Large-Scale Patterns in Diversity Flashcards
What are large scale patterns in diversity
Trends in species distribution across Earth’s surface, including species-area curves and latitudinal gradients
What is a species-area curve
A pattern showing how the number of species increases with area surveyed - follows a power function
What is the power function in species-area relationships
Species=cA^z
A = area
z = slope
log c = intercept
taking logs linearises the relationship
How does species number change with area
A 10-fold increase in area typically doubles the number of species
Name 3 mechanisms proposed to explain the species-area pattern
- Habitat diversity hypothesis
- Passive sampling hypothesis
- Equilibrium theory of island biogeography
What does the habitat diversity hypothesis propose
Larger areas have more habitat types, supporting more species
What is concluded if homogenous habitats still show increasing species with area
Suggests area itself (not just habitat variety) contributes to diversity
How can the habitat diversity hypothesis be tested
Vary area while keeping habitat constant
Vary habitat while keeping area constant
What is the passive sampling hypothesis
Islands randomly sample individuals from a mainland source, larger islands sample more individuals
Why is the passive sampling hypothesis considered a ‘null model’
It doesn’t invoke biological processes - just chance and size
What does the passive hypothesis fail to explain
High diversity on small islands
Species turnover over time
Who developed the equilibrium theory of island biogeography
MacArthur and Wilson
What does the equilibrium theory of island biogeography predict about species number
It’s a balance between immigration and extinction
What influences immigration and extinction rates
Distance from mainland (isolation)
Island size (area)
What are the key assumptions of the equilibrium theory of island biogeography
- Evolution doesn’t affect species richness
- Colonisation/extinction are independent of composition
- Big islands have big populations = lower extinction
- Isolated islands = lower immigration
What are the predictions of the equilibrium theory of island biogeography
- Species number is stable over time, but composition changes (turnover)
- Species number decreases with isolation
How is the species-area curve used in conservation
Predict species extinctions after habitat loss
Guide reserve design strategies
What key assumptions are there when the species area curve is used for conservation
Species richness is the goal
Area loss is the main driver of species loss
What does SLOSS stand for
Single Large Or Several Small reserves
What determines which part of SLOSS is better
Beta diversity – how different the communities are between sites
What is beta diversity
The turnover in species composition between communities
What is the latitudinal gradient in biodiversity
Biodiversity increases from poles to tropics
What are abiotic explanations for tropical richness
Time and stability: tropics have been stable for 150+ million years
Low extinction rates, high speciation
Evolutionary time allows communities to diversify
What is the evolutionary time hypothesis
Stable tropical environments have allowed species to evolve and persist over long timescales
