Multivariate tradeoffs, succession, and multiple coexistence mechanisms in a guild of colonial invertebrates

Background/Question/Methods

In competitive communities limited by one or few resources, species diversity is thought to be maintained by tradeoffs that allow niche differentiation without resource partitioning. However, few studies have quantified multiple key traits for each species in a guild, and shown that tradeoffs among these traits apply across the guild. Here we measure growth rate, fecundity, longevity, and overgrowth ability for six co-occurring colonial invertebrates. In this community, growth rate, fecundity, and longevity are both basic life history traits and primary components of competition for space.

Results/Conclusions

We show that growth rate is negatively correlated with longevity; fecundity is negatively correlated with longevity; growth rate is positively correlated with fecundity; and overgrowth ability is negatively correlated with fecundity. Furthermore, 87% of the variation in these traits is explained by a single ‘fast-slow’ axis that associates high growth and fecundity with low longevity and overgrowth ability. These results show mechanistically how life history variation can lead to a colonization-competition tradeoff; likewise, the position of species along the fast-slow axis predicts the timing of their peak abundance during succession. In addition to these traits, we document significant between-species differences in temporal patterns of reproduction. We find that species that are closer to each other on the fast-slow axis are more likely to show differences in phenology. Using the data derived from this approach, it will be possible to construct mechanistic models that investigate the interaction of fundamental tradeoffs with recruitment stochasticity, and that test whether the trait differences described here are sufficient to explain coexistence in this community.