The first manipulative experiment demonstrated that, despite being significantly
correlated to the abundance of crabs, neither density of pneumatophores nor cover of
algae are important factors in determining the difference in abundance of H. cordiformis
near to or away from the boardwalk. The hypothesis predicted that in the area away from
the boardwalk, densities of crabs should increase when pneumatophores and/or algae
were reduced. The results, however, were directly opposite to those predicted. Nevertheless,
these results clearly show the importance of manipulative experiments for
explaining patterns of distribution and abundance in ecology and highlight the dangers
of extrapolating causality from correlations