Patterns of Global Biodiversity Flashcards
where is genetic diversity often higher
Genetic diversity often higher than expected on boarder biomes
Australia has higher than expected
Strong correlation between spp richness and phylogenetic richness but there can be quite a bit of deviation
Measures of diversity in relationship to spatial scale
Alpha
Beta
Gamma diversity
Alpha diversity
Diversity in a given area or ecosystem. Usually spp richness. Allows us to look at latitudinal gradients. Correlations with structural complexity and productivity
Africa has higher alpha diversity because more new species as you traverse through habitats
Beta diversity
Compare different areas or ecosystems, a measure of the difference between areas. Change in spp as you move through an ecosystem. Rate at which new spp appear and others disappear throughout habitat
comparing south africa to sweden. Africa has higher beta diversity bc higher among local habitats . Beta change in diversity as you cross habitats in a region
Gamma diversity
Overall measure of diversity in all ecosystems across a large geographical scale
Change in spp richness as you traverse biomes
Species area relationships
As you increase in log space the number of species you see goes up in a linear fashion. Habitat size influence habitat heterogeneity and spp turnover. Also see this when looking at islands of different sizes eg caribbean (or habitat islands)
Has been found to be a non-linear power relationship. If you log spp and area then linear. Linear is remarkably consistent over the world
Drivers of species area rule
Available niche space should be related to area, therefore area should be related to spp number. Habitat diversity leads to species diversity, and larger area holds greater habitat diversity.
-Most common explanation ^ but causes of species area relationship still debated
Bigger ‘island’ = larger population = smaller chance of any given population going extinct. A possible ultimate explanation is the balance between local extinction (freeing niche space) and immigration - MacArthur and Wilson 1967
Proximity to mainland and large islands will affect this prediction some species are area sensitive they only exist on sufficiently large islands.
Balance between area and spp richness emigration and extinction
MacArthur and Wilson 1967
Equilibrium theory of island biogeography
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Theory attempts to explain 3 basic characteristics of island life
- species area curve
- effect of isolation
- species turnover
By looking down to see where colonisation and extinction intersect, you can read down to derive an estimate of the number of species that should occur
Why does the rate of extinction increase in MacArthur and Wilson 1967
Equilibrium theory of island biogeography
As species arrive the competition for resources increase so some populations will become very small. Small pops are vulnerable to random extinction events
What did Simberloff do
1969 carried out experiment in florida keys
Islands on mangrove trees surveyed and number of anthropoids recorded, Then covered in plastic tents and fumigated. Islands then resurveyed at intervals and process of decolonisation recorded.
These areas and isolation factors and their effects on colonisation and extinction can be combined to estimate richness of islands of different size and isolation. These ideas can be similarly appleid to patches of habits on a landscape or to protected areas
- bigger areas or many smaller ones?
Isolation effects - Simberloff?
For Remote and near island
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Rates of colonisation declines as islands and habitats become more isolated. For similar extinction rates we expect more species to occur on nearby areas
Can be seen when looking at avian richness of Pacific Islands. Closer you get to (source) island of New Guinea; richness increases to saturation point
Isolation effects
For big and small island
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As the island gets larger the rate of extinction gets smaller due to factors such as being able to support larger populations. Therefore, for constant colonisation rate the species richness should be higher
What processes drive species richness
Loads of hypotheses. Most popular
- Historial perturbations (what happened in the past to effect an area)
- Harshness
- Climatic stability (tropical forests existed long during ice age- long term, spp tend not to go extinct)
- Habitat heterogeneity
- Productivity (eg photosynthesis)
- Interspecific interactions
Several of these are correlated with latitude
Almost all of the richness bird biodiversity in Arica lies along the equator, similar pattern with trees in America and marine species
As you move higher up latitudes species richness tends to drop off, similar decline with latitude
But thats not universal because pine diversity greatest at 40-50 degrees. Wading birds also more diverse north
Altitude graph of moisture and temp
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Altitudinal diversity can peak at mid elevation because too hot low down and too dry low down eg herbaceous plans
Plus as you go higher up a mountain available area gets smaller so expect fewer species. Rahbeck found the decrease in richness with altitude was 67-91% due to area. After accounting for area hump shaped pattern
Historical perturbation and spp richness
habitats that have had historic changes ay be undersaturated because of inadequate time for spp to colonise and adapt. Islands between north american and iberia had historic perturbations and now see nearctic spp decline with distance from america and palaearctic spp decline with distance from siberia. Islands have reached equilibrium
Ice age- America has more tree species because their mountains run north to south where europes run east to west.
Refugia should have increased infraspecific biodiversity- unperturbed? However, chloroplast variation in Eu trees found to be highest away from refugee, thought to result from mixing oflineages from different refugia
