Ch 54 - Community Ecology

Question 1

Describe competition.

Answer 1

-/-

• competitive exclusion - when two populations of similar species compete for same resources, one population will use the resources more efficiently, and have an advantage leading to elimination of other population
• fundamental vs. realized niche - the fundamental niche is the niche which an organism could potentially occupy, and a realized niche is the niche which the organism actually occupies.
• resource partitioning - modification of niches so that similar species can coexist.

Question 2

Describe herbivory.

Answer 2

+/-

• The process of of eating vegetative/algae material
• Plants have chemical & physical defenses
• Herbivores have specialized chemoreceptors, teeth, & digestive systems

Question 3

Describe predation.

Answer 3

+/-

• chasers vs. stalkers/ambushers
• types of colouration:
  
  • **cryptic **describes camouflage, seen in predator & prey replationships
  • aposematic describes bright colors of toxic/distasteful species
• types of mimicry:
  
  • ​Batesian: harmless species mimics harmful/distasteful species
  • Mullerian: 2+ distasteful species resemble eachother
  • Startle: patterns, ex: big scary eyes
  • Aggressive: “wolf in sheep’s clothing,” ex: snapping turtle’s tongue

Question 4

Describe symbiotic relationships.

Answer 4

• parasitism (+/-): obtains nourishment from host; harms, doesn’t usually kill. Ectoparasite lives on the external surface, endoparasite lives on the internal surface, parasitoid lays eggs on/in an organism.
• mutualism (+/+): coevolution of beneficial adaptions. In facultative mutualism both species can survive alone, in obligate mutualism both species need the other to survive.
• **commensalism **(+/o): benefits one species with no discernible effect on another; difficult to find in nature.

Question 5

Describe pathogens.

Answer 5

+/-

• Causes disease, e.g. bacteria, viruses, protists, fungi
• Often lethal to host
• Transmission either direct or via vector

Question 6

Describe species diversity.

Answer 6

• relative abundance - the proportion each different species represents in a community
• species richness - number of different species

Question 7

Describe trophic structure.

Answer 7

• Classified as autotroph or heterotroph
• From bottom up: primary producer, primary consumer, secondary consumer, tertiary consumer, quaternary consumer.
• All ends with detrivores for decomposure

Question 8

Describe bottom-up vs. top-down control.

Answer 8

• Top-down control: “trophic cascade model” - Altering higher trophic levels alters community structure
  
  • Decreased predators = increased herbivores = decreased producers = increased nutrients
• Bottom-up** control**: altering lower trophic levels alters community structure
  
  • increased nutrients = increased producers = increased herbivores = increased predators

Question 9

Describe impactful/pivotal species.

Answer 9

• Keystone species: occupies important niche
• Dominant species: most abundant; exerts control over distribution of other species
• Foundation species: “Ecosystem engineers”, cause physical changes in the environment

Question 10

Describe disturbance & the intermediate disturbance hypothesis.

Answer 10

• Disturbance changes community structure: removes organisms & alters resource availability.
• Intermediate disturbace creates optimal condition; high levels are too disruptive, low levels create competitive exclusion.

Question 11

Describe 1˚ vs. 2˚ ecological succession.

Answer 11

• Sequential changes in community structure after disturbance:
  
  • 1°: leaves behind bare rock, 100s of years to regrow
  • 2°: leaves behind soil, 10s of years to regrow

Question 12

Describe facilitationvs.inhibitionvs.**tolerance **in terms of ecological succession.

Answer 12

• facilitaion: when one species has a positive effect on a later species; common in plant ecology, ex: increasing fertility in soil
• inhibition: when one species has a negative effect on a later species
• tolerate: when one species has no effect on a later species

Question 13

Explain latitudinal gradients.

Answer 13

• a.k.a. equatorial-polar gradients
• increased species richness & diversity in tropical regions due to evolutionary history and climate:
  
  • less disturbance by glacier activity, so continued evolution allowed
  • climate is warmer, wetter, and brighter, so “biological time” runs much faster

Question 14

Explain species-area curve.

Answer 14

• The biodiversity pattern that shows that the larger the geographic area of a community is, the more species it has.
• Allows ecologists to predict how loss of habitat may alter a community’s biodiversity.

Question 15

Descirbe island biogeography.

Answer 15

• An island is described as a habitat patch surrounded by uninhabitable area
• The Island Equilibrium Model describes that species richness is dependent on island size, distance from mainland, and species immigration/extinction rates.
  
  • More diversity on islands that are bigger & closer