its in the gameplay.constants file. the bold is what you are interested in:

PlanetData
        allegiancePassiveGainRate 0.000347222
        allegiancePassiveLossRate -0.000347222
        allegianceFriendlyMaxGainRate 0.000694444
        allegianceEnemyMaxLossRate -0.000694444
        allegianceGainFromCultureMax 0.1
        startingPopulationPercOfMax 0.5
        healthOnColonize 200.0
        healthRegenRatePercWhenBombed .000
        nearPlacementDistOffset 0
        farPlacementDistOffset 9000
        placementRadiusOffset 100
        considerBeingBombedTimeForHealthRegen 20
        considerBeingBombedTimeForPopulationGrowth 240
        populationGrowthPercWhenBombed 0.50
        minPropagatedCultureRate 0.005
        culturePropagationPerc .5
        cultureDecayRate -0.4
        moduleConstructorRespawnTime 30
        moduleConstructorRespawnTimeWithEnemies 300
        baseTaxRatePerPopulation 0.025
        planetBaseAllegianceAtDistanceCount 11
        allegiance 1.00
        allegiance 0.90
        allegiance 0.80
        allegiance 0.70
        allegiance 0.55
        allegiance 0.40
        allegiance 0.25
        allegiance 0.25
        allegiance 0.25
        allegiance 0.25
        allegiance 0.25
        planetCultureTakeOverPercWarning 0.1
        experienceGainedForDestroying 400.0
        scuttleTime 60.0