Print PageIndividual specialization is a widespread phenomenon in nature, observed in several taxa, both among vertebrates and invertebrates. Although its ecological and evolutionary implications are recognized, this type of intrapopulation variation is usually not considered in ecological studies. Furthermore, niche expansion is theoretically thought to be derived from a relaxed interspecific competition, hence more common in temperate environments with few species, whereas niche expansion in species rich regions is supposedly less common. The scarce literature about tropical environments, however, suggests the opposite pattern, in which high degrees of individual specialization are present in communities with high species diversity. The present work investigates the degree of intrapopulation diet variation and its relation to niche breadth, trophic position, and food items dominance in diet in 128 fish populations belonging to 14 species from the upper Tocantins River, Central Brazil.
Results/Conclusions
Our study confirms that high degrees of individual specialization may occur in species rich communities. Individual specialization varied both among species but also among populations within the same species, and was positively related to the population’s niche breadth, corroborating the Niche Variation Hypotheses. Individual diet specialization was shown to have a significant quadratic relation to trophic position, i.e., those populations occupying intermediate positions have the highest degrees of individual specialization. This suggests that there may be constraints limiting intraspecific variation within populations at low and high trophic levels. We found a negative correlation between diet specialization and items dominance, indicating that items consumed by populations with high degrees of individual specialization, have a more even importance for the diet. Our work provides novel data on tropical environments using fish as models, and stresses out the necessity of further investigations on this theme.
