Abstract
Trade-offs among species’ ecological interactions is a pervasive explanation for species coexistence. The traits associated with trade-offs are typically measured to mechanistically explain species coexistence at a single spatial scale. However, species potentially interact at multiple scales and this may be reflected in the traits among coexisting species. I quantified species’ ecological traits associated with the trade-offs expected at both local (competitive ability and predator tolerance) and regional (competitive ability and colonization rate) community scales. The most common species (four protozoa and a rotifer) from the middle trophic level of a pitcher plant (Sarracenia purpurea) inquiline community were used to link species traits to previously observed patterns of species diversity and abundance. Traits associated with trade-offs (competitive ability, predator tolerance, and colonization rate) and other ecological traits (size, growth rate, and carrying capacity) were measured for each of the focal species. Traits were correlated with one another with a negative relationship indicative of a trade-off. Protozoan and rotifer species exhibited a negative relationship between competitive ability and predator tolerance, indicative of coexistence at the local community scale. There was no relationship between competitive ability and colonization rate. Size, growth rate, and carrying capacity were correlated with each other and the trade-off traits: Size was related to both competitive ability and predator tolerance, but growth rate and carrying capacity were correlated with predator tolerance. When partial correlations were conducted controlling for size, growth rate and carrying capacity, the trade-offs largely disappeared. These results imply that body size is the trait that provides the basis for ecological interactions and trade-offs. Altogether, this study showed that the examination of species’ traits in the context of coexistence at different scales can contribute to our understanding of the mechanisms underlying community structure.
Highlights
Niche differences, exhibited as trade-offs among species, are one of the most common explanations for species coexistence in communities [1,2,3,4,5,6,7]
Body size was negatively correlated with population growth rate and carrying capacity; growth rate was positively correlated with carrying capacity
Species exhibited trade-offs between predator tolerance and competitive ability associated with the local-community scale
Summary
Niche differences, exhibited as trade-offs among species, are one of the most common explanations for species coexistence in communities [1,2,3,4,5,6,7]. Numerous traits have been identified as potential axes along which trade-offs occur, and these niche differences can lead to species coexistence at different spatial scales [4]. The nature of predicted trade-offs will differ according to the scale over which species interact with each other and their environment [4]. At the local community scale, numerous models predict differences in species’ resource use [14], but within a food web, the most commonly considered trade-off is between competitive ability and predator tolerance [3,15]. When all local communities are homogenous at the regional scale, a trade-off between competitive ability and dispersal ability is required for species coexistence [16]. Few examples exist of trade-offs at multiple scales, but an empirical examination of species traits within this framework may broaden our understanding of community structure and diversity patterns [20,21]
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