227 lines
8.9 KiB
Markdown
227 lines
8.9 KiB
Markdown
# terrain, substrates, and pheromone decay
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how environmental factors affect pheromone persistence. relevant to feature #7
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(substrate-dependent decay) and the worldBlur shader's per-cell decay rate.
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## substrate effects on persistence
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the key study is Jeanson et al. (2003) on Monomorium pharaonis:
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substrate chemical half-life behavioral preference half-life
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plastic ~9 min ~25 min
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paper ~3 min ~8 min
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a 3x difference in chemical half-life between two smooth artificial surfaces.
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mechanism: paper is porous and wicks the compound away from the surface,
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reducing the airborne concentration ants detect. plastic is non-porous, so the
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compound sits on top and remains available.
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no comparable controlled study exists for natural substrates (soil, rock, sand,
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leaf litter, wood). inferred from physical chemistry:
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- porous substrates (soil, sand, wood, leaf litter) behave more like paper —
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absorb compounds, accelerate apparent decay
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- non-porous substrates (rock, packed clay) behave more like plastic — keep
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compounds on the surface, slower decay
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- soil moisture complicates things further (see humidity section)
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## species variation in baseline trail longevity
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trail pheromone persistence varies enormously across species:
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species trail longevity notes
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Solenopsis invicta ~100 sec / <2 min extremely volatile compounds
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Monomorium pharaonis ~9 min (plastic) multiple pheromone types
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Aphaenogaster albisetosus minutes short-lived
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Pachycondyla sennaarensis ~30 min to half gone in 1 hr
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Monomorium spp. (general) ~1 day optimal varies
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Camponotus (carpenter ants) days hindgut-produced
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Daceton armigerum 7+ days poison gland secretion
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Eciton spp. (army ants) weeks long-chain, low-volatility
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the range is >100x. species in stable environments with permanent food sources
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use long-lasting compounds. species exploiting ephemeral food use volatile ones.
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Pharaoh's ants also use multiple pheromone types with different decay profiles:
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a long-lasting attractive pheromone, a short-lived attractive pheromone, and a
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short-lived repellent pheromone (~78 min vs ~33 min half-life).
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## temperature
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the definitive paper is van Oudenhove et al. (2011/2012), studying
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Tapinoma nigerrimum and Aphaenogaster senilis.
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key findings:
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- above ~40C: workers cannot discriminate marked substrate — pheromone is
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effectively destroyed
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- above ~30C: foraging activity drops independently, partly because trails
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decay too quickly to be useful
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- between 25-40C: decay accelerates but trails remain functional
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- the 40C threshold is a behavioral cliff, not a smooth curve
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species differ in thermal resilience:
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- T. nigerrimum (mass-recruiting): secretions highly volatile. most compounds
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vanished even at 25C. only iridodials persisted up to 55C.
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- A. senilis (group-recruiting): secretions less volatile, resisted elevated
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temperatures better. at 55C, only nonadecene and nonadecane (long-chain
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hydrocarbons) persisted.
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pheromone persistence = f(temperature, time since deposition). both interact —
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higher temperature accelerates decay at all time points.
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diurnal implications: hot midday temperatures degrade trails laid in morning.
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desert species tend to use less volatile compounds (evolutionary compensation
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via chemistry rather than behavioral compensation via deposition rate).
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## humidity and moisture
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less quantitative data than temperature.
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- higher humidity slows evaporation of polar pheromone components
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- a cuticle covered with water may hinder both reception and emission of
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pheromones — wet conditions impair laying AND sensing, not just persistence
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- army ants (Eciton burchellii) increased speed by 30% in response to increased
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humidity and rain sounds near the trail, but watering the trail directly did
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not cause load-dropping
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- extreme humidity (either direction) suppresses foraging entirely
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wet porous substrates (damp soil, wet leaf litter) would absorb pheromone
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faster than dry porous substrates, but no controlled study confirms this
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quantitatively.
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no direct evidence of ants selecting substrates specifically for pheromone
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persistence, though trail-clearing behavior (see below) effectively creates
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favorable substrate.
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## physical trail infrastructure
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### leaf-cutter ant highways (Atta spp.)
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the standout example of ants modifying their environment for trail quality:
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- colonies clear an average of 2,730 meters of trail per year
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- individual trails can exceed 200 meters
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- networks extend for kilometers cumulatively
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- construction/maintenance costs: ~11,000 ant-hours per year
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what they do: remove leaf litter, cut passes through overhanging vegetation,
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shift soil to level surfaces. selective clearing — flat objects are ignored,
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upright/folded obstructions are removed.
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coordination: trail clearing happens WITHOUT information exchange between
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workers. independent effort that adds up to emergent infrastructure. clearing
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is triggered by freshly laid pheromone on an obstructed path.
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### minim workers as trail maintainers
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the smallest workers (minims) are always present on trails but never carry
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leaves. they deposit pheromone at 83.3% frequency vs 20% for non-minims.
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they're dedicated trail maintainers — keeping the chemical signal strong while
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larger workers (2.2-2.9mm head width) handle physical clearing.
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### physical + chemical reinforcement loop
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physical clearing creates smooth packed soil (relatively non-porous) which
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retains pheromone better than leaf litter. minim workers then maintain high
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pheromone concentration. cleared trails retain pheromone better -> strong
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pheromone attracts more traffic -> more traffic means more clearing and
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reinforcement. positive feedback on two axes simultaneously.
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energetics: not always profitable. depends on workforce composition and patrol
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vs carry ratio. can amortize within days or take weeks/months.
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## emergent highway formation
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the trail network that emerges from substrate-dependent persistence:
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1. substrate quality: non-porous > porous
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2. temperature: shade > sun
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3. physical modification: cleared > uncleared
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4. traffic: popular > unpopular (reinforcement)
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5. food quality: rich source > depleted source
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a trail across cool, shaded, packed earth near a rich food source dominates
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over a trail across hot, sun-exposed leaf litter near a marginal source. no
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ant "decides" this — the pheromone math works out.
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trail bifurcation: at branch points, trail asymmetry (angle, width) influences
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decisions alongside pheromone presence. neither geometry nor pheromone alone
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dominates — non-hierarchical interaction.
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rapid decay as feature: in fire ants, trail pheromone drops below detection in
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~2 minutes. this forces continuous reinforcement, meaning only actively
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profitable routes persist. fast decay = responsive colony.
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## simulation relevance
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for the world texture's terrain type bits (3-5 in world.R):
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terrain type decay multiplier real-world analog
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0 (default) 1.0x generic surface
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1 0.5x (slower) packed earth / rock
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2 1.5x (faster) leaf litter / porous
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3 2.0x (faster) sand / loose soil
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4-7 reserved future use
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the blur shader would read terrain type per cell and multiply the base decay
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rate. ants wouldn't "know" about terrain — they'd just find that their trails
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last longer on some surfaces, and positive feedback would do the rest.
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temperature could be a global uniform rather than per-cell (simpler), or
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per-cell if the simulation adds sun/shade regions.
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## sources
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Jeanson et al. 2003
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Pheromone trail decay rates on different substrates in Pharaoh's ant
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Physiological Entomology 10.1046/j.1365-3032.2003.00332.x
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van Oudenhove et al. 2011
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Temperature limits trail following through pheromone decay
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Naturwissenschaften 10.1007/s00114-011-0852-6
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van Oudenhove et al. 2012
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Substrate temperature constrains recruitment and trail following
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J Chem Ecol 10.1007/s10886-012-0130-x
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Bruce et al. 2019
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Infrastructure construction without information exchange in Atta
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Proc R Soc B 10.1098/rspb.2018.2539
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Bruce et al. 2017
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Energetics of trail clearing in Atta
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Behav Ecol Sociobiol 10.1007/s00265-016-2237-5
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Robinson et al. 2008
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Decay rates of attractive and repellent pheromones in foraging trail network
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Insectes Sociaux 10.1007/s00040-008-0994-5
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Morgan 2009
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Trail pheromones of ants (review)
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Physiological Entomology 10.1111/j.1365-3032.2008.00658.x
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Effect of trail pheromones and weather on Eciton burchellii
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ResearchGate 225346583
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Minor workers maintain leafcutter ant pheromone trails
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ResearchGate 248591651
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Trail pheromone of Pachycondyla sennaarensis
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PMC3281317
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Monomorium trail pheromone longevity
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ScienceDirect S1226861509001034
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Uncovering the complexity of ant foraging trails
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PMC3291321
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Effect of trail bifurcation asymmetry and pheromone on trail choice
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PMC4204274
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