The past is never dead: legacy effects alter the structure of benthic macroinvertebrate assemblages

Abstract

Land use is the most common and widespread threat to lotic ecosystem health and freshwater biodiversity conservation. The legacy effects of past anthropogenic land use and cover may also affect the structure and functioning of current lotic ecosys¬tems. Therefore, the aim of this study was to use benthic macroinvertebrate assemblages to evaluate the potential legacy effects of anthropogenic land use on headwater streams in the Neotropical Savanna. We tested three hypotheses. (1) The legacy effects on macroinvertebrates of the riparian zone are more important than those of the entire catchment. (2) Recent deforestation has a stronger effect on the current taxonomic structure of benthic macroinvertebrate assemblages than historical deforestation. (3) Sen-sitive taxa respond more readily than tolerant taxa to historical deforestation. To test these hypotheses, we estimated deforestation over the last 30 years for 97 stream sites in 5 hydrological units and tested it against benthic macroinvertebrate abundance, taxa richness, EPT abundance, EPT richness, Shannon-Wiener diversity, and Simpson diversity. The two first hypotheses were cor¬roborated, as Shannon-Wiener and Simpson diversity indices were significantly correlated with deforestation in the riparian zone (p < 0.05) and these diversity variables were positively correlated with older deforestation, meaning that such sites tended to recover their diversity over time after a deforestation event. The third hypothesis was only partially supported because EPT (sensitive taxa) did not represent most taxa with significant correlations with historical deforestation at catchment scale, but were the only taxa to do so at the 200 m riparian buffer. We conclude that recent deforestation has more significant effects, but past deforestation still plays a significant role in the structure and functioning of lotic ecosystems.