Community Function

Question 1

a community’s structure and stability

Answer 1

affected by the interaction between species
(trophic, competition, positive)

Question 2

species interaction

Answer 2

• shape community membership
• whether a species is successful in a new community depends on resident species that can either promote or restrict membership
• biotic resistance: ability of resident species to exclude or slow population growth of a non-native species

Question 3

direct interaction

Answer 3

occurs between two species

Question 4

indirect interaction

Answer 4

direct relationship between two species is mediated by a third or more species

Question 5

interaction webs

Answer 5

predict community stability
- number of weak interactions increases with species richness
- presence of many weak links is associated with better outcomes after the loss of a secondary consumer
- but, species-rich communities are more resilient to keystone species loss

Question 6

trophic cascades

Answer 6

result of trophic interactions
rate of consumption at one trophic level results in a change of species abundance or composition at lower trophic levels
ex: wolves-elk-aspen trees

Question 7

competition shapes…

Answer 7

community membership
- resource mediated coexistence: environmental factors affect the dominant species’ ability to acquire resources
- disturbances may affect growth or survival of a dominant species
- certain guilds or functional groups may have higher success at different successional stages due to their ability to access limiting resources

Question 8

pioneer species

Answer 8

• able to carry out primary succession
• early successional communities are made up of species that can tolerate harsh environments
• later, these species will be replaced by others that are more tolerant of competition
  ex: lupin is a nitrogen fixer

Question 9

advanced stages of succession

Answer 9

competition is an increasingly important interaction
pioneer species make the habitat amenable for other species, which are then able to compete for limiting resources, such as nutrients and water

Question 10

disturbances

Answer 10

• create space in a community for individuals and species to thrive by disrupting competition
• In a rainforest, very little light reaches the understory so no new species cannot grow since they cannot conduct photosynthesis. However, when a big tree falls, it clears a section of the canopy and creates a disturbance, so light can reach and allow other trees to grow.

Question 11

intermediate disturbance hypothesis

Answer 11

• species diversity is often the highest at intermediate levels of disturbances
• disturbances moderate the effects of competition by preventing complete competitive exclusion
• influence of dominant species is reduced, allowing subordinate species to coexist; lower mortality rates makes extinction less likely

Question 12

foundation species

Answer 12

provide the physical habitat for many other species in their community
ex: aspen trees and kelp

Question 13

keystone species

Answer 13

have a role that is critical to the survival of their entire trophic network
ex: wolves and otters

Question 14

ecosystem engineers

Answer 14

modify the ecosystem through its morphology or behavior
allogenic: alter biotic or abiotic elements to create habitat
autogenic: modify the environment by its presence

Question 15

umbrella species

Answer 15

• label used to facilitate community conservation
• conserving or reintroducing an umbrella species has the effect of renewing or conserving the whole environment
• by conserving one species, you can conserve the ecosystem they live in