Community Ecology (W13) Flashcards
Island biogeography?
= a field within biogeography that examines the ecological phenomena & diversification on islands.
Island biogeography focus?
Focuses on factors that affect species richness in naturally isolated communities.
Island Equilibrium Theory (IET) attributes? (6)
• There’s an equilibrium in species richness on an island.
• Area & distance relationships determine the species richness on an island.
• Species richess is as a result of the rate of extinction & the rate of immigration (rate of dispersal).
• Explain that bigger & nearer islands will have higher species richness than the smaller & further islands.
• High rate of immigration is often a consequence of less species richness.
• High species richness onan island, higher rate of extinction.
Ways through which extinction can occur? (2)
• Competitive exclusion.
• Predation.
Why is a high rate of immigration a common consequence of less species richness?
It’s because there are more niches to occupy.
Island Equilibrium Theory is AKA?
Equilibrium theory of island biogeography.
Island Equilibrium Theory/Equilibrium theory of island biogeography?
= states that the number of species on an island is governed by the migration of new species & the extinction of species already there.
Explain IET graph? (8)
● x-axis = species richness.
● left y-axis = rate of immigration.
● right y-axis = rate of extinction.
● Equilibrium = where extinction & immigration rates line graphs meet/cross.
● Crossed lines also represent Species 1 (S1) and Species 2 (S2) but on different island sizes and island areas.
● Immigration rate line graphs = decreasing line graphs (one for far island & one for near island from mainland).
● Extinction rate line graphs = increasing line graphs (one for large island & one for small island).
● Interpretation.
How might immigration & extinction rates vary with island size & island isolation? (2)
● By large islands support more species than small islands.
● By isolated islands having fewer species than less isolated ones.
Island area effect (Island area)?
= extinction rate is the driver in equilibrium & determines species richness on an island.
Island distance effect (Island distance)?
= immigration rate is the driver in equilibrium & determines species richness on an island.
Immigration rate via? (2)
• Colonization.
• Dispersion rate.
Immigration rate is associated with?
Island distance from the mainland.
Extinction rate is associated with?
Island area.
Metacommunities Theory?
= a set of local communities linked by the dispersal of one or more of their constituent species (potentially interacting species).
Metacommunities Theory attributes? (2)
• Spatailly delimited.
• Analysing patterns in metapopulations as an ecologist.
Paradigms/Views for metapopulations? (4)
• Patch-dynamic view (PD).
• Species-sorting view (SS).
• Mass-effects view (ME).
• Neutral view (NM).
PD view attributes? (2)
• Assumes that patches are identical & that local species diversity is limited by dispersal.
• Doesn’t consider heterogeneity of a community.
SS view attributes? (3)
• Emphasizes spatial niche separation above & beyond spatial dynamics.
• Dispersal is important because it allows for species compositional changes.
• Considers heterogeneity of the community.
ME view attribute?
Focuses on the effect of immigration & emigration on local population dynamics.
NM view attributes? (2)
• A perspective in which all species are similar in their competitive ability, movement & fitness.
• Focus is on equivalence.
Thing to note on Metacommunities Theory?
Interactions occur across different populations (populations are separated spatially), that’s how it relates to island theory as there is immigration/dispersal of species from different populations. This in turn affects species richness & causes populations to be slightly similar.
Biome?
= the largest land community unit recognized at a continental level.
Biome attributes? (3)
• Distinct geographical region with a specific climate, vegetation & animal life.
• Consists of a biological community that formed in response to its physical environment & regional climate.
• Metacommunities at regional scales.
SA’s major biomes/metacommunities? (4) F²SG
• Fynbos.
• Forest.
• Savanna.
• Grassland.
Fynbos attributes? (3)
• Synonymous with the Cape Floristic region.
• Characterized by.
• Fire is a major influence on community processes (infrequent).
What does fire help with in the Fynbos biome?
It allows for germination of the seed bank.
What is the Fynbos bione characterized by? (3)
• Plants from the Restinacaea, Ericacaea & Proteacaea families.
• Infertile & leached soils.
• Low animal biomass.
Fynbos biome location?
E. Cape.
Forest biome attributes? (3)
• Occurs in patches around the country & are restricted to forest-free areas.
• Support evergreen trees & multi-layered herbaceous cover.
• Large mammals & birds are important Keystone species.
Mean annual winter rainfall for Forest?
> 525mm.
Mean annual summer rainfall in Forest biome?
> 725mm.
Why are large mammals & birds important Keystone species in the Forest biome?
It’s because they disperse seeds & maintain gap processes which allow succession within the forests.
Savanna biome attributes? (3)
• Largest biome in SA (46% land cover).
• Environmental factors delimiting the biome are complex.
• Fire & herbivory maintain woody cover.
Savanna biome altitude?
0–2000m.
Savanna biome rainfall?
235–1000mm/year.
Savanna biome frost?
Occurs 0–120 days/year.
Grasslands attributes? (4)
• Found on the high central plateau of SA from near sea level to 2850m above sea level.
• 2 categories.
• C4 grasses dominate throughout the biome except at the highest altitudes where C3 grasses dominate.
• Fire & grazing drive ecological processes in grasslands.
Categories of grasslands? (2)
• Sweet grasslands.
• Sour grasslands.
Sweet grasslands?
= low fiber content.
Sour grasslands?
= high fiber content.
How does SA characterize biomes? (3)
• Rainfall.
• Vegetation.
• Biotic factors (fire & grazing).
Bush encroachment in grasslands & savanna biomes kinds of drivers? (2)
• Local drivers.
• Global drivers.
Local drivers of ush encroachment in grasslands & savanna biomes? (3)
• Fire.
• Herbivory.
• Land use change.
Global drivers of ush encroachment in grasslands & savanna biomes? (2)
• Temperature.
• CO2.
Fire as local driver?
= affects tree densities, biomass & species composition.
Herbivory as local driver?
= maintains open, grassy ecosystems through their impact on adult tree mortality.
Land use change as local driver?
= leads to invasion of old …
Temperature as global driver?
= low temperatures suppress sapling growth & high temperatures result in faster growth rates.
CO2 as global driver?
= high CO2 increases plant growth rate & water use efficiency.
When is bush encroachment bad?
Bush encroachment is bad if it leads to the collapse of a community.
