I got tired of not knowing what all the minor races did and, by extension, not knowing which ones to focus on when trying to maximise my empire's benefits. Thus:

The following is a list of (all) population bonuses and (most) collection bonuses for the major and minor factions of Endless Space 2, accurate up to patch 0.3.4. Feedback to fill in any missing bonuses on this list is more than welcome.

-------------------------------------------------------

Major Races

Cravers (Militarist)
Base: +50% FIDS on Undepleted planets per Craver pop, +1 Depletion Points on planet per Craver pop.
10: +1 Militarist reaction per Craver pop.
20: +10% Ship cost reduction on systems with Cravers.
50: +40% Industry when empire is at war.

Gene Splice: +2% FIDS per pop.

Horatio (Ecologist)
Base: +2 Approval per Horatio pop.
10: +1 Ecologist reaction per Horatio pop.
20: +10 Approval on systems with Horatio.
50: -25% anarchy time in senate.

Lumeris (Pacifist)
Base: +1 Dust per Lumeris pop, +5 Dust per Lumeris pop on fertile (+6 total).
10: +1 Pacifist reaction per Lumeris pop.
20: +15% Dust on systems with Lumeris.
50: ??? [No bonus received at 50 pop; bug?]

Riftborn (Industrial)
Base: +5 Industry/Dust/Science per Riftborn pop.
10: +1 Industrialist reaction per Riftborn pop.
20: +15% Industry on systems with Riftborn.
50: Wormholes consume only half a fleet's movement.

Gene Splice: +1 Industry/Dust/Science per pop.

Sophons (Scientist)
Base: +1 Science per Sophons pop, +3 Science per Sophons pop on cold (+4 total).
10: +1 Scientist reaction per Sophons pop.
20: +15% Science on systems with Sophons.
50: -20% Technology costs.

United Empire (Industrial)
Base: +1 Influence per United Empire pop, +1 Influence per United Empire pop on temperate.
10: +1 Industrialist reaction per United Empire pop.
20: +15% Influence on systems with United Empire.
50: -20% Pacific/Cultural Conversion cost on empire.

Gene Splice: +1 Influence per pop.

Vodyani (Religious)
Base: -50% Population growth penalty on Vodyani pop, +4 FIDS per Vodyani pop.
20: .
50: .

-------------------------------------------------------

Minor Races

Amoeba (Ecologist)
Base: +2 Food per Amoeba pop.
10: +1 Ecologist reaction per Amoeba pop.
20: +15% Food on systems with Amoeba.
50: Unlocks unique Amoeba law (Thick Skins Bill: -50% Diplomatic Pressure).

Bhagaba (Pacifist)
Base: +1 Influence per Bhagaba pop, +1 Influence per Bhagaba pop on fertile.
10: +1 Pacifist reaction per Bhagaba pop.
20: +15% Influence on systems with Bhagaba.
50: Unlocks " Bhagaba Ground Battle Defense" strategy.

Gene Splice: +1 Influence per pop.

Faction Trait: Culturally Resistant (+25% Cultural/Pacific Conversion cost on own systems).

Deuyivans (Scientist)
Base: +2 Science per Deuyivans pop, +5 Food per Deuyivans pop on gas.
10: +1 Scientist reaction per Deuyivans pop.
20: +15% Science on systems with Deuyivans.
50: Unlocks unique Deuyivans law (Good Science Bill: -30% Research cost on Empire Development technologies).

Faction Trait: The Art of Science (-10% Research costs).

Epistis (Ecologist)
Base: +1 Industry per Epistis pop, +5 Food per Epistis pop on sterile.
10: +1 Ecologist reaction per Epistis pop.
20: +10% Improvement cost reduction on systems with Epistis.
50: Unlocks unique Epistis law (Fast Clean-Up Bill: +20% Ownership recovery rate on systems).

Gene Splice: +1 Industry/Food per pop.

Eyder (Religious)
Base: +1 Dust per Eyder pop, +5 Dust per Eyder pop on gas (+6 total).
10: +1 Pacifist reaction per Eyder pop.
20: +15% Improvement buyout cost reduction on systems with Eyder.
50: Unlocks unique Eyder law (Dust Diggers Bill: +100 Dust per empires at peace).

Gene Splice: +1 Dust per pop.

Gnashast (Militarist)
Base: +50 damage to attacker during ground battle per Gnashast pop, +200 damage to attacker during ground battle per Gnashast pop on fertile (+250 total).
10: +1 Militarist reaction per Gnashast pop.
20: +100 damage to attacker during ground battle on systems with Ghashast.
50: Unlocks "Ghashast Ground Battle Defense" strategy.

Haroshem (Pacifist)
Base: +1 Food per Haroshem pop, +5 Food per Haroshem pop on sterile.
10: .
20: .
50: .

Hissho (Militarist)
Base: +20 Empire Manpower per Hissho pop each turn, +30 Empire Manpower per Hissho pop on sterile each turn (+50 total).
10: +1 Militarist reaction per Hissho pop.
20: +15% System Defense capacity on systems with Hissho.
50: Unlocks unique Hissho law (Bring 'Em, Break 'Em Bill: +15% Manpower refill rate on fleets outside borders).

Kalgeros (Religious)
Base: +2 Approval per Kalgeros pop, +4 Approval per Kalgeros on fertile (+6 total).
10: +1 Religious reaction per Kalgeros pop.
20: +15% Influence on systems with Kalgeros.
50: Unlocks unique Kalgeros law (Happy Sardines Bill: -100% Overpopulation penalty).

Mavros (Industrialist)
Base: +1 Industry per Mavros pop, +2 Industry per Mavros pop on hot (+3 total).
10: +1 Industrialist reaction per Mavros pop.
20: +15% Industry on systems with Mavros.
50: Unlocks unique Mavros law (Crack Squads Bill: -40% Overcolonisation penalty).

Niris (Ecologist)
Base: +2 Food per Niris pop, +3 Food per Niris pop on fertile (+5 total).
10: +1 Ecologist reaction per Niris pop.
20: +15% Food on systems with Niris.
50: Unlocks unique Niris law (Symbiotic Living Bill: +5 Approval per system level on systems, +1 Approval per pop on systems).

Pilgrims (Religious)
Base: +1 Science per Pilgrims pop, +2 Science per Pilgrims pop on anomaly (+3 total).
10: +1 Scientist reaction per Pilgrims pop.
20: +5 Vision range on systems with Pilgrims.
50: Unlocks unique Pilgrims law (Blindsight Bill: Reveals all enemy fleets).

Tikanan (Militarist)
Base: +5 System Defense per Tikanan pop each turn, +5 System Defense per Tikanan pop on fertile each turn (+10 total).
10: +1 Militarist reaction per Tikanan pop.
20: +0.2 ??? on systems with Tikanan. [Descriptive/Informational icon is missing; bug?]
50: Unlocks unique offensive ground battle strategy (Swarm Assault: -25% health on attacking troops, +3 Battle Duration. Replaces Blitz).

Faction Trait: Swarming Infantry (x2 Infantry units in ground battles).

Z'vali (Scientist)
Base: +2 Approval per Z'vali pop, +3 Science per Z'vali pop on happy.
10: .
20: .
50: .

Gene Splice: +1 Science/Approval per pop.