Community Ecology (W11) Flashcards
List of Models that explain the nature of communities? (2)
• Organismic model.
• Individualistic model.
Organismic model attributes? (3)
• Plant communities are closely integrated systems with numerous “emergent properties”, and are analogous to a “super-organism”.
• Communities function as an organism & ultimately mature (climax community).
• Climatic climax communities.
Individualistic model attributes? (6)
• Emphasises species individuality with each having its Abiotic living requirements.
• Communities are there by chance.
• Don’t function as an organism.
• Chance occurrence of species that have similar ecological requirements.
• Emphasises environmental gradient nature of communities.
• Juxtaposition of individuals of the same/different species.
Explain Organismic model graph?
Explain Individualistic model?
Succession?
= the evolution of community structure over time leading to a stable community.
Succession attribute?
Communities develop gradually during this process.
Types of succession? (2)
• Primary succession.
• Secondary succession.
Primary succession?
= occurs in a lifeless area (soil-forming processes with no seed bank or reserve for vegetative propagules in the substrate).
Secondary succession?
= occurs in areas after disturbances (small-scale disturbancessuch as fire in grasslands, or flooding event).
Primary succession process?
Secondary succession process?
Paper to read for Observed patterns of succession?
Olivier et al, 2012.
Mechanisms fo plant succession? (3)
• Facilitation hypothesis.
• Tolerance hypothesis.
• Inhibition hypothesis.
Facilitation hypothesis?
= early species prepare ground for later species.
Tolerance hypothesis?
= early species modify the environment, but it does not affect the recruitment & growth of later species.
Inhibition hypothesis?
= early colonists secure the space/resources & thus inhibit the invasion of subsequent colonists.
Resource Ratio model of succession attributes? (2)
● Assumes that each plant species is a superior competitor for a particular proportion of the limiting resources.
● Predicts that community composition should change whenever the relative availability of two or more limiting resources changes.
Disturbance?
= events that change the biological communities by removal of nutrients.
Disturbance attribute?
Influences succession & species richness.
Explain how Disturbance influences succession & species richness? (2)
• Low disturbance, late successional species dominate.
• High disturbance, allows early successional species to persist.
Hypothesis for Disturbance?
Intermediate disturbance hypothesis (IDH).
Explain Intermediate disturbance hypothesis graph? (6)
● x-axis = disturbance frequency and/or amplitude.
● y-axis = species diversity.
● Dotted line = exponential decrease.
● Dashed line = exponential increase.
● Solid upside down U.
● All lines cross each other.
Explain IDH graph:
Dotted line? (4)
• Low DEM (growth rate).
• Low disturbance at high point.
• Starts at y axis.
• Ends at tip of solid upside-down U.
Explain IDH graph:
Dashed line? (4)
• High DEM (growth rate).
• High disturbance.
• Starts at tip of solid line (left).
• Ends at right.
Explain IDH graph:
Solid upside-down U line? (3)
• Intermediate growth rate (IDH = DEM).
• Moderate disturbance.
• High species richness.
Explain The IDH & Plant invasion graph? (6)
● x-axis
= ¹ disturbance frequency (low to very high).
² strength of competition (high to very low-left to right).
● y-axis = species diversity (low to high- bottom to top).
● Two graphs that why you have 2 x-axes.
● Light line = historical disturbance gradient.
● Dark line = human disturbance.
● Dashed line = diversity of an alien plant in high disturbance.
Hypothesis relating to Invasive species?
The Invasibility theory.
