Slide Set 8 Flashcards
3 mechanisms for succession
- Facilitation
- Inhibition
- Tolerance
sucessiion
- 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
primary succession
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)
secondary succession
- 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
autogenic succesion:
Driven by biological processes within the community
Involves accumulation of organic matter, increases in shading
allogenic succession:
Serial species replacements driven by external forces such as climate or geophysico-chemical processes (e.g., silt deposition)
autotrophic succession:
Where new habitat is invaded by green plants (autotrophs, self-feeders)
what is interrupted succession
The directional sequence of changes is arrested by an external factor, often linked to human activities & management – a so-called “deflected” succession
how does facilitation occur?
- 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
inhibition may occur because of?
- competition
- allelopathy
allelopathy
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.
what are the net effects of inhibition?
- Species resist invasion by potential competitors
- Early species are replaced only when they die
how do species become tolerant ?
- 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
what are the 3 types of disperal?
- jump
- diffusion
- secular
define dispersal
The movement of organisms away from their point of origin
migration
Directed movement from and return to an area, typically a breeding site, by an individual or its immediate descendants
what is the evolutionary role of dispersal?
- Dispersal leads to “discovery” of new habitats
- Dispersal may be necessary to complete life cycle (true for many parasites)
what are the pros and cons of dispersal?
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)
Natural selection tends to favour individuals that move at least some _________ from their “birth” place
distance
describe jumpy dispersal
- slow or rapid
- purposeful or accidental
ex. sea stars
define diffusion dispersal
- a gradual movement into new areas
- is often slow
- can expand range
ex. nine banded armadillo from mexico to southern us
secular dispersal
- also called migration
- long periods of time
- species evolve along the pathway
active dispersal
organisms move under their own power, often quite formidable power of movement
passive dispersal
organisms must depend on external processes or forces (wind, water, animals) for dispersal of themselves or their propagules
what are some barriers of dispersalists
- large bodies of water
- mountains
- major rivers
- fragmented landscapes
- diferent biomes
what are some aids of dispersalists
- orientation of river valleys,
- prevailing winds,
- anthropogenic changes
describe corridors
- Permits 2-way movement without discrimination, although movement could be (and often was) asymmetrical
- Corridor environment similar to the two connected areas
describe filetrs
- 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
what are sweepstake roles
- 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
seasonal migration
Seasonal changes in patterns of distribution
temporary migration
Temporary occupation of a region – often for the purpose of breeding or feeding
Movements can be _______ (elk in the west) or _________ (caribou, many songbirds, geese) or from one major habitat type to another (salmon)
altidudinal or latitudinal
what are the 3 surprising things found about arctic tern migration
- 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