1  

Ch  3  

BIOL  101  

•  Golden  toads    

•  Discovered  1964,  Monteverde,  Costa  Rica  

•  Mountainous  cloud  forest    

•  Perfect  climate  for  amphibians  

•  200  golden  toads  were  found  in  one  area  

•  5  m  (16.4  K)  in  diameter  

•  Monteverde  Cloud  Forest  Preserve  created  

•  exOnct  within  25  years  

•  Due  to  climate  change’s  drying  effect  on  the  forest  

•  Biological  evolu,on  

•  GeneOc  change  in  popula&ons  of  organisms  across  

generaOons  

•  Resulted  in  millions  of  species  

•  May  be  random,  or  directed  by  natural  selecOon  

•  Natural  selec,on  

•  What  traits  are  most  advantageous?  

2  

•  Why  do  we  need  to  

understand  evoluOon  for  

environmental  science?  

•  To  understand  ecology  

•  a  central  component  

of  environmental  

science  

•  Relevant  for  

•  Agriculture  

•  Medicine  

•  PesOcide  resistance  

•  Environmental  health  

•  1858  

•  Darwin  and  Wallace    

•  Both  proposed  natural  selecOon  as  the  

mechanism  of  evoluOon  

•  Organisms    

•  Constant  struggle  to  survive  and  reproduce  

•  Produce  more  offspring  than  can  survive  

•  Individuals  vary  

•  Some  be[er  suited  to  environment  

•  Survive  and  pass  their  genes  on  to  their  

offspring  

•  Genes  of  be[er-­‐adapted  individuals  (survivors)    

•  More  prevalent  in  future  generaOons  

•  Adap,ve  trait  (adapta,on)  

•  Trait  (characterisOc)  that  promotes  reproducOve  success  

•  Muta,ons  

•  Spontaneous  changes  in  DNA    •  May(?)  be  passed  to  next  generaOon  

•  Non-­‐lethal  mutaOons    

•  Provide  geneOc  variaOon    •  On  which  natural  selecOon  acts  

•  Sexual  reproducOon  

•  RecombinaOon    

•  Also  leads  to  variaOon  

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•  Results  of  natural  selecOon  evident  in    

•  Every  adaptaOon  of  every  organism  

•  Experiments  with  bacteria  and  fruit  flies  

•  SelecOve  breeding  

•  Ar,ficial  selec,on  

•  Human  directed  selecOon  

•  Biological  diversity  (biodiversity)  

•  An  area’s  sum  total  of  all  organisms    

•  The  diversity  of  species    

•  Their  genes    

•  Their  populaOons  

•  Their  communiOes  

•  Popula,on  

•  Individuals  of  a  species  in  same  place/Ome  

•  Species  

•  PopulaOon  or  group  of  populaOons    

•  Whose  members  share  characterisOcs    

•  Can  freely  breed  with  one  another  and  produce  ferOle  offspring  

4  

•  Specia,on  

•  Process  of  generaOng  new  species  

•  A  single  species  can  generate  mulOple  species  

•  Allopatric  specia,on  

•  Species  formaOon  due  to  physical  separaOon  of  populaOons  

•  Separated  by  glaciers,  rivers,  mountains,  etc.    

•  Over  Ome,  each  populaOon  accumulates  different  mutaOons  

•  Eventually  populaOons  can  no  longer  interbreed  

•  Primary  mode  of  speciaOon  

•  SpeciaOon    

•  Generates  complex  pa[erns  of  diversity  above  the  species  level.  

•  Phylogene,c  trees:  Shows  history  of  species  divergence  

•  ScienOsts  can  trace  when  certain  traits  evolved  

•  Show  relaOonships  between  species,  populaOons,  or  genes  

•  Dead  organisms    

•  OKen  buried  by  sediment  

•  Can  preserve  the  organism’s  bones,  

shells,  and  teeth  

•  Fossil  

•  Imprint  in  stone  of  a  dead  organism  

•  MineralizaOon  of  hard  structures  

•  Fossil  record  

•  CumulaOve  body  of  fossils  worldwide  

•  Geologic  processes  over  millions  of  

years  created  assemblages  of  

fossilized  organisms  

5  

•  Species  generally  evolve  from    

•  Simple  to  more  complex  

•  Small  to  big  

•  But  the  opposite  can  occur  

•  All  depends  on  natural  selecOon  

•  SpeciaOon  is  only  part  of  the  story  

•  Species  also  disappear  

•  Ex,nc,on  

•  Disappearance  of  a  species  from  Earth  

•  Average  Ome  a  species  spends  on  earth:  1–10  million  years  

•  99.9%  of  total  species  have  gone  exOnct  

The number of species in existence = speciation - extinction

•  ExOncOon  occurs  when    

•  Environment  changes  too  rapidly  for  natural  selecOon  to  keep  up  

•  Many  factors  can  cause  exOncOon:  

•  Climate  change  

•  Changing  sea  levels  

•  Arrival  of  new,  harmful  species  

•  Severe  weather  (i.e.,  droughts)  

•  Specialized  species  /  small  pops  

•  Endemic  species  

•  Species  only  exists  in  a  certain  area    

•  Very  suscepOble  to  exOncOon  

•  Usually  have  small  populaOons  (i.e.,  golden  toad)  

•  Background  ex,nc,on  rate  

•  Avg.  1-­‐10  species/year  

•  Usually  one  species  at  a  Ome  

•  Most  historical  exOncOons  

•  Mass  ex,nc,on  events  

•  5  in  Earth’s  history  

•  50-­‐95%  of  species  went  exOnct  at  one  Ome  

•  Humans  causing  the  sixth  mass  exOncOon  event  

•  1000-­‐10,000x  background  

•  PopulaOon  growth  

•  Development  

•  Resource  depleOon  

6  

•  Ecology  

•  Study  of  interacOons  among  

organisms  and  their  

environment  

•  Ecology  and  evoluOon  are  Oghtly  intertwined  

•  Biosphere  

•  All  living  things  on  Earth  and  the  areas  they  inhabit  

•  Ecologists  study  relaOonships  on  many  levels  

•  Popula,on  ecology  

•  Examines  how  individuals  within  a  

species  interact  

•  Community  ecology  

•  Focuses  on  interacOons  among  

species  

•  Ecosystem  ecology  

•  Studies  living  and  non-­‐living  components  of  systems  to  reveal  

pa[erns  

•  Nutrient  and  energy  flows  

•  Habitat  

•  Specific  environment  in  which  an  organism  lives    

•  Includes  living  and  non-­‐living  elements  

•  Scale-­‐dependent:  from  square  meters  to  miles  

•  Habitat  use  

•  Each  organism  thrives  in  certain  habitats,  but  not  in  others  

•  Habitat  selec,on  

•  Process  by  which  organisms  acOvely  select  habitats  in  which  to  live  

•  Availability  and  quality  of  habitat  are  crucial  to  an  organism’s  well-­‐being  

•  Human  developments  conflict  with  this  process  

7  

•  Niche  

•  An  organism’s  use  of  resources  and  its  funcOonal  role  in  a  community  

•  Habitat  use,  food  selecOon,  role  in  energy,  and  nutrient  flow  

•  InteracOons  with  other  individuals  

•  Specialists  

•  Species  with  narrow  niches  and  very  specific  requirements  

•  Extremely  good  at  what  they  do,  but  vulnerable  to  change  

•  Generalists  

•  Species  with  broad  niches  that  can  use  a  wide  array  of  habitats  and  resources  

•  Able  to  live  in  many  different  places    

•  All  populaOons    

•  Show  characterisOcs  that  help  scienOsts  predict  their  future  dynamics  

•  Popula,on  size  

•  Number  of  individual  organisms  present  at  a  

given  Ome  

•  Can  increase,  decrease,  cycle,  or  remain  the  

same  

In 100 years, passenger pigeons — billions of birds — were driven to extinction.

•  Popula,on  density  

•  Number  of  individuals  per  unit  area  

•  Generally,  larger  organisms  have  lower  populaOon  densiOes    

•  need  more  resources  

•  High  densiOes  -­‐  easier  to  find  mates  

•  But  increase  compeOOon  /  vulnerability  to  predaOon  

•  Low  densiOes  -­‐  harder  to  find  mates  

•  But  plenOful  resources  and  space  

•  Reduced  resources  can  lead  to  overcrowding,  disease,  predators,  parasites,  and  exOncOon  

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•  Popula,on  distribu,on  (dispersion)  

•  SpaOal  arrangement  of  organisms  

within  an  area    

•  Random  —  haphazardly  

located  individuals,  with  no  

pa[ern  

•  Uniform  —  individuals  are  

evenly  spaced  due  to  

territoriality  or  compeOOon  

•  Clumped  —  arranged  according  

to  availability  of  resources  

•  Most  common  in  nature  

•  Sex  ra,o  

•  ProporOon  of  males  to  females  

•  Monogamous  species  

•  50/50  raOo  maximizes  growth  

•  Age  structure  (age  distribu,on)  

•  RelaOve  numbers  of  organisms  of  each  age  within  a  populaOon  

•  Age  structure  diagrams  (pyramids):  show  the  age  structure  of  populaOons  

•  PopulaOon  growth  or  decline  is  due  to:  

•  Natality  

•  Births  within  the  populaOon    

•  Mortality  

•  Deaths  within  the  populaOon  

•  Immigra,on  

•  Arrival  of  individuals  from  outside  the  populaOon    

•  Emigra,on  

•  Departure  of  individuals  from  the  populaOon  

 

Growth rate = (birth rate + immigration rate) - (death rate + emigration rate)

9  

•  Exponen,al  growth  

•  PopulaOon  increases  by  a  fixed  percent  

•  Fixed  percent  of  a  large  number  

produces  a  large  increase  

•  Graphed  as  a  J-­‐shaped  curve  

•  Cannot  be  sustained  indefinitely  

•  It  occurs  in  nature    

•  With  a  small  populaOon  and  ideal  

condiOons  

•  Are  humans  in  ideal  

condiOons?