Biodiversity Flashcards
Humboldt
Mapped out climatic zones using isothermal lines
Latitudinal diversity gradient
Nearer to tropics, incr in no of species
More species and diversity at lower latitudes
Latitude
Diversity peaks in equatorial regions, especially tropical rainforests, and decr in cooler areas (as well as deserts)
Towards poles fewer species
Holds for marine ecosystems
Altitudinal gradient
As distance from sea level increases, diversity decr
Depth gradient
As one descends into the ocean, fewer species
Area effects
strong positive relationship between size of island and number of species
Larger areas support more species
alpha diversity
species richness
total species for a limited area
eveness
relative abundance of species in a habitat
beta diversity (turnover)
difference of a habitat from other habitats
endemicity
Gamma diversity
sum of everything in a region
regional diversity
functional diversity
what those species do
In a more diverse assemblage..
abundance doesn’t drop off as quickly (for different species)
Rare things are less rare
Fauna is more even
Simpson’s index
lower index means higher diversity- useful to take an inverse
calculates eveness
Beta diversity is inversely proportional to
shared species: high beta means few shared species
Beta diversity goes up with
distance
Jaccard similarity index
calculates beta diversity
measure of overlap
1- both habitats have same species
0- no species in common
Tropical overlap
overlap between different tropical habitats low
have restricted distributions
Latitudinal gradient in beta diversity
similarity decr with incr distance
but it does much faster at low latitudes
HIgh tropical diversity is a function of
high alpha and beta diversity
species-area curve:
alpha- along the left, local
Gamma: regional, on the right
Beta: links the two, determines the slope- if beta diversity high, curve will incr rapidly as you sample new habitats
See diagram
high functional diversity
diversity in size, ecology (carnivore,herbivore), locomotion (running, walking, climbing)
explanations for diversity patterns
habitat heterogeneity environmental disturbance species-area effects primary productivity temp
Habitat heterogeneity
different habitats support different species
More habitats = more species
Maybe tropics more diverse because more heterogeneity?
- BUt never been shows that the tropics are more diverse in habitats
Intermediate disturbance hypothesis
too much disturbance prevents species becoming established
Too little means a few species are able to crowd everybody else out
A goldilocks level of disturbance is low enough to let many species get established, but high enough that dominants get killed off freq- can’t take over
Problem with intermediate disturbance hypothesis
no evidence that disturbance levels are that different in tropical rainforest than in other habitats
Historical effects
Are the tropics more stable?
Predicted effects of climate change worse at higher latitudes
WArming/cooling more severe at high latitudes
Species-area effects
explains to some extent why so many species in the tropics- large area
Problem with species- area
Asia largest land mass- temperate
If species diversity were just driven by area, Russia and Siberia would have more species
Mid domain effects
argues if you have a bunch of species with varying latitudinal ranges and randomly arrange them, the widely distributed species will include the tropics
Wide ranging things overlap in the middle
Problem with mid domain effects
assumes tropics have lots of things with large geographic ranges but tropics have lots of things with v small ranges (high beta diversity)
Primary productivity
Relationship between PP and diversity complicated
Low productivity ecosystem have few species, but some high productivity environments have lots of species, and some don’t
Diversity incr with PP up to a point, then levels out/decreases
PP measured in terms of
evapotranspiration etcc
Temp
strong positive correlation between temp (SST) and diversity
Bacterial diversity
diversity, measured by sequencing dna, shows a correlation between latitude and temp, but weak with PP or abundance
Evolutionary dynamics
Tropics have high BRS/ diversification, and low extinction
Dispersal dynamics
many groups originate at low latitudes, then spread to high latitudes
Conclusions
species-area effects, mid-domain effects, habitat heterogeneity and disturbance effect diversity, but not enough to explain diversity gradient
Productivity and temp main drivers of latitudinal diversity gradients, but why is poorly understood
Not only is diversity diff in tropics, evol dynamics is too- high speciation and low extinction
isothermal line
a line on a weather map or chart connecting points having equal temperature.
