Comparing abundance and biomass in describing arthropod communities in citrus canopies.

The abundance of each species is the most common metric used in community ecology studies. Depending on the goal of the study, the use of biomass instead of, or in addition to, abundance could lead to different results, or at least give a very different perspective. This is especially true when there are several orders of magnitude differences in the mass of the study species, as happens in most arthropod communities. The goal of the present study is to compare the community structure using both abundance and biomass data. To do so we replicated the study of Piñol et al. (2012) on the effect of ant exclusion on community structure in the canopy of an organic citrus orchard. To compare the abundance and biomass composition, we obtained a mean weight for every species and transformed the original abundance data into biomass data. The results showed a very different community structure in the control trees when using abundance compared to biomass. The use of biomass did not change the results of ant exclusion. Using abundance the community was dominated by Psocoptera (33%), whereas it was dominated by Dermaptera (54%) using biomass. This result simply reflects the fact that an earwig is three orders of magnitude heavier than a psocopteran. However, the above result did not translate into a different outcome of the ant-exclusion experiment. Still, the community structure is completely different using the abundance or biomass.