Competition and phylogeny determine community structure in Müllerian co-mimics

• Published in: Nature (London) Vol. 469; no. 7328; pp. 84 - 88
• Main Authors: Alexandrou, Markos A., Oliveira, Claudio, Maillard, Marjorie, McGill, Rona A. R., Newton, Jason, Creer, Simon, Taylor, Martin I.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.01.2011; Nature Publishing Group
• Subjects: 631/158/853; 631/181/757; 631/601/2722; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Bayes Theorem; Bayesian analysis; Behavior; Biological and medical sciences; Body size; Body Size - physiology; Catfishes - anatomy & histology; Catfishes - classification; Catfishes - genetics; Catfishes - physiology; Community structure; Competition; Competition (Biology); Competitive Behavior - physiology; Ecosystem; Food Chain; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Genetic aspects; Genetics; Humanities and Social Sciences; Influence; letter; Likelihood Functions; Mass spectrometry; Mimicry (Biology); Models, Biological; Molecular Mimicry - physiology; multidisciplinary; Phylogeny; Pigmentation - physiology; Predatory Behavior - physiology; Resource partitioning; Science; Science (multidisciplinary); South America; Standard deviation; Studies; Synecology; South America; America; United Kingdom; Freshwater environment; Community structure; Vertebrata; Geographic distribution; Animal community; Batesian mimicry; Pisces; Interspecific competition; Stream; Coexistence; Phylogeny; Neotropical Region
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature09660

Mimic prey species keep their distance Müllerian mimics are poisonous or unpalatable potential prey species that are not closely related to the species they mimic but have evolved similar warning coloration to discourage shared predators, gaining in the process through strength in numbers. It is not clear if this effect is sufficient to maintain coexistence when competitive exclusion would be expected to favour one mimic at the expense of the others. Martin Taylor and colleagues address that question in a study of Müllerian mimicry in a species-rich group of tropical catfish. Using morphometric and stable isotope analysis, they find that mimics do not occupy identical niches so are not in direct competition for food, thus explaining their ability to coexist. Müllerian mimics have convergently evolved similar warning colouration because of the advantage of strength in numbers. However, it is not clear if this effect is sufficient to maintain coexistence when competitive exclusion would be expected to favour one mimic at the expense of the others. Here, Müllerian mimicry in catfish is characterized, and it is shown through morphometric and stable isotope analysis that mimics do not occupy identical niches, so are not in direct competition, thus explaining their coexistence. Until recently, the study of negative and antagonistic interactions (for example, competition and predation) has dominated our understanding of community structure, maintenance and assembly 1 . Nevertheless, a recent theoretical model suggests that positive interactions (for example, mutualisms) may counterbalance competition, facilitating long-term coexistence even among ecologically undifferentiated species 2 . Müllerian mimics are mutualists that share the costs of predator education 3 and are therefore ideally suited for the investigation of positive and negative interactions in community dynamics. The sole empirical test of this model in a Müllerian mimetic community supports the prediction that positive interactions outweigh the negative effects of spatial overlap 4 (without quantifying resource acquisition). Understanding the role of trophic niche partitioning in facilitating the evolution and stability of Müllerian mimetic communities is now of critical importance, but has yet to be formally investigated. Here we show that resource partitioning and phylogeny determine community structure and outweigh the positive effects of Müllerian mimicry in a species-rich group of neotropical catfishes. From multiple, independent reproductively isolated allopatric communities displaying convergently evolved colour patterns, 92% consist of species that do not compete for resources. Significant differences in phylogenetically conserved traits (snout morphology and body size) were consistently linked to trait-specific resource acquisition. Thus, we report the first evidence, to our knowledge, that competition for trophic resources and phylogeny are pivotal factors in the stable evolution of Müllerian mimicry rings. More generally, our work demonstrates that competition for resources is likely to have a dominant role in the structuring of communities that are simultaneously subject to the effects of both positive and negative interactions.