The Nature of Communities, Succession and Doubling Times Flashcards
(33 cards)
Define Community?
An assemblage of species populations which occur together in space and time.
Give examples of collective properties?
Species diversity, total biomass.
Give examples of emergent properties?
Stability of food web, niche differentiation, energy flow, nutrients cycling
How is diversity calculated?
Species richness combined with relative abundance:
D = 1/ sum of p squared
What is succession?
non-seasonal, directional and continuous pattern of colonisation and extinction on a site by species populations
Define primary succession?
occurs on land where there has been no previous history of vegetation i.e no soil. e.g. sand dunes, lava flows, glacier retreats.
Define secondary succession?
occurs where an existing community has been destroyed i.e.on well- developed soil containing seeds and other propagules. e.g. after fire, on abandoned fields, after forest clearance.
In what circumstances will a species occur at a particular site?
If It can reach it, if appropriate conditions and resources exist there, competitors and predators must not exclude it.
How can succession be measured?
Observe changes along a chronosequence.
What is facilitation?
The entry of new species to a community because of the alteration of conditions or resources by a previous species.
List general characteristics of early succession?
Rapid growth, small body size, early reproduction, many offspring, short life span, good colonisers, ‘r’ selected.
List general characteristics of late succession?
Slower growth, large body size, later reproduction, fewer offspring, longer life span, good competitors, ‘k’ selected.
What may alter the course of succession?
Light grazing and burning.
How do you calculate doubling time?
t = 0.69 / r
Roughly 70 / %
What decreases during succession?
Soil Ph, plant growth rate
What increases during succession?
Soil carbon, soil nitrogen, plant competition for light
What aided Geese establishment on Surtsey?
Vegetation to eat.
What aided mosses and lichens establishment on Surtsey?
Tiny windblown spores for dispersal
What aided shore plants’ establishment on Surtsey?
Buoyant seeds for dispersal
what aided flowering plants establishment on Surtsey?
Seed dispersal on sea birds
What is commensalism?
Positive effect on one species, no effect on the other
What is amensalism?
Negative effect on one species, no effect on the other
Define competition in terms of negative effects?
Negative effect on both species.
What is true of moss dominated mountain plateaus in Scotland?
Moss abundance decreases with increasing sheep numbers, Sheep numbers influence vegetation and vegetation influences sheep numbers, Shading decreases moss growth,
Grass abundance increases with increasing sheep numbers.
