Trait-based community assembly along a secondary succession in a tropical dry forest

Background/Question/Methods

Ecological succession has been studied for a long time. However, the mechanisms driving successions are still debated. Here we use a trait-based approach to understand the mechanisms underlying community assembly during succession. While trait-based approaches to community assembly have been used in the past to understand community assembly, it has rarely been applied in a successional context.  Here we analyze multiple tree communities differing in age since the last disturbance within a tropical dry forest of Guanacaste, Costa Rica. We assess changes in species abundance and biomass as well as changes in several key traits. We mainly focus on two key leaf traits, specific leaf area (SLA) and leaf dry matter content (LDMC), which have been identified as key markers of community assembly in a similar system. We analyze the change in community-level mean, variance, skewness, and kurtosis of the traits and identify underlying environmental drivers of succession. Specifically, we cast traditional successional theory within the light of trait-based community ecology. We expect that (1) at early successional stages habitat filtering and trait convergence is strong; however, (2) later in succession we expect a shift to trait divergence as a result of greater niche differentiation.

Results/Conclusions

Trait distributions in early successional environments support habitat filtering, whereas niche differentiation provides a better explanation for the patterns seen in late successional environments. In other words, we view a shift from habitat filtering in early succession to niche differentiation in late succession. We use changes in trait distributions to explain this shift. We found species with low SLA and high LDMC in early succession while species with high SLA and low LDMC in late succession. This pattern was explained primarily by water limitation in early succession versus light limitation and greater competition in late succession. Abundance-weighted variance of SLA also showed an increase through time, suggesting higher niche differentiation at advanced successional stages. The lower more peaked variance found in early successional environments also suggests strong habitat filtering. Altogether this original trait-based approach highlights the non-random community-level mechanisms driving ecological successions.