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Ecology, Week 4

by: Rheanna Gimple

Ecology, Week 4 LIFE 320

Rheanna Gimple

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About this Document

Week 4 notes: Evolution and Life Histories
Dale R Lockwood
Class Notes
Biology, Ecology, Biology: Ecology and Evolution, Animal Science, evolution, ecology&evolution, Life Science
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This 6 page Class Notes was uploaded by Rheanna Gimple on Wednesday September 21, 2016. The Class Notes belongs to LIFE 320 at Colorado State University taught by Dale R Lockwood in Fall 2016. Since its upload, it has received 10 views. For similar materials see Ecology in Biology at Colorado State University.


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Date Created: 09/21/16
Evolution  and  Life  History     Evolution  Part  2   •   Genetic  drift:  random  evolutionary  force   o   Stronger  in  smaller  populations   o   Results  in  fixation  of  alleles   -­‐  tends  towards  homozygosity   o   Never  maintains  allele  diversity   •   Always  decreases  diversity   •   Base  pair  mutation  typ es:   o   Point  mutation:  single  base  pair  change   •   Due  to  errors  in  DNA  replication  or  repair   o   Insertion/Deletion:  add/lose  base  pair(s)   •   AKA  shift  mutations   o   Synonymous:  silent  mutations   •   Change  in  base  pair  but  amino  acid  remains  the  same   •   Creates  redundancy  in  genetic  code   o   Non-­‐synonymous:  base  pair  change  causes  amino  acid  change   •   Mis-­‐sense:  amino  acid  change   •   Non-­‐sense:  stop/start  codon  change   •   Frame-­‐shift:  insertion/deletion   •   Chromosomal  mutations:   o   Changes  to  area  of  a  chromosome   •   Deletion   •   Duplication   •   Inversion     • Translocation   o   Duplicate  entire  chromosome   •   Trisomies   o   Duplicate  entire  genome   •   Polyploidy   •   Migration   o   Gene  flow:  transfer  alleles  from  one  population  to  another   o   Allele  frequencies  change  in  a  given  gene  pool  (population)   •   Doesn't  change  frequency  in  entire  species   o   Implies  individuals  reproduce  with  individuals  from  different  populations   •   Not  just  physical  migration   •   Adaptation:  trait  naturally  selected  for  because  it  increases  fitness   o   Adaptations  come  from:   •   Mutations  that  create  new  phenotypes   §   If  creates  more  fitness,  that  trait  will  become  more  common   •   Can  be  deleted  by  random  chance   §   Mutations  allow  for  populations  to  change  in  new  ways  over  time   §   Less  fit  genotypes  controlled  by  differences  in  fitness   o   Constraint:   •   Environment  influences  adaptations   §   Beneficial  adaptation  in  one  environment  can  be  disadvantage  in  another   •   Some  differences  are  not  adaptive   •   Population  genetics:  study  of  how  genetic  composition  of  populations  change   o   Mathematically  predictable  rates  of  genetic  change   •   Phenotypic  plasticity:  ability  to  have  different  phenotypes  for  a  genotype  under  different   environmental  conditions   o   Phenotype,  not  genotype,  responds  to  natural  selection   •   Phenotype  is  combination  of  genes  and  environment   o   Natural  selection  favors  organisms  with  phenotypic  plasticity   •   Able  to  adapt  better   o   Spatial  variability  due  to  microhabitats  and/or  temporal  variation   •   Areas  of  environment  with  different  distinct  conditions   §   Temperature,  food,  humidity,  water   •   Organism  may  have  to  move  from  one  microhabitat  to  other  to  satisfy  constraints   o    acclimations   •   Phenotype  changes  due  to  change  in  environment   §   Winter  coat,  enzyme  with  certain  temperature  optima,  red  blood  cell  count   •   Capacity  usually  reflects  an  organisms'  range  of  environmental  conditions   •   Species  in  constant  environments  lose  ability  to  acclimate   §   Uses  a  lot  of  energy  to  acclimatize   •   Acclimations  usually  can  be  reversed   •   Can  occur  during  development   §   Persistent  structural  environmental  conditions  give  rise  to  structural  changes   §   Longer  response  times   •   i.e.  developmental  stage  or  life  long   •   Polyphenic  traits:  multiple  different  phenotypes  due  to  environmental  conditions   o   i.e.  snow  hares  -­‐  brown  in  summer,  white  in  winter   •   Why  populations  differ:   o   Environment   o   Genes   o   Combination  of  both   •   Lots  of  genes  respond  to  a  certain  environment     • Adaptions  can  be  advantageous  an d  disadvantageous   o   Environment  dictates  success   •   Ex:  if  a  species  has  recently  dealt  with  a  bacterial  pandemic,  population  will  have  a   high  proportion  of  individuals  with  resistance  to  that  bacteria   §   Population  without  the  pandemic  will  have  low  proportion  of  individuals  with   resistance  -­‐  no  selective  pressure         Life  Histories   •   Resource  allocation   •   Trade-­‐offs   •   Strategies  for  reproducing  and  when  to  die   •   Life  History:   o   The  schedule  of  life  of  an  individual  in  a  species   •   Age  of  maturity   •   Number  of  offspring   •   Life  span   o   These  include  behavioral  and  physiological  adaptations     •   Important  points     o   Evolution  should  act  to  maximize  optimal  life  histories   •   Pushes  towards  optima  but  things  push  against  that   o   Not  all  life  histories  are  perfectly  optimized:   •   Constraints:   §   Not  enough  time  and/or  genetic  variation  to  evolve  to  new  optimum   •   Tradeoffs:   §   Size  v.  number  of  offspring   §   Number  of  offspring  v.  parental  survivorship   §   What  is  best  for  mother,  father  and  offspring  can  be  different   •   Life  history  tradeoffs   o   Individuals  need  to  maximize  reproduction  with  limited  time  and  energy   •   Tradeoffs  are  required   §   Investments  in  one  part  of  reproduction  means  less  investment  in  another     •   Example  of  tradeoffs   §   Invest  in  growth  v.  early  reproduction   §   Invest  in  current  offspring  v.  future  offspring   §   Invest  in  a  lot  of  small    v.  few,  big  offspring   •   Classic  Study   o   David  Lack,  Oxford  University   -­‐  placed  life  histories  in  evolutionary  context:   •   Tropical  songbirds  lay  less  eggs  per  clutch  than  temperate  counterparts   •   Lack  thought  this  difference  was  because  of  different  abilities  to  find  food  for  babies:   §   Birds  nesting  in  temperate  regions  have  longer  days  to  find  food  during   breeding  season   •   Lack's  proposal   §   3  key  points:    suggesting  life  histories  shaped  by  natural  selection:   •   Because  life  history  traits  (i.e.  nu mber  of  eggs  per  clutch)  contribute  to   reproductive  success  -­‐  also  influence  evolutionary  fitness   •   Life  histories  vary  in  consistent  way  due  to  factors  in  the  environment     • Hypotheses  about  life  histories  are  subject  to  experimental  tests   •   An  experimental  test   §    Someone  could  artificially  increase  the  number  of  eggs  per  clutch  to  show  that   number  of  offspring  is  limited  by  food  supply   §   This  proposal  has  been  tested  a  lot   •   Goren  Hogstedt  used  European  magpies   •   About  50%  survive  up  to  a  clutch  of  7   •   Over  that  all  tend  to  start  starving   •   Living  in  the  oceans   o   Lecithotrophy   •   Egg  yolk  provides  nutrients   §   Larvae  don't  have  to  find  food  right  away   •   Few  big  larvae   o   Planktotrophy   •   Feed  on  plankton   •   Lots  of  smaller  larvae   o   Right  whales-­‐  produce  single  calf  every  3 -­‐5  years   •   Reproductive  tradeoff  in  sand  crickets   o   Female's  have  two  forms:   •   Long-­‐winged  forms   §   Resources  allocated  to  flight   §   Delayed  ovary  development  (produce  fewer  offspring)   •   Short-­‐winged  forms   §   Poorly  developed  wings  and  limited  ability  to  fly   §   Quick  ovary  development   •   Reproduce  early   •   You  can  grow  or  reproduce,  not  both   o   Reproductive  effort:  time  and  energy  allocated  to  reproduction   o   Trade-­‐off  between  growth,  maintenance  and  reproduction   •   negative  relationship  between  annual  growth  and  allocation  of  reproduction   §   If  you  grow  more  you  reproduce  less   •   Fecundity:  ability  to  reproduce  sexually   o   Largely  depends  on  size   o   Maturity  and  fecundity  are  size  dependent   •   Age  and  size  go  together   o   Range  of  fecundity  is  vast   •   Rats  reach  maturity  in  20  days   •   Rockfish  take  15  years   •   Saguaro  cacti  at  50  years   o   Ectothermic  animals     •   Production  of  offspring  in  fish  increases  with  size/age   •   Gizzard  shad:    at  2-­‐yr  produces  59,000  eggs,  at  3 -­‐yr  produces  379,000  eggs   o   Percentage  of  annual  production  (energy)  devoted  to  reproduction:   •   Perennials:  15-­‐20%   •   Wild  annuals:  15 -­‐30%   •   Crops:  25-­‐30%   •   Maize/barley:  35 -­‐40%   •   Lizard:  7-­‐9%     • Salamander:  48%   •   Larger  organisms  tend  to  devote  more  energy   o   Annual  fecundity  and  annual  mortality  rate  correlate   •   Species  differ  in  timing  of  reproduction   o   Semelparity   •   Use  all  resources  for  one  reproductive  effort,  then  death   •   Most  insects,  other  invertebrates,  some  fish  (salmon)  and  a  lot  of  plants  (bamboo,   ragweed)   •   organisms  are  often  small,  short  lived,  grown  in  disturbed  habitats   •   Environmental  effect  can  be  disastrous   •   Example:  Talipot  palm   §   Leaves  up  to  5  m  in  diameter   §   Flowers  once  at  30  to  80    years   §   Dies  after  fruiting   •   Example:  octopus   §   Produce  thousands  of  eggs  before  starving  to  death  while  protecting  eggs   o   Iteroparity   •   Produce  less  young  at  one  time  but  repeat  reproduct ion  throughout  lifetime   •   Multiple  reproduction  cycles   §   balance  growth,  maintenance,  escaping  predation,  defending  territory,  etc.   against  reproduction   •   Most  vertebrates,  perennial  herbaceous  plants,  shrubs  and  trees   o   Oncorhynchus  mykiss:  rainbow  trout/  steelhe ad  salmon   •   Can  do  both   o   Anadromous:  migrating  up  freshwater  rivers  from  ocean  to  reproduce   o   Catadromous:  migrating  down  rivers  to  ocean  to  reproduce   o   Why  semelparity  (or  iteroparity)   •   Three  proposed  explanations   §   Bet  hedging  model   •   Iteroparity  preferred  in  varied/unpredictable  environments   •   Risky  to  limit  reproduction  to  one  year  if  there  is  a  bad  year   •   Some  semelparous  plants  can  be  in  habitats  that  are  more  variable   •   Annuals  and  biennials  are  typically  found  in  habitats  that  are   transient  and  unpredictable   •   Successionally  (disturbed  sites)   •   Cities   •   Edaphically  (deserts  and  dunes)   •   Related  to  soil  content   •   In  annual  plants   •   Strong  seed  dormancy  gives  a  lot  of  variation  in  generation  time   within  each  cohort   •   In  non-­‐annual   •   Varied  post-­‐germination  maturation  times     •   possibly  genetically  based   •   likely  due  to  micro-­‐environmental  changes   §   Reproductive  effort  model   •   Want  offspring  produced  to  be  at  max  compared  to  offspring  forgone   •   When  reproductive  success  per  unit  of  reproductive  effort  has  positive   correlation,  semelparity  favored   •   If  no/negative  relationship,  iteroparity  favored   §   Demographic  models   •   Mathematically  analyze  when  semelparity  makes  sense   •   Semelparity  favored  when     •   High  population  growth  rate   •   Low  adult  survivorship  (after  first  reproduction  event)   •   Long  time  periods  between  reproductive  events   •   High  %  juvenile  survivorship   •   Early  senescence   •   Senescence:  traits  that  contribute  to  death  at  old  age   •   Increased  mortality  and  decreased  fecundity  over  time   •   senescence  is  life-­‐history  trait   •   Most  organisms  show   drop  off  in  fecundity  and   increased  risk  of  mortality  with  age   •   senescence  seem  to  be  under  natural  selection   •   Selection  against  early  senescence  rises  as   survivorship  rises   •   Lots  of  early  deaths  mean  senescence  isn't   selected  against   •   Environment  works  with  genetics  for  senescence    


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