The Relationship Between Brain Size And Vulnerability To Extinction In Birds

The current extinction rate is 100 to 1 000 times higher than it was pre-human.If all of species recently considered "threatened" go extinct in this century,the future extinction rate would be ten times higher than the recent one.Identifying traits connected with rapidly increased extinction risk is the most important premise for developing effective conservation strategies to reduce future biodiversity losses.The birds is an ideal group for analyzing traits connected with rapidly increased extinction risk.There has been a lot of research in taxonomy,phylogeny,physiology,ecological and life-history traits on birds.Bird is one of the few groups that are adequately described.Conservation biologists have evaluated the extinction risk of almost all bird species at global scales.Previous studies have addressed that brain size was directly(and indirectly)associated with life-history traits.We selected brain size,global distribution range and life-history traits(body size,developmental mode,developmental time,egg size,clutch size,reproductive output,incubation period and fledging period)as independent variable,IUCN Red List as response variable.Then we evaluated how each factors influences vulnerability to extinction in separate models with Markov Chain Monte Carlo GLMMs(MCMCglmm)analysis and PGLS(Phylogenetically controlled generalized least-squared)analysis.We analyzed 1 892 species of extant 10 966 birds species,non-passerine birds(1 164 of extant 10 966 birds species),and nine orders with high extinction risk(Charadriiformes,Columbiformes,Gruiformes,Galliformes,Piciformes,Pelecaniformes,Anseriformes,Psittaciformes,Accipitriformes).Our results shows that: 1)brain size was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds,Gruiformes,Psittaciformes and Accipitriformes;2)the relative brain size,controlling for body size,also was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds and Psittaciformes;3)body size was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds,Columbiformes,Gruiformes and Accipitriformes;4)distribution range was negatively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds,Charadriiformes,Columbiformes,Pelecaniformes,Anseriformes,Gruiformes,Psittaciformes and Accipitriformes;5)extinction risk was not affected by developmental mode across each analyses;6)developmental time was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds,Columbiformes,Psittaciformes and Accipitriformes;7)fledging period was positively correlated with extinction risk across Psittaciformes;8)incubation period was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species,non-passerine birds,Charadriiformes,Galliformes,Psittaciformes and Accipitriformes;9)reproductive output was positively correlated with extinction risk across 1892 species of extant 10 966 birds species;10)egg size was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species;11)clutch size was positively correlated with extinction risk across 1 892 species of extant 10 966 birds species.We also explored how life-history traits and distribution range size of a species indirectly affect the relationship between relative brain size and vulnerability to extinction using phylogenetic path analysis.In the best supported causal scenario,brain size affected vulnerability to extinction indirectly by acting on distribution and life-history traits.The results of MCMCglmm analysis and PGLS analysis were almost consistent.The factors which influence extinction risk are almost same in two groups(1 892 species of extant 10 966 birds species and non-passerine birds,it verified the universal adaptation in birds.Analysis results of the 9 extinction risk orders were different.We found that larger brained species,larger bodied species,small distribution range species,prolonged developmental time species,prolonged incubation period species,high reproductive output species,small clutch size species or big egg size species have a higher extinct risk.Our research indicated that the constraints outweigh the beneficial effects of enlarged brain size in birds in the case of current threat factors.Larger brains have become a white elephant for the bird species.Depending on the specificity of each orders,conservation biologists can develop more efficient protection strategies and carry out targeted protection.