How competition affects evolutionary rescue: theoretical insight - PowerPoint PPT Presentation

How competition affects evolutionary rescue: theoretical insight Matthew Osmond Claire de Mazancourt MM Osmond

Evolutionary rescue MM Osmond

Evolutionary rescue Mean fitness 0 Mean trait value MM Osmond

Evolutionary rescue Mean fitness 0 Mean trait value MM Osmond

Evolutionary rescue Abundance 0 0 Time MM Osmond

Evolutionary rescue Abundance 0 0 Time MM Osmond

Evolutionary rescue So, which populations are likely to be “rescued” by evolution? MM Osmond

Evolutionary rescue Likelihood of rescue increases with: ◮ genetic variation / mutation rate (faster adaptation) ◮ initial population size (slower extinction) Gomulkiewicz & Holt (1995), Orr & Unckless (2008), Chevin & Lande (2010) MM Osmond

Extending evolutionary rescue MM Osmond

Extending evolutionary rescue: competition Competition reduces the abundance of a species ... Maynard Smith (1989) MM Osmond

Extending evolutionary rescue: competition � � dN 1 − N dt = rN K K Abundance ( N ) Time ( t ) MM Osmond

Extending evolutionary rescue: competition � � dN 1 − N dt = rN K K K − C � � dN 1 − N + C dt = rN Abundance ( N ) K Time ( t ) MM Osmond

Extending evolutionary rescue: competition Competition reduces the abundance of a species ... ... which must make extinction more likely . Maynard Smith (1989) MM Osmond

Extending evolutionary rescue: competition But , competition also influences selective pressures ... MM Osmond

Competition and selection Fitness (isolated) Trait value ( z ) Fitness (in isolation): ——– MM Osmond

Competition and selection Fitness (isolated) Competition ( C ) Trait value ( z ) Decreases selection strength Fitness (in isolation): ——– Competition (C): - - - - - - - MM Osmond

Competition and selection Fitness (isolated) Competition ( C ) Trait value ( z ) Trait value ( z ) Decreases selection Increases selection strength strength Fitness (in isolation): ——– Competition (C): - - - - - - - MM Osmond

Extending evolutionary rescue: competition But , competition also influences selective pressures ... ... and selection affects the rate of adaptation. MM Osmond

Extending evolutionary rescue: competition But , competition also influences selective pressures ... ... and selection affects the rate of adaptation. So, competition can sometimes help evolutionary rescue? MM Osmond

Adaptive dynamics ◮ Large asexual population ◮ All individuals have same phenotype ◮ Beneficial mutations rare and small MM Osmond

Adaptive dynamics The rate of evolution: dz dt = µ · n ( z ) · g ( z ) z : phenotype µ : per capita mutational input n ( z ): abundance g ( z ): selection gradient MM Osmond

Adaptive dynamics The rate of evolution: dz dt = µ · n ( z , C ) · g ( z , C ) z : phenotype µ : per capita mutational input n ( z , C ): abundance g ( z , C ): selection gradient C: competition MM Osmond

Competition and adaptation A Fitness (isolated) Competition ( C ) B Trait value ( z ) Decline in abundance: A > B Increased selection: A < B ⇒ Rate of adaptation: A < B MM Osmond

Conclusions 1. Competition lowers abundance, slowing adaptation 2. Competition also impacts selection, potentially speeding adaptation 3. If selection imposed by competition is strong enough to overcome negative effect on abundance , competition can help evolutionary rescue MM Osmond

Circumstantial evidence Extinction rate (Er) of birds on islands increases with sqaure of species number, suggesting competition increases extinction Moulton & Pimm 1983 Fitness (isolated) Competition ( C ) Trait value ( z ) MM Osmond

Evidence A high * * * Adaptation of algae to increased CO 2 slowed by competition Collins 2011 473 high Fitness (isolated) Competition ( C ) 2699 high Trait value ( z ) 2137 high MM Osmond

Evidence for ‘helpful’ competition? Fitness (isolated) Competition ( C ) Trait value ( z ) MM Osmond

Adaptive response K K z n * z n * ^ ) ^ ) Abundance ( n Trait value ( z N c z N c z 0 * z 0 * 0 0 0 50000 50000 t r Time ( t ) t r obs MM Osmond

Time at risk influenced by: Time at risk ( t r ) Time at risk ( t r ) 0 0 0 ∆ z ** ∆ z * 0 1 * − z n * ) Magnitude of change ( z 0 Critical fraction of max abundance ( N c K ) K Original environment Time at risk ( t r ) New environment N c K n 0 σ k * σ k ** 0 0 z N c ^ ) z 0 * z n * Trait value ( z Environmental tolerance ( σ k ) MM Osmond