Ch. 5: Population
Structure and Changes
Plants “Special”
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High phenotypic plasticity (Done)
Indeterminant growth (Done)
Clonal growth (Done)
Seed dormancy
Dana Carvey
as the Church
Lady
Plant Features
• 4) Seed dormancy
• Dormancy: arrested growth embryo
– Lupinus arcticus (10,000 yr)
• (arctic lupine)
– Lotus (400 yr)
Seed dormancy
• Seed bank: pop’n dormant seeds
– In soil
Seed dormancy
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Seed bank (/m2):
Ag fields: 20,000-40,000
Tropical forest: <1,000
Subarctic forest: 10-100
Seed dormancy
• Seed bank: population dormant seeds
– On plant
• closed cone pines (ex, knobcone pine)
– Serotinous cones (open postfire)
• Banksia (Australia)
Dormancy mechanisms
• 1) incomplete embryo development
Dormancy mechanisms
• 2) biochemical trigger
– environment cue starts germ.
– stratification: cold)
– sumorization: heat. Some desert annuals. Max.
germ.: 50 C, 4 wk
Dormancy mechanisms
• 3) impermeable seed coat/fruit wall
– scarification: breaks
Sand paper!
Dormancy mechanisms
• Scarification: Fire
• Ex: chaparral (shrub vegetation:
Mediterranean climate)
– Pine Hill flannel bush
(Fremontodendron decumbens)
– Best germ.: 5 min @ 100 C!
Another study by Tony Danza!
Dormancy mechanisms
• Scarification: Mechanical abrasion
• Ex, smoke tree in arroyo (
Dormancy mechanisms
• 4) germination inhibitors (seed coat/fruit
wall)
Importance of seed banks
• 1) May differ from vegetation
– Ex, African rain forest
• 147 tree spp.
• 22 in seed bank (none same as growing)
Importance of seed banks
• 2) Most pop’n: seed bank
– Ex, CA annual grassland.
– 100 grasses/m2, 30,000 seeds/m2
Importance of seed banks
• 3) Seed bank genetic reservoir
– Differ from
Ch. 5: Population
Structure and Changes
Population Models
• 1) Simple discrete-time model
– N(t) = number now
• Future time (t+1):
• N(t+1)=N(t) + B + I - D – E
Population Models
• 1) Simple discrete-time model
• Usu. ignore I & E
Population Models
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1) Simple discrete-time model
Usu. ignore I & E
Important metapopulations (
Ex, Cakile (sea rocket)
Population Models
• Ex, Cakile (sea rocket)
summer
winter
Tony D!
Population Models
• Ex, Cakile (sea rocket)
– Beach pop’n “source”, dune
“sink” pop’n
winter
summer
Population Models
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1) Simple discrete-time model
Nt = number now
At time (t+1):
N(t+1)=Nt + B + I - D – E
Population Models
• 2) Continuous time models
– b=birth rate
– d=death rate
– rmax=b-d; intrinsic rate of natural increase
– Rate pop’n change=dN/dt
– dN/dt=Nrmax
Curve?
Population Models
• 2) Continuous time models
– dN/dt=Nrmax
– Exponential growth.
Ideal conditions…
Population Models
• 2) Continuous time models
– Limiting
– Logistic growth. Pop. max. @ K (carrying capacity):
Population Models
• 2) Continuous time models
– Eqn.? Start dN/dt=Nrmax
– Add “scaling factor” (K-N)/K
• dN/dt=Nrmax (K-N)/K
N small, (K-N)/K almost 1
N near K, (K-N)/K very small
Population Models
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Plant Point 1: K based on density
Animals: most inds.
Plants: hi modular
Crowding capacity: combine density