Biodiversity Flashcards
What were Alexander von Humboldt’s greatest discoveries?
> mapping out climatic zones of the earth
> the latitudinal diversity gradient
What is the latitudinal diversity gradient?
The nearer to the tropics
= the greater increase in variety of structure, grace of form, mixture of colours & species
What are the other patterns/gradients?
> altitudinal gradient
= more species at lower altitudes
> depth gradient
= fewer species at greater depths
How does area affect diversity?
Larger islands have more species
= positive correlation
How can we measure diversity?
> alpha diversity > beta diversity > gamma diversity > evenness > functional diversity > sampling
What is alpha diversity?
Total no. of species in a habitat
=species richness
What is beta diversity?
Difference of a habitat from other habitats
= Ratio between regional and local species diversity
What is gamma diversity?
Total species diversity in a region
What is evenness?
Relative abundance of species in a habitat
= how much 1 species dominates
What is functional diversity?
What a species does
Explain the shape of the asymptotic graph of species against time when sampling
Curve rises quickly as you find the common species
Discovery then slows as it gets harder to find the rarer species
When curve levels out = found all species
What does a lower Simpson’s index indicate?
So, what is normally done to make more sense?
Higher diversity
Take the inverse
What is beta diversity inversely proportional to?
What does a high beta mean?
Shared species
Few shared species
What does beta diversity increase with?
Distance
- move farther away, beta goes up
What is the equation for calculating beta diversity?
Jaccard Similarity Index:
J = C / (C+U1+U2)
C: common species
U1: species unique to habitat 1
U2: species unique to habitat 2
What does the latitudinal gradient in beta diversity show?
There are fewer shared species at low latitudes
e.g. more shared in Eastern Canada + Alaska
than Florida + California
What are the possible explanations for explaining higher diversity in the tropics?
> habitat heterogeneity > environmental disturbance > species-area affects > primary productivity > temp
What is habitat heterogeneity?
Different habitats support different species
- more habitats = more species
Tropics have higher heterogeneity? - hypothetical but never proven
What is the intermediate disturbance hypothesis?
Too much disturbance (drought fire, flood etc) prevents species from becoming established
Too little means a few species can crowd all other species out
What is the ideal situation in the intermediate disturbance hypothesis?
Disturbance is low enough to let many species get established
BUT high enough that dominants get killed off frequently - preventing them from taking over
What are the historical effects that could lead to higher diversity in the tropics?
Predicted affects of climate change worst at higher latitudes
Milankovitch cycles every 26,000 years cause poles to freeze & heat up again
BUT lesser effect on tropics
How could species-area effects cause greater diversity in the tropics?
Greater surface area in the tropics than at the poles
PROBLEM - Russia & Siberia should have many species
What is the mid-domain effect?
If you have lots of species w/ varying latitudinal ranges & randomly arrange them, the widely-distributed species will include the tropics
PROBLEM: assumes tropics have species w/ large geographic ranges (actually have small range = high beta diversity)
What is the relationship between primary productivity & diversity?
Low productivity ecosystems have few species
Some high productivity environments have lots of species, some don’t
U-shaped = diversity increases w/ productivity up to a point & then decreases
What is the relationship between diversity & temp?
As temp increases, diversity increases
Where do many groups originate?
Low latitudes & then spread to high latitudes
How are evolutionary dynamics different in the tropics?
High speciation rate
Low extinction rate
