Community Assembly Flashcards
lecture 4/5
What is community assembly?
Species present in a local community is a subset of species that exist in broader species pools.
Global -> continent/regional -> biome/habitat -> local ecological community
What is a regional species pool?
The set of species present in a region from which local communities are assembled.
e.g. - all the plants in South Africa
Where did this theory originate from?
Theory of island biogeography - MacArthur and Wilson 1963.
Ultimately led to the filtering of this process of regional species pools.
Whether species will persist or not on the island - immigration and extinction balance.
close islands have high immigration levels, and far-away islands have low immigration rates.
large islands have more species with low extinction rates; small islands have fewer species with high extinction rates.
Each island is a regional pool with a subset of habitat pools
What is the historical influence on regional biota?
Natural occurring barriers that separate species over long periods of time.
biogeographic barriers decreasing immigration rates.
Wallace line
Floral Kingdoms (Good 1947)
Zoogeographic realms (Holt et al 2013 Science)
How are regional pools determined/origins?
Biogeographic filters (keep the global diversity …-> Immigration / Emigration -not as important
Speciation/extinction.
Examples of regional pool origins
Australian flora (Crisp and Cook 2013)
Galapagos birds (Valente et al 2015)
What are biogeographic filters?
Deep ocean trenches
e.g., The great American Interchange following the closing of the Isthmus of Panama.
South American species pool was homogenized when species from North America migrated down.
What are environmental barriers?
different environments that border on each other.
Species don’t occur everywhere.
e.g. Tree lines - trees drop out at some altitude in the system.
What is an ecological niche? First definition
John Grinnell
The Grinnellian niche = “ …. the ultimate distributional unit, within which each species is held by its structural and instinctive limitations” (1924)
Every species has a physiological, morphological, and behavioral profile that makes it suitable to occupy a particular space offered by nature.
NICHE = part of the environment that a species can occupy
Regional habitat species pool
Different biomes = different climates, different
abiotic drivers, different vegetation contexts
finer habitat difference than biome differences:
Jonkershoek & cederberg
Type 1 and Type 2 curve graph
slide 23 lecture 4/5
What is a species pool?
Set of species available to colonize a local community.
Originates through evolutionary/biogeographical processes and adaptation to macro-habitats.
How does a community get assembled from the species pool?
Observation: not all species present in the species pool are present in each community
Implication: Local processes are important for community assembly:
Biotic interactions:
* COMPETITION
* Predation
* Facilitation
* Mutualism
dispersal
What is competition?
A mutually negative interaction among species at the same trophic level directly or indirectly resulting in reduced fitness.
What is exploitative competition?
depletion of limiting resources.
What is interference competition?
exclusion by aggressive interactions
What is apparent competition?
reduction of a species though influence of a second species of predation.
What is the Lotka-Volterra model?
lecture 4_5 slide 28 + 29
dN1/dt = r1N1 ((K1-N1-aN2) /K1)
dN2/dt = r2N2 ((K2-N2-βN1) /K2)
N1, N2 : population size
r1, r2 : maximum population growth rate
K1, K2 : carrying capacity
α, β : interspecific competition
logistic growth:
dN1/dt = r1N1(1- N1/K1)
When α, β < 1 : interspecific competition is weaker than intraspecific competition. STABLE CO-EXISTENCE of species.
When α, β > 1 : interspecific competition is stronger than intraspecific competition. COMPETITIVE EXCLUSION of weaker
competitor.
What is the competitive exclusion principle? (Gause 1936)
Two species must differ in some aspect of their niche in order to coexist.
What is an ecological niche? Second definition
Second definition – Charles Elton
The Eltonian niche = “ …. the status of an animal in its community, to indicate what it is doing and not merely what it looks like” (1927)
NICHE = functional role of a species in a community
Niche is a property of the species and not the environment.
Defined by biotic interactions and resource-consumer dynamics.
What is an ecological niche? Third definition
The Hutchinsonian niche “… an n-dimensional hypervolume, enclosing the complete range of conditions under which an organism can reproduce itself”
NICHE = physical and biological conditions needed to maintain a stable population size NB
What is the realised niche?
ecological niche a species actually occupies in the presence of other species
(and dispersal limitation).
What is the fundamental niche?
ecological niche a species could occupy in the absence of other species (and
dispersal limitation).
What is competitive exclusion?
Exclusion by negative biotic interactions