Biogeography & Biodiversity: Evoltion test 1

The organisms we see in any given place are different than most other places. whyy?

(also biological evidence for evolution)

• Similar climates occur across the globe, but the organisms inhabiting different regions are often unrelated

• Barriers to dispersal are related to differences in the assemblage of species.

What is associated with greater differences between sp.?

larger barrier

Remote islands have mostly species capable of long-distance dispersal But, when introduced by humans other species flourish. So why are islands biased towards having certain types of species?

Evolutionary history

Island species usually most closely related to

species on nearest mainland

Phylogeny often reflects

history of geographic barriers

Dispersal

movement to new areas

Vicariance

physical barrier splits ranges

Extinction (of populations)

removes parts of a geographic range

is extinction frequent? why?

Frequent cause of discontinuous distributions (e.g. after glaciation)

Why are there limits on species’ ranges?

1. Dispersal limited by physical barriers, low mate availability, ecological conditions

2. Competition

3. Climate & ecological niche

diversification rate

r

• net rate of change in number of species over time

Speciation rate

(λ)

• rate at which new species are formed

– Extinction rate

(μ)

• rate at which species are lost

diversification rate formula

r = λ - μ

Diversification rates vary greatly across

taxa, even those of similar age

Three major patterns in fossil record

1. Mass extinctions are common

2. Diversity often sits at an equilibrium

3. Diversity rebounds after mass extinctions

Diversity often sits at an equilibrium

Diversity rebounds after mass extinctions

These two patterns suggest

competition

Direct competition

one taxon outcompetes another

Incumbent replacement

a taxon takes advantage of the other’s absence

Diversity is highest in

• The tropics (vs. the temperate zone)

• At middle elevations (in mountains)

• On land (vs. in the water)

Evolutionary hypotheses to explain diversity differences:

• H1: Positive feedback hypothesis

• H2: Time for speciation hypothesis:

• H1: Positive feedback hypothesis

higher diversity leads to higher diversification rates

H2: Time for speciation hypothesis

Habitats with high levels of diversity are older, so there has been more time for speciation to take place

sp. are more diverse in places

they have inhabited longer