Slide Set 8

Question 1

3 mechanisms for succession

Answer 1

• Facilitation
• Inhibition
• Tolerance

Question 2

sucessiion

Answer 2

• A sequence of species that changes over time
• A series of colonizations and replacements
  Gradual community change
• A predictable general direction of change
• An alteration of the habitat attributable to the biota

Question 3

primary succession

Answer 3

Involves the colonization of bare ground on newly exposed geological surfaces (e.g., following retreat of glaciers, on newly-formed volcanic surfaces, on exposed surfaces following severe mud slides or avalanches – resulting in destruction of soil)

Question 4

secondary succession

Answer 4

• Involves the recolonization of an established ecosystem that has been affected by a disturbance, but where the soil has not been destroyed
• Soil type, seed bank, microbiota of soil – all influence the speed of re-colonization by various species of plants
• Typically, involves abandoned agricultural lands, or lands affected by fire

Question 5

autogenic succesion:

Answer 5

Driven by biological processes within the community

Involves accumulation of organic matter, increases in shading

Question 6

allogenic succession:

Answer 6

Serial species replacements driven by external forces such as climate or geophysico-chemical processes (e.g., silt deposition)

Question 7

autotrophic succession:

Answer 7

Where new habitat is invaded by green plants (autotrophs, self-feeders)

Question 8

what is interrupted succession

Answer 8

The directional sequence of changes is arrested by an external factor, often linked to human activities & management – a so-called “deflected” succession

Question 9

how does facilitation occur?

Answer 9

• involves changes to the soil conditions
• nitrogen fixation by dryas and alnus
• accumulation of organic material improves soil texture, depth, and nutrient levels
• Acidification of the soil due to activity of Alnus (in 50 y, pH drops from 8 to ~5)
• Shading by alder – suppresses herbaceous plants or prostrate forms
• Acid conditions encourage colonization by Sitka spruce, which displaces the alders
• Hemlocks also require shade conditions to get established

Question 10

inhibition may occur because of?

Answer 10

• competition

- allelopathy

Question 11

allelopathy

Answer 11

the chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors.

Question 12

what are the net effects of inhibition?

Answer 12

• Species resist invasion by potential competitors

- Early species are replaced only when they die

Question 13

how do species become tolerant ?

Answer 13

• Unlike the facilitation or inhibition models, modification of the environment by the early colonists has little or no effect on recruitment of other species
• Competition for diminishing resources governs the successional sequence of later species (as in the facilitation model), as they can tolerate lower levels of resources

Question 14

what are the 3 types of disperal?

Answer 14

1. jump
2. diffusion
3. secular

Question 15

define dispersal

Answer 15

The movement of organisms away from their point of origin

Question 16

migration

Answer 16

Directed movement from and return to an area, typically a breeding site, by an individual or its immediate descendants

Question 17

what is the evolutionary role of dispersal?

Answer 17

• Dispersal leads to “discovery” of new habitats

- Dispersal may be necessary to complete life cycle (true for many parasites)

Question 18

what are the pros and cons of dispersal?

Answer 18

pros:
- Reduces competition with parent
- Reduces competition with siblings
- There is a chance of finding a similar (& possibly better) environment
cons:
- New environment could be worse – role of distance
- can lead to range extensions
- disjunct distributions (related but separated geographically)

Question 19

Natural selection tends to favour individuals that move at least some _________ from their “birth” place

Answer 19

distance

Question 20

describe jumpy dispersal

Answer 20

• slow or rapid
• purposeful or accidental
  ex. sea stars

Question 21

define diffusion dispersal

Answer 21

• a gradual movement into new areas
• is often slow
• can expand range
  ex. nine banded armadillo from mexico to southern us

Question 22

secular dispersal

Answer 22

• also called migration
• long periods of time
• species evolve along the pathway

Question 23

active dispersal

Answer 23

organisms move under their own power, often quite formidable power of movement

Question 24

passive dispersal

Answer 24

organisms must depend on external processes or forces (wind, water, animals) for dispersal of themselves or their propagules

Question 25

what are some barriers of dispersalists

Answer 25

• large bodies of water
• mountains
• major rivers
• fragmented landscapes
• diferent biomes

Question 26

what are some aids of dispersalists

Answer 26

• orientation of river valleys,
• prevailing winds,
• anthropogenic changes

Question 27

describe corridors

Answer 27

• Permits 2-way movement without discrimination, although movement could be (and often was) asymmetrical
• Corridor environment similar to the two connected areas

Question 28

describe filetrs

Answer 28

• Filters are selective
• Certain types of organisms can pass but not others
• Factors restricting movement may be abiotic or biotic
• Filters are identified by directional decreases in # of species, or changes in frequency of occurrence, with distance from a source area

Question 29

what are sweepstake roles

Answer 29

• involves isolation
• role of chance and extreme events
• role of relatively rapid movement
• Arrival at an isolated and ecologically simple environment is followed by adaptive radiation

ex. iguanas is lesser antilles, hurricanes caused 15 animals to travel 200 km from guadeloupe to anguilla

Question 30

seasonal migration

Answer 30

Seasonal changes in patterns of distribution

Question 31

temporary migration

Answer 31

Temporary occupation of a region – often for the purpose of breeding or feeding

Question 32

Movements can be _______ (elk in the west) or _________ (caribou, many songbirds, geese) or from one major habitat type to another (salmon)

Answer 32

altidudinal or latitudinal

Question 33

what are the 3 surprising things found about arctic tern migration

Answer 33

• Southward migration is slow; much time spent on rich feeding grounds in N Atlantic
• South of the equator, there is a split in the routes; 1 along coast of Africa, 1 along coast of S America
• Northward migration is fast, does not follow southward routes; is “S” shaped route up the mid-Atlantic