EVS Chapter 4

Natural Selection  (1858, Darwin & Wallace) 
Shapes organismsActs as evolutionary mechanismActs on genetic variation  1) Directional: drives feature in 1 direction2) Stabilizing: produces intermediate traits, status quo preserved 3) Disruptive: drives trait in 2 or more directions  
Biological Diversity
Area’s sum total of all organisms
Allopatric Speciation
Main mode. Formation of new species due to physical separation of populations. -Ex: by mountains, glaciers, rivers
Sympatric Speciation
Populations reproductively isolated within the same area – reproduction leads to new group – gene pool alteration – reproduction of new group – can lead to new species Hybridization and/or mutation  
Divergent Evolution
One species evolves in many different directionsEx: Birds developing different beak shapes based on the food they eat.


Convergent Evolution
Different species evolve towards one common form Ex: similarity in wings of insect, bird, pterosaur and bat. Trait is shared, but each evolved independantly  
Endemic Species
Can only exist in a specialized area. -Very susceptible to extinction -Usually have small populations 
Gaia Hypothesis
Through complex system of positive/negative feedback, life on Earth regulates planetary environment to help sustain life
Eutrophication Process
Nutrient over-enrichment, algal blooms, increased production of organic matter, ecosystem degradation Primary limiting factor of eutrophication is phosphorus availability 
Photic and Aphotic Zones in Lakes and Oceans
Photic: zone of intense sunlight Aphotic: usually deep waters, little or no sunlight 
Form of anaerobic respiration in methanogen microbes. The process absorbs carbon dioxide but emits methane, a significantly more potent GHG.  
Biological Pump
Oceanic sequestration of carbon from atmosphere -; deep sea. Cycling of organic matter produced by phytoplankton during photosynthesis.

 Cycling of calcium carbonate (CO3) 

Microbial Carbon Pump
Transformation of bioavailable carbon into pools of inert organic carbon deeper in the ocean.
Microbial Loop
Transformation of dissolved organic carbon into particulate organic carbon via heterotrophic bacteria. Recycling carbon back to food webs Zooplankton can access POM and not DOM