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Table 1 Model parameters, ranges of values tested, and reference values

From: Strategies of offspring investment and dispersal in a spatially structured environment: a theoretical study using ants

Parameter

Description

Values

Reproduction (fixed parameters)

 Dispersal range

Maximum distance new propagules can disperse from the parent colonya

DCF: 1; ICF: 30

 Dispersal mortality

Chance dispersing propagules die from predation or environmental hazards (% mortality)

DCF: 10; ICF: 90

 Offspring size

Size of new propagules

DCF: half of the colony†; ICF: 20

 Offspring number

Number of new propagules

DCF: 1; ICF: 1/40 colony sizeb

Life-history

 Longevity

Number of steps colonies can live for (= queen lifespan)

5; 6; 7; 8; 9; 10; 15; 20; 25; 30; 35

 Maintenance cost

Percentage of resources (= individuals) “consumed” for survival per time step

1–10 % by 1 % increments; 15 %; 20 % (5 %)

 Maximum growth rate

Maximum multiple by which colonies can grow each step (provided they collect sufficient resources)

×1, ×2, ×3, ×4, ×5, ×6, ×8, ×10, ×15, ×20, ×25

 Maturity threshold

Size at which colonies reproduce

100 to 1400 workers by 100 increments (700)

 Reproductive investment

Percentage of resources (= individuals) invested into offspring when reproducing

5 %; 10–90 % by 10 % increments; 95 % (50 %)

Environmental

 Disturbance

Percentage of patches on which all agents are killed via catastrophic events each step

0, 1, 2, 3, 4, 5, 7, 10, 15, 20 and 25 % (5 %)

 Resources

Resources in each patch are reset at each step. Good patches receive 100 % and bad patches 50 % of the base value.

150–450 by 25 increments (300)

 Aggregation

Spatial aggregation of patch quality based on Hurst exponents (H) in a fractal algorithm

Uniformc, random, H = 0, H = 0.5, H = 1

  1. Fixed parameters are those that define the reproduction strategies and are unique to each. Life-history parameters were shared between strategies while environmental parameters defined the spatio-temporal environment. Values in ‘aggregation’ refer to Hurst exponents in the fractal algorithm. Reference values are shown in italics. All simulations lasted 1000 steps, which ensured equilibrium was reached at the end of the simulations, except simulations of invasion. These lasted 3000 steps with 1 colony of the invading strategy added after completion of step 500, and visual checks showed that all simulations reached equilibrium whether invasion occurred or not
  2. Random and aggregated (H = 0, 0.5 and 1) environments had 50 % good and 50 % bad patches. Uniform environments consisted entirely of medium patches, with resources intermediate between those of good and bad patches (i.e., 75 % of a good patch in the other simulations) to maintain a constant amount of resources landscape level
  3. aFor each propagule, the actual distance of dispersal was drawn from a uniform distribution between 0 and the maximum distance. A uniform distribution was chosen as we have no information regarding dispersal kernels in ants or reason to expect that an alternative distribution would apply equally well to both strategies
  4. bNote that offspring size and number were only partially fixed, as these factors also depended on reproductive investment for one of the two strategies in each case (see main text), and the values given assume reference levels of reproductive investment (50 %). The size of new DCF propagules was derived as (colony size × reproductive investment) whereas in the case of ICF, colonies produced (colony size × reproductive investment/20) new propagules
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BMC Ecology

ISSN: 1472-6785

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