Experimental Ecology. Controls. Manipulation. Replicates Experimental Ecology Controls Manipulation Replicates Pseudoreplication Rocky Intertidal Space Limited System Paine’s Pisaster removal experiment Connell: Balanus and Chthamalus Menge’s Leptasterias and Pisaster experiment Dunham’s Big Bend saxicolous lizards Brown’s Seed Predation experiments
R. T. Paine (1966)
Joseph Connell (1961)
Bruce Menge (1972)
Menge 1972 Bruce Menge
Grapevine Hills, Big Bend National Park Sceloporus merriami and Urosaurus ornatus Six rocky outcrops: 2 controls, 2 Sceloporus removal plots and 2 Urosaurus removal areas. ======================================== 4 year study: 2 wet and 2 dry: insect abundances Monitored density, feeding success, growth rates, body weights, survival, lipid levels Urosaurus removal did not effect Sceloporus density No effects during wet years (insect food plentiful) Insects scarce during dry years: Urosaurus growth and survival was higher on Sceloporus removal plots Arthur Dunham
James Brown
Experimental Design of Seed Predation in the Chihuahuan Desert ___________________________________________________ Plots Treatments ___________________________________________________ 11,14 Controls 6,13 Seed addition, large seeds, constant rate 2,22 Seed addition, small seeds, constant rate 9,20 Seed addition, mixed seeds, constant rate 1,18 Seed addition, mixed seeds, temporal pulse 5,24 Rodent removal, Dipodomys spectabilis (largest kangaroo rat) 15,21 Rodent removal, all Dipodomys species (kangaroo rats) 7,16 Rodent removal, all seed-eating rodents 8,12 Pogonomyrmex harvester ants 4,17 All seed-eating ants 3,19 All Dipodomys plus Pogonomyrmex ants 10,23 All seed-eating rodents plus all seed-eating ants ___________________________________________________________ Munger, J. C. and J. H. Brown. 1981. Competition in desert rodents: an experiment with semipermeable enclosures. Science 211: 510-512.
open circles = rodents removed solid circles = controls
Simberloff and Wilson 1970
Evidence for Stability of Trophic Structure Evidence for Stability of Trophic Structure? First number is the number of species before defaunation, second in parentheses is the number after _____________________________________________________________________________ Trophic Classes ____________________________________________________________ Island H S D W A C P ? Total _____________________________________________________________________________ E1 9 (7) 1 (0) 3 (2) 0 (0) 3 (0) 2 (1) 2 (1) 0 (0) 20 (11) E2 11 (15) 2 (2) 2 (1) 2 (2) 7 (4) 9 (4) 3 (0) 0 (1) 36 (29) E3 7 (10) 1 (2) 3 (2) 2 (0) 5 (6) 3 (4) 2 (2) 0 (0) 23 (26) ST2 7 (6) 1 (1) 2 (1) 1 (0) 6 (5) 5 (4) 2 (1) 1 (0) 25 (18) E7 9 (10) 1 (0) 2 (1) 1 (2) 5 (3) 4 (8) 1 (2) 0 (1) 23 (27) E9 12 (7) 1 (0) 1 (1) 2 (2) 6 (5) 13 (10) 2 (3) 0 (1) 37 (29) Totals 55 (55) 7 (5) 13 (8) 8 (6) 32 (23) 36 (31) 12 (9) 1 (3) 164 (140) _____________________________________________________________________________ H = herbivore S = scavenger D = detritus feeder W = wood borer A = ant C = carnivorous predator ? = undetermined
Wilson 1969
Predation and Parasitism
Predator-Prey Experiments Georgii F. Gause
Predator-Prey Experiments Georgii F. Gause
Predator-Prey Experiments Georgii F. Gause
Predation Equations coefficients of predation, Lotka-Volterra Predation Equations coefficients of predation, p1 and p2 dN1 /dt = r1 N1 – p1 N1 N2 dN2 /dt = p2 N1 N2 – d2 N2 No self damping (no density dependence) dN1 /dt = 0 when r1 = p1 N2 or N2 = r1 / p1 dN2 /dt = 0 when p2 N1 = d2 or N1 = d2 / p2 Alfred Lotka Vito Volterra