Lecture 27 - Assemblages

Question 1

communities

Answer 1

organisms interacting with other species (interspecific)

Question 2

primary characteristics of communities

Answer 2

1. diversity
2. trophic structure

Question 3

Explain how the presence of a particular species can influence how a community is structured

Answer 3

• > bottoms-up vs top-down control
• > dominant species are the most abundant in the community/consist of highest biomass
• > keystone species are not abundant but play pivotal ecological roles
• > ecosystem engineers (foundation species) change the physical environment

Question 4

keystone species

Answer 4

a species which has a disproportionately large effect on its natural environment relative to its abundance

Question 5

species composition

Answer 5

number and variety of organisms

Question 6

species richness

Answer 6

absolute number of species

Question 7

relative abundance

Answer 7

proportional representation of each species

Question 8

advantages of higher-density communities

Answer 8

• > more productive
• > able to withstand and recover from stress

Question 9

does productivity increase with diversity?

Answer 9

• > it was heavily belived that productivity would increase with diversity amongst all species but this is false
• > however, productivity DOES increase with diversity IN SOME CASES but is NOT UNIVERSAL

Question 10

How is water a good predictor of diversity

Answer 10

• > evapotranspiration is a good indicator of the area’s water availability, solar radiation and temperature
• > higher levels evapotranspiration indicates higher tree species richness and higher levels of vertebrate species richness

Question 11

evapotranspiration

Question 12

disturbance

Answer 12

event that removes organisms or alters resource availibility

• > moderate levels of disturbance promote diversity
• > frequency and intensity of disturbance influence species diversity

Question 13

ecological succession

Answer 13

gradual colonization and continual replacement by a variety of species

Question 14

primary vs secondary succession

Answer 14

primary

• > the area is previously uninhabited when the gradual colonization occurs

secondary

• > area with previously established community and/or soil

Question 15

humans __________ and __________ disturbance

Answer 15

humans alter and cause disturbance

Question 16

trophic structure

Answer 16

feeding relationship

• > food chain

Question 17

food chain vs food web

Answer 17

• > food chain is linear hierarchy of organisms
• > food web is the more realistic representation of the relationships between organisms of a community
• > food chain is also embedded in the food web

Question 18

why are trophic structures/food chains usually fewer than 5 levels

Answer 18

1. Energetic restrictions
   - > only around 10% of energy stored as organic matter at one level is converted to biomass at the next level
   - > carnivores are larger at successive trophic levels
2. Stability requirements
   - > fluctuations at lower trophic levels are magnified at higher levels