5. Community Ecology (Biodiversity - measuring, causes, consequences)

3 levels of biodiversity

1. genetic diversity

2. species diversity

3. ecosystem/landscape diversity

species diversity of a community

is the variety of organisms that make up the community

two components of species diversity

• species richness

• relative abundance

species richness

the total number of different species in the community

relative abundance

is the proportion each species represents of the total individuals in the community

S is:

the number of species

(pic)

solve

whats is disturbance?

is an event that changes a community, removes organisms from it, and alters resource availability

ex. fire

intermediate disturbance hypothesis suggest that":

moderate levels of disturbance can foster higher diversity than low levels of disturbance

human disturbance

• most widespread agents of disturbance

• usually reduces species diversity

• also prevent some naturally occurring disturbances, which can be important to community structure

ecological succession is the:

sequence of community and ecosystem changes after a disturbance

primary succession

occurs when no soil exists when succession begins

secondary succession

begins in an area soil remains after the disturbance

xerarch succession

low water

hydrarch succession

saturates soil

two factors correlated with a communities species diversity

• geographic locations

• size

two key factors in equatorial-polar gradients of species richness are probably

• evolutionary history

• climate

rate of evapotranspiration

is evaporation of water from soi plus transpiration of water from plants

ecologists observed:

• islands contain fewer species than does a nearby mainland

• small islands contain fewer species than do larger islands

• islands closer to the mainland contain more species that do similar size islands located at a greater distance from the mainland

island equilibrium model

species richness on islands depends on island size, distance from the mainland, immigration, and extinction

four major threats to biodiversity

1. habitat destruction

2. introduced species

3. overexploitation

4. disruption of “interaction networks“

habitat destruction

• human alterations

  • threat to biodiversity

• natural landscapes have been broken up, fragmenting into small patches

introduced species

• those humans move from native locations to new geogrpahic regions

  • gain footholds in a new habitat, and usually disrupt their adopted community

• humans have deliberately introduced some species with good intentions but disastrous effects

overexploitation

• poaching

• fishing

• deforestation

• pet trade

disruption of interaction networks

• extermination of keystone species by humans can lad to major changes in community structure