of abundance. On a diagram, it is ordered by the most abundant species to the least abundant species.
What is species richness?
(S). The number of species in the community
What is species evenness?
How equally individuals are distributed among the species
What can you interpret from the curves on a rank abundance diagram?
Steep curve: Indicates that a few species dominate - suggests low species evenness
Shallow/Flat curve: Species abundance is more even – suggests high species evenness
Curve length: number of points on the x-axis indicates species richness. A long curve suggests higher species richness.
What are the 2 components of species diversity in a community?
Species richness & species evenness
What is Simpson’s Diversity Index?
(D). Used to quantify biodiversity by taking into account species richness and evenness. It reflects the probability that 2 randomly selected individuals from a sample will belong to the same species.
What is the formula for Simpsons Index (D)?
What do the variables represent?
D = (sum total of)p^2
p = proportion of total individuals in a community represented by species 1
^^ remember relative abundance formula
Add together all the p^2 values to get the D-value
What can you interpret from the D value? Why is this the interpretation?
As D approaches 1, there is less diversity.
The probability of selecting the same species is higher = less species to choose from
As D approaches 0, there is more diversity.
What is Simpson’s Reciprocal Index Formula and interpretation?
1/D
Higher values = Higher diversity
What is Simpson’s Index of Diversity Formula and interpretation?
1-D
The likelihood that 2 individuals randomly chosen belong to different species.
A higher value means a higher likelihood that they belong to different species.
How can you calculate species evenness using the D-value? What do the variables mean? How can you interpret this?
ED = (1/D) / S
E(subscriptD) = value of evenness
S = species richness
The closer the value of evenness is to 1, the closer to equal abundance of species.
S is the maximum value of the index (since it is the amount of species present in a community)
Define the Shannon Index
A widely used index of diversity to consider species richness and evenness
What is the formula for the Shannon Index? What do the variables represent?
H = -(sum total of)(p)(LNp)
p = proportion of community made up of species x
n = number of individuals in species x
LN = natural log
What are the minimum/maximum values of the Shannon Index?
Minimum = 0, where this only 1 species present
Maximum = lnS (natural log of S). This value shows all species in equal numbers.
What does the maximum value of H for Shannon Index tell us?
It tells us what a community’s maximum potential diversity is, and allows us to see how close the actual community’s diversity is to this value.
Can set (H’) / (Hmax) to find species evenness
What are dominants in a community?
Species that predominate within a community. Most often defined separately/in different groups within the community
ex. A community may have a dominant tree species and a dominant small mammal species.
Does abundance sufficiently measure dominance?
No. Different species may have different relative abundance compared to relative biomass. It is better to define dominance by using a combination of different characteristics.
What is a keystone species?
A species that has a disproportionate impact on the community relative to its abundance.They function in a unique/significant way within a community.
What determines if something is a keystone species (2 factors):
- their effect must be greater and disproportionate to their numerical abundance
-Role may be to create/modify habitats or influence species interactions.
What could the removal of a keystone species result in?
Changes in community structure and/or loss of biodiversity
How can keystone herbivores modify the community?
By reducing certain plant density and creating habitats for smaller animals.
What is a food chain?
Representation of feeding relationships within a community.
Define primary producer
Photosynthetic organism. Forms base of the food web.
Define primary consumer
Heterotroph. Transfers energy from the producers to the rest of the food web.
Define a food web
Diagram that represents the interactions between predators and prey in a community. A mesh of different food webs.
Define a link on a food web
Arrows from the consumed to the consumer
Define a basal species
Autotrophs (A) that do NOT feed on other species but are fed on by other species
Define an intermediate species.
Either Herbivores (H) or Carnivores (C). That feed on other species AND are the prey of other species.
Can also be an omnivore
Define a top predator
(P) Feed on intermediate and sometimes basal species, but are NOT preyed upon.
How many trophic interactions were found in a caribbean marine food web between how many species?
3313 trophic interactions aong 249 species.
How was this food web compartmentalized to make it understandable?
They categorized all organisms into 5 compartments based on their:
1) differences in body size
2) range of prey sizes
3) shore VS off-shore habitat
4) associated predators.
Do community dynamics only involve direct species interactions?
No. A predator can reduce competition between 2 prey species by keeping their population sizes below carrying capacity.
Define autotroph
Primary producer. Derive energy from sunlight.
Define heterotroph
Consumer. Derive energy from consuming plant and animal tissues.
Define trophic levels
A functional classification that define groups of species based on the way they acquire their energy.
Define guilds
A subdivision of trophic levels. Species in the same guild exploit a common resource in a similar way.
What do guilds create the potential for?
Strong interactions between species in the same guild (as they are competing for the same resources), and weaker interactions with the rest of the community.
What characteristics of a species’ groups them together as a functional type group (4)?
- common responses to the environment
- life history characteristics
- role within the community
- photosynthetic pathway/shade tollerance (PLANTS)
How is the physical structure of a community influenced?
By abiotic and biotic factors
