13 Community Ecology

Question 1

Define Ecological Community

Answer 1

scientific study of interactions between species in communities

Question 2

Define ecological niche and distinguish it from habitat.

Answer 2

• ecological niche describes a species’ role and interactions within an ecosystem
• habitat on the other hand is the specific physical environment where a species lives.

Question 3

Contrast fundamental and realized niches. Explain what factors may drive these to be
different, and interpret the results of an experiment to determine whether a particular
population is occupying all of its fundamental niche.

Answer 3

• Fundamental Niche: full range of conditions under which a species can survive and reproduce
• abiotic factors drive fundamental niches to be different from realized niches due to determining range of conditions a species can tolerate (ex: temperature, nutrients, light)
• Realized Niche: actual space and resources that an organism occupies in its environment
• biotic factors drive realized niches to be different from fundamental niches because it can restrict realized niches. (ex: competition, predation, disease, mutualism)

Question 4

Understand which species benefits and which species is harmed in each of the following interactions:
- Parasitism
- Predation
- Competition
- Mutualism
- Commensalism
Be able to give an example of each from nature.

Answer 4

• Parasitism: one species benefits at the expense of the other species
  (Benefits: Parasite / Harms: Host)
  ex: tick (parasite) feeding on a deer (host)
• Predation: one species benefits by killing and consuming the other species
  (Benefits: Predator / Harms: Prey)
  ex: lion (predator) hunting a zebra (prey)
• Competition: Both species fighting for the same limited resources are harmed
  (Benefits: NONE / Harms: both)
  ex: trees in a dense forest compete for sunlight
• Mutualism: Both species benefit from interaction
  (Benefits: both / Harms: NONE)
  ex: bees get nectar from plant for food, plants get pollinated
• Commensalism: one species benefits, other species neither helped or harmed
  (Benefits: one species / Harms: NONE)
  ex: barnacles (benefitted species) on a whale (neutral species).

Question 5

Compare and contrast the 3 possible outcomes of competitive interactions between
species (competitive exclusion, resource partitioning, character displacement)

Answer 5

• Competitive Exclusion: two species cannot coexist indefinitely on the same limiting resource (One species is limited)
• Resource Partitioning: species evolve to use different resources or the same resource at different times/ways to reduce competition (Species Coexist by using resources differently)
• Character Displacement: Evolution of distinct traits in competing species to minimize competition when they coexist in the same habitat (Reduce competition results from resource partitioning)

Question 6

Describe mechanisms (adaptations) species use to avoid predation.

Answer 6

1. coloration
2. herbivory predation
   - plants have thorns and spines
   - bark and waxy cuticles
   - volatile compound

Question 7

Define cryptic and aposematic coloration and explain how they protect against
predation

Answer 7

• Cryptic Coloration: ability to camouflage, blending in with their surrounding environment. (blending in with their surrounding environment makes it hard for predators to see them)
• Aposematic Coloration: an organism having markings on their external appearance (warns off predators)

Question 8

Given a diagram of a food chain and information about whether it is a top-down or bottom-up system, predict how change in the population size of one species would affect the population size of another species in the chain

Answer 8

• Top down:
  Community structure is determined from above by predation. Increases population of Predators means decrease in population of herbivores, which means more vegetation.
• Bottom up:
  Community structure is determined from below by abiotic nutrients. Abiotic nutrients control vegetation (primary production), which controls herbivores, which control predators.

Question 9

Compare and contrast top-down and bottom-up control of communities.

Answer 9

• Top-Down Control of Communities:
  community structure is determined from above by predation. More predators = Fewer herbivores = More vegetation
• Bottom-Up Control of Communities
  community structure is determined from below by abiotic nutrients. More nutrients = More vegetation = More herbivores = More Predators

Question 10

Given some basic information about trophic interactions.
Be able to draw a food web.
Understand what type of relationships are represented in a food web.
Identify organisms based on their trophic level as producers (autotrophs), consumers
(heterotrophs; primary, secondary or tertiary consumers), or decomposers
(detritovores)

Answer 10

• Food chains can be linked together into food webs. Arrows indicate consumption. Compilation of a food web for any ecosystem isa daunting task

Question 11

Explain how the addition of wolves to Yellowstone affected the biotic and abiotic
components of the ecosystem described in the video. Draw a food web of the trophic
relationships described in the video

Answer 11

The addition of wolves affected the biotic and abiotic components of the ecosystem by acting as a keystone species. They ate elk, reducing their population. As a result, vegetation increased since fewer elk were eating it. The increase in vegetation stabilized rivers and forests, leading to an increase in birds and beavers.

Question 12

Understand and give examples of species that have a strong influence on communities
(dominant and keystone species). (This is partly in the reading.)

Answer 12

• Dominant Species: most abundant or largest biomass
  (ex: trees and plants, elk)
• Keystone Species: species with a large impact on the ecosystem despiite not being the most abudant
  (ex: Wolves in Yellowstone)