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Ecological Processes

Table 2 Subjects and timing of stochasticity in the PEKRIS model with a short explanation

From: The impact of salps (Salpa thompsoni) on the Antarctic krill population (Euphausia superba): an individual-based modelling study

Subject

Timing

Explanation

Placement

(1) Model setup and; (2) each time step

Individuals are distributed randomly over the modeled domain during the creation of krill and salps in the model setup, during the immigration of salp and krill individuals, and during the birth of clutches (sexual reproduction of krill). See Sects. 1.2 and 1.4.6 of Additional file 1: S1

Movement

Each time step

Each salp and krill individual moves to a randomly chosen neighboring grid cell at each time step. The probability of each of the eight neighboring grid cells being chosen as the new position is equal. See Sect. 1.4.8 of Additional file 1: S1

Mortality

Each time step

Death is simulated by drawing random numbers for each krill and salp individual separately. If the drawn number is below the predefined threshold, the individual dies. Thresholds for all entities are 2.5% for salps, 0.07% for krill, and 5.0% for clutches. See Sect. 1.4.5 of Additional file 1: S1

Immigration

Each time step

Immigration of salps during the spring, summer, and autumn is simulated by drawing a random number each day as long as no salps are present. If this number is below the threshold of 0.85%, ten salp individuals are created within the modeled domain. See Sect. 1.4.6 of Additional file 1: S1

Chlorophyll-a availability

(1) Model setup and; (2) each year

Suppose chlorophyll-a supply is set to follow a lognormal distribution during the simulation. These parameters were derived from the US Antarctic Marine Living Resource (AMLR) program run by the National Oceanic and Atmospheric Administration (NOAA), as described in Groeneveld et al. (2020). See Sects. 1.2 and 1.4.7 of Additional file 1: S1

Reproduction

Each time step

A random number is drawn during each salp’s reproduction event. With a probability of 70%, blastozooids and oozoids are produced. In 30% of all cases, only blastozooids are generated by the individual salp for the given reproduction event. See Sects. 1.4.3 and 1.4.4 of Additional file 1: S1

  1. Stochasticity occurs during the model setup (placing the krill and salp individuals) and during the movement, mortality, immigration, and reproduction of both species
  2. More details on each process listed here are described in the corresponding Details in Sects. 1.2 and 1.4 of Additional file 1: S1
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