Disturbance

Hypotheses Equilibrium Dynamic Equilibrium Intermediate Disturbance Island biogeography Robert MacArthur and E. O. Wilson Dynamic Equilibrium Michael Huston 1979 Intermediate Disturbance Joe Connell 1978 and earlier (+ Hutchinson, etc.) Wayne Sousa (< 1984) Colin Townsend et al. 1997

Ward

Perturbation = disturbance + response Disturbance = the “force” Physical Biological? Response Biological Community/Assemblage Population Physical as well

From Sousa (1984)

Downes et al. 2002

Press vs. Pulse Downes et al. 2002

What Level of Biological Organization Responds Can be any Community Assemblage Grouped Taxonomic FFGs Population Organism

When push comes to shove Population When push comes to shove

Population Growth Concepts Exponential  Malthus Non-overlapping (i.e., most bugs) Nt+1 = NtR (R = offspring/survivor) Or  dN/dt = rN r = birth - death Logistic  Verhulst-Pearl: limiting factors Nt+1 = Nt * exp [R0 * (1- Nt/K)] Or  dN/dt = rN * [(K-N)/K]

Possible Outcomes Parameter r is: 1. Malthusian parameter 2. Intrinsic rate of increase 3. Population growth rate And represents r = birth - death r > 0 r = 0 r < 0 Alexei Sharov

But also – What limits K (carrying capacity) Many interactions within and between: Abiotic (resources and constraints) Habitat (temperature, space, etc.) Biotic (resources and constraints) Food Competition/Predation

What We Really Need To Do Better understand those factors responsible for mortality Key factor analysis Morris (and Miller) K-factor analysis Varley and Gradwell Used in forestry and agricultural settings

Survivorship

Cumulative Numbers Hynes 1970

In “reality” What factors may influence the estimates? Variable time/instar within population Spatial variability Sampling error Benke 1984

Growth Benke 1984

Temperature Sweeney 1984