Landscape ecology and biogeography Flashcards
Biogeography
geography of
biodiversity, past and present
– History of taxonomic lineages across
space and time
– Global and continental scales
Landscape ecology
influence of the
composition and arrangement of
habitats across a large spatial area
Legacy effects
: long-term effects of past events
on current ecology (e.g. glaciation, ancient
human settlements)
Alpha, α, (local) diversity
of
species in a relatively small area
Beta, β, diversity
species
differing between two (local)
habitats
Gamma, γ, (regional) diversity
species in all habitats of a large
geographic area
γ diversity
combines α and
β diversity
Ecosystem engineers
Species that have a disproportionate effect (relative
to their biomass) on landscapes
Many human activities lead to…
fragmentation
– decreases patch/habitat area
– increases patch number, amount of
edge, and patch isolation
Small habitats have small
populations which are more likely
to…
go extinct
MacArthur & Wilson
larger areas
contain more species
Among islands of similar size
near islands contain more species than far
islands
Equilibrium Theory of Island Biogeography
Number of species on an “island” reflects a balance between colonization and extinction rates that are impacted by island isolation and size
The equilibrium number of species is the point where…
the number of species being gained is “balanced” by the
number being lost
Colonization rates…
decrease with species number
Extinction rates…
increase with species number
Smaller islands should have…
higher extinction rates
Islands nearer to source habitat
should have…
higher colonization rates
– More species capable of dispersing
that far
– By chance more individuals will
disperse successfully
If extinction and colonization continue at equilibrium
Species turnover results changing species composition
Florida Keys Experiment
Observed: islands closer to mainland had higher insect richness
* Methods: Built tents and fumigated
selected islands to kill all insects
* Results:
– More insects re-colonized nearer islands
– Final richness similar to initial richness
(dashed lines)
Six Global Biogeographic Regions
Neartic
Neotropic
Palearctic
Afrotropic
Indomalaya
Australasia
Pangea
single landmass 250 million years ago
Gondwana
what is now So. America, Africa, Antarctica, Australia and India
Laurasia
what is now No. America, Europe and Asia
Continental drift
has allowed individual continents independently to evolve groups of organisms for long periods
Vicariance
splitting of a widely distributed ancestral
population by continental drift
gradual cooling of Earth
→ climate oscillations known as
Ice Ages
– glacial advances in No.
Hemisphere drove temperate
species southward
– Evidence: distributions of forest
trees in eastern No. America
Proposed explanations for the latitudinal
diversity gradient
- Solar radiation:
– higher energy sites should be able
to support more species - Longer evolutionary history
- Climate stability
- Many other hypotheses
Longer Evolutionary History Hypothesis
- Tropics are persistent over
geologic time - No glaciation
- Large land area
→ More time and space for
evolutionary diversification of
tropical species to occur
Climate Stability Hypothesis
Fewer species can tolerate climatically unfavorable or variable conditions. More can tolerate climatically favorable conditions
